Proceedings of the International Symposium on Marine Engineering

(ISME) October 17-21, 2011, Kobe, Japan Summary or Paper-ISME585

MAN B&W ME-GI ENGINES. RECENT RESEARCH AND RESULTS

Lars R. JULIUSSEN, Michael J. KRYGER and Anders ANDREASEN

Marine Low Speed Research and Development, MAN Diesel & Turbo, Teglholmsgade 41, DK-2450

Copenhagen SV, Denmark

ABSTRACT This paper presents the latest research, development and tests activities of MAN Diesel & Turbo’s ME-GI

engines. The overall aim of the research is to support a new generation of electronically controlled two-stroke low speed

marine diesel engines that operate on high-pressure Compressed Natural Gas (CNG). On the 4T50ME-GI-X research engine

functional tests of the gas engine and tests for benchmarking of the ME-GI potential in term of reduction of engine-out

emission as well as potential efficiency improvements are carried out. Advanced measurement and diagnostic methods were

applied in order to gain insight in the physical processes of gas injection, pilot fuel injection, ignition as well as combustion

and emission formation. The results from the first performance and emission measurements from the 4T50ME-GI-X research

engine show a NOx reduction of 24%, a reduction in CO2 emissions of approx. 23%, and very low emissions of methane. No

deterioration of engine stability is found and the results indicate improved efficiency of the ME-GI engine compared to the

conventional ME engine.

Keywords: Marine engines, two-stroke Diesel engines, LNG, ME-GI, dual fuel engines, green house gas

emissions

1. INTRODUCTION

At present time, most large vessels all over the world

operate on heavy fuel oil (HFO). The genuine portfolio of

the two-stroke engines of MAN Diesel & Turbo (MDT)

supports efficient ship propulsion with low emission values

fulfilling current emission legislation and contributing to

the improvement of the Energy Efficiency Design Index

(EEDI)(1)

. New emission requirements and increasing fuel

costs have however led the marine industry to seek

alternative competitive fuels.

In this connection, natural gas is considered as an

important and clean source of energy for sea going vessels.

By using natural gas as fuel, the CO2 footprint from sea

transportation can be further reduced. The volume of global

natural gas resources combined with the emerging gas

availability at the busiest ports, contribute to making gas an

attractive alternative.

Today the four-stroke engine has been introduced to the

LNG carrier market as part of a dual fuel diesel electric

system, but also the electronically controlled two-stroke

ME-C heavy fuel oil burning engine have successfully been

introduced to this market segment, offering high system

efficiency. A high pressure gas injection dual fuel

two-stroke engine in combination with the higher system

efficiency offers a significant reduction in emission for

LNG carriers as well as other ocean going vessels.

This has initiated a huge research and development

effort at MAN Diesel & Turbo and this article presents the

latest information and achievements of the ME-GI concept

for high pressure gas injection system for electronically

controlled two-stroke engines. The research activities

presented in this paper are organised in and part of the EU

project “Helios” (2)

.

2. ME-GI CONCEPT

The two stroke low speed high-pressure gas injection

engine, developed in the eighties by MDT, was a

mechanically controlled engine (MC-GI engine). It aimed

at the stationary power plant market and as an alternative to

steam turbines, which for years had powered Liquefied

Natural Gas (LNG) vessels using boil-off gas from storage

tanks. The result was the first MC-GI engine installed on

the Chiba power plant in Japan (3)

. In contrast to the MC-GI

engine, the ME-GI engine is an electronically controlled

engine, which introduces electronic control of both oil and

gas injection, ensuring that the process of mixture

formation, ignition and combustion is optimised.

The concept of the ME-GI system is based on a high

pressure gas injection principle with pilot fuel ignition.

With this principle the diesel combustion process can be

fully utilised and thereby the same high thermal efficiency

as for the heavy fuel oil burning two-stroke engines can be

obtained. The diesel combustion process has a significant

advantage compared to carburetted premixed Otto cycle gas

process, due to the fact that gas does not take part in the

compression stroke. This eliminates the risk of knocking

and thereby high compression/expansion ratios can be

utilised, offering high energy efficiency and low exhaust

gas emission.

The ME-GI engine is developed as a duel fuel engine

and is able to operate at 100% Maximum Continuous

Rating (MCR) on either Compressed Natural Gas (CNG) or

Heavy Fuel Oil (HFO) as well as on Marine Diesel Oil

(MDO) without loss of efficiency in any of the operating

modes and thereby offers full fuel flexibility to the ship

owner.

In order to support the ME-GI research, MAN Diesel &

Turbo’s 4T50ME-X research engine at the Diesel Research

Centre in Copenhagen has recently been rebuilt as a

4T50ME-GI-X engine in order to allow operation on

natural gas. To ensure efficient gas injection, the ME-GI

engine requires CNG is supplied at a pressure in the range

from 150-300 bars, depending on the engine load and at a

temperature of 45 °C (4)

.

Dedicated gas supply systems are being offered for the

fulfilment of these conditions. Solutions exist based on gas

compressors or cryogenic pump systems.

3. 4T50ME-GI-X RESEARCH ENGINE

The 4T50ME-GI-X research engine is a four cylinder

uni-flow scavenge two-stroke diesel engine, with a bore of

0.5m and a stroke of 2.2m and delivers approx. 7MW at

123 rpm. The research engine has been retrofitted to gas

operation by the following main features:

FGS System

The Fuel Gas Supply System (FGS System) of the

4T50ME-GI-X test engine has been provided by Daewoo

Shipbuilding & Marine Engineering CO., Ltd. (DSME) and

is based on a high pressure cryogenic pump system.

The system consists of a cryogenic storage tank, a feed

pump, suction drum, high pressure cryogenic pump,

pulsation damper, vaporizer, gas flow/pressure /temperature

control system as illustrated in Figure 1.

Figure 1: DSME FGS System

The cryogenic centrifugal pump supplies the LNG from

the cryogenic storage tank to the suction drum placed at the

inlet of the cryogenic high pressure (HP) pump, which

pressurizes the LNG to the desired pressure. The vaporizer

is connected to the HP pump outlet and the LNG is heated

to the desired 45 °C and gas changes phase to CNG. The

ME-GI engine control system supplies a gas pressure set

point to the gas supply system depending on engine load,

i.e. gas pressure dynamics follows engine dynamics.

Double-walled gas pipes

The high pressure gas is supplied from the FGS System

to the engine room through a double-walled air ventilated

piping system (See Figure 2). This specific installation

secures that the engine room is kept as an ordinary engine

room and not as a hazardous area, which complies with

IMO guidelines “Gas safe machinery spaces” (5)

. The space

between the inner high pressure pipe and the outer pipe is

continuously ventilated with a mechanical ventilator, which

is installed outside the engine room.

Figure 2: Double-walled gas pipes

In the event of a gas leakage, the leakage will be

maintained by the outer pipe and detected with a Hydro

Carbon (HC) sensor installed in the ventilation pipe outlet.

The double wall ventilation system is also part of the

engine internal gas system and all valves, gas injection

valves and high pressure sealings are connected to this

system.

Gas Injection System As a part of the gas injection system, a gas block is

applied, incorporating an accumulator, a window/shut down

valve and two purge valves (See Figure 3).

Figure 3: Gas block

When operation in gas mode, the window/shut down

valve is hydraulically opened by the pilot valve for the

electrical window and gas shut down valves. The window

valve is a double safety function, securing that gas injection

in the combustion chamber, is only possible at the correct

injection timing. From the gas window/shut down valve,

the gas is led to the gas injection valves via bores in the

cylinder cover.

Dual fuel operation requires valves for injection of both

pilot fuel oil and gas. The valves are of separate types; two

fitted for gas injection (See Figure 4) and two for pilot fuel

oil.

Figure 4: Gas injection valve

Gas Leakage Control

In order to prevent gas leakage and to resist high gas

pressure, a new sealing feature is installed on both the gas

injection valve and the window/shut down valve. Moreover,

a high pressure sealing oil system is introduced to prevent

gas from entering the control oil system.

At the end of gas operation, the gas pipes are purged by

N2, securing that no gas leakage can occur during operation

on HFO/MDO over a longer period of time nor during

maintenance and overhaul.

ME-GI Engine Control System (ME-GI ECS)

The ME-GI ECS is an add-on system to the ME Engine

Control System. This system is taking responsibility for the

ME-GI gas operation as well as major safety functions. The

ME-GI ECS is divided into separate gas control and safety

units as well as Human Machine Interface (HMI) by the

Gas Main Operation Panel (GMOP).

4. RESULTS

In this section, the first full performance and

emission measurements on 4T50ME-GI-X are presented.

The present results serve as a baseline and as an indication

of the potential of the ME-GI in terms of emissions and

Specific Fuel Oil Consumption (SFOC) and Gas

Consumption (GC). Further optimization of the concept in

terms of performance and emissions is currently in

progress.

4.1 Test program and pilot oil amount

A total of eight full engine tests are presented, four

reference tests on diesel (gas oil) and four tests on CNG.

For both modes tests, according to the ISO E3 cycle, have

been conducted i.e. 25, 50, 75, and 100% load with the

engine speed given by a propeller curve.

The measured amount of pilot oil for tests GI1-GI4 is

summarized in Table 1. Thus, the results clearly

demonstrate that operation on CNG with a pilot oil amount

of 5% (or less) of the MCR fuel amount is indeed possible.

Previous results for the MC-GI engine were obtained with

8% pilot oil amount (6)

.

Table 1: Pilot oil consumption

Test

Load

(%)

Pilot amount

(% of heat rate) (% of MCR)

GI1 25 11.3 3.0

GI2 50 7.3 3.6

GI3 75 4.7 3.4

GI4 100 4.4 4.4

4.2 Performance and SFOC

The comparison of performance the 4T50ME-GI-X

vs. 4T50ME-X is shown in Figure 6. The graph confirms

that the performance adjustment has been satisfactory.

Further, it is noticed that the main difference between diesel

and CNG fuel, is slightly lower exhaust gas temperatures,

both out of cylinders as well as in and out of the turbine.

This is compensated by a higher heat capacity due to a

higher water content in the exhaust gas.

Figure 6: Performance curves: Pressure Exhaust gas

temperatures (upper) and Turbo Charger (TC) Speed

(lower).

In general, it was observed that both turbocharger

speed and scavenging air pressure dropped slightly when

changing from diesel to CNG. According to turbocharger

calculations with a constant heat rate and unchanged heat

release, it is found that the scavenging air pressure should

increase slightly (0.02 bar). Thus, the experimental results

suggest a slightly improved efficiency of the ME-GI engine.

An indicated SFOC is calculated by the following formula:

iSFOC = Qgros/(LCV∙W), where Qgross refers to the gross

heat release (heat loss is assumed to account for 5%). LCV

is the lower heating value of the fuel. A value of 42.7 MJ/kg

is used. The results are shown in Figure 7.

Figure 7: Calculated change in iSFOC from diesel to CNG

Generally, a considerable improvement in iSFOC

is found for gas at all loads, although less pronounced at

low load. Thus both iSFOC and the turbocharger

considerations seem to indicate an improved SFOC with

CNG compared to diesel. The results look promising and

optimisation tests will continue

4.3 Heat release

The calculated heat release rates are shown in Figure

8. As seen from the Figure, at 75% load the heat release rate

for CNG closely resembles that of diesel, although minor

differences appear. Starting with the same initial increase in

heat release rate, CNG seems to be somewhat quenched

from the point of half of the maximum heat release rate,

and until the maximum has been reached. From that point

the shape of the heat release rate is nearly identical.

The injection timings and injection lengths are

compared in Table 2. As seen from the table, the injection

length is comparable for the 75% load case, but for the

100% load case, the CNG injection length is shorter than

that of the diesel reference. This may explain the shorter

heat release rate profile seen in Figure 8. The reason for the

similar heat release rates may be due to comparable

injection intensity. It should be noted that the results shown

are of preliminary nature and that an optimization of gas

atomizer layout as well as gas injection pressure is

continued.

75% load

100% load

Figure 8: Single zone heat release rates

Table 2: Injection indicators

Load Pilot SOI CNG SOI Pgas CNG inj.

length

Ref. inj.

length

(%) (ms) (ms) (bar) (ms) (ms)

25 -1.4 5.6 202 17.6 15.4

50 -4.2 2.8 246 19.8 21.7

75 -3.0 -1.6 281 26.2 27.0

100 -0.8 -0.2 300 27.3 32.4

4.4 Emissions

Specific emissions are displayed in Figure 9 and 10. In

Figure 9, it is clearly seen that the NOx emission is reduced

significantly. The reduction is smallest at low load and

highest at around 75% load (3)

. The E3 NO cycle values (6),

(7) for diesel and CNG are 15.7 g/kWh and 11.9 g/kWh,

respectively. The reduction in NOx is 24%. A rough back on

the envelope kind of calculation assuming equilibrium and

stoichiometric combustion estimates that CNG potentially

has 30% lower NOx emission, primarily due to a lower

flame temperature. The lower flame temperature is, despite

a higher heating value, due to a higher air mass required for

stoichiometric combustion, thereby a higher heat capacity

of the stoichiometric mixture.

Figure 9: Specific NOx emissions as a function of load

Figure 10: Specific CO2 emissions as a function of load

From Figure 10, it is observed that CO2 is generally

reduced to the same degree more or less independent of

engine load (approx. 23%). The level of the reduction is a

function of the pilot oil amount, the quality (carbon

content/LCV) of the fuel oil and the quality of the gas.

It was also observed that CO generally decreased with CNG,

most pronounced at low load. Thus, as smoke/soot

generally correlates with CO emission, the ME-GI engine

should have even better low load emission characteristics

than the ME engine. The amount of unburned hydrocarbons

(HC) Slightly increases when using CNG as fuel, possibly

due to gas left-over in the gas nozzle sac.

As the ME-GI concept is based on direct gas

injection with the engine operated as a conventional diesel

engine, methane slip is minimized to a level comparable to

operation on conventional liquid fuel. FTIR exhaust gas

measurements during a recent measurement campaign have

revealed a methane slip of 0.2 g/kWh independent on

engine load. For comparison, the methane slip for most

modern 4-stroke state-of-the-art dual-fuel engines operated

either as lean-burn or dual-fuel engines utilising the Otto

principle, is in the range 4-8 g/kWh, resulting in 20-40

times lower methane slip of the ME-GI engine than the

most modern Otto gas engines(8)

. Especially at low load, the

methane slip from 4-stroke gas engines can be several times

higher than at high load (8),(9)

. This is not a problem for the

ME-GI engine.

The global warming potential, GWP, of methane is

72 times as high as CO2 over a 20 year time interval (10)

.

Thus, when calculating the total GWP, in addition to CO2,

CH4 must be considered as well. Taking the methane slip of

the ME-GI engine into account, the total GWP is still

significant lower than normal (diesel) fuel oil operation,

approx. 20% lower.

4.5 Engine stability

The stability in terms of cycle-to-cycle variation for

operation on CNG is compared to that for diesel fuel in

Figure 11. Only results for 75% load are showed, however

the results are representative for the general case. As seen

from the Figure, no deterioration of the cycle-to-cycle

variation is observed. On the contrary the cycle-to-cycle

variation seems to be decreased slightly in the proximity of

the maximum cylinder pressure.

4.6 Engine operation and failure mode demonstration

In June 2011, a demonstration programme on

4T50ME-GI-X with HFO as pilot fuel was tailored in order

to visualise the operation of the ME-GI system under

realistic conditions, both in terms of normal operation (fuel

change-over, engine load up/down etc.) and fault mode

operation (gas system shutdown). The demonstration

programme contained the following conditions:

Change-over HFO to gas at 15% load

Load change on gas from 15% load to 100% load

Gas shut-down at 100% load (emergency stop

button)

Change-over HFO to gas at 100% load

Load change 100% to 50% load on gas

Gas shut-down at 50% load (simulated gas

leakage)

Load change to 25% load on HFO

Change-over from HFO to gas at 25%

Load change from 25% to ~9% load on gas

Gas shut-down (safety system)

Engine data from the programme is seen in Figure 12.

As seen from the engine load and speed, the fuel

change-over both from HFO to gas at both 15% (t=13:43)

and 100% (t=14:07) appear bumpless. A slight change in

maximum cylinder pressure is observed, but this is a matter

of optimising the commissioning of both engine running

modes. A total of three engine shut-downs are demonstrated.

During shut-down, the engine load/rpm drops briefly due to

the gas cut-off i.e. a single engine revolution is with pilot

oil only, and the engine recovers rapidly even despite the

lack of inertia from a propeller on the research engine.

Diesel 75% load

Gas 75% load

Figure 11: Consecutively measured cylinder pressure for

cylinder 1 (gray) with added indicators for mean, minimum,

and maximum as well std. deviation. 500 consecutive

cycles are recorded

Figure 12: ME-GI operation and safety demonstration

program

5. SUMMARY

In this paper, the ME-GI concept for operation on

LNG/CNG with the electronically controlled ME-GI dual

two-stroke engine has been described, and main

components of the system as well as results are presented.

The electronically controlled ME-GI engine show

significant advantages in the optimisation of the

combustion process and is a major step for efficiency and

emission improvements. In addition to safe and reliable

operation on gas, the ME-GI offers improved exhaust

emission footprint compared to the standard ME engines

running on conventional diesel/heavy fuel oil (HFO) in

which CO2, CO and NOx emissions are lowered. The NOx

cycle value is lowered approx. 24% and the SFOC is

estimated to be improved in the order of 0-3 g/kWh

compared to diesel operation. However, since GC is not

measured directly, these results await confirmation in future

engine tests. At all tests, the pilot amount has been kept

below 5% of the MCR fuel amount. The cycle-to-cycle

stability is unaffected or even slightly improved by

changing from diesel to CNG. Finally, methane emissions

are at a very low level.

REFERENCES

(1) MAN Diesel & Turbo. “Propulsion of 46,000-50,000

dwt Handymax Tanker”, Technical Paper, Low Speed

(2011) http://goo.gl/krMxV

(2) Helios. “High Pressure Electronically controlled gas

injection for marine two-stroke engines”, The 7th

EU

Framework programme (2010) http://goo.gl/9Xd3U

(3) Beppu, O., Fukuda, T., Komoda, T., Miyake, S., Tanaka,

I. “Service experience of Mitsui gas injection diesel

engines, Mitsui-MAN B&W 12K80MC-GI-S and

Mitsui 8L42MB-G”, CIMAC Congress 1998

Copenhagen, Denmark (1998).

(4) MAN Diesel & Turbo. “World Premiere of the MAN

B&W ME-GI engine. Gas engine debuts at ceremony

in CPH”, DieselFacts (2011) http://goo.gl/vfVx1

(5) IMO. “International code on safety for gas-fuelled

ships (IGF Code)”, IMO sub-committee BLG, draft.

(6) ISO.”International Standard ISO 8178-1: Reciprocating

internal combustion engines - Exhaust emission

measurement - Part 1: Test-bed measurement of

gaseous and particulate exhaust emissions”,

International Organization for Standardization, 2nd

Edition (2006).

(7) IMO. “Annex VI of MARPOL 73/78 Regulations for

the prevention of Air polution from ships and NOx

technical code”, International Marine Organization.

London, UK (1998).

(8) Nielsen, J. B., Stenersen, D., “Emission factors for

CH4, NOx, particulates and black carbon for domestic

shipping in Norway”, MARINTEK report , MT22

A10-199, Klima og Forurensningsdirektoratet, Norway

(2010).

(9) Järvi, A.,“Methane slip reduction in Wärtsilä lean burn

gas engines”, CIMAC Congress 2010 Bergen, Norway

(2010).

(10) Forster, P.V., et al., “Changes in Atmospheric

Constituents and in Radiative Forcing”, Climate

Change: The Physical Science Basis, Contribution of

Working Group I to the Fourth Assessment Report of

the Intergovernmental Panel on Climate Change in S.

Solomon et al. (eds.), Cambridge (2007).

NOMENCLATURE

ATDC : After Top Dead Centre

CNG : Compressed Natural Gas

CO2 : Carbon Dioxide

CO : Carbon Monoxide

CH4 : Methane

DSME : Daewoo Shipbuilding & Marine Engineering

Co., LDT.

EEDI : Energy Efficiency Design Index

FGS : Fuel Gas Supply

FTIR : Fourier Transform Infrared spectrometer

GC : Gas Consumption

ECS : Engine Control System

GMOP : Gas Main Operational Panel

GWP : Global Warming Potential

HC : Hydro Carbon

HFO : Heavy Fuel Oil

HMI : Human Machine Interface

HP : High Pressure

HPS : Hydraulic Power Supply

IMO : International Maritime Organisation

iSFOC : Indicated Specific Fuel Oil Consumption

LCV : Lower Calorific Value

LNG : Liquefied Natural Gas

MCR : Maximum Continuous Rating

MDO : Marine Diesel Oil

MDT : MAN Diesel & Turbo

ME : Electronically Controlled Engine

N2 : Nitrogen

NO : Nitrogen Monoxide

NOx : Nitrogen Oxide

Pgas : Gas Supply Pressure

SFOC : Specific Fuel Oil Consumption

SOI : Start Of Injection

TC : Turbo Charger

TDC : Top Dead Centre

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.