Efficiency and Emissions Benefits of Ultra-Lean Engine ... Presentations... · – Distributed...

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Michael BunceTechnical SpecialistMAHLE PowertrainPlymouth, MI

Efficiency and Emissions Benefits of Ultra-Lean Engine Operation as Enabled by Jet Ignition

This presentation does not contain any proprietary, confidential, or otherwise restricted information1

MAHLE Powertrain LLC, November-2016

Background

Lean Combustion: Advantages and Disadvantages

Advantage of lean combustion

– Increase in thermal efficiency

– Reduced heat losses

Disadvantage of lean combustion

– Higher NOx in near-lean region (1>λ>1.2)

– Challenging thermal environment for aftertreatment

SI lean operation limited by:

– Degradation of combustion stability (COV>3-5%)

Ultra-lean combustion

– Increase in thermal efficiency

– Reduced NOx

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Limit of acceptable combustion

stability

Ultra-lean region

beyond lean limit

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Background

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MAHLE Jet Ignition® Overview

Pre-chamber-based combustion system: high ignition energy from turbulent radical jets

– Amplifies the ignition energy from the spark with a pilot combustion event

Spark plug and low-flow DI injector located in pre-chamber

– Auxiliary injection – up to ~3% of fuel

Pre-chamber mixture ignited with conventional spark

– Burned gases exit through nozzle as jets

Main chamber combustion proceeds from ignition sites initiated by jets

– Distributed sites result in fast burn rates

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Passive system: Enhances stoich and near-lean operation with no auxiliary fuel injection

– Knock reduction due to distributed ignition

– Increased combustion stability

Background

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MAHLE Jet Ignition® Overview

System can operate with single-source (main chamber) fueling

Active system: Enables ultra-lean operation using auxiliary fuel injection

– Reduction in drive-cycle BSFC

– Reduced engine-out NOx

CFD simulation, WOT, λ=1.9, iso-surface temperature (1500 K)

Auxiliary fueling effectively decouples chamber AFRs

– Main chamber lean capable

– Pre-chamber λ≤1

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Non-auxiliaryfueling

History

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Abridged History of Pre-Chamber Research

Pre-chamber combustion

systemsAuxiliary Fueling

Large pre-chamber volume

Miniaturized pre-chamber

(≤3% clearance volume)

Gaseous auxiliary fuel

Liquidauxiliary fuelinjection

Concept Organization YearTurbulence Generating Pot Toyota 1974

Torch Ignition Ford 1979Pre‐chamber Engine VW 1980

Swirl chamber spark plug Bosch 1980‐1984Torch jet Tokai University 1987

Catalytic pre‐chamber ign University of Idaho 1988Smartplugs Cherry 1989‐1995

Swirl chamber spark plug Caterpillar 1992Pre‐chamber spark plug Sabol 1993Torch jet spark plug GM 1995

Bowl‐prechamber ignition Multitorch 1999‐2005Directed spark plug Delphi 2001Torch ignition system UFMG 2005

Auxiliary comb chamber Nissan 2007

Concept Organization YearDolphin Ricardo 1918

Pre‐chamber Summers 1926Pre‐chamber Mallory 1938Pre‐chamber Bagnulo 1947Pre‐chamber Barnes 1952Pre‐chamber University of Rochester 1952‐1954Torch ignition Nilov 1958

Ram‐Straticharge Heintz 1959Pre‐chamber Barnard / Brewer 1964Pre‐chamber University of Wisconsin 1970

CVCC Honda 1973Prechamber injection VW 1973‐1976

Prechamber GM 1974Pre‐chamber Nissan 1974Pre‐chamber Eaton 1974EFI Torch GM 1975‐1979

SKS Porsche 1975Pre‐chamber Ford 1976‐1981

HCRI Huang 1992Variable volume prechamber Caterpillar 2004‐2008

Concept Organization YearLAG Gussak 1963‐1974

Pulsed combustion jet UC Berkeley 1990‐2002HAJI University of Melbourne 1993‐2009HFJI Toyota 1993

Pulsed jet combustion Warsaw University 1999Scavenged swirl chamber FEV 1999

APIR University of Orleans 1999‐2001PCFA GM 2003

Jet ignition Bosch 2005Igniter H. Durling Savage 2006

Prechamber spark plug IAV 2007HCRI Blank 2007

Concept YearMAHLE Jet Ignition 2010‐2016

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History

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Technology Differentiators

Auxiliary direct liquid fuel injection

– Ensures precise metering of fuel and spray targeting

Small volume pre-chamber (<5% of compression vol)

Orifice diameter promotes high degree of flame quenching during jet formation form auto-ignition sites

Ignition site distance from bore center, from optical engine

Design Cn4i3: Spray-wall interactions 3 CAD after injection

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MAHLE Powertrain LLC, November-2016 © MAHLE

Efficiency: Lean Limit Extension

Jet Ignition combustion enables extension of the lean limit

– Higher energy ignition source thermo-chemical

– Multiple ignition sites distributed

2.4L homogeneous lean

Results

Auxiliary fuel injection

No auxiliary fuel injection

Speed: 1500 rpmBMEP: 7 barCR: 14

Lambda

COV ≤ 3%

Min BSFC

Min COV

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Low BSFC throughout map has potential to produce low drive-cycle fuel consumption

– Minimum steady state BSFC < 200 g/kWh

Further low load optimization expected to improve <2 bar BMEP fuel economy further

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Efficiency: Brake Thermal Efficiency and Fuel Consumption

42% peak BTE to-date

Large area of 40+% BTE

Results

BTE Decoupled minima due to few data

points in between

Transition to min COV

BSFC (g/kWh)

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Results

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Efficiency: Fuel Consumption Reduction Mechanisms

Contributions to BSFC reduction:

– Stable enleanment

Gamma effect

– Reduced heat loss

– Reduced pumping work

– Knock reduction

Increased CR

More optimal phasing Addition of auxiliary fuel

Reduced exhaust and cylinder heat loss

De-throttling

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Engine-out NOx(ppm)

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Emissions: NOx

Low engine-out NOx helps to mitigate aftertreatmentchallenge associated with lower exhaust temperature

2.4L homogeneous lean

Results

Auxiliary fuel injection

No auxiliary fuel injection

Speed: 1500 rpmBMEP: 7 barCR: 14

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Results

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Emissions: NOx

Percentage magnitude of NOxreductions and dependency on lambda are largely independent of speed and load

Typical Jet Ignition engine operation produces 95%+ reduction in engine-out NOx from stoichlevels

95% reduction

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Engine-out HC emissions are similar: homogeneous lean vs. production strat lean

– MJI capable of maintaining relatively high combustion efficiency in ultra-lean region

2.4L homogeneous lean 2.0L stratified lean

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Emissions: HCResults

Engine-out HC

Acknowledgement: J. Parks – Oak Ridge National Lab

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Emissions: Particulates

PN emissions homogeneous lean MJI

– Similar to or slightly elevated vs. PFI

– Multiple powers of 10 below typical DI

PM trends similar

Particulate behavior may be most sensitive to main chamber fueling configuration

Results

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Results

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Knock Reduction

Reduced burn duration (30-50%) with Jet Ignition vs. SI

– Shorter endgas residence time = knock benefit

– Particularly beneficial at high speed when burning velocity limits combustion efficiency

Enables higher CR and/or more optimal combustion phasing

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0.6L single-cylinder 2500 rpm / 12 bar IMEPgCR: 14


Results

Multiple operating strategies possible: active system with or without boost

– Lean boost: apply boost to match NA full load curve, lean throughout map highest CR

– NA: lean up to mid-load, transition to stoich at full load highest cost-benefit

– Lean downsized: lean up to max boost, transition to stoich at full load highest power

Lean Boost Naturally Aspirated Lean Downsized

Operating Strategy: Active System

Throttled, λ≥1.9

WOT, λ≥1.9 WOT, λ=1.9 WOT, λ≥1.9

Full load, λ≥1.9

Throttled, λ≥1.9

Throttled, λ≥1.9

Full load, λ≤1

Full load, λ≤1

λ reduces

λ reduces

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Highest CR potential? Lowest cost? Highest output


Results

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The Challenges of Ultra-Lean Operation

Reduced exhaust temperature

– Engine-out emissions vs. tailpipe emissions

Managing NOx and HC with a sub-400°C manifold temp

– Boost system requirements

Low exhaust enthalpy at lean conditions

Need to minimize back pressure

Lambda as additional degree of freedom

– Narrow transient lambda control needed to minimize impact on aftertreatment

Add-on cost

– Auxiliary fuel injector

– Boost system


Summary

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Summary

Ultra-lean combustion in SI engines produces significant performance and emissions benefits:

– Map-wide reduction in fuel consumption

– Significant reductions in engine-out NOx

Jet Ignition is an effective enabling technology for ultra-lean combustion

– Lean limit extended to ultra-lean region while maintaining acceptable combustion stability

A fully optimized Jet Ignition engine incorporates multiple criteria, including:

– Operating strategy

– Boost requirements

– Compression ratio vs. desired peak power

– Cost-benefit

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Thank you for your attention

[email protected]

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AcknowledgementsDOE VTO: Roland GravelFord: Steve WooldridgeDelphi: Dan Kabasin, Joe Kazour, Mark SellnauMPT: Hugh Blaxill, Graham Irlam, Prasanna Chinnathambi


Results

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Cold Start and Idle

Cold start and idle performance are traditional weaknesses of pre-chamber technologies

MAHLE Jet Ignition capable of effective idle operation

– Work ongoing to improve idle performance

Cold start strategies currently being developed

– Jet Ignition components provide degrees of freedom for achieving cold start not present in many traditional pre-chamber technologies

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