man diesel and turbo me gi engines isme585
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me-giTRANSCRIPT
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.