Advanced Powertrain Report - 2012.pdf

The Advanced PowertrainReport2012 Edition

SupplierBusiness

The Advanced Powertrain Report

SupplierBusiness Published by Willoughby House 2 Broad Street Stamford Lincs PE9 1PB United Kingdom

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IHS SupplierBusiness is a specialist consultancy providing analysis of the automotive industry for the automotive industry. Contributors to this report include: Alex Boekestyn, Alistair Hill, Gaby Leigh, Stewart Pedder. © 2011 IHS Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher, IHS Global Ltd. This report is the product of extensive research work. It is protected by copyright under the Copyright, Designs and Patents Act 1988. The authors of these research reports are drawn from a wide range of professional disciplines. The facts within this report are believed to be correct at the time of publication but cannot be guaranteed. All information within this study has been reasonably verified to the author’s and publisher’s ability, but neither accept responsibility for loss arising from decisions based on this report. This title is provided to you on a single-user basis, supplied on the strict understanding that each title is not to be copied or shared. Alternatively, our reports can be shared within departments or entire corporations via a cost-effective multi-user license. Multi-user licenses can also save you money by avoiding unnecessary order duplication. To further add value all multi-user copies are hosted on a password protected extranet for your department or company – saving you time, resources and effort when sharing research with your colleagues. To find out more about multi-user pricing, please contact Sarah Graham; [email protected]

CONTENTS

Introduction ................................................................................................................ 7 Market drivers ............................................................................................................. 8

Fuel economy and CO2 emissions ............................................................................. 8 Europe .................................................................................................................. 8 The United States .................................................................................................. 8 Japan .................................................................................................................... 9 China .................................................................................................................... 9 South Korea ........................................................................................................ 10 Other countries .................................................................................................... 10

Fuel prices .............................................................................................................. 10 Criterion emissions ................................................................................................. 12

Light-duty vehicles .............................................................................................. 12 Medium- and heavy-duty vehicles ........................................................................ 18

Spark-ignition engine technologies ............................................................................. 19 Downsizing and down-speeding ............................................................................. 19 Combustion cycles .................................................................................................. 20 Stratified charge combustion ................................................................................... 21 Variable valve control ............................................................................................. 22

Variable valve timing and lift ............................................................................... 22 Electro-hydraulic valve actuation ......................................................................... 27 Electromagnetic valve actuation ........................................................................... 27 Cylinder deactivation ........................................................................................... 28

Direct injection technology ..................................................................................... 30 Spray-guided injection ......................................................................................... 32

Forced induction .................................................................................................... 34 Multi-stage turbocharging .................................................................................... 34 Twin-scroll turbochargers .................................................................................... 35 Variable-geometry turbochargers .......................................................................... 36 Turbocharger plus supercharger ........................................................................... 37 Superchargers ...................................................................................................... 38 Multi-speed superchargers ................................................................................... 39 Electric superchargers .......................................................................................... 40 Charge air coolers (intercoolers) ........................................................................... 40

Ignition systems ..................................................................................................... 41 Exhaust after-treatment .......................................................................................... 42

Catalytic converters ............................................................................................. 42 Exhaust gas recirculation ..................................................................................... 44

Thermal management ............................................................................................. 45 Alternative engine designs ...................................................................................... 46


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Variable compression ratio engines ...................................................................... 46 Other radical engine designs ................................................................................ 47

Alternative fuels ..................................................................................................... 53 Alcohols .............................................................................................................. 53 Algal biofuels ...................................................................................................... 56 Bacterial biofuels ................................................................................................. 57 Biogasoline.......................................................................................................... 58 Dimethyl ether .................................................................................................... 58 Hydrogen ............................................................................................................ 58 Hythane .............................................................................................................. 59 Liquefied petroleum gas ....................................................................................... 59 Natural gas .......................................................................................................... 60 Coal-to-liquid fuels .............................................................................................. 61

Compression-ignition engine technologies .................................................................. 62 Combustion cycles .................................................................................................. 63 Downsizing ............................................................................................................ 63 Weight reduction and materials .............................................................................. 64

Cylinder blocks and heads ................................................................................... 64 Pistons ................................................................................................................ 64

The potential of applying new technologies ............................................................. 65 Variable valve technology ....................................................................................... 66 Injection technology ............................................................................................... 68 Forced induction .................................................................................................... 69 Turbo-compounding ............................................................................................... 71 Exhaust after-treatment .......................................................................................... 71

Diesel oxidation catalyst ...................................................................................... 72 Selective catalytic reduction ................................................................................. 72 NOx adsorber catalyst ......................................................................................... 72 Diesel particulate filter ......................................................................................... 73 Syngas systems .................................................................................................... 73 Exhaust gas recirculation ..................................................................................... 74 The SCR versus EGR debate ............................................................................... 74

Alternative engine designs ...................................................................................... 75 Alternative compression-ignition technologies ......................................................... 77

Homogeneous charge compression ignition .......................................................... 77 Reactivity controlled compression ignition ........................................................... 78 Gasoline direct-injection compression ignition ..................................................... 79

Alternative fuels ..................................................................................................... 80 Alcohols .............................................................................................................. 81 Biodiesel ............................................................................................................. 81 Dimethyl ether .................................................................................................... 82


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Natural gas .......................................................................................................... 82 Combined spark and compression ignition engines ..................................................... 83

LIST OF FIGURES Figure 1: China’s fuel economy standards programme Source: Volkswagen China ............ 9

Figure 2: Current and pending fuel economy standards of selected countries in g CO2/km Source: Daimler ....................................................................................... 10

Figure 3: WTI crude oil price, 2007 to January 2012 (USD per barrel) Source: US EIA . 11

Figure 4: US gasoline and crude oil prices, 2008 to 2013 (USD per US gallon) Source: US EIA ..................................................................................................................... 11

Figure 5: The progress of EU gasoline emissions regulations Source: Johnson Matthey ... 14

Figure 6 Criterion emissions reductions in the EU, the US and Japan, 1992 – 2015 Source: Daimler ..................................................................................................... 16

Figure 8 Emissions standards timetable in selected countries, 2001 – 2010 Source: Implats ........................................................................................................................... 17

Figure 10 NOx limits in the EU, Japan and the US, 1995 – 2010 (g/kWh) .................. 17 Figure 11: PM limits in the EU, Japan and the US, 1995 – 2010 (g/kWh) ................... 18 Figure 12 The effects of downsizing on fuel consumption Source: Ricardo ..................... 19

Figure 13 Honda i-VTEC system Source: Honda Civic Forum ........................................ 24

Figure 14 BMW Valvetronic system Source: Tech-On ................................................... 25

Figure 15 Fiat MultiAir system Source: Fiat ................................................................. 26

Figure 16 Valeo e-valve system Source: Valeo ............................................................... 27

Figure 17 Camless, electromagnetic valve control on test at Lotus Engineering Source: Lotus ................................................................................................................... 28

Figure 18 A comparison of wall-guided and spray-guided direct injection Source: Mercedes-Benz ....................................................................................................... 33

Figure 19 Twin-scroll versus mono-scroll turbocharger performance Source: BorgWarner ........................................................................................................................... 35

Figure 20 VGT versus conventional turbocharger performance Source: BorgWarner ...... 36

Figure 21 Eaton Twin Vortices Series compressor rotors Source: Eaton ......................... 38

Figure 22 Antonov two-speed supercharger Source: Antonov......................................... 39

Figure 23 Exploded view of a Rotrak variable-speed supercharger Source: Rotrak ......... 39

Figure 24 Controlled Power Technologies electric supercharger Source: Controlled Power Technologies .......................................................................................................... 40

Figure 25 Federal-Mogul ACIS unit Source: Federal-Mogul ........................................... 41

Figure 26 Three-way catalytic converter Source: Eberspächer ......................................... 43

Figure 27 Delphi electronic gasoline EGR valve Source: Delphi .................................... 45

Figure 29 2/4SIGHT V6 research engine Source: Ricardo ............................................. 47

Figure 28 2/4SIGHT engine concept Source: Ricardo ................................................... 48

Figure 30 Scuderi split-cycle engine design Source: Scuderi ........................................... 49

Figure 31 TourEngine split-cycle engine design Source: Captive Pulse ........................... 50

Figure 32 Wave Disk Generator principles Source: New Scientist ................................... 51


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Figure 33 Detonation Cycle Gas Turbine engine Source: Turbine Truck Engines ............. 52

Figure 34 Cyclone external combustion engine Source: Cyclone Power Technologies ....... 53

Figure 35 Switchgrass Source: College of Chemistry, University of California, Berkeley ......... 54

Figure 36 SunEco algal fuel production ponds Source: SunEco ..................................... 56

Figure 37 New diesel car registrations, Western Europe, 1990 – 2010 Source: ACEA..... 62

Figure 38 Comparison of airflow with VVT on a diesel engine Source: Mechadyne International ......................................................................................................... 66

Figure 39 Variable valve actuation on 6.7-litre Cummins diesel Source: Cummins ......... 67

Figure 40 Comparison of piezo-actuated and servo-hydraulic-actuated injector spray patterns Source: Delphi .......................................................................................... 68

Figure 41 BorgWarner variable-geometry turbocharger Source: BorgWarner .................. 71

Figure 42 EcoMotors OPOC engine Source: EcoMotors ................................................ 75

Figure 43 RadMax RTE engine driving a pump Source: RadMax .................................... 76 Figure 44 Axial Vector engine Source: Axial Vector ....................................................... 77

Figure 45 Criterion emissions from RCCI engine by % gasoline Source: University of Wisconsin, Madison ............................................................................................... 78

Figure 46 GDICI emissions results for single, double and triple injection Source: Delphi 79

Figure 47 GDICI emissions compared to a conventional diesel Source: Delphi .............. 80

LIST OF TABLES Table 1: Euro 5 emissions limits for light gasoline vehicles (g/km) Source: DieselNet ..... 12 Table 2: Euro 5 emissions limits for light diesel vehicles (g/km) Source: DieselNet ......... 13

Table 3: US emissions standards for light-duty vehicles, to five years/50,000 miles (g/mile) ............................................................................................................... 14

Table 4: Japan emissions limits for light gasoline & LPG vehicles (g/km) Source: Japan Department of the Environment ................................................................................ 15

Table 5: Japan emissions limits for light diesel vehicles (g/km) Source: Japan Department of the Environment ................................................................................................. 15


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INTRODUCTION

During recent years, huge research and design investment has been dedicated to improving the performance and fuel efficiency of the internal combustion engine while also reducing its emissions output. Driven by regulations, dramatically increased fuel prices and consumer demand, the resultant technological advances have achieved a great deal and further investigation holds the promise of even more.

Spark-ignition engines, typified by the ubiquitous four-stroke gasoline engine, have made advances through the application of fuel injection, forced induction, valve actuation control, exhaust emissions after-treatment and other technologies. Alongside these developments, a range of alternative fuels are now being supplied in steadily increasing volumes to further address concerns regarding energy security, the increasing demands being made on petroleum oil supplies and reducing carbon emissions. Similarly, compression-ignition engines, typified by the familiar diesel engine, have also made significant advances through the application of similar technologies and a range of alternative fuels.

In addition to the many advances that have been achieved with these ‘conventional’ internal combustion engines, many researchers have been investigating and developing a growing list of alternative engine designs, some of which are at, or approaching, market readiness. These include the use of different combustion cycles and variable internal geometry, to name only two of the technological approaches currently being pursued. Within this group lie engines that combine elements of spark- and compression-ignition, prototypes of which are already demonstrating improved fuel economy and, in most cases, reduced emissions.

While the use of hybrid-electric and other hybrid technologies that combine an alternative powertrain with a conventional internal combustion engine are now well established in the marketplace, they are referred to only in passing in this report. For an in-depth review of hybrid drivetrain technologies and the vehicles on which they are installed, see SupplierBusiness’ Hybrid Electric Light Vehicles Report – 2012 edition


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MARKET DRIVERS

The central drivers of engine technology developments include the quest to improve fuel economy as consumers and countries alike try to reduce their dependence on petroleum-derived fuels and ameliorate their increasing cost. At the country level, this is being driven by increasingly demanding standards of fuel economy expressed either as distance travelled per volume of fuel or as carbon dioxide (CO2) emissions per distance travelled.

Alongside this, the on-going pursuit of lower levels of toxic chemical (criterion) and other greenhouse gas (GHG) emissions, begun in the 1960s, presents ever-more stringent standards with yet another round approaching with Euro 6 in 2014/15 and further US standards within the next few years.

FUEL ECONOMY AND CO2 EMISSIONS

During recent years, the major automotive manufacturing countries have enacted fuel economy and CO2 emissions regulations that demand ever-increasing standards of fuel economy. OEMs are addressing these challenges with a range of technologies that are reviewed below in this report.

Europe

The EU is targeting reductions in carbon dioxide (CO2) emissions to 130 grams per km (g/km) for all new passenger vehicles, with the target being phased in from 60% of new vehicles in 2012 to 100% by 2015. The emphasis is on engine fuel efficiency although 10g/km can be achieved by measures such as improved transmission efficiency and low-resistance tyres. For light vans, the limit will be 175g/km by 2017 and 147g/km by 2020. The target envisaged for cars by 2020 is 90g/km. In 2010, the average for all new light passenger vehicles in the EU was 140.9g/km, down from 145.8g/km in 2009.

In 2009, the EU launched a project to develop CO2 emissions standards for medium and heavy commercial vehicles. However, it is not expected that the standards will be developed in time for the introduction of Euro 6 and that regulations cannot reasonably be constructed around the concept of an OEM average since some produce only heavy-duty vehicles. An approach related to engine horsepower and vehicle type is considered likely.

The United States

After remaining unchanged for many years, the US sales-weighted Corporate Average Fuel Economy (CAFE) standards were revised in 2007 and again in 2009 so that each OEM’s annual production of new cars is required to average 39mpg (US gallon) by the 2016 model year, while ‘light trucks’, which include pick-ups, SUVs and MPVs, will have to average 30mpg. The combined average of 35.5mpg is equivalent to around 155g/km of CO2. The 2011 model year average has been estimated at around 27.3mpg or 200g/km. Penalties remain at the earlier level of USD5.50 per 0.1mpg per vehicle if the annual production fleet does not meet the standard.

In August 2011, new standards were announced, setting a target of 54.5mpg by 2025 with new passenger cars required to average 62mpg by then and ‘light trucks’, 44mpg.


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These targets will require a 5% annual improvement in fuel economy throughout the period by passenger cars and a 3.5% annual improvement by ‘light trucks’ through to 2021 with a 5% annual increase tentatively planned from then until 2025.

In the US, the National Highway Transport Safety Administration (NHTSA), the National Academy of Sciences and the National Research Council have been researching the task of setting fuel economy regulations for medium and heavy commercial vehicles while ensuring that the economic consequences of such regulations are well considered. It is planned that the first regulations will begin to come into effect in 2014 with full implementation by 2018.

Developing regulations for commercial vehicles is difficult because of a number of factors such as variations in size and weight, not only between different vehicle models and types, but also between the same chassis models fitted with different body types, and when vehicles are empty or carrying a full load.

Japan

Japan’s fuel economy regulations require OEMs to improve fuel economy by 23% over 2004 levels by 2015. The standards are defined in 16 weight categories, and the overall average required by 2015 is 39.5mpg (US). The 2004 average was around 32mpg (US). In August 2011, Japan announced that a standard of 48mpg was being considered for 2020.

China

Figure 1: China’s fuel economy standards programme Source: Volkswagen China

China also defines 16 weight categories of light vehicles up to 3,500kg (7,716lb) and first introduced fuel economy standards in 2004. In 2009, standards for 2015 were announced that require increases in fuel economy ranging from 9% to 26% across the categories from lightest to heaviest, respectively, which will take the volume-weighted average to


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42.2mpg. The average in 2010 was around 37mpg. The standards for vehicles exceeding 1,900kg (4,189lb) are more stringent than Japan’s standards but less stringent for those lighter than 1,900kg.

South Korea

South Korea’s standards require an OEM’s new light vehicle fleet to average 40mpg or 140g/km by 2015. By 2012, 30% of each OEM’s new vehicles must meet the standard, rising to 60% in 2013 and 80% in 2014.

Other countries

Several other countries have also set fuel economy or CO2 emissions standards. Taiwan, for example, tends to follow US standards while Australia and Canada, like South Korea, have set their own.

(It is important to note that fuel economy measurements are arrived at using different test protocols in different countries, rendering the above figures as only indicative.)

Figure 2: Current and pending fuel economy standards of selected countries in g CO2/km Source: Daimler

FUEL PRICES

Crude oil prices have fluctuated substantially during the last decade. From the mid-1980s through to 2002, the price per barrel mostly remained in the USD20 to USD25 range (in 2008-equivalent dollars) but then steadily increased to around USD135 per barrel in mid-2008. It then fell back to around USD35 in January 2009 and remained in the USD40 to USD60 range for the first few months of 2009, before increasing again to between USD70 and USD85 for much of 2010. It then increased rapidly to around USD115 per barrel in April 2011 before easing to around USD75 per barrel in August 2011 and then increasing again to around USD100 by the end of the year. As of January 2011, the US Energy Information Administration (IEA) expected that spot prices would average


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around USD100 per barrel in 2012 before increasing to around USD106 by the fourth quarter of 2013.

Figure 3: WTI crude oil price, 2007 to January 2012 (USD per barrel) Source: US EIA

Consequently, retail fuel prices increased dramatically during 2008 and exceeded USD4.00 per gallon for gasoline. They then eased back considerably until early 2009 and then steadily increased during the remainder of the year, stabilised for a time in 2010 but then sharply increased again to almost USD4.00 per gallon again in May 2011, before drifting down to around USD3.30 by the end of the year. As of January 2012, the US EIA forecast regular gasoline would average around USD3.50 per gallon throughout 2013.

The price of diesel in the US has, of course, followed a similar pattern, peaking at USD4.70 in July 2008 before falling steadily to USD2.10 in March 2009 and then gradually increasing to exceed USD4.00 in April 2011. In January 2012, it stood around USD3.80 and the EIA forecast that it would remain in the USD3.80 to USD4.00 range through 2013.

Figure 4: US gasoline and crude oil prices, 2008 to 2013 (USD per US gallon) Source: US EIA


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CRITERION EMISSIONS

Exhaust and fuel system emissions from vehicles have been associated with a range of health problems including serious respiratory illnesses and cancer. The issue is more serious in congested urban environments to the degree that the US Environmental Protection Agency (EPA) has estimated that emissions from road transportation account for as much as half of all cancers attributed to outdoor sources of airborne toxic substances. In Europe, it has been estimated that as many as 300,000 die prematurely each year because of atmospheric pollution, much of which results from transport emissions. To date, the regulations in these and other jurisdictions cover carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), particulate mass (PM) and, in the US, formaldehyde (HCHO).

California developed the world’s first emissions standards in 1959 and the US federal government followed suit in 1970 with the Clean Air Act. Japan introduced regulations in 1966, and the first European countries and South Korea did so during the 1970s. Most other countries did not introduce criterion emissions regulations until the 1990s.

Light-duty vehicles

Europe

Various countries in western Europe began to adopt emissions regulations from the mid-1970s, and in 1984 the European Commission (EC) began to introduce standards. In 1988, an agreement to halve exhaust emissions by the early 1990s was reached among eight of the governments, although France later reversed its decision. In 1989, the EC adopted a directive on emissions for vehicles with engines smaller than 1.4 litres.

The first of the modern EU emission standards, Euro 1, was introduced in 1991, followed by Euro 2 in 1996. In 1999, there was an amendment that introduced emission limits and test cycles for compression-ignition engines and spark-ignition engines fuelled with natural gas or LPG used in heavy-duty vehicles. Euro 3 was introduced in 2000 and Euro 4 in 2005, setting increasingly stringent limits. Euro 5 was introduced in September 2009 and Euro 6 is scheduled for 2014/15, and essentially lowers emissions limits for HC and NOx for diesel light vehicles only. The standards apply to new type approvals from the year of introduction and for previously type-approved vehicles one year later.

Table 1: Euro 5 emissions limits for light gasoline vehicles (g/km) Source: DieselNet

Standard Date CO HC NOx PM

Cars Euro 4 Jan 2005 1.00 0.10 0.080

Euro 5 Sep 2009 1.00 0.10 0.060 0.005

Euro 6 Sep 2014 1.00 0.10 0.060 0.005

Light commercial vehicles Euro 4 Jan 2005 1.00 0.10 0.080

• 1,305kg Euro 5 Sep 2009 1.00 0.10 0.060 0.005

Euro 6 Sep 2014 1.00 0.10 0.060 0.005



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Standard Date CO HC NOx PM

from 1,305kg to 1,760kg Euro 5 Sep 2010 1.81 0.13 0.075 0.005

Euro 6 Sep 2015 1.81 0.13 0.075 0.005


over 1,760kg Euro 5 Sep 2010 2.27 0.16 0.082 0.005

Euro 6 Sep 2015 2.27 0.16 0.082 0.005

Table 2: Euro 5 emissions limits for light diesel vehicles (g/km) Source: DieselNet

Standard Date CO HC+NOx NOx PM*

Cars Euro 4 Jan 2005 0.50 0.300 0.250 0.025

Euro 5 Sep 2009 0.50 0.230 0.180 0.005

Euro 6 Sep 2014 0.50 0.170 0.080 0.005

Light commercial vehicles Euro 4 Jan 2005 0.50 0.300 0.250 0.025

• 1,305kg Euro 5 Sep 2009 0.50 0.230 0.180 0.005

Euro 6 Sep 2014 0.50 0.170 0.080 0.005


from 1,305kg to 1,760kg Euro 5 Sep 2010 0.63 0.295 0.235 0.005

Euro 6 Sep 2015 0.63 0.195 0.105 0.005


over 1,760kg Euro 5 Sep 2010 0.74 0.350 0.280 0.005

Euro 6 Sep 2015 0.74 0.215 0.125 0.005

The United States

California’s first standards set limits for CO and HC emissions from gasoline engines and the 1970 Clean Air Act launched non-mandatory inspection and maintenance programmes that were first adopted by New Jersey in 1974. However, there was considerable variability between states for many years, and in 1992 the EPA set minimum procedural and administrative standards that were amended further in 1990 and 1992. In 2000, the EPA set standards for model year 2007 vehicles that included a complex system of phasing in, averaging, banking and trading of emissions. Those standards included PM for the first time, and NOx and NMHC standards were phased in between 2007 and 2010. Diesel engines were also included and are required to meet Supplemental Emissions Test (SET) and Not-To-Exceed (NTE) limits of 1.5 times the basic standards.

US light vehicle standards apply to all new light-duty vehicles including medium-duty passenger vehicles up to 10,000lbs (4,536kg) and light-duty ‘trucks’, which include pick-


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ups, minivans and SUVs up to 8,500lb (3,856kg). The standards include a set of eight ‘Bins’ in which the allowable limits vary from no toxic emissions at all in Bin 1 through to the most relaxed standards in Bin 8. Each OEM must balance the production of Bin 5 to 8 standard vehicles with those that comply with the standards in Bins 1 to 4. Credits for NOx can be held over from previous years or traded with other OEMs and the standards apply to new vehicles for five years or 50,000 miles (80,000km), whichever occurs first.

Table 3: US emissions standards for light-duty vehicles, to five years/50,000 miles (g/mile)

CO NMHC NOx PM HCHO

Bin 1 0.0 0.000 0.00 0.00 0.000

Bin 2 2.1 0.010 0.02 0.01 0.004

Bin 3 2.1 0.055 0.03 0.01 0.011

Bin 4 2.1 0.070 0.04 0.01 0.011

Bin 5 3.4 0.075 0.05 0.01 0.015

Bin 6 3.4 0.075 0.08 0.01 0.015

Bin 7 3.4 0.075 0.11 0.02 0.015

Bin 8 3.4 0.100 0.14 0.02 0.015 Source: DieselNet

In November 2011, the California Air Resources Board (CARB) announced a target of reducing smog-forming emissions by a further 75% between 2016 and 2025. HC and NOx emissions can react in sunlight or warm conditions to form ozone, which is a primary component of smog.

Figure 5: The progress of EU gasoline emissions regulations Source: Johnson Matthey

Japan

Japan introduced standards for CO emissions from ‘ordinary-sized’ and ‘small-sized’ gasoline vehicles in 1966. These were followed in 1976 by the Motor Vehicle Exhaust


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Emission Regulations, which set standards for CO, HC and NOx for gasoline, liquefied petroleum gas (LPG) and diesel vehicles.

New emissions limits were set in 1989 with short-term and long-term targets, in 1993 new NOx limits were set and in 1997 new standards were set for implementation in 2002. In 2005, more stringent limits were introduced for HC, NOx and PM and a further reduction in the PM limit was set in 2009. In the table below, the PM limits for gasoline and LPG vehicles apply only to lean-burn, directed-injected vehicles with NOx adsorber catalysts.

Table 4: Japan emissions limits for light gasoline & LPG vehicles (g/km) Source: Japan Department of the Environment

CO NMHC NOx PM*

Passenger < 3,500kg 1.15 0.05 0.05 0.005

Commercial < 1,700kg 1.15 0.05 0.05 0.005

Commercial 1,700 - 3,500kg 2.55 0.05 0.07 0.005

Table 5: Japan emissions limits for light diesel vehicles (g/km) Source: Japan Department of the Environment

CO NMHC NOx PM

Passenger < 1,250kg 0.63 0.024 0.14 0.013

Passenger 1,250kg – 3,500kg 0.63 0.024 0.15 0.014

Commercial < 1,700kg 0.63 0.024 0.14 0.013

Commercial 1,700 - 3,500kg 0.63 0.024 0.25 0.015

Progress to date

The introduction of new standards in the three vanguard regions during the decade to 2010 resulted in substantial reductions in criterion emissions standards.

The three jurisdictions now also have PM limits in place for gasoline engines.

China

China’s first regulations became effective in the 1990s, but standards equivalent to Euro 1 were introduced nationally in 2000, Euro 2 in 2004, Euro 3 in 2007 and Euro 4 in 2011. However, the large metropolitan areas of Beijing, Guangzhou and Shanghai have adopted more stringent regulations on an accelerated schedule, with Beijing taking the lead by adopting Euro 4 in 2008 and scheduling the adoption of Euro 5 in 2012. Standards for light commercial diesel vehicles were introduced in July 2011.


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Figure 6 Criterion emissions reductions in the EU, the US and Japan, 1992 – 2015 Source: Daimler

Other countries

Eastern and central European countries have had to accelerate their standards to harmonise with EU regulations as they have joined the EU, and Russia adopted Euro 1 in 1999, Euro 2 in 2006 and Euro 3 from January 2008. Switzerland is also moving to harmonise with the EU.

In North America, Canada first set standards in 1971 and aligned them with the US federal standards from 1988. Mexico has also tended to adopt standards based on US standards although compliance can be certified with either US or EU standards.

In South America, Argentina, Brazil and Chile, emission standards have been in place since the early 1990s and tend to follow the EU standards although some US standards are also implemented.

India has had emissions regulations since 1989 that were tightened during the 1990s, and in 2000 it began adopting EU emissions and fuel regulations. Euro 2 was adopted nationwide in 2005 but Euro 3 was applied in the National Capital Region around Delhi and in nine other major cities.

In 1977, South Korea enacted regulations that took effect from 1980 that affected vehicles that were already in use as well as new vehicles. From 1985, all new gasoline and LPG vehicles were required to have catalytic converters, and unleaded fuel became mandatory in 1987. In 1993, new emissions regulations were introduced along with fuel quality standards.


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Australia introduced standards based on Euro 1 from 1995 and then implemented Euro 2 between 2002 and 2004, and Euro 4 during 2008/09.

Figure 7 Emissions standards timetable in selected countries, 2001 – 2010 Source: Implats

Figure 8 NOx limits in the EU, Japan and the US, 1995 – 2010 (g/kWh)

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Figure 9: PM limits in the EU, Japan and the US, 1995 – 2010 (g/kWh)

Medium- and heavy-duty vehicles

As with light-duty vehicles, since heavy commercial vehicle emissions standards were first introduced in the three vanguard jurisdictions, the allowable limits for emissions from new engines have steadily been reduced.

In the Californian and federal US standards, the limits for CO and HC remained unchanged, while those for NOx and PM were steadily reduced through to 2004 when the limits for all four were reduced and more stringent standards were phased in between 2007 and 2010.

The first heavy-duty emissions standards that were introduced in the EU in 1992 were voluntary and only for urban buses. Since then, the allowable limits have been steadily reduced. A smoke opacity test was introduced with Euro 3, and ammonia and particle number limits will be introduced with Euro 6 in 2013.

Japan’s heavy-duty emissions standards were quite relaxed through the 1990s, although in 1992 the Ministry of the Environment adopted regulations aimed at reducing NOx pollution from the oldest and most polluting in-use vehicles in certain geographical areas. The regulation was amended in 2001 to include PM limits, and in 2005 Japan introduced more stringent standards that were essentially aligned between those in the US and the EU.

Therefore, in all three jurisdictions, NOx and PM, which are the emissions of greatest concern from diesel engines, have reduced dramatically, as is illustrated in the two graphs below. It must be noted, however, that the test cycles used are different and the comparisons are indicative only.

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SPARK-IGNITION ENGINE TECHNOLOGIES

The quest for improved fuel efficiency from spark-ignition (usually gasoline) engines has driven the development of a range of technologies, including advanced valve train control, fuel injection patterns and the use of turbocharging and supercharging to enable engine downsizing. While gains in fuel efficiency tend to reduce criterion emissions, under some conditions some criterion emissions actually increase without the use of exhaust after-treatment technologies. Additionally, the production and use of alternative fuels can help reduce CO2 and criterion emissions.

Alongside the advances achieved for conventional internal combustion engines, a range of alternative engine designs are under investigation, some of which demonstrate the possibility of significant efficiency gains.

Figure 10 The effects of downsizing on fuel consumption Source: Ricardo

DOWNSIZING AND DOWN-SPEEDING

Engine efficiency improvements enable the use of smaller-capacity engines with similar performance but improved fuel economy. Downsizing the engine also tends to reduce weight, which, in turn helps to improve fuel economy. Bosch presented something of a benchmark a few years ago that has been validated by several OEMs, when it asserted that current technologies enable downsizing from a 2.0-litre, port-injection, normally-aspirated gasoline engine to a 1.4-litre unit with direct injection, variable valve timing and turbocharging, while delivering a fuel economy improvement of as much as 22% while complying with Euro 6 emissions standards.

Bosch further asserted that with higher boost pressure and variable valve lift, the 2.0-litre engine could be replaced with a 1.1-litre, three-cylinder unit that would provide a fuel economy gain of as much as 30% when powering a 3,086lb (1,400kg) car.


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The 70% downsizing and 22% fuel economy gain figures that Bosch referred to have been validated by major OEMs in their current, mass-market gasoline engines. Ford’s EcoBoost technology, for example, combines smaller displacement engines with turbocharging and direct fuel injection. It was originally featured on the 2007 Lincoln MKR concept vehicle ‘Twin-Force’, but Ford renamed it to reflect its potential for fuel efficiency rather than its potential for performance enhancement. It was launched on the Lincoln MKS flagship in 2009 with the 340hp (253kW), 3.5-litre V6 replacing the company’s 5.0-litre, normally-aspirated V8 with comparable performance and a 20% fuel saving as well as a weight reduction of around 150lbs (68kg).

GM has used the same technologies on its Ecotec 2.0-litre, four-cylinder gasoline engine that was launched on the Cadillac ATS compact luxury sedan at the 2012 Detroit Auto Show. It features a twin-scroll turbocharger with an air-to-air intercooler to minimise transient lag and deliver a broad torque curve from 1,500rpm to 5,800rpm, during which it achieves 90% or more of its peak output of 255lb.ft (353Nm). The engine also features four valves per cylinder with continuously variable valve timing and direct fuel injection. To further enhance efficiency, it also features a two-stage, variable-displacement oil pump with jet-spray piston cooling.

The company describes the new 2.0T engine as one of the most power dense automotive engines at 135hp (101kW) per litre, challenging high performance engines from luxury competitors including Audi, BMW and Mercedes-Benz. “The 2.0T is one of the most advanced and efficient engines of its kind and contributes to the ATS’s exceptional balance of performance and great fuel efficiency,” said Mike Anderson, chief engineer for the 2.0T engine. “It has the exhilarating, responsive power available when you want it, yet can provide the fuel efficiency that will make the ATS a fully competitive vehicle in global markets.”

Another strategy that can improve fuel economy in a gasoline engine in conjunction with downsizing, is that of down-speeding. The technologies used to achieve downsizing can be optimised to increase maximum torque output, particularly in the lower engine speed ranges, and this enables the use of taller transmission ratios to take advantage of the improved torque. The lower overall engine speeds required result in lower fuel consumption.

COMBUSTION CYCLES

The most popular combustion cycle used in the gasoline internal combustion engine is the four-stroke Otto cycle, named after Nikolaus Otto, who developed the first successful four-stroke cycle engine in collaboration with Eugene Langen in 1876. The Otto cycle produces good power without forced induction but is not as optimised for fuel efficiency as alternatives such as the Atkinson and Miller cycles, which have been less popular while the emphasis has been on power.

Although the original Atkinson cycle achieved the four Otto cycles in one engine revolution rather than two through the use of a crankshaft design that resulted in differing expansion and compression volumes, the name has more recently been applied to Miller cycle engines used on several hybrid-electric vehicles, on which fuel efficiency is the primary goal and power output can be supplemented by the electric drivetrain.


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Prior to hybrid applications, Miller-cycle engines have tended to feature forced induction to compensate for the lower specific power that results from the extended inlet valve timing. In the Miller cycle, the inlet valve is kept 20% to 30% open beyond piston bottom dead centre in order to reduce the energy lost during the first, least-efficient part of the compression stroke. This results in some fuel mixture being forced back along the inlet tract, reducing the potential for power output.

Although a supercharger can be used to increase fuel charge volume, the resultant power gain must be balanced against the parasitic loss incurred to drive it. Lotus Engineering, in collaboration with Continental, used turbocharging in conjunction with direct injection and camshaft phasing to enable a switch from Otto-cycle operation to a Miller cycle under low-load conditions on their Sabre engine project. Mazda used a Miller-cycle engine without forced induction on the Mazda2 by coupling the engine to a continuously variable transmission that enabled the engine to remain within its most efficient operation range.

STRATIFIED CHARGE COMBUSTION

Stratified charge combustion, or ‘lean burn’, engines use a rich air-fuel mixture in a small area or compartment within the combustion chamber to initiate the ignition process through a lean mixture in the rest of the chamber. The overall lean mixture helps to further enhance fuel efficiency by reducing pumping losses. Fuel economy gains of up to 20% have been claimed for stratified combustion engines compared to non-stratified designs. But research by Ford with engines that used spray-guided injection to achieve a stratified charge indicated that gains of between 10% and 15% were achievable at low engine speeds, but these diminished exponentially with engine speed so that almost no gain was measured at highway speeds.

Honda introduced the concept on a production engine during the 1970s with the launch of the Compound Vortex Controlled Combustion (CVCC) engine that featured a third inlet valve through which a rich mixture was supplied to a small space around the spark plug separated from the rest of the chamber by a perforated metal plate. Honda has achieved stratified charge operation with air-fuel ratios as low as 1:22 compared to the traditional stoichiometric gasoline ratio of 1:14.7 although the lean-burn operation can only be achieved under lower engine speeds and light loads. Furthermore, lean combustion leaves high proportions of oxygen in the exhaust gases which results in increased NOx emissions, necessitating the provision of additional exhaust after-treatment such as a lean NOx trap (LNT) as well as the conventional three-way catalytic converter and the use of ultra-low sulphur fuel.

The Merritt Unthrottled Spark Ignition Combustion (MUSIC) engine, which was initially developed by Dr. Dan Merritt at Coventry University in the UK, uses a redesigned cylinder head on an otherwise conventional engine and demonstrated a 19.8% fuel economy improvement compared to a baseline 2.0-litre Ford Duratec engine. The cylinder head incorporates specially-designed injectors and a separate, cylindrical combustion chamber on each cylinder that has an inbuilt helical swirl pattern. During the compression stroke, the piston forces air to spin around the periphery of the combustion chamber with a strong forward bias towards the far end of the chamber where the spark plug is situated, thereby creating a helical swirl motion. This helical swirl motion has the effect of stacking layers of rotating gas so that air delivered early in


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the compression stroke is situated near the spark plug end of the combustion chamber and remains in this location throughout the compression stroke.

The external combustion chamber is connected to the main cylinder by an orifice large enough to minimise the pumping losses associated with the gas transfer, but which forces air to emerge as a powerful jet as it enters the combustion chamber so that its velocity, density and temperature all increase during the compression stroke. As the air jet emerges from the orifice, a GDI system delivers gasoline, or other fuels, directly into it. Fuel delivered early in the compression stroke finds its way to the spark plug end and remains there, ensuring spark ignition even when air with no fuel follows the fuel injection stops. The resultant stratified charge keeps the air-fuel mixture separate from the air with no fuel while ensuring a very rapid vaporisation of injected fuel, enabling the engine to operate without throttling from idle to full load.

Load and speed control are achieved throughout a normal operating range through precise control of injection timing and duration. To support high load conditions, the MUSIC system delivers fuel to the air jet until the end of the compression stroke, when the air mass flow is very rapid and time is short using a second fuel injector – the Power Injector. The Power Injector injects axially into the air jet when the air is hot and dense, enabling rapid vaporisation and can also deliver some fuel to the air contained in the bump clearance above the piston at top dead centre at the end of the compression stroke. It may be possible to incorporate the functions of the two injectors into one complex injector, but the cost and complexity of such an injector may exceed the cost of two simple solenoid injectors that are currently mass-produced.

The MUSIC engine has been shown to be self-sustaining on ultra-lean mixtures of more than 100:1. Furthermore, NOx emissions are extremely low, possibly because of the cooling effect of the high surface area of the helical chamber and the high proportion of air.

VARIABLE VALVE CONTROL

For much of its existence, the valve timing and valve lift on internal combustion engines were both fixed and each engine had to be ‘tuned’ for the intended speed range and power output characteristics. The extremes of engine tuning ranged from strong low-speed power with limited capacity to produce high-speed power through to high-revving, high-output engines with poor performance in terms of low torque output and high emissions at low speeds. However, advanced valve control has enabled variable engine tuning that results in efficient and clean operation through an extended engine speed range.

Variable valve timing and lift

Fiat launched the first production application of variable valve timing (VVT) on the 1980 Alfa Romeo Spider 2.0 L, which used a mechanical system despite the company having developed a hydraulic system several years earlier. Hydraulic pressure is generally favoured to power VVT systems, although Ford and Subaru, for example, have used the BorgWarner Cam Torque Actuated system that draws power from the camshaft itself on several engines.


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Honda was the first OEM to combine variable lift with variable timing on a mass-production car when it launched its electronically controlled VTEC (Variable Valve Timing and Lift Electronic Control) on the 1989 Civic, CRX and Integra models. The VTEC system switches between two different cam profiles, one which optimises performance at low engine speeds to provide good driveability, good fuel efficiency and low emissions, while the other delivers high power output at high engine speeds. However, VTEC tends to leave the mid-range poorly served, particularly in its more extreme variants such as on the S2000 sports car. In the S2000 VTEC delivers very high specific power at high engine speeds (240hp; 177kW at 8,300rpm and 153lb.ft; 208Nm at 7,500rpm) but relatively modest output up to engine speeds that would be regarded as high in most other road-going cars – including sports cars.

To address this shortcoming and those of cam-phasing VVT systems, Honda followed VTEC with i-VTEC (Intelligent Variable Valve Timing and Lift Electronic Control), which enables advancing and retarding of the camshaft in order to increase or decrease valve overlap to further enhance performance at high and low engine speeds, respectively. It was launched on the 2001 Civic Type R and Stream MPV models, underscoring its adaptability to two very different engine power characteristic profiles. For the Stream, the two-stage variation in valve timing and lift is applied to only one of the two inlet valves, similar to the VTEC-E system fitted to the Honda Insight. For the higher-powered engine variant, the DOHC VTEC system uses three cam lobes for the two inlet and exhaust valves associated with each cylinder.

At lower engine speeds each pair of valves is operated by the two identical profile outer cam lobes, via roller cam followers. In between the two, the third rocker is actuated by the centre cam lobe. This lobe provides higher lift and will open the valves for longer than the outer matched pair. At lower speeds, the centre third rocker merely follows its cam lobe profile but serves no other function. The pivot shaft for the cam followers feeds oil under pressure through it to the centre rocker. At a pre-programmed engine speed, the engine ECU opens a valve and the pressurised oil pushes two pins from the centre rocker through its adjacent rockers. Locked together, all three rockers then follow the centre lobe high lift/ longer dwell cam profile, improving gas flow. The result is a higher specific power output and a broader spread of torque across the engine’s operating range.

For lower rated engines, the design is more conventional. There is a pair of cam lobes for each pair of valves on the inlet camshaft. One lobe has a fairly normal cam profile while the other is almost circular, opening the valve sufficiently to create swirl in the cylinder at lower speeds, permitting the use of a lean mixture. As engine speeds rise, a pin again locks the two followers and both valves follow the more normal cam profile increasing mixture flow and power output. The exhaust cam is completely conventional without any VTEC component.

The inlet cam in the current i-VTEC engine is attached to its sprocket drive by a collar with a helical gear on its outer surface. This in turn fits into a corresponding helical gear at the centre of the drive sprocket. Hydraulic pressure acting inside the helical gear unit can force the camshaft and its drive sprocket further apart which, via the helical gear, rotates the camshaft relative to the sprocket, advancing or retarding inlet valve timing relative to the exhaust valves. Again, the engine ECU controls the oil pressure valve regulating pressure in the helical gear.


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Whereas the cam profile change is in two fixed stages, the system is continuously variable according to the ECU mapping. The better torque characteristics of the i-VTEC engine are the result of the greater degree of valve overlapping the system permits. Gas flow can be improved at any engine speed, it is no longer restricted to the ‘fast cam’/high rpm phase of Honda’s conventional VTEC. The variable cam phasing also offers reduced fuel consumption and emissions performance, through improved exhaust gas recycling. Although this tends to result in lower maximum power output, maximum torque is produced at lower speeds and the torque curve is flatter. For example, over 90% of maximum torque is available by 3,000 rpm in the Civic Type R and the Stream engine delivers 95% by the same engine speed although its torque curve is not as flat.

Figure 11 Honda i-VTEC system Source: Honda Civic Forum

BMW favours a continuously-variable valve lift system it calls Valvetronic, in which valve lift to control air intake is varied mechanically through an ‘intermediate arm’ located between each camshaft lobe and its inlet valve, pivoted at both the top and centrally, close to the cam. An electric motor with worm gear and eccentric drive atop the valvetrain acts upon a shaft close to the upper top pivot point that in effect moves the intermediate arm closer to, or further away from, the camshaft which in turn effects the valve opening. The closer the central pivot point is to the cam, the wider the valve opening with lift variable from zero to 9.7mm, and the adjustment of the worm gear from one extreme to the other takes only 300 milliseconds. Combined with BMW’s Double Vanos valve timing technology, the camshaft angle relative to the crankshaft can be adjusted by up to 60º.

The intermediate arm is finished to a tolerance of 0.008 mm and the cams controlling the eccentric shaft are machined to tolerances of a few hundredths of a millimetre. The entire system is pre-assembled and dropped as a module into position in the cylinder head. A 40 Mhz 32-bit engine management system CPU reflects the speed at which the system needs to operate with another processor controlling the Valvetronic system. Other advantages include improved atomisation at low throttle openings due to gas velocity of around 320 per square metre through the part open valves, and cleaner valve seats due to the high velocity.


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Figure 12 BMW Valvetronic system Source: Tech-On

This Valvetronic system enables the intake charge to be controlled entirely by the intake valves, eliminating the need for a throttle valve and greatly reducing pumping loss. The reduction of pumping loss accounts for more than a 10% increase in power output and fuel economy. Indeed, BMW claims a fuel economy gain of 10% for the system on its four-cylinder engines and 14% on its V8s. Consequently, BMW has claimed that the technology is as significant as the change from carburettors to fuel injection some years ago, and it has become a fundamental building block in the company’s efforts to reduce CO2 emissions from its production fleet, despite the estimated 15% increase in production cost compared to its original VVT system.

Nissans VVEL, which was introduced with the Nissan VQ Engine VQ37VHR in 2007, features a rocker arm and two types of links to close the intake-valves by transferring the rotational movement of a drive shaft with an eccentric cam to the output cam. Rotating the control shaft within the DC motor and changing the fulcrums of the links can vary the movement of the output cam. This makes a continuous adjustment of the valve lift amount possible. C-VTC and VVEL together control the valve phases and its valve events and lifts, allowing free-control of the valve timing and lift. This results in more efficient airflow through the cylinder and significantly improves responsiveness, optimising the balance between power and environmental performance. It functions similarly to BMW’s Valvetronic system, and similar systems have been developed by Honda (Advanced VTEC or AVTEC) and Toyota (Valvematic). Toyota claims a fuel efficiency gain of 5% to 10% for the Valvematic system, largely through the reduction in pumping losses achieved by eliminating intake throttling.


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Figure 13 Fiat MultiAir system Source: Fiat

BorgWarner’s Cam Torque Actuated (CTA) utilises the torsional energy of the camshaft to achieve phase shifts more quickly than those that use engine oil pressure and is capable of a mid-position lock default position that enables a greater range of cam phase variation in order to achieve better control over airflow to improve fuel economy. Other cam phasing systems default to one end of the variable range, which limits the degree of variation that can be designed into the system. BorgWarner also claims that the CTA system is fully functional shortly after engine start when a large proportion of emissions occur. According to Subaru, the use of the CTA system has resulted in fuel economy improvements of up to 6% on its 2.5-litre, four-cylinder engine and up to 10% on the 2.0-litre engine.

Delphi has also developed a cam phasing system that is independent of the engine oil pressure and which provides extended variation under all temperature conditions and engine speeds. The compact electric variable cam phasing (eVCP) system includes a phasing mechanism, an electric motor and an electronic controller.


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Figure 14 Valeo e-valve system Source: Valeo

Electro-hydraulic valve actuation

In collaboration with Schaeffler, Fiat developed and patented an electro-hydraulic valve actuation system that can vary valve timing, dwell and lift. While it employs a conventional camshaft and valve springs, each intake valve stem features a hydraulic piston that can vary its actuation via a solenoid-actuated bleed valve. When the solenoid valve is closed, the chamber remains full and extends the inlet valve to its maximum extent so that it follows the cam profile, which is optimised for high-end power. If the chamber were to be emptied, the inlet valve would remain fully closed, but variable partial filling results in different inlet valve actuation patterns.

The system, which Fiat calls MultiAir, was launched on the 2010 Alfa Romeo MiTo 1.4 MultiAir and is used on the two-cylinder, 875cc, fuel-injected, turbocharged engine on the 500 model. Fiat claims that the system enables downsizing and can achieve fuel consumption and CO2 reductions of up to 25% along with improved starting, part-load and acceleration performance. During warm-up, HC emissions are reduced by as much as 40% and NOx by as much as 60%. The two-cylinder engine develops 79hp (59kW) and emits 69g/km of CO2, and its design is modular enabling four-, six- and eight-cylinder variants.

Electromagnetic valve actuation

Several suppliers, including AVL, Eaton, FEV, Jacobs, Lotus Engineering, Ricardo, Sturman and Valeo, have been investigating camless engines that employ electromagnetic valve actuation using solenoids to open and shut the valves. While enabling infinitely-variable valve timing and lift, and the elimination of intake throttling, the technology also offers the possibility of eliminating the mechanical energy losses produced by the camshaft drive system, the friction between the cams and followers, and the compressing of valve springs.


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However, because magnetic force varies in proportion to the square of the gap between magnet and disc, there is clearly a limit to the maximum lift the system can provide. Also, experience has shown that this same effect produces a relatively violent valve shutting action, which as well as being inherently noisy, in the long term use it threatens undue valve seat recession wear. Systems to date have also presented packaging difficulties, since electromagnets powerful enough to provide the force required tend to be heavy and large, although it is offset by the weight and space reduction achieved by the removal of the camshafts and other components usually used for valve actuation.

Figure 15 Camless, electromagnetic valve control on test at Lotus Engineering Source: Lotus

BMW, in co-operation with Continental, developed an electronically controllable VVT system that exhibits several of the possible benefits of the technology. The BMW system replaces the camshaft with powerful electro-magnetic actuators, one to each valve. Each actuator consists of two electro-magnets each side of a ferrous disc that is part of a vertical shaft, one end of which terminates in the valve head. This shaft and disc are loaded by compression springs, explaining why the generic name adopted by some for this type of mechanism is a mass resonance system. However, given that such an arrangement can attract the disc fully up, fully down or, with equal magnetic flux from both coils, midway, it is limited by the capacity to put the valve head in just three positions – fully open, fully closed, or halfway between.

Cylinder deactivation

The switching on and off of cylinders is known as cylinder deactivation, variable displacement engine or displacement on demand technology and the concept underwent something of a revival a few years ago due to advances in electronic engine management and the associated software control algorithms. The cylinder deactivation systems used in some cars in the 1980s – such as in a Cadillac V-8-6-4 engine in 1981 – were noisy when operating on four cylinders and were unable to make a seamless transition to eight-cylinder operation because the limitations of on-board computers of the day.


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The technology re-appeared successfully on the 1999 Mercedes-Benz S-Class 5.0 litre DOHC V8 using electronic control. The Mercedes-Benz V8 simply cut back to four-cylinder operation without the intermediate step to six and the company claimed a fuel economy improvement of about 7% in city-cycle driving and as much as 15% in steady highway cruising at 56mph (90kph), while 13% could be achieved at 75mph (120kph). Mercedes-Benz offered the technology on its V12 from 2001, claiming a 20% gain in fuel economy, but discontinued it in 2005.

As its various names suggest, the technology reduces fuel consumption by reducing the number of operating combustion chambers when the engine only has to supply part of its power and torque, for example in urban traffic, on country roads or when cruising on the motorway at a constant speed in the medium range. Normally, under these conditions, a conventional engine loses efficiency due to incomplete cylinder filling and high losses during the gas cycle. As soon as the engine is only operating in the part-load range, the electronic engine control unit deactivates half of the combustion chambers.

The work of determining which cylinders are not necessary is handled by a microprocessor that controls the opening and closing of selected intake and exhaust valves. With the valves closed, piston movement continues, but there is no mechanical work lost because the air in the cylinder is simply compressing and expanding. Engine displacement quickly switches back to the full number of cylinders as soon as the driver depresses the accelerator, such as in an overtaking situation.

The fuel consumption of the Mercedes-Benz S 500 in the NEDC driving cycle is reduced by an average of up to 7%, the same figure claimed by Ford for its 5.4 litre Ford F-150 4x4. Ford claims an 11% saving for its 6.8 litre V10. These figures can be further improved depending on driving style. According to figures published by Daimler, gasoline consumption is reduced by about 15% when cruising at a constant speed of 90 kph and by 13% at a constant 120 kph.

In 2001, GM announced that it would be implementing a much-updated version of cylinder deactivation technology, which the company called Displacement on Demand (DOD) and which was targeted initially at the Vortec family of V8 engines used in its various pick-up and SUV models. It was launched on the 2005 GMC Envoy XL. GM's implementation is made relatively simple by virtue of the engine’s pushrod-actuated overhead-valve architecture. It utilises a series of computer-controlled solenoids, developed by Eaton, to selectively unlock specific valve lifters as required, thus deactivating the associated cylinders and turning the V8 into a V4. When the power of all eight cylinders is required it is only a few microseconds away. Under acceleration and medium to heavy load conditions the powertrain control computer commands the solenoids to lock the lifters so the valves regain their function. Software algorithms eliminate driveability and durability concerns, and the transition is transparent to the driver. As well as improving fuel economy, the technology extends a vehicle’s range and helps to meet lower exhaust emission requirements.

In 2003, Honda introduced a new V6 engine featuring cylinder deactivation coupled with i-VTEC technology and launched it on the Inspire/Accord model. Using the new 'Variable Cylinder Management' (VCM) technology, the J30A 3.0 litre i-VTEC V6 runs on all six cylinders during acceleration and when high output is required but cuts back to three cylinders during cruising and at low engine loads. The VCM system analyses throttle opening, vehicle speed, engine speed, and gearing to determine that the car is


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cruising and then closes the intake and exhaust valves and shuts off the fuel injection of the three cylinders in the rear cylinder bank. When operating in three-cylinder mode, engine vibration is reduced by extrapolating vibration from the change in crankshaft rotation speed and sending the information to an 'active control' engine mount, which compresses and extends an actuator in same-phase, same-period motion to dampen the engine mount. Similarly, a speaker creates an opposite phase sound, or 'active noise control', to provide a cancelling effect for a quieter interior, which leaves the driver and passengers unaware of changes in cylinder activation.

As well as incorporating cylinder deactivation, the J30A engine has integrated exhaust manifolds with high-density, low back-pressure catalytic converters located directly below each cylinder head for improved exhaust gas processing at low engine temperatures, combined with exceptionally fine air-fuel ratio control to reduce emissions. The adoption of a variable intake system and over-sized intake valves further improves engine respiration efficiency. According to Honda, the engine delivers the normal maximum power expected of an engine of its size, but with the fuel economy and lower emissions of a smaller engine. The J30A engine was launched on the Inspire/Accord models, including the V6 Accord Hybrid, and the Odyssey MPV.

Chrysler introduced cylinder deactivation in some models, beginning with the 2005 Chrysler 300C and Dodge Magnum RT. The company made it a standard feature of the 5.7 litre Hemi engine that is fitted to vehicles as diverse as the Jeep Grand Cherokee and the Dodge Charger. Chrysler calls their cylinder deactivation system ‘Multi-Displacement System’ (MDS) and claims that fuel economy gains of up to 20% under various driving conditions are possible, with a projected 10% aggregate improvement. The Hemi can transition from eight cylinders to four in 40 milliseconds.

In September 2011, Audi announced a new V8 engine that will replace the V10 used on the S6, S7 and S8 models. Using variable camshaft profiles, four cylinders can be shut down during light-load conditions. Audi claims that the engine will be able to operate as a V4 at speeds up 87mph (140kph) on a flat road and that fuel economy will be improved by nearly 20%.

DIRECT INJECTION TECHNOLOGY

Gasoline direct injection (GDI) is an alternative to port injection technology and, as the name suggests, injects fuel directly into the cylinder. GDI operates at much lower injection pressures than commonrail diesel systems (around 2,000psi/140bar compared to diesel’s 29,000psi/2,000bar) and can enable either a homogeneous or stratified air-fuel mixture within the combustion chamber. Typically, several spray jets are employed to produce spray patterns that can be customised to suit different combustion chamber shapes and to enable spray-guided combustion. Its advantages include that the fuel does not displace air during the intake process as port injection does, so the amount of air trapped in the cylinder is increased and, as the fuel evaporates, it cools the charge in the cylinder, reducing the likelihood of knock and allowing a higher compression ratio to be used. These effects can improve power output and fuel economy by as much as 15% compared to a carburettor-equipped engine in part because it reduces pumping losses.

Injector actuation is achieved through ‘direct actuation’ in which a ceramic piezo actuator directly moves the injector needle, or through ‘servo actuation’ in which a


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solenoid or a piezo valve moves the needle electro-hydraulically. Direct actuation systems operate up to three times more rapidly than servo actuation systems and can achieve up to 4% better fuel economy through more precise operation. The capacity to provide up to seven injection events per intake cycle enables the injection system to adapt to all engine loads and speeds with greater accuracy, while reducing emissions, fuel consumption and combustion noise. Nevertheless, Delphi launched a solenoid-based system in late 2008 on its new spray stratified ‘Multec 20’ GDI system because of the lower production cost compared to piezo-based systems.

Although direct fuel injection has been used for many years on diesel engines and in aircraft engine applications, its first use on a production road vehicle was on the 1967 Volkswagen 1600 TL, which used Bosch’s D-Jetronic system. In 1997, the Mitsubishi 1.8 GDI engine entered production and represented such a significant advance that it prompted many undecided car manufacturers to commit to the concept. Growing concerns over particulate emissions were threatening diesel acceptability for light vehicles, making non-diesel high efficiency engine concepts even more attractive.

Direct injection systems have also been used in motorsport. Audi used a Bosch direct injection to advance on its landmark 1-2-3 success at Le Mans in 2000. The move to GDi became a core part of Audi’s drive to reduce emissions and fuel consumption across its range. Termed the FSI principle by Audi, its significance is on a par with that of the TDI diesel engine, combining high power output and lower fuel consumption to a previously unattainable degree. Torque and power output are both increased, and fuel consumption is claimed to be reduced by up to 15% in early stratified versions of the engine. Most FSI engines now operate with homogeneous, lambda 1, combustion systems.

It was the introduction of a number of key technological features in the early FSI engines that Audi maintains moved the goalposts for production gasoline engines. This includes a high-pressure ‘commonrail’ fuel injection system with a single-piston injection pump specially developed for this purpose – it only supplied sufficient fuel to maintain the desired pressure in the system and enabled the elimination of fuel coolers and return flow pumps, which in turn eliminated pumping losses as a much as 1.34hp (1kW). The engine also had a new cylinder head with four valves per cylinder, valve operation by roller cam followers and a developed version of the air-guided combustion process with continuous control of charge movement. Finally, early versions of the engine also featured an exhaust emission control system with a NOx storage-type catalytic converter and NOx sensor.

In the FSI combustion chamber, the injector is located in the side of the cylinder head and the injection period is controlled to within a thousandth of a second at injection pressures of up to 1,600psi (110bar). In the stratified-charge operating mode, fuel is injected on the engine’s compression stroke and is picked up by the movement of the air that has been drawn into the combustion chamber. This movement is imparted to the air by a movable flap in the intake pipe and by the shape of the intake port and the piston crown. The resulting controlled movement is known as ‘tumble’.

After combustion, a layer of insulating air remains between the ignited mixture and the cylinder wall, reducing the amount of heat lost to the engine block and increasing the engine’s operating efficiency. In the stratified charge operation, overall lambda values of up to 4.0 are achieved, which is essential if fuel consumption is to be reduced at low and


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medium engine speeds. At full load, the fuel is injected synchronously with the air intake phase to fill the combustion chamber homogeneously.

After having been brought to market with the Volkswagen Lupo FSI, it was subsequently introduced on the Volkswagen Golf and the Audi A4, by which time a number of OEMs were also showing their own approaches to the technology. For example, at the IAA Show in Frankfurt in September 2001, GM unveiled an innovative V8 that showcased several advanced technologies including an air-assisted direct injection petrol system developed by the Orbital Engine Corporation and Delphi. The air-assisted direct injection system was integrated into a unique three-valve cylinder head design with dual cams in the block, enabling optimal positioning of the injector and spark plug in the centre of the combustion chamber.

BMW also claimed a first at that time with an all-new 6.0-litre, V12, aluminium engine featuring GDI, Valvetronic technology and fully variable bi-Vanos camshaft control. The company claimed that the combination of these technologies allowed unparalleled fuel economy and exceptional specific torque and power output. However, its greatest advantage is that, contrary to GDI engines incorporating a lean-burn concept and a DeNOx catalytic converter, the BMW Valvetronic + DI concept with lambda 1 emission technology is suitable for use worldwide, regardless of the level of sulphur in the fuel available, without any increase in fuel consumption.

Daimler’s first use of modern direct fuel injection technology was achieved with the M 271 – a turbocharged Mercedes-Benz four-cylinder gasoline engine. Compared to its predecessor, fuel savings averaging 18% were achieved while complying with the then-current Euro IV emission limits.

It is expected that direct injection engines will continue to make inroads in the market. Stratified combustion will be increasingly used as lean NOx catalysis becomes cost effective and the fuel efficiency gains offered by lean combustion can be realised over a wider speed range. Direct injection technology will also be an enabler for a wider range of technologies.

Spray-guided injection

Mercedes-Benz introduced the world’s first gasoline engine with Bosch piezoelectric direct injection and spray-guided combustion – the Stratified-Charged Gasoline Injection (CGI) engine – on the C 350 CGI BlueEfficiency model in 2008 with claims of a 14% improvement in fuel economy and a 15% improvement in power over a wall-guided injection system. The main advantage of the CGI engine is in the stratified operating mode from which it takes its name. During this mode, the engine is run with a high volume of excess air and the deployment of multiple injection events extends this lean-burn operating mode to higher rpm and load ranges.

In a wall-guided injection system, the stream of fuel hits the piston floor, forming a cloud of fuel and air that moves toward the spark plug (top). In comparison, in a spray-guided system, a hollow cone of fuel is produced at the injection nozzle. This cloud of fuel and air, which is formed adjacent to the spark plug, is relatively stable and is readily ignited by the spark.


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Figure 16 A comparison of wall-guided and spray-guided direct injection Source: Mercedes-Benz

Spray guided injection uses the precise control characteristics of piezo injector technology, the power of modern electronic engine management and high pressure (2,900psi; 200bar) commonrail technology to increase performance and optimise the use of stratified operation. Continental claims that its piezo injectors offer higher speed, precision and control compared to solenoid gasoline direct injection technology. In comparison to a port fuel injection engine, a piezo direct gasoline injection, spray-guided engine with stratified-charge operation is estimated to deliver fuel savings of up to 20%, while also improving emission values.

The stable spray characteristics of the piezo injectors and the fine atomization of the fuel, in combination with the ability for multiple injections, are ideally suited to spray-guided combustion at partial load. During the combustion process, gasoline is directly injected into the combustion chamber near peak cylinder pressure to better utilise the gasoline, resulting in a combustible mixture only in the immediate area of the spark plug. Because this mixture is formed in the upper part of the combustion chamber and there is no mass of combustible mixture below, it is a stratified charge. Piezo injectors allow the use of a stratified charge at higher driving speeds and engine loads and enable it to be applied on larger-capacity engines.


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FORCED INDUCTION

Forced induction, whether by exhaust-powered turbocharging or mechanically- or electrically-powered supercharging, increases the amount of air-fuel charge drawn into the combustion chamber by compressing it and consequently enables engine downsizing to around 70% of the swept volume of a normally aspirated engine with similar power output, while improving on its fuel economy by up to 15%. A typical example of this is illustrated by Renault’s use of 1.4-litre turbocharged Nissan engine in place of its own 2.0-litre naturally aspirated unit. The smaller, turbocharged unit developed almost identical power and torque to that produced by the normally aspirated engine but reduced CO2 emissions by 16%.

However, turbochargers and engine-powered superchargers have their downsides. Although turbochargers utilise exhaust system energy that would otherwise be wasted to power a turbine which drives a compressor, they exhibit a response delay while the turbine is brought up to speed, typically when the engine is operating in a relatively low-torque range so that there is a pause before the vehicle accelerates as required. Also, although turbochargers are often represented as not draining any engine power, supercharger engineers assert that when turbochargers are throttled, or a smaller one used in a twin-turbo system to increase turbine pressure at low engine speeds, the exhaust back pressure increases and consumes engine power equivalent to that required to power a supercharger.

Although superchargers do not exhibit the same transient response delay, the power they draw from the engine reduces some of the advantage gained through compressing the air-fuel charge, although this can be optimised using a clutch to disengage the compressor when it is not required. Electrically powered superchargers can be programmed to automatically stop functioning when not required in order to minimise the electrical power drain.

The use of direct fuel injection can reduce the impact of turbocharger delay and other approaches that also improve it include multi-stage turbocharging, twin-scroll turbocharging, variable geometry turbochargers and combining a supercharger and a turbocharger.

Multi-stage turbocharging

Multi-stage turbocharging systems, most of which employ two compressor stages, essentially use two turbochargers that are designed to function optimally in two different engine speed ranges. Typically, a smaller, high-pressure unit is used to minimise the response delay and increase torque output at lower engine speed while a larger, low-pressure unit gradually takes over at higher engine speeds. In this way, effective forced induction is provided across a wide engine speed range while the inherent delay of the larger unit is masked by the operation of the smaller one. Because of the additional cost of producing a multi-stage system, they tend to be fitted to only high-end vehicles.

Parallel twin turbocharging systems have two identical turbochargers that simultaneously and equally share the workload with the engine cylinders receiving compressed air from both through a common intake manifold. They are often used to supply both banks of V-shaped engines, such as on the 2011 Range Rover TDV8’s 4.4-litre V8 that is equipped with a Honeywell TwoStage Parallel turbocharger. Land Rover


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claimed best-in-class transient response for the new engine, which replaced the previous 3.6-litre turbo-diesel to provide a power increase of 15% and a torque increase of 9% while improving fuel economy by 19% and reducing CO2 emissions by 14%.

In sequential twin turbocharging, during lower speeds the engine only uses one turbocharger to utilise all the exhaust energy with the second one shut down by a shut-off valve. At high speeds, the second turbocharger is activated and both units function to provide maximum power output. Lag is reduced and the required level of boost is maintained, even at low engine speeds. Sequential systems tend to be complex and expensive, and have limited wider application.

BorgWarner, in collaboration with BMW, developed a ‘regulated’ or ‘modulated’ two-stage system that enables continuously variable adaptation of the turbine and compressor sides of the turbocharger for every operating point of the engine by using two turbochargers of differing sizes connected in series – a smaller, high-pressure unit that operates to minimise lag and a larger, low-pressure unit that provides sufficient boost at higher engine speeds. The design enables the use of a smaller high-pressure turbocharger than the one fitted on a standard two-stage system, which aids the reduction of lag and increases performance. On light vehicle applications there tends to be an additional bypass on the low-pressure turbine and an extra compressor bypass compared to the configuration that has been traditional on heavy commercial vehicles.

Twin-scroll turbochargers

Twin-scroll turbochargers have dual openings, or volutes, into the turbine housing, which contains two scrolls of differing size. The primary scroll is designed for low-speed operation with the secondary one to protect the energy of the exhaust pulse all the way through the turbine to create peak pressure rather than an average pulse pressure. Both scrolls are used for high-speed operation. The technology is well suited to smaller-displacement engines, particularly four-cylinder units that have a low pulse rate per crank rotation.

Figure 17 Twin-scroll versus mono-scroll turbocharger performance Source: BorgWarner


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In 2009, the BMW 535i Gran Turismo 3.0-litre, six-cylinder, direct-injection gasoline model was launched featuring a BorgWarner twin-scroll turbocharger. BMW claimed that the car outperformed many fitted with naturally aspirated V8 engines while significantly improving fuel economy and reducing emissions. “The twin scroll technology produces results similar to twin-turbo applications but in a smaller package with lower weight and cost,” said Roger Wood, president and general manager at BorgWarner Turbo Systems. BMW followed in 2011 with the twin-scroll TwinPower Turbo system on a four-cylinder, 2.0-litre gasoline engine on the X1 SUV and announced that the technology will be applied to a new family of three-cylinder engines that the company plans to produce for the next generation Mini and entry-level BMW models.

In October 2011, Honeywell announced that its next generation of gasoline turbochargers will be launched on new vehicles within three years. The company claims that the ‘Gasoline VNT DualBoost’ turbochargers, which feature two back-to-back, twin-scroll compressor wheels mounted on ball bearings within a single housing, will be 30% smaller, 30% lighter and provide 70% less inertia compared to current models.

Variable-geometry turbochargers

Variable-geometry turbochargers (VGT), as the name implies, vary the geometry of the turbine or compressor in order to optimise their functioning across a wide engine speed range. The most common VGT design uses a set of movable vanes in the turbine housing, which control boost by varying the exhaust turbine inlet pressure. At low engine speeds when exhaust flow is low, the vanes are partially closed to increase exhaust pressure and make the turbine spin faster to generate more boost. As engine speed and exhaust flow increases, the vanes are opened to reduce turbine pressure and hold boost steady or reduce it as required. By responding to a manifold pressure sensor, a Powertrain Control Module (PCM) can adjust turbine inlet pressure to control boost at any speed or load, and to limit boost at full load.

Figure 18 VGT versus conventional turbocharger performance Source: BorgWarner


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Advanced materials and precision engineering are needed to keep these moving parts operating smoothly in the hottest part of the turbocharger and there are two different basic designs. The most common design rotates the vanes like slats in a window blind to open and close the flow area. The vanes are mounted in the turbine housing so they can pivot about one end. A plate with pins projecting into the centre of each vane is rotated, causing the vanes to rotate together about their pivot points. Another commonly used VGT design uses a single sliding nozzle to guide the exhaust flow while a sliding piston controls the size of the exhaust turbine inlet. This design is theoretically a little less efficient but much simpler and is therefore likely to prove more durable and lower in cost.

VGTs have been used for some years on large, commercial vehicle diesel engines, but Honda was one of the first OEMs to develop one for a light, gasoline-powered vehicle, launching one on the Wing Turbo V6 engine in 1989. Honda called the system ‘Wing Turbo’ because of the movable ‘wings’ in the nozzle area that opened to allow low-speed exhaust gas flow through the turbine when boost pressure was not required. To provide power to the turbine when boost pressure was required, the wings closed, reducing the nozzle area through which the exhaust gas flowed quickly, driving the turbine. The wings were actuated by boost pressure and controlled by an electronic control unit (ECU) via a solenoid valve. Negative pressure was generated from intake vacuum and accumulated in a reservoir that was also solenoid controlled. The ECU responded to signals regarding boost pressure, intake temperature, coolant temperature, throttle opening, engine speed and vehicle speed.

Honeywell developed its variable nozzle turbine (VNTTM) turbochargers in 1989 and launched the third generation of the technology in late 2008. The system involves the use of a turbine housing that can change its internal configuration to adapt to variations in the engine’s air boost requirements enabling the turbocharger to supply greater engine boost at lower speeds than a smaller unit, yet match the performance of a larger turbo at higher speeds. The latest developments include systems suitable for small engines from 1.2- to 1.7-litres, a size range that Honeywell forecasts will account for more than 50% of all turbocharged engines by 2014.

Porsche combined VTG that utilises electronically controlled guide vanes with the water-cooled, twin-turbo system on the 911T. This enables higher turbine speeds and higher boost pressure at lower engine speeds so that cylinder charging is significantly improved, increasing both power and torque. Maximum torque is reached at lower rpm and is retained across a wider engine speed range so that, according to Porsche, every throttle input is met with exceptional response and improved acceleration. When the boost pressure reaches its maximum value, the guide vanes are opened further, and by varying the vane angle, it is possible to achieve the required boost pressure over the entire engine speed range, eliminating the need for excess-pressure valves.

Turbocharger plus supercharger

Volkswagen combined a supercharger and a turbocharger on the 1.4-litre TSI engine fitted to the Golf GT, Jetta and Touran models. The supercharger provides increased torque at low engine speeds while the turbocharger increases power at higher engine speeds. The 1.4 TSI’s output, which peaks at 168hp (125kW) and maintains 177lb.ft


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(245Nm) or torque from 1,750rpm to 4,000rpm, exceeds that of the company’s normally aspirated 2.0-litre gasoline engine and equals that of its turbocharged 2.0-litre diesel unit.

Superchargers

The origin of superchargers goes as far back as far as 1860 when the first patented twin-rotor air pump designed by American Francis Roots became the blueprint for the modern day Roots type supercharger. In 1900, Gottlieb Daimler patented a forced-induction system for internal combustion engines, which led to the birth of the supercharger in custom racing cars in the 1920s.

Simply put, superchargers (sometimes called ‘blowers’) are based on the same principle as turbochargers with a compressor to increase the amount of air forced into the inlet manifold of the engine. However, the engine directly drives the compressor rather than a turbine powered by the exhaust gases, which eliminates the need for cooling or special bearing and lubrication systems.

Figure 19 Eaton Twin Vortices Series compressor rotors Source: Eaton

Eaton Corporation is something of a champion of supercharging and in 2011 launched the sixth generation of its modern supercharger technology that emerged in 1990. On the company’s Twin Vortices Series, a bypass valve releases boost pressure when the required level is reached, or if none is needed, and the compressor rotors are precision manufactured from extruded aluminium and finished with a patented coating that actually has the rotors touching until a break-in process wears the coating to leave an extremely fine clearance.

Eaton claims that downsizing a 2.8-litre, normally-aspirated V6 gasoline engine using a 2.0-litre supercharged engine improves fuel economy by more than 14%, whereas using a 2.0-litre turbocharged engine gains less than 10%. According to Eaton, this superiority occurs in part because the supercharged engine can be down-speeded.

Nissan chose clutched supercharging for the new 1.2-litre, three-cylinder DIG-S (Direct Injection Gasoline – Supercharger) engine that was launched during 2011 on the Micra. The DIG-S uses the Miller cycle and GDI so that the compression ratio can be increased to 13:1 and power output is 98hp (72kW) and 103lb.ft (142Nm). Fuel economy on the


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combined cycle is 68.9mpg and CO2 emissions are just 95g/km for the manual version and 115g/km for the CVT version.

Multi-speed superchargers

In a different approach, Antonov has developed a two-speed supercharger by combining the company’s proprietary transmission technology with a supercharger. With two operating speeds, the supercharger can be driven at the higher speed when the engine in its low speed range and at a lower speed when the engine is rotating faster. Antonov claims that its two-speed system could enable engine downsizing by 25% to 50% while delivering similar power and torque output to the normally aspirated equivalent.

Figure 20 Antonov two-speed supercharger Source: Antonov

Supercharger supplier, Rotrex, and continuously-variable transmission suppler, Torotrak, have established a 50:50 joint-venture, Rotrak, to develop a range of variable-speed, centrifugal superchargers that can optimise the supercharger’s efficiency to suit engine speed and power requirements.

Figure 21 Exploded view of a Rotrak variable-speed supercharger Source: Rotrak


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Electric superchargers

An electrically-powered supercharger, as illustrated by the Variable Torque Enhancement System (VTES) developed by Controlled Power Technologies (CPT), can provide 90% of its maximum power by spinning up to 70,000rpm in less than one third of a second and, according to the company, increase engine torque output by as much as 50% in the low to medium engine speed range. CPT claims that this capacity enables “extreme” downsizing from a 2.5-litre normally aspirated engine to a 1.2-litre engine while delivering a fuel economy gain of at least 20%.

“Our electric supercharger is an ideal enabling technology for the extreme engine downsizing being advocated by carmakers,” said CPT senior engineering manager, Mark Criddle. “The technology has been designed to be sufficiently flexible to enable use of a common solution across a wide range of engine platforms. It delivers the required economies of scale and matches existing micro-hybrid strategies.”

The VTES supercharger uses an electronically controlled, switched-reluctance electric motor that can operate in a 12/14-volt electrical system but can draw heavily on it during full-power operation. However, it is required for only about 10% of the time, typically during acceleration and hill climbing. In September 2011, CPT launched a 48-volt version of the VTES to take advantage of the 48-volt power systems planned for introduction by European OEMs. In December 2011, Valeo purchased the VTES technology from CPT.

Charge air coolers (intercoolers)

Compressing the air charge produces heat and the hot, less dense charge will lower the engine’s efficiency unless it is cooled between the supercharger or turbocharger compressor and the intake port. To achieve this, charge air coolers (CAC), or ‘intercoolers’, are used, cooling the charge in a heat exchanger cooled either by air or water. Research has indicated that the use of a CAC with a supercharger can double the effect of the supercharger, but only within part of the engine’s operating range. However, the low air temperature during turbocharger lag results in little useful effect from the CAC.

Figure 22 Controlled Power Technologies electric supercharger Source: Controlled Power Technologies


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Delphi has developed a range of liquid-to-air CACs that the company claims provide several advantages over air-to-air systems. Unlike air-to-air systems, the liquid-to-air CACs can be integrated into the intake manifold, they do not require large-diameter elastomeric tubing to route the charge air to and from them, reducing pressure losses, packaging requirements and service-life issues. Engine response to sudden throttle demand is improved because of the smaller volume of intake air between the boosting device and the engine, and the intake air stays cooler, helping to limit NOx emissions during transient driving conditions. Additionally, coolant flow to the CAC can be limited to optimise engine warm-up under cold conditions or increased under partial-load conditions to heat the intake air and reduce throttling losses by allowing a wider throttle opening.

IGNITION SYSTEMS

Gasoline engines use a spark to initiate ignition in the combustion chamber and have traditionally used only a single spark event so that the flame front propagates from that location throughout the compressed air-fuel charge. However, research has indicated that the use of multiple spark events enables lean air-fuel mixtures to be used, improving fuel efficiency. Because of this, several different ignition technologies are being investigated.

Delphi developed its Multi-Charge Ignition System specifically for use with spray-guided GDI to enable stratified combustion. It provides increased spark energy that is delivered in multiple events which results in fuel economy gains of as much as 20% under part-load conditions. Furthermore, engine performance is smoother and emissions are reduced during cold start conditions.

Etatech developed a high-frequency ignition system which uses a high-energy electric field to ionise the air-fuel mixture and initiate combustion at multiple points. Independent laboratory tests indicated that the technology provided a 50% reduction in CO2 emissions, a 40% improvement in peak energy efficiency and an 80% reduction in NOx emissions. BorgWarner acquired Etatech’s ignition technology in 2009.

Figure 23 Federal-Mogul ACIS unit Source: Federal-Mogul

Federal-Mogul’s Advanced Corona Ignition System (ACIS) utilises the same principles as the BorgWarner/Etatech system and enables lean-burn combined with EGR, under


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which conditions the effectiveness of a conventional spark plug is reduced. Whereas a spark plug initiates combustion with heat, the ACIS achieves it via a chemical reaction in which the fuel and air are ionised and react with one another. The company claims to have measured a 10% fuel economy gain through using the technology on a 1.6-litre, turbocharged, GDI engine.

Enerpulse, in collaboration with the US National Energy Technology Laboratory, integrated a capacitor into a conventional spark plug and claimed that the resultant spark quality increased engine power by as much as 11% while improving fuel economy by up to 8%.

In 2009, researchers at Liverpool University in the UK reported the development of a laser ignition system suitable for a GDI engine that resulted from a programme launched in 2002 in collaboration with Ford and Spectron Laser Systems. The team tested different ways of delivering a laser beam to a combustion chamber with particular interest in delivering it via optical fibre, although this proved to be difficult to achieve because of limitations encountered when bending the fibre and its susceptibility to vibration, in order to facilitate its positioning in the chamber.

In 2011, it was announced that Nippon Soken, a Denso subsidiary, was discussing the possible development of a laser ignition system that had been developed by engineers in Japan and Romania. The lasers were reportedly made of ceramic powder that can withstand the heat of a combustion chamber, and developers claimed that the technology has potential to deliver improved fuel efficiency and reduced emissions, along with durability far superior to conventional spark plugs.

In addition, in 2011, Mahle presented the findings of a study of its Turbulent Jet Ignition pre-chamber combustion system. The test engine was based on a production port-injection, four-cylinder, 2.4-litre GM Ecotec unit with a compression ratio of 10.4:1. In the jet ignition system, hot gas jets produced within a small pre-chamber are introduced into the main cylinder to rapidly induce ignition via small orifices. The small orifice size causes the burning mixture the travel quickly, which extinguishes the flame and seeds the main chamber with partially-combusted products deep into the main charge. The main chamber charge is ignited through chemical, thermal and turbulence effects that produce a distributed ignition system. The system can be used on homogeneous or stratified fuel supply to the main combustion chamber. Mahle claims a 13% improvement in fuel economy over the NEDC or FTP test cycles compared to the baseline stoichiometric spark ignition combustion system with a more than 99% reduction in NOx emissions.

EXHAUST AFTER-TREATMENT

Catalytic converters

Even when operating correctly with an ideal (stoichiometric or lambda 1) air-fuel mixture, a conventional gasoline engine emits NOx, HC and CO. While several of the technologies described above have helped to significantly reduce the volumes of these substances, a catalytic converter is required to reduce the volumes further and comply with the increasingly stringent emissions regulations that have been introduced during the last decades.


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The first catalytic converters for gasoline engines were launched in the US in 1973. They were two-way converters that oxidised CO and HC but they had no effect on NOx emissions, which were not regulated at the time. From 1981, three-way catalytic converters (TWC) were launched to break NOx down into non-polluting substances. A TWC contains precious metal catalysts held in a stainless steel or ceramic honeycombed substrate so that the exhaust gases flow over them. The substrate is coated with a mixture of silica and alumina to provide a rough, irregular surface and is then wrapped in a mat that expands when heated, securing and insulating the substrate. The catalyst itself is usually one or more of the precious metals, platinum, palladium and rhodium, although cerium, iron and manganese are also used in order to control hydrogen sulphide and ammonia emissions. The precious metals used as catalysts are very expensive and are used in the minimum quantities possible in order to create an effective converter.

Figure 24 Three-way catalytic converter Source: Eberspächer

The first reaction in the TWC is a reduction in which NOx is broken down using some of the CO and HC present in the exhaust gas. As a result, nitrogen (N2), oxygen (O2), carbon dioxide (CO2) and water (H2O) are produced. Passing over a platinum, palladium or rhodium catalyst, the CO combines with one oxygen atom from the NOx to produce CO2 and the HC combines with oxygen from the NOx to produce CO2 and water. The second reaction, which is what was used in two-way converters, is an oxidation process that takes oxygen produced in the reduction process and, using a platinum or palladium catalyst, converts CO to CO2 and HC into H2O and CO2. To supply oxygen for the oxidation process when the engine is running rich under acceleration conditions, for example, the TWC stores oxygen using cerium.


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To facilitate the reduction and oxidation processes, the air-fuel mixture must be rapidly alternated between oxygen-rich and oxygen-lean states. A rich mixture supports the oxidation process and a lean mixture the reduction. This can be achieved by injecting air between the reduction and oxidation stages but modern systems rapidly cycle the fuel injection system to alternatively produce rich and lean mixtures.

A major challenge to the effective operation of a TWC is that of achieving the necessary operating temperature. A TWC is not effective when cold, yet a large proportion of a gasoline engine’s total emissions are produced under cold start and warm-up conditions. To address this problem, some systems use a pre-catalyst to reduce start-up emissions and burn off the HCs which are present when a cold engine is running rich. Another approach is to ensure that the TWC is ‘close coupled’ – as near to the warm engine as possible, which helps the catalyst achieve early ‘light off’ so that emissions treatment begins as soon as possible after the engine has started. Some OEMs have tried pre-heating the catalyst in various ways, such as electrically, but this approach has not been used in mainstream production. FEV has developed an insulated exhaust manifold to accelerate catalyst ‘light-off’.

While the TWC must be brought up to operating temperature as quickly as possible, allowing it to over-heating can permanently damage it. A number of sensors of various kinds help to control its temperature by providing information to the engine management system, and upstream and downstream parts of the TWC may also be separated to ensure an optimum working temperature and to allow space for the various lambda sensors. Sensors are also used to inform the on-board diagnostic system that the TWC may be becoming less effective as it ages and is gradually exposed to contaminants that coat the surface of the catalysts, in which case the system alerts the driver that the TWC needs to be checked or replaced.

Exhaust gas recirculation

At the elevated temperatures of an internal combustion engine, oxygen and nitrogen react to form NOx. However, by cooling some of the exhaust gas and recirculating it into the combustion chamber, the volume of oxygen and the temperature in the chamber are both reduced. The reduced combustion temperature lowers the formation of NOx but can result in increased PM emissions.

EGR is used more extensively on diesel engines, but on gasoline engines where it is used, typically 5% to 15% of the partially oxygen-depleted exhaust gases from the engine are mixed with air and recycled back into the intake system. For smooth running, the engine management system usually prevents EGR from occurring at idle and under high load conditions.

A study by the High-Efficiency, Dilute Gasoline Engine (HEDGE) consortium at the Southwest Research Institute in the US found that the use of high levels of cooled EGR led to lower peak cylinder temperatures that resulted in improved thermal efficiency, to the degree that fuel economy improved between 5% and 30%. NOx emissions were reduced by as much as 80% and CO by 30%.

Renault claims to have developed and validated a concept based on the use of cooled, low-pressure EGR during high or full load conditions in a ‘highly Millerised’ engine cycle, intake VVT, turbocharging, a high degree of combustion chamber air motion and


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an optimisation of ignition energy. This enables the use of a higher compression ratio while reducing the tendency to knock, lowering the exhaust temperature, reducing enrichment and down-speeding the engine. The down-speeding enabled the use of taller gear ratios, which together improved fuel economy by around 5%.

Delphi offers a family of electronically-controlled gasoline EGR valves that are available with solenoid, torque motor, or direct current motor actuators to help meet individual customer requirements for force, response, cost and leak. Delphi also offers an EGR valve that can help manufacturers reduce NOx emissions in GDI spray stratified engines, which typically generate more NOx because of their lean burn operation.

Figure 25 Delphi electronic gasoline EGR valve Source: Delphi

THERMAL MANAGEMENT

Warming an engine from cold start or a partially cooled state to its optimal operating temperature drains energy that could be better used for propulsion, and engineers have always made efforts to help engines warm up as quickly as possible through, for example, the use of thermostats in the coolant system to trap coolant around the engine until it approaches the desired temperature.

To manage this process even more effectively, MileageMatrix has developed a valve system that uses digital data to actively manage the coolant temperature throughout all load and ambient temperature conditions. The company researched the application of its Digital Rotary Control Valve for three years and estimated that it improved fuel economy by as much as 8% during winter and up to 5% over a full year when compared to a traditional thermostat.

However, recent attention has also focused on keeping the engine as hot as possible when it is stopped. An internal combustion engine typically operates with the coolant at


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around 176° Fahrenheit (80° Centigrade) but will tend to cool quite rapidly once stopped. Thermal insulation of the engine can slow cooling markedly so that it might cool to around 104° Fahrenheit (40° Centigrade) after as long as 12 hours.

BMW has investigated the use of engine insulation and has estimated that ‘wrapped’ engines could improve fuel economy by 1.5% to 2.0% overall with up to 15% improvement possible during journeys that incorporate several short stops.

ALTERNATIVE ENGINE DESIGNS

Variable compression ratio engines

FEV

Several companies have been investigating the use of variable engine geometry, particularly variable compression ratio, in order to modify the combustion cycle and achieve improved fuel efficiency. For example, FEV developed a way of varying the compression ratio by adjusting the bore centre of the little-end bearing to achieve a two-step variation. The company claimed that efficiency was improved and NOx emissions reduced, and the design was applicable to gasoline and diesel engines.

MCE-5

The MCE-5 engine can also vary its compression ratio so that it can be increased during part load and decreased during full load in order to eliminate knocking. The variation is achieved by sliding the big-end bearing, via hydraulic actuation, along a rack on a wheel on the crankshaft so that the stroke length is varied. The design lends itself to Atkinson/Miller cycle operation with a supercharger and no throttling, and early tests of a 1.5-litre demonstration engine indicated a fuel economy increase of as much as 40%. The engine developed 217hp (168kW) and 304lb.ft (420Nm) of torque without the use of GDI, which the developers estimated could increase power to 266hp (198kW) and 333lb.ft (460Nm) when combined with further combustion chamber development and thermal management.

Gomecsys GoEngine

In another approach to achieving variable compression ratio, the Gomecsys GoEngine has an eccentric device comprising two cams and a gear wheel between each big-end bearing and connecting rod so that the piston completes only one cycle every two engine revolutions. This enables a higher compression ratio at low loads and lower compression with forced induction at high engine speeds along with a reduced intake stroke and an extended expansion stroke. The company claimed that the engine’s efficiency would enable a 1.0-litre, two-cylinder variant to develop the power output of a 1.8-litre conventional, four-cylinder engine while reducing fuel consumption and CO2 emissions by as much as 50%. Furthermore, packaging and space requirements would also be reduced by around 50% and production cost by around 30% compared to the conventional engine.


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Lotus Engineering

Lotus Engineering developed a single-cylinder, two-stroke demonstration engine that varied the compression ratio through the use of a moveable puck in the top of the combustion chamber. The so-called ‘omnivore’ engine was designed to operate on gasoline or any alcohol-based fuel and featured direct fuel injection and EGR, which was enabled through the use of a valve in the exhaust port that could continuously vary the exhaust port opening point. The company claimed that it could operate in compression ignition mode down to very light load conditions and that it achieved a fuel efficiency gain of 10% to 15% compared to a stratified combustion GDI engine.

Other radical engine designs

Ilmore five-stroke

So-called ‘five-stroke’ engines have been developed by researchers including Ilmore. Typically, development engines have added a third cylinder between or alongside a traditional, 360° two-cylinder configuration with the third cylinder providing an additional expansion process – the fifth stroke. Ilmore claimed that its ‘five-stroke’ design enabled an expansion ratio that approached that of a diesel engine and that fuel consumption and CO2 emissions were both reduced by about 10% without the use of GDI or turbocharging. The concept 700cc, three-cylinder, turbocharged engine, which featured electrically powered oil and water pumps, developed 128hp (96kW) at 7,000rpm and 120lb.ft (166Nm) at 5,000rpm.

Ricardo 2/4SIGHT engine

Ricardo led a project team that developed the 2/4SIGHT V6 concept engine which featured electro-hydraulic valve actuation, Denso GDI and ignition timing management, forced induction via a Rotrex supercharger and a Honeywell turbocharger, and the capacity to automatically and seamlessly switch between two-stroke and four-stroke operation.

Figure 26 2/4SIGHT V6 research engine Source: Ricardo


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Figure 27 2/4SIGHT engine concept Source: Ricardo

Following completion of the test programme, Ricardo carried out a vehicle drive cycle and acceleration performance simulation. The baseline vehicle for the study was an 1,800kg passenger car sold in the European market with a 3.5-litre, naturally aspirated V6 gasoline engine and a five-speed conventional automatic transmission with torque converter. To verify the validity of the models and input data, the baseline vehicle fuel consumption results were compared with published data, and the simulation results indicated that vehicle acceleration performance, including launch from rest, can be maintained with a 2.0-litre V6 2/4SIGHT gasoline engine replacing the 3.5-litre baseline power plant. This would deliver fuel savings of 27% over the New European Drive Cycle (NEDC) and reduce CO2 emissions of the baseline from 260g/km to 190g/km.

In parallel with the prototype engine development effort in the UK, Ricardo engineers at the company's Detroit Technology Campus designed a patented mechanical cam switching system which is capable of delivering the required switching performance for the control strategies developed on the test bed using the EHV system for the 2/4SIGHT engine. This not only opened the way for packaging and integration of the 2/4SIGHT engine into a production vehicle but also represents a highly cost-effective means of implementation of this efficient combustion concept.

Scuderi

Scuderi has developed a split-cycle engine that has separate compression and power cylinders, and completes a combustion cycle each engine revolution. Ignition is delayed


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until after top dead centre and a variable valve actuation system operates the cross-over valves, so that the cross-over section holds the air charge at high pressure while enabling charge cooling and high forced induction pressure. In its naturally aspirated variant, this delivers a 10% to 15% improvement in efficiency at part load compared to an equivalent conventional engine but little improvement at full load. However, the turbocharged variant is reported to achieve 15% to 20% efficiency improvement at part load and a 5% to 10% improvement at full load. In gasoline versions, NOx emissions are claimed to be reduced by 80%, reducing the exhaust after-treatment requirements.

Figure 28 Scuderi split-cycle engine design Source: Scuderi

Because the intake side of the engine is essentially a pump, it can be used to power a pneumatic hybrid system under regenerative braking to further improve fuel efficiency. Scuderi announced in 2009 that it had a normally-aspirated prototype of the split-cycle engine operating and in September 2011, it released the results of a simulation study showing that a turbocharged, air-hybridised 1.0-litre Scuderi engine can achieve at least 77mpg (Imperial) with CO2 emissions of 85g/km.

Tour Engine

OdedTour has developed the split-cycle, opposed-cylinder TourEngine that avoids the need for an intermediate connecting chamber between the two cylinders. A single crossover valve controls the flow of charge between the cylinders to enable the integration of the compression and combustion cycles with ignition occurring at the end of the compression process while the crossover valve remains open. Simulation studies have suggested that brake thermal efficiency of 56% is possible, although Tour believes that, in practice, 45% brake thermal efficiency is more likely.


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Figure 29 TourEngine split-cycle engine design Source: Captive Pulse

Transonic Combustion

Transonic Combustion has developed a gasoline engine that operates on compression ignition by heating the gasoline to around 700° Fahrenheit (371° Centigrade) and injecting it at 2,900psi (200bar) directly into the combustion chamber at piston top dead centre. The idea of heating gasoline is not new but has usually encountered problems with deposits in the injectors. Transonic claims to have overcome this problem and achieved a fuel efficiency improvement of up to 30% with minimal exhaust after-treatment required for HC and CO emissions and a simple NOx trap. The company has trialled the technology in a 2.2-litre mid-size car and claims fuel economy of 65mpg (US).

Pinnacle Engine

Pinnacle Engine, in collaboration with FEV, has developed an opposed-piston, sleeve-valve, spark-ignition engine for which it claims a 30% to 50% improvement in fuel efficiency. The Pinnacle engine employs the Cleeves cycle, named after Monty Cleeves, the company’s founder, in which it uses the Otto cycle or the diesel cycle depending on operating conditions, and features variable valve timing, GDI, turbocharging and the company’s low-cost variable compression ratio mechanism.

Wave Disk Generator

During 2011, researchers at Michigan State University announced a prototype gasoline engine that requires no crankshaft, pistons, valves or cooling system. The ‘Wave Disk Generator’ has a rotor equipped with wave-like channels that trap and mix oxygen and fuel as it spins. At a point during rotation, the central inlets and external exhaust ports are blocked and cause a shock wave and pressure increase within the chamber that ignites the air-fuel mixture. The developers claim that the Wave Disk Generator utilises 60% of its fuel’s thermal content making it around 350% more fuel efficient than


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conventional gasoline engines. Furthermore, the engine is 25% lighter than an equivalent conventional internal combustion engine and is considered highly suitable for range-extender applications in series hybrid-electric vehicles.

Figure 30 Wave Disk Generator principles Source: New Scientist


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Turbine Truck Engines

Although gas turbine technology has been investigated on light- and heavy-duty vehicles in the past, high fuel consumption and other issues, such as noise, prevented it being pursued. However, Turbine Truck Engines has developed fuel-efficient turbine technology in the Detonation Cycle Gas Turbine (DCGT) engine invented by Alpha Engines Corporation founder, Robert L. Scragg. The DCGT uses what is described as an ‘electromagnetic isothermal’ combustion process and can be operated on gasoline, diesel, methanol, ethanol, liquefied petroleum gas, propane, butane, acetylene, natural gas, hydrogen or a mixture of these fuels. It has few moving parts, is light and requires no coolant or lubrication.

The engine includes a turbine rotor within a turbine housing. When combustion gases are detonated by an ignition system in one of the combustion chambers, the pressure produced shuts off the air-fuel supply to that chamber and redirects it to the other one. Exhaust ports on the combustion chambers that are located on opposite sides of the rotor then direct combustion gases towards the turbine. The process repeats cyclically, and power can be taken off the rotor shaft either mechanically or electrically.

Figure 31 Detonation Cycle Gas Turbine engine Source: Turbine Truck Engines

In 2008, Turbine Truck Engines announced a merger with Highpoint Transport, which acquires and integrates transportation companies and technologies. Also in 2008, Turbine Truck Engines announced the establishment of a joint-venture with Beijing Royal Aerospace Facilities to produce the engine. In 2009, the company formed a strategic alliance with China’s Aerospace Machinery & Electric Equipment Company to collaboratively develop light- and heavy-duty engines based on the DCGT technology.


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A prototype engine produced 540hp (403kW) and the company claimed that it was capable of up to 700hp (522kW). No forced induction system is required and the combustion process is almost complete so that criterion emissions production is low. With thermal efficiency estimated at around 40%, the design has the potential to deliver fuel savings of up to 30% compared to conventional gasoline and diesel engines.

Cyclone Power Technologies

Cyclone Power Technologies has developed an external combustion engine that is suitable for automotive and other applications and which can operate on any liquid or gaseous fuel. It is a high-efficiency steam engine that the company claims produces far fewer toxic emissions than comparable internal combustion engines.

Figure 32 Cyclone external combustion engine Source: Cyclone Power Technologies

ALTERNATIVE FUELS

A range of alternative fuels can be used in spark ignition engines. The two that currently attract the most publicity are ethanol and natural gas but other alcohols can be used and there is a range of biofuel and synthetic process that produce suitable fuels.

Alcohols

Methanol

Methanol, ethanol, propanol and butanol are all clean-burning liquid fuels with energy densities that range from around half to more than 90% that of gasoline. Apart from methanol, which is volatile, all can easily be transported and stored in unpressurised, liquid form. All have high octane ratings and all can be used in engines originally designed for gasoline with only minor modifications to the fuel and ignition systems,


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although a higher compression ratio than that used for gasoline is needed to gain the most benefit from the higher octane rating.

Methanol, the lightest of the alcohols, has an energy density of around 16 MegaJoules per litre (MJ/litre) but its high octane rating of 136 RON has made it a popular choice in motor sport for many years. It can be mixed with gasoline but it is toxic and it burns with a colourless flame which, combined with its volatility and the tendency for it to remain near the ground in vaporised form make it unsuitable as a mass-market automotive fuel. Although it can be produced via several synthetic biofuel processes, most methanol is produced from natural gas via the ‘syngas’ process.

Ethanol

Ethanol has an octane ration of 129 RON but at around 21MJ/litre, it has about two thirds the energy density of gasoline and, as a result, it provides poorer fuel economy by volume. Currently, most ethanol is produced by fermenting sugar-rich biomass such as sugar cane, sugar beet, corn, wheat and waste from sugar refineries. However, the poor energy balance of the production processes, the limited greenhouse gas savings that result, and the large fertile land areas required for these crops have prompted widespread research into the use of other feedstocks, particularly non-food, cellulosic sources that can be cultivated on poorer quality land.

For example, switchgrass and other, similar hardy grasses can provide cellulosic biomass suitable for the production of ethanol. Switchgrass grows prolifically in a wide range of conditions and has a more efficient CO2 fixing process than most other biomass feedstocks, so that it can deliver up to five times more energy than it consumes during cultivation, harvesting and ethanol production than corn-based feedstock with significantly lower GHG emissions.

Figure 33 Switchgrass Source: College of Chemistry, University of California, Berkeley

Sweet sorghum is another promising source of ethanol feedstock. It is similar to sugarcane but can be cultivated in marginal soil and requires less water than sugarcane or corn. It provides a high ethanol yield per acre – 500 to 800 gallons – and requires only


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around half the energy required to process corn. In August 2011, plant scientists at the Oxford University Faculty of Agriculture, Food and Natural Resources announced that the succulent agave, used in Mexico to produce tequila, has good potential as a feedstock for ethanol production. Agave grows in arid places and does not compete with food crops and returns five times the energy required to produce ethanol from it.

Brazil has been the global leader in using ethanol as a fuel, where normal gasoline at the pump contains 25% ethanol (E25) and ‘flex-fuel’ vehicles are able to operate on E85 or E100. Sweden also has a well-established ethanol industry that uses waste wood from its timber industry and straw as feedstock to produce ethanol that is blended to E85 with gasoline. Ethanol has also been promoted in the US for some years, but although the Department of Energy determined that a blend of up to 20% (E20) in gasoline is safe for use in engines originally designed for gasoline only, the Environmental Protection Agency (EPA) issued a waiver in 2010 that E15 could be used in vehicles manufactured from model year 2007. The waiver was extended in 2011 to include vehicles from model year 2001 but industry groups have opposed the waiver, claiming that blends of no more than E10 are safe and that higher proportions of ethanol could damage fuel system and exhaust catalyst components. The debate continues between US government and industry groups.

In Brazil, around 90% of new vehicles are flex-fuel capable. In the US, Ford and GM produce flex-fuel engines that can operate on E85 and Ford of Europe markets the flex-fuel version of the Focus in Sweden. In France, Renault produces E30 and E85 engines. In order to run on ethanol, gasoline or a range of blends, some fuel system components must be upgraded because ethanol can contain contaminants and water that corrode metal components and degrade some polymer components. A sensor system is also required to detect the fuel content and provide data to a variable ignition map, and the engine warm-up system must be able to accommodate the inferior cold starting capability of ethanol. The cost of these systems is relatively low and has been estimated at around USD200. The retail price premium for a flex-fuel Renault Clio in France is around EUR200.

On a well-to-wheels (WTW) basis, the most optimistic estimates for GHG reduction by using bioethanol instead of gasoline is 40% but more pessimistic estimates place it at only 10%. Typically, first-generation ethanol is estimated to save around 20% with corn-based ethanol at 18% and canola at 13%. Coskata has claimed an 84% reduction for ethanol produced from Switchgrass in its bioreactor process, but a study by the Canadian Renewable Fuels Association estimated at 38% reduction using ethanol from eight Canadian plants. WorldAutoSteel estimated that corn ethanol results in GHG reductions of only 11% while cellulosic ethanol results in a 65% reduction when compared to gasoline.

According to the US Renewable Fuels Association, ethanol reduces CO emissions by as much as 30%, HC by 13% and PM by 50%. However, NOx emissions increase, a finding supported by an Australian government study that found that while NOx emissions from E10 were similar to those from gasoline, E20 emitted 30% more although the level was still only half the allowable limit.


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Propanol

Current production processes for propanol are very inefficient, ruling it out as a contender for development as a mass-market fuel.

Butanol

Butanol has an energy density of around 29MJ/litre and an octane rating of 96 RON. It is less corrosive than ethanol and does not absorb water, making it more suitable as an automotive fuel. Furthermore, research indicates that engines originally designed for gasoline can operate without modification on a blend of up to 85% butanol in gasoline and those designed to operate on E10 can operate safely on 100% butanol. The US EPA has approved the use of up to 16% butanol in gasoline.

While most current butanol production is from petroleum, it can be produced from the same biomass feedstocks as ethanol using a similar fermentation process, although the use of cellulosic feedstocks is inefficient and the process ceases earlier than it does with ethanol with only about half the concentration of butanol (7% versus 14% to 16%). However, several companies are investigating processes to produce a higher yield of butanol with some claiming success to the degree that production can compete economically with petroleum fuels.

The US EPA conducted tests on a 1992 Buick Park Avenue that was using 100% butanol and found that NOx was reduced by 37%, HC by 95% and CO was almost eliminated.

Algal biofuels

Currently, the investigation of the use of algae to produce fuels is one of the leading edges of the alternative fuels sector. Processes under investigation include using algae to produce hydrocarbons from a range of nutrient feedstocks combined with either atmospheric or industrial-sourced CO2. ExxonMobil and Synthetic Genomics, for example, established a greenhouse facility in California in 2010 to investigate different strains of algae, different growth systems under a wide range of temperature, light and nutrient conditions, and different harvesting methods.

Figure 34 SunEco algal fuel production ponds Source: SunEco


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Some researchers are investigating the use of open-air ponds while others are focusing on closed environments using fresh, salt or waste water sources. The feedstocks include those used in other biofuel processes such as food crops, animal waste, sewage and industrial by-products.

For open pond systems, hydrocarbon ‘biocrude’ yields vary but costs are very competitive with current petroleum crude prices. BioFields, for example, has claimed that its Florida-based algae fuel plant, which uses industrial-sourced CO2, is capable of producing 6,000 gallons per acre at a cost equivalent to USD50 per barrel. Texas-based Photon8 claims that it has developed a low-cost system that can produce up to 10,000 gallons per acre per year at around USD1.25 per gallon and California-based SunEco has claimed as much as 33,000 gallons per acre-foot of water.

Closed photobioreactor processes enable control of light, temperature and nutrient conditions and avoid the evaporation and contamination problems to which open ponds are vulnerable and they can more easily use industrial-sourced CO2 from, for example, flue gas from fossil-fuel power stations. One such example is that established jointly by OriginOil of California and MBD Energy of Australia. The companies claim a yield of 11 million litres of oil per year from 80 hectares of algae production using CO2 sourced from one of MBD Energy’s power stations. Another Australian venture by Algae.Tec in Perth, Western Australia, claims a yield of 32,000 gallons per acre using industrial CO2 and sunlight directed via fibre optics.

In October 2011, OriginOil announced the development of a new harvest pre-treatment process that unexpectedly also substantially increased the growth rate of algae. The pre-treatment uses extremely low-power electromagnetic fields that can be powered by solar panels.

In November 2011, researchers at Iowa State University announced the discovery of a genetic method that can increase biomass in algae by 50% to 80%. Two genes in the Chlamydomonas reinhardtii aglae were ‘turned on’ simultaneously, compounding the effect of turning them on sequentially to increase the photosynthetic carbon conversion into organic matter. Furthermore, by using some existing mutated genes, the algae will make oil instead of starch.

Also in November 2011, scientists at the US Department of Energy’s Los Alamos National Laboratory announced that they had genetically engineered algae to produce magnetic properties that enable magnetic separation that could reduce harvesting and lipid extraction costs.

Bacterial biofuels

Both ExxonMobil and BP are supporting research into the use of cyanobacteria by Arizona State University and Synthetic Genomics to produce biofuels. Cyanobacteria are less complex and easier to genetically manipulate than algae and can photosynthesise CO2 and water into hydrocarbons or ethanol. In June 2011, researchers at Arizona State University announced that they had reprogrammed photosynthetic cyanobacteria to secret high-energy fats, making recovery and conversion to biofuels more commercially viable.

In July 2011, Joule Unlimited Technologies secured US patents for is method of producing ethanol without the need for feedstock using a photosynthetic microorganism.


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Rather than producing ethanol by fermenting sugars from biomass feedstocks, Joule’s microorganism is engineered to produce and secrete ethanol in a continuous process, converting more than 90% of the CO2 it consumes directly into ethanol. Joule has set a target of harvesting 25,000 gallons per acre annually for as little as USD0.60 per gallon, largely because the process eliminates the need for biomass feedstock or the energy required during the traditional fermentation process.

In August 2011, scientists at Tulane University announced the discovery of a bacterium strain that consumes the cellulose in recycled newspaper into butanol.

Biogasoline

Biogasoline can be produced from the same biomass feedstocks that can be used to produce alcohols but producers claim that it is more efficient than producing ethanol because of the product’s higher energy density and a better energy balance during production. Global Clean Energy in Canada and Virent Energy Systems in the US, for example, have developed a catalytic process that converts sugars into gasoline. The US companies, Amyris, LS9 and Synthetic Genomics, have genetically engineered bacteria to produce hydrocarbons in mixtures similar to crude oil, gasoline or diesel but free of sulphur compounds.

Dimethyl ether

Dimethyl ether (DME) has the same empirical formula as ethanol but has a different molecular structure. It has a boiling point of -9.4° Fahrenheit (-23° Centigrade) and exists under normal atmospheric conditions as a colourless gas with a distinctive smell and similar properties to liquefied petroleum gas (LPG). It is widely used as an aerosol spray propellant but is highly volatile and can form an explosive mixture in air. It is clean burning and has a high cetane number or 55, which is higher than that of diesel.

DME can adversely affect several types of rubber and plastic, and metal-to-metal seals are required in place of such products in some engine components. It also has poor lubrication properties so that injector systems need high-pressure lubrication. DME is usually produced via the dehydration of methanol or the syngas process that synthesises it from hydrogen and CO. It can also be produced from biomass, natural gas or coal.

Hydrogen

Hydrogen can readily be used as fuel in engines originally designed for gasoline. Its energy density is high at 143MJ/kg compared to that of natural gas at only 55MJ/kg, and thermal efficiency as high as 45% has been achieved under research conditions. However, storage both on-board and in refuelling stations presents challenges. As the lightest naturally occurring element, it tends to leak past all but the most effective seals and when compressed as a gas, storage cylinders must be robust and present size and weight challenges. It can be liquefied at -487° Fahrenheit (-253° Centigrade), which requires significant energy for refrigeration and the safety systems that are necessary for the relief of excessive gas pressure..

Currently, most hydrogen is produced via the steam reformation of methane, which is the main constituent of natural gas, to supply the oil refining and fertiliser industries. It can also be produced via the electrolysis of water or methanol, but most of the world’s


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electricity is generated using fossil fuels and methanol, which is mostly produced from natural gas, so that both processes result in substantial CO2 emissions.

However, new, more efficient electrolysis processes are being developed. For example:

In August 2011, ITM Power announced a significant reduction in the cost of electrolysis using a new alkaline solid polymer membrane in place of the traditional platinum catalyst. The high ionic conductivity of the process enables high current densities, reducing the size of the equipment and the high water permeability simplifies water management.

In September 2011, researchers at the University of Kentucky-University of Louisville announced that the use of an alloy of antimony and gallium nitride effectively catalysed photo-electrochemical hydrolysis.

In November 2011, researchers at the Massachusetts Institute of Technology (MIT) announced the development of an inexpensive electrolysis catalyst composed of a compound of cobalt, iron and oxygen with other metals that increased catalytic activity tenfold.

In December 2011, researchers at the US Argonne National Laboratory announced the development of a highly efficient, two-stage electrolysis process that uses clusters of nickel hydroxide attached to the usual platinum catalyst. The combination increased catalytic activity tenfold.

In August 2011, the Orange County Sanitation District sewage treatment plant in Fountain Valley, Southern California, began providing hydrogen for vehicle refuelling. The experimental plant has a fuel cell that produces hydrogen and electricity using biogas feedstock from wastewater treatment.

In October 2011, researchers at MIT announced an ‘artificial leaf’ that can use solar energy to produce hydrogen and oxygen from water. The silicon solar cell has two different inexpensive catalytic materials bonded onto its two sides, and when it is placed in water and exposed to sunlight, it generates streams of hydrogen bubbles on one side and oxygen on the other. The catalysts consist mostly of cobalt, nickel, molybdenum and zinc.

BMW and Mazda are both promoting the use of hydrogen as an internal combustion engine fuel. In 2009, BMW, in collaboration with TU Graz, HyCentA and Hoerbiger, developed a hydrogen engine with diesel-typical geometry and progressive, high-pressure hydrogen injection. BMW claimed thermal efficiency of 42%, equivalent to the most efficient diesel engines.

Hythane

Hythane is a mixture of hydrogen and natural gas. Typically it is around 20% hydrogen by volume, which improves engine efficiency although it directly contributes only around 5% to 7% of the energy produced.

Liquefied petroleum gas

Liquefied petroleum gas (LPG) consists mostly of propane and butane along with small quantities of other hydrocarbons and it is sourced as a by-product of natural gas and crude oil extraction. Its energy density is only 26MJ/litre but its octane rating is around


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108 RON so that it provides internal engine performance similar to that of gasoline if the compression ratio is increased. In dual-fuel vehicles, the lower compression ratio results in performance somewhat lower than gasoline. It provides a shorter range by volume and it must be kept under pressure, which limits the shape of the fuel tank, which is often additional to the gasoline tank in a dual-fuel vehicle. It also has poor lubricating properties so that additional upper cylinder lubrication is necessary.

According to the US Propane Education & Research Council, LPG produced 20% less NOx, 60% less CO and 78% less PM than gasoline.

Natural gas

Natural gas is found in large natural deposits and in association with coal and petroleum oil. It is also produced during the oil refining process and has been traditionally burned off, although this practice is coming under increased scrutiny because of the resultant CO2 emissions and the increasing value of the product. Natural gas is usually 85% to 90% methane, although the proportion can be higher, with the remainder being other hydrocarbon gases such as ethane, butane, propane and pentane. There may also be small quantities of CO2, helium, hydrogen sulphide and nitrogen.

Although its energy density by weight is good at 55MJ/kg, it is low by volume and even when stored at the necessary 2,900psi (200bar) in industrial gas cylinders, its use as an automotive fuel results in reduced range compared to gasoline. As per LPG, unless the engine’s compression ratio is increased to take advantage of its 120 RON octane rating, performance is reduced by as much as 15% compared to gasoline.

It is used widely for electricity generation and heating and an extensive distribution infrastructure exists in many regions enabling widespread use as an automotive fuel. It is also transported by sea or land transportation in liquefied form at atmospheric pressure but refrigerated to -260° Fahrenheit (-162° Centigrade). This requires heavily insulated tanks with comprehensive safety systems.

Natural gas is comparatively inexpensive as a fuel and its popularity in some developing countries is increasing rapidly. Light vehicles have usually been converted to natural gas using after-market equipment but some OEMs now produce dedicated natural gas cars and light commercial vehicles.

Methane can also be produced in an anaerobic digester from biomass, in which case it is called ‘biogas’ although it is typically only around 50% methane, with the remainder being mostly CO2 along with small quantities of hydrogen, hydrogen sulphide, nitrogen, oxygen, siloxanes and water vapour. Feedstocks include agricultural and food waste, animal manure, sewage, and landfills also tend to produce it as the organic content breaks down.

In November 2011, HyperSolar announced a new technology to produce natural gas using solar energy, water and CO2. The process uses a solar-powered nanoparticle system that mimics photosynthesis to separate hydrogen from water. The hydrogen is then reacted with CO2 to produce methane. The process occurs at normal temperature and pressure enabling the use of low-cost production facilities.


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According to Natural Gas Vehicles for America, natural gas emits up to 90% less CO, up to 95% less NOx and up to 75% less HC than gasoline but NaturalDrive Partners puts the figures at 51% for CO and 41% for NOx.

Gas-to-liquid fuels

Natural gas is also used to synthesise liquid hydrocarbons via two main processes: direct conversion and indirect conversion via synthesis gas (syngas) production. However, none of the direct approaches are economically viable.

Steam methane reformation and the partial oxidation of methane can be used in parallel to produce CO and hydrogen in proportions that can be controlled by altering the proportions of water and gas in the process. A second catalysed process is then used to synthesise methanol and water. The methanol is then dehydrated to produce DME and water, and then further dehydrated over a catalyst to produce gasoline. Alternatively, a process developed by Mobil converts that methanol to a mixture of methanol, DME and water, which is mixed over a catalyst with recycled gas to produce hydrocarbons in the gasoline range and water.

The Fischer-Tropsch process, which was initially developed as a coal-to-liquids process, uses syngas produced from any hydrocarbon feedstock and utilises several competing chemical reactions that produce mixtures of hydrocarbons, alkenes, alcohols and other oxygenated hydrocarbons. Altering the temperature and pressure conditions and the catalysts used, so that hydrocarbons in the gasoline range can be targeted as required, can control the product mix.

Carbon Sciences has developed what the company calls a “breakthrough technology” that uses a dry reforming catalyst that transforms methane and CO2 into syngas.

Coal-to-liquid fuels

Coal can also be used in a steam-based process as a feedstock to produce syngas. The coal must be milled or ground into slurry, the process results in a wet slag and syngas that contains a range of impurities that must be removed before the process of synthesising it into hydrocarbons via either the syngas or Fischer-Tropsch processes.

Direct liquefaction processes have been investigated but not pursued, and liquid hydrocarbons can be produced during the low temperature production of coke, which results in tars that contain lighter hydrocarbons than coal tar.

Coal-to-liquids are cost competitive, with petroleum fuel costing more than USD35 per barrel, but it is more carbon intensive, producing greater volumes of CO2 through the production.


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COMPRESSION-IGNITION ENGINE TECHNOLOGIES

The compression-ignition engine was first developed in 1893 by Rudolph Diesel, who was pursuing the concept of ignition using the heat of compression without the need for a spark system. Although Diesel’s first successful engine ran on peanut oil fuel, petroleum diesel (petrodiesel) has been the fuel of choice for more than a century, although several alternative fuels are now also used either on their own or blended with petrodiesel.

Diesel engines have higher thermal efficiency than gasoline engines in part because of the higher compression ratio used to achieve compression ignition and in part because diesel fuel is more energy dense than gasoline. Diesel engines have also advanced through the application of technologies that, in general, parallel those used on spark-ignition engines and include direct injection, forced induction, variable valve control technology and exhaust gas recirculation. Exhaust after-treatment technologies have advanced to comply with ever-decreasing criterion emissions limits, and alternative fuels are increasingly being used to help reduce operating costs and emissions, including CO2 emissions.

While diesel engines have been the dominant choice for medium- and heavy-duty commercial vehicles for many years, the advances in diesel technology have also made light-duty diesel engines far more attractive to consumers. The image of the noisy, dirty diesel engines of the past has faded, albeit slowly in the US, and modern light diesels offer superior driveability through developing up to 50% more torque at low engine speeds than gasoline engines of the same capacity, along with up to 30% better fuel economy and nearly 25% less CO2 emissions.

Because of these advances, the diesel share of the new car market has increased in many countries. In western Europe (EU15+EFTA), the new diesel car share has increased from around 14% in 1990 to more than 52% in 2007 and 2008 although it fell in 2009 but exceeded 50% again in 2010. In some countries, including Belgium, Norway and France, the diesel share has exceeded 70% in recent years.

Figure 35 New diesel car registrations, Western Europe, 1990 – 2010 Source: ACEA

However, India is currently the only major market in which diesel is popular. It stood at around 30% there in 2007 and is forecast to increase to at least 40% by 2020. By contrast, in the US, where some states actually banned diesel cars until the recent advent of ultra-low sulphur fuel and advanced exhaust after-treatment technology, new diesel car


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penetration was a mere 3% in 2010 although that significantly exceeded the 0.2% in Japan. Diesel car penetration is also very low in China, where the government has restricted diesel sales in the large, heavily-polluted cities, the diesel supply is under pressure from the heavy transport sector and consumers avoid the price premium associated with a diesel engine compared to a gasoline equivalent.

COMBUSTION CYCLES

Diesel fuel is less volatile than gasoline or liquid alcohols and does not lend itself to carburation so that it has always been introduced into the engine by injection. Most diesel engines utilise the four-stroke Diesel cycle, as derived from Rudolf Diesel’s first design, with separate induction, compression, power and exhaust strokes. The induction stroke draws air into the combustion chamber, typically aided by forced induction via a turbocharger, and the compression stroke compresses it with a compression ratio that can be as high as 22:1, generating heat. At around the top of the compression stroke, fuel is injected either directly into the combustion chamber or indirectly into a small chamber adjacent to it. The heat of the compressed air vaporises the fuel and ignites it so that the rapidly-expanding burnt fuel forces the piston down on the power stroke. The exhaust valve is then opened and the exhaust gas expelled during the exhaust stroke.

However, some larger diesel engines used on locomotives and ships operate on a two-stroke cycle and rely on forced induction to expel (scavenge) the exhaust gases while filling the cylinder with air again once the power stroke is completed. As in a four-stroke cycle, the intake air is compressed and fuel injected when the piston is near top dead centre. The exhaust and intake valves (or intake ports) are opened towards the end of the power stroke and the scavenge cycle initiated. Two-stroke diesels can be operated in reverse, making them ideal for large marine engine applications.

DOWNSIZING

Downsizing diesel engines, as with gasoline engines, is achieved by turbocharging and modifications to the combustion and fuel injection systems. For the diesel engine, the key constraints on power output are peak cylinder pressure and the compression ratio. Not very many years ago, the compression ratio was typically 20:1 in order to facilitate cold starting. Now, however, compression ratios are typically 17:1 with cold starting less of a problem because of the use of advanced glow plugs and commonrail fuel injection systems. Using a lower compression ratio combined with high maximum cylinder pressures also allows increased boost levels resulting in higher specific ratings. Maximum cylinder pressures are now approaching 2,600psi (180bar) in production engines, whereas ten or fifteen years ago, 1,900psi (130bar) was the norm. This advance has required developments in structural design, materials and engine control techniques.

Downsizing from 2.0 litres to 1.4 litres can be expected to yield a 10% to 15% gain in fuel economy and this can be extended with hybridisation and further advances in forced induction technologies, which also bring gains in power output, drivability and emissions reduction. To illustrate this, the maximum power of the Volkswagen 1.9- litre diesel engine has increased from 90hp (67kW) to 158hp (118kW) since 1993, with the 2.0-litre version achieving 177hp (132kW), making them competitive in terms of specific output with all but the most highly rated gasoline engines.


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Diesel engines have traditionally enjoyed fuel economy benefits of around 15% compared to gasoline engines – a difference that is expected to be maintained and will sustain the volume and growth through its contribution to CO2 reduction. However, it has been the advent of commonrail fuel injection, variable geometry turbochargers coupled with improvements in cooling techniques that have given what once appeared to be a fading technology, a vigorous new lease of life, with increasing penetration in many new vehicle markets.

WEIGHT REDUCTION AND MATERIALS

Weight reduction and new materials are assisting with the downsizing and fuel economy gains being realised with diesel engines.

Cylinder blocks and heads

For larger Vee-type engines and in-line four- and six-cylinder engines, cast iron is being replaced with spheroidal graphite cast iron (SGI), which is tougher and can be used in thinner structural sections. This saves around 10% of the weight or allows very high specific engine ratings (over 60kW/litre). Aluminium is also being used in larger engines to save weight. For the smaller engines (under 1.5 litres), aluminium is being used extensively, saving between 30% and 60%, resulting in engines weighing less than 220lb (100kg).

Although there have been several technical challenges to overcome, the use of Compacted Graphite Iron (CGI) is also making inroads into the diesel engine sector. During the last decade or so, CGI has become an important material across the automotive industry, being used for brake discs, exhaust manifolds, engine heads and diesel engine blocks. The superior strength characteristics of CGI, as compared to grey iron, allows the manufacturing of engines for higher pressure operating combustion chambers, therefore more efficient and with lower emissions levels, while also allowing thinner walls and lighter engines. The technology has been adopted by several OEMs including Audi, Jaguar/ Land Rover, Hyundai and PSA Peugeot-Citroën for diesel car engines.

A number of components are also now being developed in plastic to facilitate weight saving, including manifolds, covers and sumps.

Pistons

The combined effect of higher fuel injection and, in many cases, peak combustion pressures, together with reductions in fuel sulphur and the adoption of EGR and after-treatment technologies is unavoidably bringing higher piston loadings. Consequently, piston durability is being challenged.

The attraction of aluminium’s low inertia weight, good heat conductivity and cost-efficient manufacturing has to be set against its fatigue strength limitations. An NiResist top groove insert and an annular cooling gallery have helped improve durability, as have brass gudgeon pin bushings, but a more durable material for the main body of the piston has also been required.


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Mahle, Europe’s largest piston manufacturer, has formulated two new higher-grade aluminium alloys to withstand higher heat and pressure loadings. Crucially, the copper content (by weight) has been increased from the 0.8% to1.5% found in regular ‘Mahle 124’ piston material to 2.5% to 4% in the latest ‘Mahle 142’, and 4% to 6% in the even tougher ‘Mahle 174’ specification. The nickel content has also been increased from 0.8% to 1.3% to 1.75% to 3% in both new alloy grades, while the silicon and magnesium content is largely unchanged. The new alloys not only promise up to 60% better fatigue characteristics, they also result in up to a 15% friction wear reduction, bringing gains in engine service life.

In 2009, Federal-Mogul announced the development of an innovative aluminium piston design that can reliably withstand the mechanical and thermal loads produced by heavily boosted engines. The crown of the piston is strengthened by locally re-melting the alloy around the hollow bowl typically used as part of the combustion chamber in a diesel engine, which significantly improves fatigue strength where it is most needed. The company’s researchers determined that piston failure is often caused by the presence of free primary silicon particles within the aluminium allowed, in part because aluminium expands eight times as much as silicon, resulting in increased stresses in the aluminium. The re-melted alloy cools around one thousand times faster than it did during casting, which leads to smaller silicon particles and leaves the alloy stronger and more durable.

As an alternative piston material, forged steel offers clear fatigue strength and wear resistance advantages over aluminium in the extreme cylinder pressure and temperature conditions associated with future low-emission diesel technology. However, those merits are offset by higher weight, poorer heat conductivity and higher machining costs. On Mahle’s latest Monotherm forged steel piston design, however, the elimination of lower-stressed areas of the skirt portion has helped to reduce reciprocating weight, almost to that of an aluminium equivalent.

Mahle anticipates a move away from manganese-rich micro-alloyed steels towards quenched and tempered chromium-molybdenum or even chromium-silicon rich steels. The latter could tolerate surface temperatures up to 1,112° Fahrenheit (600° Centigrade) although there was an unavoidable trade-off in heat conductivity. With hotter surface temperatures of 450ºC or more, there is an increased likelihood of material oxidation and the formation of scale, with an attendant risk of cracking. Mahle has addressed the problem with two different strategies: the use of a nickel-chromium alloy protective coating applied by thermal spray; and protecting the part of the piston crown most vulnerable to scaling and subsequent cracking, namely the bowl rim, with a ‘ring’ of higher-grade steel.

THE POTENTIAL OF APPLYING NEW TECHNOLOGIES

As an example of what can be achieved by using currently-available technologies, FEV’s High Efficiency Combustion System (HECS) engine, which was presented at the 2011 SAE World Congress in Detroit, is said to achieve a 17% reduction in fuel consumption while meeting Euro 6 emissions standards. To achieve the fuel efficiency gains claimed, second-generation HECS technology was applied to a 1.6-litre, four-cylinder diesel engine by redesigning the cylinder head, using the company’s proprietary variable valve lift technology and cam phasers, low-pressure EGR, and sophisticated thermal management.


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VARIABLE VALVE TECHNOLOGY

The adoption of variable valve actuation (VVA) on diesel engines has lagged somewhat behind its application to gasoline engines. In part, this has been because the high compression ratios used in diesels results in very limited clearance between the pistons and valves at top dead centre, severely limiting valve lift during the overlap phase. The use of four valves per cylinder further reduces space confining the use of VVA to the timing of the intake valve closing and the exhaust valve opening and limits the useful application of cam phasing.

Figure 36 Comparison of airflow with VVT on a diesel engine Source: Mechadyne International

However, during the late 1990s, researchers began reporting on the findings of simulation studies that preceded the experimental application of the technology to diesels. One such study, published by Mechadyne in 1998, reported that simulation of the use of VVA on both intake and exhaust valves on a light-duty diesel engine that was also equipped with VGT and EGR, indicated that transient response and power output are both improved.

The same researcher also found that simulated VVT on both intake and exhaust valves, in combination with VGT and EGR, predicted a fuel economy improvement of between 6% and 19% under light part-load conditions.

Another simulation study by Mechadyne and DaimlerChrysler on a four-cylinder, 2.2-litre, twin overhead cam Daimler-Benz OM611 diesel engine found that:

At low speeds (1,600 to 2,000rpm) and loads, early intake closing decreased brake specific fuel consumption (BSFC), with the greatest improvement of 2.3% occurring at low loads and decreasing as load increased.

At low speeds and loads, late intake valve closing decreased BSFC with the greatest improvement of around 1% occurring at low loads and decreasing as load increased.

Steady-state, full-load operation a 1,000rpm and 1,600rpm resulted in torque increases of:


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o From 6.3% to 8.2% by advancing intake valve closing o From 8.6% to 12.6% by advancing exhaust valve opening o From 15.4% to 16.4% by advancing exhaust valve opening and intake valve

closing.

The current version of the Cummins B-Series engine that has been used in Dodge Ram trucks for more than 20 years uses many technologies that were unheard of in the mainstream diesel market only a few years ago. Substantial changes came in 2007 with the introduction of the 6.7-litre engine, which included digital commonrail injection, VGT, EGR, a closed crankcase with coalescing filter, lean-operating catalytic converters, NOx absorbers, and diesel particulate filters.

Cummins' light-duty diesel programme has a goal of 10% better brake thermal efficiency over its current line-up of engines, which is a massive jump in efficiency for diesel engines. At the same time, Cummins plans to meet Tier 2, Bin 5 emissions requirements while maintaining the same power density it has today.

Figure 37 Variable valve actuation on 6.7-litre Cummins diesel Source: Cummins

MAN Diesel & Turbo has stated that, among the improvements in the company’s diesel engines to comply with the IMO Tier II emissions regulations that came into effect in 2011 is VVT, which enabled its engineers to counter the disadvantage of the Miller Cycle – heavy smoke build-up in the partial load range because of the early inlet valve closure and the resultant reduction of air intake and reduced combustion temperature. VVT solves this problem, enabling the engine to always be operated with optimal efficiency. MAN recorded a fuel economy gain of up to 8%, along with a 15% increase in specific power output and a 30% reduction in NOx emissions.


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The mechanical core of MAN’s VVT is an eccentric shaft, which has a direct influence on valve lift. As the shaft turns, the inlet rocker arm moves into the required position and influences the valve’s opening and closing time. MAN’s VVT system is powered mechanically or electrically, depending on the engine type, but both versions enable the Miller Cycle to be enabled or disabled as required and engine performance optimised in every load range.

In 2010, Mitsubishi launched the first variable valve timing system on a mass-produced, light-duty diesel engine – the four-cylinder, double overhead cam, 1.8-litre 4N13 engine.

INJECTION TECHNOLOGY

Fuel injection systems are at the heart of the diesel engine, and an important advance in injection technology occurred in 1994 when Bosch and Fiat developed the commonrail injection system. In a commonrail system, the fuel is distributed to the injector nozzles at a high pressure of up to 43,500psi (3,000bar) via a common distribution pipe – the commonrail – while electronic control adjusts the injection pressure as a function of engine speed and throttle position data provided by sensors.

Figure 38 Comparison of piezo-actuated and servo-hydraulic-actuated injector spray patterns Source: Delphi

However, high-pressure injection has the potential to cause an increase in combustion noise, but this has been resolved by a technique called ‘pilot injection’ in which a small amount of fuel pre-injected into the cylinder ignites immediately, thereby preconditioning the combustion chamber. As a result, ideal conditions are created for the main injection process so that the fuel ignites more rapidly, but the temperature does not rise so abruptly, which reduces combustion noise. Other significant advantages of the


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commonrail system are reduced CO2 emissions, lower PM emissions, improved fuel consumption, reduced NVH and improved drivability to the degree that modern light-duty diesels now complete on equal terms with their gasoline-powered counterparts in even the premium vehicle segments.

In parallel with the development of commonrail technology, the development of piezo technology has enabled much faster and more accurate injector responses, improved spray atomisation and the use of more injector events than can be achieved with solenoid operation, although the lower cost of solenoid systems still makes them attractive for many applications. It is also possible to combine the two technologies, so that piezo control is used for the initial pre-injection and servo control for the ‘main’ injection event.

The multi-layer piezo actuator system developed by Siemens VDO for the Peugeot 307 operated at four times the speed of a solenoid-actuated system with up to six injection events achievable during one injection cycle. Another example of an ultra-high pressure, piezo-controlled, commonrail injector system is Delphi’s Direct Acting Diesel Commonrail System, which operates at 29,000psi (2,000bar). The superior spray pattern, compared to a servo-hydraulic system, results in an increase in power and torque of as much as 10% and NOx emissions reduction by as much as 30%.

The use of several precise injector events enabled through piezo actuation has several benefits including:

Slower pressure build-up and pre-heating via a pilot injection combined with a steep slope of the injection rate during the main injection;

The use of several post-injections to burn soot particles more efficiently; and

One of the post-injections can be utilised to help regenerate a particulate filter.

For optimal combustion under different load and speed conditions, multiple injections can be used at lower engine speeds, double or triple events in the middle speed range and single injections at full load and throttle.

To alleviate concerns regarding the implications for reliability of the stresses on high-pressure systems, Bosch developed a two-stage pressure-generation system for heavy commercial vehicle applications. The rail pressure is kept to only 12,200psi (840bar), but each injector is equipped with a hydraulic pressure amplifier that can increase it to 30,500psi (2,100bar) and two solenoid valves that enable the creation of flexible injection patterns.

FORCED INDUCTION

The use of turbochargers and superchargers on diesel engines follows the same principles as their use on gasoline engines. Turbocharging has been used for many years on heavy-duty diesel engines and the advance of technologies such as turbocharging has, in part, driven the increase in popularity of light-duty diesel engines in the passenger car segments.


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An example of the use of multi-stage turbocharging on a diesel engine is provided by the BorgWarner regulated two-stage system used on the Mercedes-Benz 220 CDI and 250 CDI four-cylinder models. As per two-stage systems used on gasoline engines, a smaller, high-pressure unit is used to increase torque at low engine speeds and a larger, low-pressure one for higher engine speeds when exhaust gas flow and pressure are higher. When compared to the previous 2.2-litre diesel engine, the 220 CDI engine develops around 20% more power while reducing fuel consumption and CO2 emissions by around 13%. BorgWarner also produces twin-scroll turbochargers, which the company claims produce similar improvements in power output and fuel economy but with smaller packaging requirements and lower weight and cost.

Mann+Hummel took a slightly different route to two-stage turbocharging by incorporating a shut-off valve placed between a larger, constantly-operating turbocharger and a smaller secondary one that can spool up within one tenth of a second one under high load conditions to add its charge pressure to that of the larger unit.

Honeywell claimed that is sequential turbocharging system that was launched on the 2009 Jaguar XF 3.0-litre V6 diesel reduced fuel consumption by 12% and CO2 emissions by 10%, compared to its predecessor while maintaining the performance of the previous V8 diesels. Torque is increased 38% compared to the previous V6. The system incorporates two small turbochargers and Honeywell’s patented sequential control technology. A VNT (Variable Nozzle Turbocharger) provides boost at low engine speeds while the second turbocharger is activated in parallel at high engine speeds.

Honeywell’s VNT technology has also been applied to the VW Polo BlueMotion 1.2-litre diesel with the result that fuel consumption and CO2 emissions are both reduced by 15% when compared to the previous generation Polo’s 1.4-litre diesel, while maintaining a similar level of performance despite the car’s increased size and weight.

Variable geometry turbochargers (VGT) have been used on large diesel engines since the 1990s, but the technology has penetrated the medium- and light-duty diesel segments during recent years. BorgWarner is supplying its VGT turbochargers to JCB Power Systems’ Dieselmax 4.4-litre, four-cylinder diesel engines. The technology will help JCB to meet Interim Tier 4/Stage IIIB emissions regulations without exhaust after-treatment or diesel particulate filters.

BorgWarner has also combined two-stage turbocharging with VGT on the unit supplied to International for the PowerStroke 6.4-litre diesel engine. As on most other two-stage systems, the smaller, high-pressure turbocharger responds at low engine speeds while the larger, low-pressure unit provides boost at higher engine speeds. However, the high-pressure unit also uses electrical actuation to vary the geometry of the vanes on the turbine to further adapt boost to deliver the required torque output.


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Figure 39 BorgWarner variable-geometry turbocharger Source: BorgWarner

TURBO-COMPOUNDING

Turbo-compounding involves the introduction of a power turbine downstream of the turbocharger that is connected by a gear to the engine, typically at the flywheel. In this manner, further energy is extracted from the exhaust gases to help drive the engine, typically increasing the overall thermal efficiency of a diesel engine to as much as 46% instead of the typical 42%. The secondary turbine also increases exhaust back pressure that assists the EGR system.

However, past studies of the technology in practice revealed that it is of little benefit in heavy traffic or hilly terrain where a lot of gear changing is required, but on long-haul applications where relatively steady cruising speeds can be maintained, fuel savings of 3% to 4% can be achieved. This modest level of gain, especially when confined to certain duty cycles, does not usually justify the extra expense of adding it.

More recently, with the advent of sophisticated electronic engine management and injection systems that enabled better optimisation of engine speed and load, and its capacity to add extra exhaust back pressure assisted exhaust gas recirculation (EGR), interest in it has revived. Nevertheless, the technology is still largely targeted at long-haul, heavy-duty applications where the cost-benefit ratio makes it viable.

In 2009, Detroit Diesel’s DD15 engine turbo-compounding received a Technical Achievement Award from Truck Writers of North America. On the DD15 system, the secondary exhaust turbine is coupled hydro-dynamically to the engine’s drive gears. Detroit Diesel claims that the technology can improve fuel economy by up to 5%.

EXHAUST AFTER-TREATMENT

Among the main challenges facing diesel engine manufacturers during recent years has been that of substantially reducing criterion emissions. As well as the more obvious


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sooty PM emissions that diesels produce, particularly during rich-mixture, acceleration or heavy load conditions, the diesel combustion process also tends to produce high quantities of NOx and HC. The most widespread technologies used to reduce HC, NOx and PM emissions from diesel engines are diesel oxidation catalysts (DOC), selective catalytic reduction (SCR), NOx adsorber catalyst (NAC) and the diesel particulate filter (DPF).

Diesel oxidation catalyst

DOCs are essentially two-way catalytic converters similar to those initially used on gasoline engines, which oxidise the gaseous and liquid HC absorbed onto carbon particles that form the core of PM but do not treat NOx emissions. Consequently, they must be used in conjunction with after-treatment technologies that do treat NOx. The level of PM reduction is influenced by the proportion of the gaseous and liquid HC in the exhaust with the potential to increase them by as much as 90%, while reducing total PM emissions by 40% to 50% under certain operating conditions.

Selective catalytic reduction

SCR technology can reduce NOx emissions by 75% to 90%, HC emissions by 50% to 90% and PM emissions by 30% to 50% and is achieved by injecting urea or hydrocarbon fuel into the exhaust gas stream before it reaches the catalyst although urea SCR is generally the more favoured option. Urea injection into the exhaust gas produces ammonia, which reacts with NOx to produce nitrogen and water. While SCR systems can tolerate sulphur in the fuel, they emit some ammonia although it can be minimised through the use of ammonia sensors in the exhaust system to provide data to the SCR control system.

The use of urea SCR requires the vehicle to carry a urea tank, the refilling of which requires a distribution infrastructure, which is already becoming well established in Europe and North America, typically associated with the diesel fuel distribution infrastructure, although some large truck fleet operators have developed their own. Another issue is that urea freezes at 14° Fahrenheit (-10° Centigrade), requiring urea tank heaters in some regions.

NOx adsorber catalyst

An NAC adsorbs NOx for later release and treatment rather than continuously treating it like an SCR system. During lean fuel mixture operation, any NO is oxidised to NO2 when passing over a precious metal catalyst. The NO2 is then stored on a chemical trap composed of an alkaline earth or nitrate site. When the storage trap approaches full capacity, the fuel system provides a rich mixture, which reduces the stored NO2, is released and reduced to nitrogen and water over another precious metal catalyst. The storage media in NACs are susceptible to contamination by sulphates and they can only be used with ultra-low sulphur diesel fuel.

Renault developed an NAC for light-duty diesels that can replace a DOC because it controls CO and HC as well as treating NOx, which is trapped in a barium nitrate solution and then purged every ten minutes or so through adjustments to the exhaust gas recirculation rate and the injection timing, in order to create a rich fuel mixture and heat


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the catalyst. The NOx is reduced by the excess hydrocarbons in the rich mixture to nitrogen and CO2.

Diesel particulate filter

In a DPF, liquid and solid particles in the exhaust stream are collected in a porous substrate structure of ceramic cordierite of silicon carbide and then, when the engine is heavily loaded, the exhaust gases heat the substrate core so that most of the collected particles are oxidised. Sensors in the exhaust system measure the backpressure across the filter to determine when it has become clogged enough to require regeneration.

However, this passive ‘regeneration’ of the DPF is not always frequent enough or of sufficient duration to oxidise all the particles and active regeneration is necessary. This can be achieved through heating the substrate core with an electric, microwave or fuel-powered heater or through transient adjustments of the fuel mixture to enrich it so that unburned HC passes over it. Alternatively, the engine management system can adjust the combustion process so that it produces excess NOx, which oxidises the PM at lower temperatures than are required for the other methods, or a fuel-borne catalytic additive can be used to oxidise the PM. However, the latter method requires on-board storage and delivery systems.

‘Wall-flow’ DPFs are constructed so that the exhaust gases are forced through the wall of the filter. They typically use cordierite or silicon carbide, of which cordierite is the less expensive option but is vulnerable to melting at the temperatures required for regeneration. ‘Flow-through’ filters typically consist of metal fibres woven into a mat that the exhaust gas can flow through and which can be heated to bring about regeneration. However, they tend to be more expensive than wall-flow DPFs.

DPFs can reduce PM emissions by 60% to 90% but sulphur in the fuel interferes with the chemical reactions used to reduce emissions and can lead to the creation of PM, so that they are not effective unless used with ultra-low sulphur diesel.

Many DPFs incorporate a DOC using a catalytic coating on the filter or as a separate element. The DOC component can eliminate as much as 30% of the PM. Four-way systems can also be created through the integration of a DOC to reduce CO, HC and PM emissions with a SCR system or NAC to reduce NOx. Mercedes-Benz has developed two integrated, four-way systems for its ‘Bluetec’ emissions control products. One uses a DOC to reduce CO and HC, and an NAC with a DPF and a SCR system fitted in sequence further downstream to reduce NOx and PM emissions. The other uses a SCR system and an integrated DOC-DPF.

Syngas systems

Syngas, which consists of CO, CO2 and hydrogen, can be used to control NOx and PM. A reformer is used to convert the vehicle’s fuel into syngas, which is then pumped into the exhaust stream and over a catalyst. Regeneration is achieved at relatively low temperatures, making syngas systems suitable for light- and medium-duty commercial vehicles that typically operate on urban duty cycles. NxtGen claims that its retrofit syngas systems can reduce NOx by up to 70% and PM by up to 85% while improving fuel economy by as much as 10%.


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Exhaust gas recirculation

As has been described in the Spark-ignition engine section, EGR can be used to reduce NOx emissions, which are formed by the reaction of nitrogen and oxygen in the high temperatures of the combustion process. This is achieved by cooling some of the exhaust gas and recirculating it into the combustion chamber, which reduces the volume of oxygen in the chamber and lowers the combustion temperature, both elements of which reduce NOx formation by as much as 60%. However, the use of EGR increases heat output and an increase in engine cooling capacity is required.

EGR can occur externally by recirculating exhaust gas collected from the exhaust system, either before or after the turbocharger turbine, and directed back into the intake system. Alternatively, it can occur internally through managing the valve train so that some exhaust gas is held back, or even drawn back through the exhaust valve.

The SCR versus EGR debate

A few years ago, when the EU and US were setting the standards for Euro 4, 5 and 6, and US2007/10 respectively, the EU opted to establish an SCR infrastructure to support adoption of the technology but the US was reluctant to do so, and North American truck and bus engine manufacturers pursued the use of EGR alone for NOx emissions reduction. However, the US EPA changed position in the lead up to US2010, because it was becoming apparent that, without further breakthrough technology, a combination of EGR and SCR would be necessary to meet the pending emissions limits.

Furthermore, in order to achieve the required reductions in NOx emissions, it was found that EGR rates would have to be increased from around 25% or 30% to as much as 45%. Such a high proportion of EGR reduces engine power and torque and increases fuel consumption while increasing PM emissions to the degree that PM deposits in the EGR cooler. Furthermore, exhaust gas contains water which can condense and affect lubrication in the cylinder.

Consequently, led by Cummins and with the sole exception of Navistar, the North American heavy-duty engine manufacturers adopted the SCR route. Cummins made it known that the challenges of using increased EGR alone were proving to be substantial and that using SCR brings a fuel economy advantage that outweighs the cost of adding the technology and the on-going cost of the urea reductant. Indeed, in 2009 representatives of the main North American truck and heavy-duty engine manufacturers present at the Mid-America Truck Show opined that using SCR results in a fuel economy gain of between 3% and 5%.

Navistar continues to champion the use of EGR without SCR, despite the fact that its 2010 models did not meet the new NOx limits and the company relied on clean-air credits while it developed its engines to full compliance. Interestingly, MAN, through which Navistar’s MaxxForce engine designs are sourced, had opted for SCR to meet Euro 5 requirements. Navistar launched a campaign to discredit the effectiveness of SCR and point out that there is no guarantee that a commercial vehicle operator will fill the vehicle’s urea tank in order to gain the benefits of the technology.

In July 2011, Navistar filed a lawsuit against the EPA to try and force the agency to retest SCR-equipped engines for compliance with clean air standards under “actual


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current driving conditions”. On 20 January 2012, a US District Court ruled that Navistar cannot force the EPA to undertake retests and denied leave for Navistar to seek further discovery from EPA records.

ALTERNATIVE ENGINE DESIGNS

Achates Power opposed-piston engine

Achates Power has developed an opposed-piston, two-stroke engine design for which the company claims a 20% improvement in fuel efficiency compared to a new, award-winning four-stroke diesel engine. Brake thermal efficiency of 45.1% was demonstrated at the engine’s best operating point while meeting the US2010 emissions standards. The engine has 40% fewer components than a conventional diesel engine because it has no cylinder head or valvetrain. Piston-controlled intake and exhaust ports are at opposite ends of the cylinder.

EcoMotors OPOC

Another opposed-piston, two-stroke diesel engine has been developed by EcoMotors, although the design uses a combination of internal and external connecting rods than enable the use of only one crankshaft whereas other opposing designs require two. The OPOC (opposed piston, opposed cylinder) engine is said to be around half the size and weight of an equivalent conventional diesel engine while providing a 15% improvement in fuel economy. Furthermore, the modular design enables cylinder deactivation via a clutch to improve fuel economy under low-load conditions by as much as 50%. EcoMotors has also developed an electrically driven supercharger that assists with increasing power delivery and decreasing emissions. In 2010, EcoMotors announced that it was developing a 300hp (224kW) truck engine for an unnamed OEM, and in February 2011 Navistar announced that it had signed a development agreement with the company.

Figure 40 EcoMotors OPOC engine Source: EcoMotors


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RadMax Rotary Turbine Engine

The RadMax Rotary Turbine Engine (RTE) utilises a disc-shaped rotor mounted on the driveshaft, which turns the engine housing. Vanes slide backwards and forwards along the outside of the rotor, in a direction parallel to the driveshaft so that they follow a sinusoidal track along the inside of the housing. Combustion chambers are formed between the rotor, the housing walls and the vanes, and their volumes change as the vanes move during rotation. Combustion takes place externally with the fuel preheated by heat from the engine and then forced into it by a supercharger. There are 24 combustion events per engine rotation.

Because of the high number of combustion events per revolution, the engine weighs around one sixth of a conventional diesel engine and is scalable from 10hp (7.5kW) to almost any size.

Figure 41 RadMax RTE engine driving a pump Source: RadMax

The compression ratio is higher than 20:1, enabling the use of a wide range of oil-based fuels. Diesel fuel, for example, provides specific fuel consumption around 20% better than a conventional gasoline engine. Acceleration response is similar to that of conventional internal combustion engines and combustion is nearly complete, so that NOx emissions are low.

Axial Vector

During recent years, the Axial Vector Energy Corporation (AVEC) has distributed several press releases regarding its compression-ignition Axial Vector engine, which a spokesman once described as being based on a 1952 design. In 2006, AVEC acquired the assets of Dyna-Cam Engine Corporation, which patented a similar engine in 1941 and tested it in a light aircraft in 1988.


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AVEC has produced generator sets powered by the engine. Instead of using a crankshaft, the engine uses a sinusoidal cam to create reciprocating movement in six double-ended pistons. The engine is said to have far fewer components, and hence is smaller and lighter than conventional engines of a similar capacity. Power output is claimed to be higher and torque three times as much as that produced by a similar conventional engine.

Figure 42 Axial Vector engine Source: Axial Vector

In 2010, AVEC announced that it had signed a 24:76 joint-venture agreement with Kirloskar Oil Engines of India to mass-produce the engine. In 2011, an AVEC licensee was awarded a contract by the US Navy to supply marine engines based on the technology.

ALTERNATIVE COMPRESSION-IGNITION TECHNOLOGIES

Homogeneous charge compression ignition

HCCI in diesel engines has been researched for some years in efforts to reduce NOx and PM emissions, which can be achieved through the homogeneous mixing of the air-fuel charge and lowering the combustion temperature below the NOx threshold. Also, because diesel is difficult to fully vaporise, researchers have investigated using naphtha and kerosene as a compression-ignition fuel.

The slow vaporisation rate of diesel also led researchers to investigate the potential for injecting the fuel into the intake manifold to extend the time for vaporisation, but while homogeneous mixing could be achieved, fuel economy was reduced significantly. However, it has been found that diesel can be vaporised if it is injected well before top


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dead centre, or if water is injected to slow the temperature rise, or if high levels of EGR are used in combination with late fuel injection.

Research has indicated that the main controlling factors in achieving diesel HCCI are compression ratio, the EGR rate and the air-fuel ratio. Premixing can also be optimised by using preheated intake air, EGR and two-stage injection with a small quantity of fuel injected close to top dead centre in order to initiate combustion.

Researchers at the Oak Ridge National Laboratory in the US investigated ‘premixed charge compression ignition’ (PCCI) in a four-cylinder, 1.7-litre diesel engine that was equipped with two cooled EGR loops, a VGT and a commonrail fuel injection. PCCI operation was enabled by using high EGR rates, increased injection pressure and advanced timing of fuel injection to produce a more homogeneous air-fuel mixture. However, while NOx emissions were dramatically reduced, CO, HC and aldehyde emissions increased, and this pattern was observed across several steady-state engine speeds and loads. The lower levels of NOx enabled reduced regeneration of the lean NOx trap used, and the increased other emissions were reduced by a diesel oxidation catalyst (DOC) although control was temperature dependent, particularly because of the low combustion temperature achieved.

Reactivity controlled compression ignition

At the 2010 Deere Conference, Rolf D. Reitz of the Engine Research Center at the University of Wisconsin, Madison, presented a paper titled ‘High Efficiency Fuel Reactivity Controlled Compression Ignition (RCCI) Combustion’ in which gasoline and diesel, or E85 and diesel, were mixed in different proportions in a heavy-duty Caterpillar diesel engine and a light-duty GM diesel engine. The gasoline was port injected and the diesel direct injected.

Figure 43 Criterion emissions from RCCI engine by % gasoline Source: University of Wisconsin, Madison


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The concept was to take advantage of the different reactivity of the two fuels:

Diesel is easy to ignite but difficult to vaporise while gasoline is difficult to ignite but vaporises easily.

Diesel is good for premixed low-load operation while gasoline exhibits poor combustion at low loads.

Diesel causes combustion to occur too early at high loads while gasoline allows extension to higher load conditions.

Fuel efficiency and criterion emissions were measured with the gasoline proportion varied from 76% to 82% to 89%. It was claimed that thermal efficiency of 53% to 59% was achieved and fuel efficiency increased by to 15% to 20% while criterion emissions were lower than the US2010 heavy-duty limits – with PM almost eliminated – without exhaust after-treatment for both fuel combinations. Furthermore, the engines converted to the technology can retain the capacity to operate under either spark ignition or conventional diesel compression ignition and any two fuels of differing reactivity can be used.

In July 2011, the University of Wisconsin, Madison, announced the RCCI technology would be applied to a student hybrid-electric vehicle project. The post-graduate team estimates that the test vehicle will emit 75% less GHG and fewer criterion emissions than the US2010 limits with minimal exhaust after-treatment.

Gasoline direct-injection compression ignition

Also at the 2010 Deere Conference, Delphi researchers presented a seminar on gasoline direct-injection compression ignition (GDICI), in which gasoline’s volatility enables rapid fuel vaporisation and mixing, and its high octane rating enables increased ignition delay for longer mixing time. The research involved the development of a single-cylinder, four-valve, 499cc compression ignition engine with a compression ratio of 16.2:1, GDI for multiple, late injection events, a lean mixture, controlled stratification and EGR.

Figure 44 GDICI emissions results for single, double and triple injection Source: Delphi


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Single, double and triple injection events using 91RON unleaded gasoline were investigated with triple proving to provide the desired characteristics for fuel efficiency, noise, exhaust temperature, CO, HC and PM targets. However, triple injection was the worst of the three for NOx emissions.

When compared to normal diesel operation in the same engine, CO2 emissions were 14% lower and fuel consumption by mass was down 9.5%, but fuel consumption by volume was 4.5% higher because of the greater energy density of diesel. However, the difference was considerably less than the usual difference between a conventional spark-ignition gasoline engine and a diesel. NOx emissions were lower but CO, HC and PM levels were elevated.

Figure 45 GDICI emissions compared to a conventional diesel Source: Delphi

ALTERNATIVE FUELS

Several of the alternative fuel production technologies described in the Spark-ignition engines section above produce ‘bio-crude’ or synthetic crude oil, or some other mixture of hydrocarbons that can be synthesised into either gasoline or diesel. These include:

Algal biofuels (bio-crude) Bacterial biofuels (bio-crude) Gas-to-liquids (DME, methanol, synthetic diesel or synthetic gasoline) Coal-to-liquids (synthetic diesel or synthetic gasoline)


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Alcohols

Ethanol can be blended with diesel but is usually done so in relatively low proportions. For example, O2Diesel produces a 7.7% blend along with a proprietary additive (1%) and a cetane enhancer. A University of Illinois agricultural engineer, Alan Hansen, carried out field tests on John Deere and Caterpillar tractors with a 10% ethanol, 89% diesel, 1% additive blend. The operators could not detect any differences in performance, although, because of the ethanol’s lower energy density, fuel consumption increased from 3% from 5%. Hansen suggested a rule-of-thumb that each 5% of ethanol added would increase fuel consumption by around 2%.

However, emissions tests indicated that PM emissions were reduced by as much as 25% to 30%. Hansen has also tested the use of 15% ethanol but reported that it reduced the fuel’s capacity to lubricate the engine so that an additive was required and there was increased deterioration of the resin that encapsulates sensors in the injection system after only 500 hours.

Biodiesel

Several innovative processes are under investigation, but biodiesel is usually produced via the transesterification of vegetable oils or animal fats. A wide range of feedstocks are used and include canola (rapeseed), soybean, sunflower, palm, mustard, flax, hemp, and waste vegetable oils; fish oil, chicken fat, tallow, lard and yellow grease. It is most commonly produced from soybean in the US, canola in Europe and palm oil in tropical countries. Promising feedstocks that are being investigated include camelina, which is of the mustard and canola family, and jatropha, which grows even in arid land. Jatropha beans can be up to 40% oil and each hectare can produce around 3,000 litres of biodiesel per year.

Biodiesel yield per acre for various feedstocks varies considerably, with palm oil capable of supplying around 500 gallons per acre, coconut 230, jatropha 200, canola around 100, soybean between 60 and 100, peanuts around 90 and sunflowers around 80.

The oils are reacted with methanol or ethanol, which results in short-chain, methyl or ethyl esters, which exhibit similar viscosity to petrodiesel fuel, although it has better lubricating properties and reduces wear in injectors and pumps. It has a higher flash point and a higher cetane value than petrodiesel, but its energy density is lower at 33 to 36MJ/litre, depending on the feedstock used, compared to petrodiesel’s 42.3MJ/litre.

Unfortunately, biodiesel tends to oxidise and form sediments that block filters and injectors, and it degrades natural rubber seals and hoses in older fuel systems, and its superior solvent properties can result in it breaking down deposits in the fuel system that can also cause blockages. It can also absorb water, and the traces of glycerides that are produced in the transesterification process can act as an emulsifier to mix the water with the biodiesel so that fuel system components and engines can be damaged, the fuel can gel earlier as the ambient temperature decreases, PM emissions can increase and performance can be impaired.

Pure biodiesel tends to gel sooner than petrodiesel, which contains proportions of anti-gelling additives depending on the climate conditions in which it is intended to be used.


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Unfortunately, there are very few effective anti-gelling agents for biodiesel although in blends with a high proportion of petrodiesel, no extra anti-gelling additive is required.

The early gelling problem can be overcome by heating the fuel. However, if this is achieved by using waste engine heat by running coolant pipes through the biodiesel tank, the vehicle also requires a supply of petrodiesel with which to start and warm up the engine.

Blends of biodiesel range from around 10% biodiesel (B10) through to 100% (B100). Blending only 1% petrodiesel into B99 adds toxicity sufficient to prevent mould and the US EPA has authorised blends of up to B35 for commercial sale although trucking operators and groups in North America are currently opposed to blends of more than 15%.

Dimethyl ether

Compression-ignition engines can operate on DME, which has a higher cetane number than diesel, or a blend of DME and diesel. When used as the sole fuel, PM emissions are eliminated and HC and CO emissions are substantially reduced compared to petrodiesel. However, different researchers have reported different results regarding NOx emissions. Generally, NOx emissions have been reported as being significantly lower than petrodiesel, but some researchers have found them to be similar or even higher.

However, DME has low viscosity and low lubricity, and it must be stored on-board within the distribution infrastructure, in a similar manner to LPG. It is known to adversely affect many types of plastics and rubbers.

Researchers at Pennsylvania State University’s Energy Institute investigated the use of DME in a Navistar T444E 7.3-litre turbodiesel engine in a shuttle bus. The fuel injector system was modified to provide higher pressure, and the researchers found that adding DME in blends up to 25% by weight resulted in significant reduction of PM emissions. Because DME exists as a gas at normal temperature and pressure, a propane tank was modified to store it on-board.

Natural gas

Compression-ignition engines can be modified to operate on a mixture of natural gas in diesel, with diesel constituting only 2% to 5% of the fuel in order to provide ignition. The natural gas and diesel are injected separately, requiring the fitment of a tandem gas injection system and a high-pressure pump to balance diesel and gas pressure prior to injection. Otherwise, the engines operate normally using EGR and exhaust after-treatment for PM and NOx, and can still run on diesel alone.

Westport Innovations produces natural gas engines based on Cummins units and supplies them to OEMs including Paccar’s Kenworth and Peterbilt, and Daimler’s Sterling. Clean Air Power has had experience carrying out similar dual-fuel conversions on Caterpillar engines and has developed engines for Navistar and Volvo Trucks. The American Power Group, through its GreenMan Technologies subsidiary, produces an after-market system for retrofitting to existing diesel engines.


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COMBINED SPARK AND COMPRESSION IGNITION ENGINES

Gasoline homogeneous charge compression ignition (HCCI), which is also known as ‘controlled auto ignition’ (CAI), can achieve fuel efficiency similar to that of a diesel engine with very low emissions levels through the use a premixed lean charge, no intake throttling, EGR and low peak combustion temperatures. The aim of the technology is to achieve a homogeneously mixed, lean air-fuel charge in the combustion chamber that will spontaneously ignite under a high compression ratio. The flame propagates from multiple ignition points and burns at a lower temperature than combustion in conventional engines, reducing NOx and PM emissions. The clean combustion of a lean mixture results in improved fuel economy.

However, control of the ignition point has been one of the main challenges to developing the technology, along with problems achieving effective operation during engine warm-up and very light load conditions, when the temperature of the compressed air-fuel charge is too low to produce auto-ignition. Conversely, full-load operation also presents challenges, because the high compression ratios necessary to generate sufficient heat for auto-ignition at lower loads tend to cause auto-ignition too soon, resulting in knock and very high peak pressures. Furthermore, although the low peak combustion temperature results in very low NOx emissions, can result in higher levels of CO and HC, and the low exhaust temperatures render catalytic converter less effective.

To overcome the problems achieving auto-ignition under low-load conditions, spark ignition has been used in development engines to date, and the problems of pre-ignition under high-load conditions can be addressed by late direct injection after top dead centre and would be much more manageable if the engine featured a variable compression ratio. Controlling the ignition point through medium-load conditions can be achieved by controlling the intake charge with GDI, VVA and EGR. To achieve the accurate valve control required for successful HCCI operation, Lotus Engineering, for example, applied camless, electro-hydraulic valve actuation. Sturman has also developed a hydraulic and electromechanical valve actuation system that can be applied to HCCI engines.

Several automotive OEMs, universities and other research institutions have been researching the technology since the 1970s, but in 2007, both GM and Daimler presented prototype HCCI engines. The GM prototype featured GDA, VVA with variable phasing and lift on both camshafts and cylinder pressure transducers to help control combustion and the transition between ignition modes. It used spark ignition under low- and high-load conditions, and test drivers reported that the transition from spark to compression ignition was detectable. During 2008, GM announced that the engine now operated on compression ignition under low-load conditions but spark ignition was still required for starting. In a Saturn Aura, the 2007 version of the modified EcoTeck engine operated on compression ignition from low-load up to around 55mph (88kph) while by 2009, the compression ignition range was extended from idle to 60mph (97kph). For both versions, a fuel economy gain of 15% compared to a conventional gasoline engine was claimed.

As well as also featuring GDI, VVA and EGR, Daimler’s ‘DiesOtto’ engine also featured turbocharging, a variable compression ratio and mild hybrid-electric technology using an integrated starter generator. Daimler claimed a fuel economy improvement of as much as 42% compared to a conventional gasoline engine and 29% compared to a


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Advanced Powertrain Report - 2012.pdf

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