Proceedings of the International Symposium on Marine Engineering

(ISME) October 17-21, 2011, Kobe, Japan Summary or Paper-ISME586

Tier III EGR FOR LARGE 2-STROKE MAN B&W DIESEL ENGINES

Johan Kaltoft

MAN Diesel & Turbo, Teglholmsgade 41, 2450 Copenhagen SV, Denmark

Abstract The IMO Tier III NOx regulations that will come into force in 2016 means that NOx emissions from

large two-stroke diesel engines must not exceed a cycle value of 3.4 g/kWh, and NOx emission must not exceed

5.1 g/kWh at individual load points of the load cycle. To comply with the Tier III requirements, MAN Diesel &

Turbo (MDT) is involved in targeting development of Exhaust Gas Recirculation (EGR). This paper describes

the EGR principle, the investigation of EGR on two-stroke diesel engines as well as service test experience and

test results. Test on MAN Diesel & Turbo´s two-stroke diesel engine in Copenhagen has proved that EGR is a

compliant IMO Tier III NOx technology and service tests are currently ongoing in order to investigate long term

influence on engine components and the EGR system.

Keywords: IMO Tier III, Exhaust Gas Recirculation (EGR), MAN B&W engines.

1. INTRODUCTION

The worlds marine engine manufacturers have since the

ratification of the IMO Tier III criteria for NOx emission in

Emission Controlled Areas (ECA´s) from large marine

diesel engines, been challenged to develop new measures in

order to reduce NOx. The extend of the necessary measures

for NOx reduction up to 80% for meeting the IMO NOx

criteria from January the 1st 2016, is beyond well known

adjustments of the combustion process in two-stroke diesel

engines. NOx reduction in his magnitude on two-stroke

diesel engines, requires “add-on” technologies like Exhaust

Gas Recirculation (EGR) or Selective Catalytic Reduction

(SCR) as described in the ISME paper number 587 (2011).

Back in 2004, MAN Diesel & Turbo started the first test

program with EGR on the large 4T50ME-X two-stroke

diesel test engine in Copenhagen, in order to verify the

effect of EGR. The effect of EGR on smaller four-stroke

diesel engines used in the automotive sector has been

known since the 1970’ies as a very efficient means to

reduce NOx in combustion engines. The HFO burned in

large marine engines is a challenge when using EGR, due to

the presence of high sulphur content and high content of

solids thus a wet scrubber was introduced in the EGR

system.

In parallel with the EGR investigation on the 4T50ME-

X test engine, MAN Diesel & Turbo planned to make a

service test on a ship in order to investigate long term

effects on the engine components. In March 2010, a retrofit

EGR system was installed on a 10MW 7S50MC Mk-6

engine onboard A.P. Moeller Maersk 1100 TEU container

vessel Alexander Maersk.

The recent EGR investigation and service test is a part of

the large European development project named

HERCULES-B with focus on high engine efficiency and

low emissions.

This paper describes the investigation and testing which

MAN Diesel and Turbo have completed with EGR on large

two-stroke diesel engines.

2. EXHAUST GAS RECIRCULATION

The principle of EGR is based on exchange of the in-

cylinder oxygen (O2) with carbon dioxide (CO2) from the

exhaust gas which is re-circulated into the scavenge air. The

exchange of O2 with CO2 leads to a decrease of combustion

speed, resulting in lower peak temperatures during

combustion. Besides the exchange of O2 with CO2 results in

a higher in-cylinder heat capacity of the gas, which also

lowers the combustion temperature. Lower combustion

temperatures and especially lower peak temperatures result

in lower formation of thermal NOx during the combustion

process.

There are different ways to utilise EGR on a two-stroke

diesel engine:

A) Internal EGR (primary methods)

- Poor scavenging of the combustion chamber.

- Internal trapping of combustion gas in the

combustion chamber.

B) External EGR (secondary methods)

- Low pressure EGR on the exhaust side of the

turbocharger, downstream the turbine.

- High pressure EGR on the engine side of the

turbocharger, upstream the turbine.

3. THE EGR SYSTEM FOR A MAN B&W ENGINE

The reasons why the high pressure EGR in MAN Diesel

& Turbo´s large two-stroke diesel engines is chosen as the

preferred EGR solution are:

- The system is compact compared to the low

pressure EGR system and is an “on engine”

system.

- The turbo compressor is not exposed to additional

sulphur, particles and water droplets than

conventional engines. - Only the rugged engine components from the

scavenge air receiver to the exhaust gas funnel is

affected. The components from air intake to the

scavenge air receiver, i.e. the main engine cooler,

is not exposed to additional sulphur, particles and

water droplets than in conventional engines.

Figure 1: Basic EGR system layout diagram

The MAN Diesel & Turbo EGR system basically

consists of three flow loops:

- EGR gas loop.

- Scrubber water loop.

- Water cleaning loop.

As seen from Figure 1, the EGR system comprises the

following main components:

EGR blower for creating a flow from the exhaust

receiver to the scavenge air receiver of up to around 40% of

the total exhaust gas amount. The pressure difference

between the receivers is around 0.3 bar at 100% engine load

and the EGR blower has to overcome this pressure

difference as well as the pressure loss through the scrubber,

cooler, pipes etc., which is approx. 0,2-0,3 bar. The EGR

blower speed is controlled by a frequency converter control

of the blower motor.

Pre scrubber for removal of SO2 and for energy

conversion by humidification, in order to precondition the

exhaust gas before the gas enters the EGR scrubber. The

exhaust gas is washed with re-circulated fresh water with

addition of sodium hydroxide (NaOH). NaOH neutralizes

the sulphuric acid that is formed in the scrubber water.

Around 95% of the scrubber is continuously re-circulated.

The temperature of the exhaust gas entering the Pre

scrubber can vary from 200-500ºC over the engine load

range.

Scrubber for removal of particles and residual SO2 in

the exhaust gas before it is introduced into the scavenge air

receiver and further into the combustion chamber. The gas

is washed with re-circulated scrubber water supplied from

the same pipe that feeds the Pre scrubber. The temperature

of the EGR gas entering the EGR Scrubber varies from 50-

100°C over the load range.

Drainers for separation of the scrubber water and the

EGR gas before collecting the scrubber water in a buffer

tank. The drainer’s ensure that only scrubber water is

discharged from the scrubber to the buffer tank without

leakage of EGR gas.

EGR cooler for cooling of the EGR gas and conversion

of the enthalpy in the EGR gas to the cooling water. The

water evaporated in the pre scrubber is condensed in the

EGR cooler. The EGR cooler cools the scrubbed gas down

to approx. scavenge air temperature between 35-40ºC.

Shut Down valve (S/D valve) for switching on and off

the EGR system. The valve is gas tight and ensures no flow

of scavenge air into the exhaust system, while the EGR

system is not operated. The valve is “on/off” controlled.

Change over valve (C/O Valve) for control of the EGR

gas amount in cooperation with the EGR blower speed. The

valve is operated as a throttle valve with variable

positioning.

Oxygen sensor for measurement of the oxygen content

in the scavenge air receiver. The EGR gas amount is

controlled by the oxygen content in the scavenge air

receiver, which varies from 16-21 % v/v.

Water Treatment System (WTS) for handling of the

scrubber water in the system. The system controls the water

supply to the scrubber (quality and amount) dependant on

engine load. The quality (pH, turbidity and poly aromatic

hydrocarbons) of the scrubber water, for discharge to the

sea, is also controlled by the WTS. The quality of the

discharge water to the sea is hereby ensured to be within the

IMO criteria’s for scrubber water discharge criteria’s. Alfa

Laval and MAN Diesel & Turbo are via continuous

cooperation developing a WTS solution on a unit base, for

installation in an adjacent room close to the engine.

Buffer tank is a part of the WTS.

NaOH tank for bunkering and storage of the NaOH.

The size of the NaOH tank is depending on the engine size,

sailing patterns, bunkering facilities and NaOH

concentration. A guiding size for a container vessel is

approx. 2.0 m3/MW (installed engine power).

Sludge tank for collection of sludge from the WTS

system. The Sludge tank size is depending on engine size,

sailing patterns and disposal facilities. A guiding size for a

container vessel is approx. 1.5 m3/MW (installed engine

power).

EGR control system for starting and stopping the EGR

system and for controlling of the amount of EGR gas

reintroduced to the scavenge air receiver, depended on

engine load and engine mode. The safety of the EGR

system is covered by the EGR control system via

appropriate alarms and an EGR shut down sequence if

necessary. Input is O2 concentration in the scavenge air and

controlled components are the S/D valve, C/O valve, EGR

Blower and the WTS system.

The design of the EGR system is currently being

matured and the target for MAN Diesel and Turbo is to

integrate the engine related EGR components on the engine

to an extent that is viable in order to keep the engine

installation as simple as possible and with a minimum need

for additional space around the engine.

The system components described above is the current

system design for engines with only one turbo charger. For

engines with more than one turbo charger, other system

layouts will be relevant utilizing turbocharger cut valves for

compensating the reduced exhaust gas during EGR

operation, see Figure 2 below.

Figure 2: Design of 6S80ME-C9 engine with EGR and two

turbochargers.

4. INVESTIGATION OF EGR ON 4T50ME-X TEST

ENGINE

4.1 Objective of the EGR test programme

During 2009 and 2010 EGR was thoroughly

investigated on MAN Diesel & Turbo’s 7MW 4T50ME-X

test engine in Copenhagen.

The objective of the test programme was to examine

how IMO Tier III NOx compliance could be achieved by

using high pressure EGR on a large two-stroke diesel

engine. The investigation covered influence of variations on

different engine parameters; maximum pressure (Pmax),

compression pressure (Pcomp), scavenge air pressure

(Pscav), scavenge air temperature (Tscav), hydraulic

injection pressure (Phyd) etc. The effect on NOx, Specific

Fuel Oil Consumption (SFOC), Particulate Mass (PM),

carbon monoxide (CO) and hydro-carbons (HC) were

studied.

Moreover, both IMO Tier III (ECA) operation and Tier

II (Non ECA) operation and the switch between the two

modes were tested as well as different control strategies.

Also the EGR scrubber was tested during the test

programme in order to verify the performance with regard

to particle trapping and SO2 removal.

4.2 Test results from EGR test on 4T50ME-X engine

The study of engine parameter variations during EGR

operation revealed the following effects on SFOC and

emissions as also seen from Table 1:

- Increased Pcomp/Pscav ratio has a positive impact

on the SFOC penalty.

- Increased Phyd has a positive impact on the SFOC

penalty.

- Increased Pscav has a positive impact on the

SFOC penalty.

- Increased Tscav has a negative impact on the

SFOC penalty.

- Increased Phyd has a positive impact on CO and

hereby also visible smoke.

Table 1: Test results from engine parameter variations at

75% engine load (auxiliary power for EGR blower,

separator and pumps is not included in dSFOC).

NOx

(g/kWh)

dSFOC

(g/kWh)

CO

(g/kWh)

Pmax

(bara)

EGR rate

(%)

O2

(vol. %)

No EGR 17.8 0 0.65 152 0 - Max.

EGR 2.3 +4.9 4.17 151 39 16.0

EGR ref. 3.7 +3.0 2.57 151 36 16.8 Incr.

Pcomp/

Pscav

4.0 +2.5 2.18 156 36 16.8

Incr. Phyd 4.2 +2.8 1.83 151 37 16.6 Incr.

Pscav 3.6 +1.9 2.12 156 37 16.6

Incr.

Tscav 3.9 +3.6 2.82 156 34 16.8

Tier III

setup 3.4 +0.6 1.34 157 41 16.2

The reduced energy to the turbine side of the turbo

charger, up to around 40%, when operating the EGR

system, results in reduced scavenge air pressure and hereby

negative effects on the SFOC. This highlights the need for

compensating means. Both variable turbine geometry and

cylinder bypass has been tested and seems to be able to

compensate the decrease in scavenge air pressure. Figure 3

shows the two very different operating areas for the

compressor running with and without EGR, corresponding

to utilisation of a turbocharger cut out solution.

Figure 3: Turbocharger compressor maps running the

engine with and without EGR.

As seen from Figure 4, the heat release is only slightly

affected by EGR. Increased hydraulic injection pressure can

compensate for reduced heat release in the early part of the

combustion.

Figure 4: Heat release running with and without EGR.

The scrubber performance was also measured during the

EGR test programme and showed a particle trapping

efficiency of around 70% according to ISO 8178 standard

for PM measurements. The SO2 removal efficiency could

more or less be controlled by the amount of added NaOH in

the scrubber water.

The investigation on the 4T50ME-X test engine has

showed that IMO Tier III NOx compliance is achievable by

use of High Pressure EGR solely. A cycle value below

3.4g/kWh of NOx was obtained and also the Not To Exceed

(NTE) level of 5.1 g/kWh of NOx at each engine load point

25, 50, 75 and 100% were proved during the test, see

Figure 5 below.

Figure 5: NOx emission at different engine loads as a

function of oxygen content in the scavenging air.

5. EGR service test

5.1 Objectives of the EGR service test

The main objective of the service test, which still is

ongoing, is mainly to investigate the long term impact on

the engine during EGR operation.

The more detailed objectives is outlined below:

- Investigate impact of EGR operation on engine

components: cylinder liner, piston, piston rings,

piston rod, cylinder cover, exhaust valve etc, when

burning HFO with high content of sulphur and

solids.

- Reduce NOx with 50% during the test.

- Investigate impact on the EGR components.

- Hand over operation of the EGR system to the ship

crew in order to get feedback on operation of the

system, in order to adjust the system for easy,

reliable and safe operation.

5.2 Preparation for EGR service test

During the summer 2008, A. P. Moeller Maersk and

MAN Diesel and Turbo agreed on testing a High Pressure

EGR system on one of A. P. Moeller Maersk’s smaller

container vessels. The vessel pointed out was Alexander

Maersk a 1092 TEU container feeder operating in the

Mediterranean. Alexander Maersk is installed with a 10,126

kW, 127 rpm 7S50MC Mk 6 engine produced by Hitachi

Zosen Cooperation.

A retrofit EGR system was designed by MAN Diesel

and Turbo from August 2008 to March 2009. Components

were manufactured and the main EGR components were

installed in August 2009 at Lisnave shipyard in Lissabon in

Portugal.

Figure 6: Arrangement of the EGR system on Alexander

Maersk.

It was necessary to exchange the two existing turbo

chargers on the 7S50MC engine with one new larger

turbocharger with variable turbine geometry in order to

compensate for the reduced exhaust gas amount in EGR

running mode. An ABB A175L VTG turbocharger was

chosen for this purpose.

The EGR scrubber, EGR blower and the EGR cooler is

integrated in one unit mounted on the fore end of the engine

as seen from Figure 6 and 7.

On Alexander Maersk, the EGR gas is introduced before

the main engine coolers in order to ensure good mixing of

the EGR gas and the compressed air from the turbo

compressor. Besides, it was of interest to investigate how

the main engine coolers were affected by the sulphur and

particles in the EGR gas.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

22.0

24.0

15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0

Sp

eci

fic

NO

x (

g/k

Wh

)

Oxygen conc. in Scav.Rec (wet, vol %)

100% load

75% load

50% load

25% load

NTE NOx

IMO Tier 3 cycle value

Figure 7: EGR unit on board Alexander Maersk

Below in Table 2, the capacities and material of some

selected specified EGR components for Alexander Maersk

are listed:

Table 2: List of capacities and materials for selected

components specified for Alexander Maersk.

Component

s

Capacity Material

EGR Blower Flow: 4.5 kg/s

dp: 0.6 bar

Power: 240

kW

Wheel: Corten steel.

Housing: coated mild

steel.

EGR

Scrubber

Gas flow:

4.5 kg/s

Stainless steel 316L.

EGR Cooler Heat transfer:

2300 kW

Copper tubes and nano

coated copper fins.

Housing: coated mild

steel.

NaOH tank 4 m3

Stainless steel 316L

NaOH pump Flow: 60 l/min Teflon, 316L

Sludge tank Approx. 20 m3 Coated mild steel

WTS

separator

30 m3/h Rotating parts is stainless

steel and housing is

coated mild steel.

In order to ensure an efficient WTS solution for the EGR

system, different separators from Alfa Laval have been

tested at the 4T50ME-X test engine.

Figure 8: Left - Alfa Laval testing a separator at 4T50ME-X

test engine. Right – scrubber water samples before and after

test of discharge scrubber water.

5.3 EGR service test results

Currently the EGR system onboard Alexander Maersk

has been in operation close to 500 hours with the engine

running on HFO with 3% sulphur. The EGR system is

currently operated by the ship crew. The EGR system is a

push bottom system controlled from the engine control

room, except for the separator in the WTS system, which

has to be started up on-site by the crew.

Figure 9: Measurements of NOx reduction on board

Alexander Maersk during a performance test.

The thermo dynamical performance of the EGR

components was successfully tested and the EGR

components fulfilled the expected performance.

Commissioning of the EGR system in automatic mode was

also successfully completed.

Until now, the combustion chamber components and the

exhaust gas path are not negatively affected by EGR

operation. Figure 10 shows the piston rings before and after

approx. 300 running hours in EGR operation.

Figure 10: Piston rings before and after approx. 300

running hours in EGR operation on HFO.

The service test, which still is ongoing, has been quite

challenging due to HFO operation with high sulphur and

solids content. The challenges have mainly been related to

the following issues:

- Corrosion of non stainless components, e.g. due to

insufficient coatings. Heavy corrosion has been

experienced on the EGR cooler housing, EGR

cooler element, EGR blower wheel, drainers, EGR

pipe and separator in the WTS system.

- Difficulties with controlling the dosing of the

correct amount of NaOH.

- Water carry over from the scrubber system,

resulting in heavy deposits in the EGR system.

Figure 10: Left – deposits of sodium sulphate, iron sulphate

and soot on main engine cooler top, caused by water carry

over from the scrubber system. Right – almost no deposits

when water carry over from EGR scrubber system is

avoided.

In order to deal with corrosion challenges, the following

components have been exchanged with stainless steel: EGR

blower wheel, drainers and some valves in the WTS

system. The EGR cooler element will be exchanged with a

stainless steel element. In addition, a comprehensive repair

of the EGR cooler housing and the EGR pipe from the

blower to the connection on the charge air pipe have been

completed due to insufficient coatings.

The service test has gained a lot of important learning

and information on what the challenges are when running

EGR on a HFO burning two-stroke marine diesel engine.

Corrosion of EGR components and deposits in the EGR

system is important to target. Until this state of the service

test the engine components is not affected by high pressure

EGR operation.

8. CONCLUSIONS

The comprehensive investigation in High Pressure EGR

on large two-stroke marine diesel engines carried out at

MAN Diesel & Turbo’s test centre in Copenhagen have

proven that the IMO Tier III NOx emission limits coming in

to force by January 1st 2016 are possible to meet with

EGR. A cycle value below 3.4g/kWh of NOx was obtained

and also the NTE level of 5.1 g/kWh of NOx at each engine

load point 25, 50, 75 and 100%, were proved during tests.

The tests have also revealed which parameters to adjust in

order to obtain the optimal trade off between SFOC, NOx

CO and HC.

The EGR service test on Alexander Maersk has until

now, and will be in the future, an important test platform for

knowledge on how the engine and the EGR components are

affected by EGR and for identifying by which means

reliable and safe operation can be ensured. The test has

after approx. 500 running hours with EGR on HFO with 3%

sulphur showed no negative impact on vital engine

components. The EGR system is operated in fully

automated mode by the ship crew. The challenges have so

far been related to corrosion of EGR components, deposits

in the EGR system and deposits on the main engine coolers.

Furthermore, water carry over from the EGR scrubber

system, NaOH dosing and scrubber water quality control

are equally important parameters to control.

Regarding compliance on the scrubber water discharge,

the development in separator designs for this purpose, have

successfully shown that the discharge criteria’s can be met.

At current state, the overall conclusion is that High

Pressure EGR on large two-stroke marine diesel engines

burning HFO is a very promising measure for IMO Tier III

NOx compliance, although there still is a need for further

investigation and testing of the technology.

NOMENCLATURE

EGR : Exhaust Gas Recirculation

ECA : Emission Controlled Area

SCR : Selective Catalytic Reduction

IMO : International Maritime Organisation

HFO : Heavy Fuel Oil

NTE : Not To Exceed

SFOC : Specific fuel oil consumption [g/kWh]

TEU : Twenty-foot equivalent units

WTS : Water Treatment System

S/D : Shut Down

C/O : Change Over

WMC : Water Mist Catcher

Pscav : Scavenge air pressure [bara]

Pmax : Maximum pressure [bara]

Pcomp : Compression pressure [bara]

Phyd : Hydraulic Injection Pressure [bara]

Tscav : Scavenge Air Temperature [°C]

PM : Particulate Mass

ISO : International Organization for

Standardization

NOx : Nitrogen Oxides

CO : Carbon Monoxide

CO2 : Carbon Dioxide

SO2 : Sulphur Dioxide

HC : Hydro Carbon

DISCLAIMER

All data provided in this document is non-binding. This

data serves informational purposes only and is especially

not guaranteed in any way. Depending on the subsequent

specific individual projects, the relevant data may be

subject to changes and will be assessed and determined

individually for each project. This will depend on the

particular characteristics of each individual project,

especially specific site and operational conditions.