1. LNG Carriers with ME-GI Engine and
High Pressure Gas Supply System
Contents: Introduction ......................................................................... 3
Propulsion Requirements for LNG Carriers with
Dual-Fuel Gas Injection ...................................................... 4
Fuel Gas Supply System – Design Concept ...................... 5
Fuel Gas Supply System – Key Components .................... 6
Capacity Control – Valve Unloading .................................. 9
Compressor System Engineering – 6LP250-5S ................. 10
ME-GI Gas System Engineering .......................................... 11
ME-GI Injection System ....................................................... 12
High-Pressure Double-Wall Piping ..................................... 13
Fuel Gas System - Control Requirements ......................... 15
Machinery Room installation – 6LP250-5S ....................... 18
Requirements for Cargo Machinery
Room Support Structure ..................................................... 19
Requirements for Classification ......................................... 20
Actual Test and Analysis of
Safety when Operating on Gas .......................................... 20
Main Engine Room Safety ................................................. 20
Simulation Results .............................................................. 21
Engine Operating Modes ................................................... 22
Launching the ME-GI .......................................................... 23
Machinery Concepts Comparion ........................................ 24
Concluding Remarks ................................................................... 28
References ................................................................................... 28
Appendices: I, II,III, IV, V, VI,VII ................................................... 28
MAN Diesel A/S, Copenhagen, Denmark

3. LNG Carriers with ME-GI Engine and
High Pressure Gas Supply System
Introduction • low speed, heavy fuel oil burning die-
sel engine combined with a relique-
The latest introduction to the marine faction system for BOG recovery
market of ship designs with the dual-
fuel low speed ME-GI engine has been • medium speed, dual-fuel engines
very much supported by the Korean with electric propulsion.
shipyards and engine builders, Doosan,
Hyundai, Samsung and Daewoo. A further low speed direct propulsion
alternative, using a dual-fuel two-stroke
Thanks to this cooperation it has been engine, is now also available:
possible to introduce the ME-GI en-
gines into the latest design of LNG car- • high thermal efficiency, flexible fuel/
riers and get full acceptance from the gas ratio, low operational and instal-
Classification Societies involved. lation costs are the major benefits of
this alternative engine version
This paper describes the innovative de- • the engine utilises a high-pressure
sign and installation features of the fuel gas system to supply boil-off gas at
gas supply system for an LNG carrier, pressures of 250-300 bar for injection
comprising multi-stage low temperature into the cylinders.
boil-off fuel gas compressor with driver
and auxiliary systems, high-pressure Apart from the description of the fuel
piping system and safety features, gas supply system, this paper also
controls and instrumentation. The discusses related issues such as re-
paper also extensively describes the quirements for classification, hazardous
operational control system required to identification procedures, main engine
provide full engine availability over the room safety, maintenance requirements
entire transport cycle. and availability.
The demand for larger and more energy It will be demonstrated that the ME-GI
efficient LNG carriers has resulted in based solution has operational and
rapidly increasing use of the diesel en- economic benefits over other low
gine as the prime mover, replacing tra- speed based solutions, irrespective of
ditional steam turbine propulsion plants. vessel size, when the predicted criteria
Two alternative propulsion solutions for relative energy prices prevail.
have established themselves to date on
the market:
3

4. Propulsion Requirements manufacturer Burckhardt Compression, Redundancy in terms of propulsion is
for LNG Carriers with AG (BCA), the classification society not required by the classification socie-
Dual-Fuel Gas Injection and MAN Diesel has been mandatory ties, but it is required by all operators on
to ensure a proper and safe design of the LNG market. The selection of the
In 2004, the first diesel engine order the complete gas distribution system, double engine ME-GI solution results
was placed for an LNG carrier, equip- including the engine. This has been not only in redundancy of propulsion,
ped with two MAN B&W low speed achieved through a common Hazid / but also of redundancy in the choice of
6S70ME-C engines. Today, the order Hazop study. fuel supply. If the fuel gas supply fails, it
backlog comprises more than 90 en- is possible to operate the ME-GI as an
gines for various owners, mainly oil Configuration of LNG carriers ME engine, fuelled solely with HFO.
companies, all for Qatar gas distribution utilising the boil-off gas
projects. For many years, the LNG market has
The superior efficiency of the two- not really valued the boil-off gas, as this
While the HFO burning engine is a well stroke diesel engines, especially with a has been considered a natural loss not
known and recognised prime mover, directly coupled propeller, has gained accounted for.
the low speed dual-fuel electronically increasing attention. On LNG carriers,
controlled ME-GI (gas injection) engine the desired power for propulsion can Today, the fuel oil price has been at a
has not yet been ordered by the market. be generated by a single engine with a high level, which again has led to con-
single propeller combined with a power siderations by operators on whether to
Although the GI engine, as a mechani- take home system, or a double engine burn the boil-off gas instead of utilis-
cally operated engine, has been avail- installation with direct drive on two pro- ing 100 % HFO, DO or gas oil. Vari-
able for many years, it is not until now pellers. This paper concentrates on the ous factors determine the rate of the
that there is real potential. Cost, fuel double engine installations boil-off gas evaporation, however, it is
flexibility and efficiency are the driving estimated that boil-off gas equals about
factors. 2 x 50 %, which is the most attractive 80-90 % in laden voyage, and in ballast
solution for an LNG carrier of the size voyage 40-50 % of the energy needed
The task of implementing the two- 145 kcum and larger. By selecting a for the LNG vessel at full power. There-
stroke ME-GI engine in the market has twin propeller solution for this LNG car- fore, some additional fuel oil is required
focused on the gas supply system, rier, which normally has a high Beam/ or alternative forced boil-off gas must
from the LNG storage tanks to the high- draft ratio, a substantial gain in propeller be generated. Full power is defined as
pressure gas compressor and further efficiency of some 5 % for 145 kcum a voyage speed of 19-21 knots. This
to the engine. A cooperation between and larger, and up to 9 % or even more speed has been accepted in the market
the shipyard HHI, the compressor for larger carriers is possible. as the most optimal speed for LNG car-
Table I: Two-stroke propulsion recommendations for LNG carriers in the range from 145-270 kcum
LNG carrier size Recommended Propulsion power Propulsion Beam/ Estimated gain in efficiency
(cum) two-stroke solution (kW) speed (knots) draft ratio compared to a single propeller
145,000- 2 x 6S60ME-GI 2 x 14,280 19-21 3.8 5%
150,000 2 x 5S65ME-GI 2 x 14,350
160,000- 2 x 5S70ME-GI 2 x 16,350 19-21 4.0 > 5%
170,000 2 x 7S60ME-GI 2 x 16,660
200,000- 2 x 6S65ME-GI 2 x 17,220 19-21 4.2 9%
220,000 2 x 6S70ME-GI 2 x 19,620
240,000- 2 x 7S65ME-GI 2 x 20,090 19-21 4.5 > 9%
270,000 2 x 7S70ME-GI 2 x 21,770
4

5. riers when both first cost investment In order for the ME-GI to achieve this Fuel Gas Supply System
and loss of cargo is considered. superior efficiency of 50 % (+/− 5 %fuel – Design Concept
tolerances) during gas running, the gas
To achieve this service speed, a two- fuel requires a boost to a pressure of The basic design concept of the fuel gas
stroke solution for the power require- maximum 250 bars at 100 % load. supply system presented in this paper
ment for different LNG carrier sizes is At lower loads the pressure required considers the installation of two 100 %
suggested in Table I. decreases linearly to 30 % load, where fuel gas compressors. Full redundancy
a boost pressure of 150 bars is re- of the fuel gas compressor has been
With the high-pressure gas injection quired. To boost this pressure, a high- considered as a priority to satisfy classifi-
ME-GI engine, the virtues of the two- pressure compressor solution has been cation requirements (see Fig. 2).
stroke diesel principle are prevailing. developed by BCA, which is presented
The thermal efficiency and output re- in this paper. Each compressor is designed to deliver
main equivalent to that obtained when the boil-off gas at a variable discharge
burning conventional heavy fuel oil. Fig. 1 shows an example of an LNG pressure in the range of 150 to 265
The high-pressure gas injection system carrier with the recommended ME-GI bar g (15–26.5 MPa g), according to
offers the advantage of being almost application. required engine load to two 50 % in-
independent of gas/oil fuel mixture, as stalled ME-GI engines A and B. The
long as a small amount of pilot oil fuel is selected compressor runs continuously,
injected for ignition. and the standby compressor is started
manually only in the event of malfunc-
tion of the compressor selected.
LNG Tank Compressor Oxidiser The amount of boil-off gas (BOG), and
hence the tank pressure, varies consid-
erably during the ship operating cycle.
The design concept therefore requires
ME-GI that the compressors be able to oper-
ate under a number of demanding con-
ditions, i.e. with:
• a wide variation of BOG flow, as ex-
perienced during loaded and ballast
Compressor
voyage,
High pressure gas
• a variation in suction pressure ac-
FPP
ME-GI cording to storage tank pressure,
ME-GI PSC Clutch
• a very wide range of suction tempera-
tures, as experienced between warm
start-up and ultra cold loaded opera-
tion, and
Fig. 1: LNG carrier with the recommended ME-GI application.
• a variable gas composition.
The compressor is therefore fitted with
a capacity control system to ensure gas
delivery at the required pressure to the
ME-GI engine, and tank pressure con-
trol within strictly defined limits. These
duty variables are to be handled both
simply and efficiently without compro-
mising overall plant reliability and safety.
5

6. The compressor is designed to effi- Fuel Gas Supply System The fuel gas compressor with the des-
ciently deliver both natural boil-off gas – Key Components ignation 6LP250-5S_1 is designed
(nBOG) and, if required, forced (fBOG) to deliver low-temperature natural or
during the ballast voyage. Fuel gas compressor forced boil-off gas from atmospheric
6LP250-5S_1 tank pressure at an inlet temperature
Finally, the basic design concept also as low as −160°C, up to a gas injection
considers compressor operation in The compression of cryogenic LNG pressure in the range of 150 to 265 bar.
alternative running mode to deliver low boil-off gas up to discharge pressures A total of five compression stages are
pressure gas to the gas combustion in the range of 10-50 barg (1.0 to 5.0 provided and arranged in a single verti-
unit (GCU). Operation with gas delivery MPa g) is now common practice in cal compressor casing directly driven
simultaneously to both GCU and ME-GI many LNG production and receiving by a conventional electric motor. The
is also possible. terminals installed world wide today. guiding principles of the compressor
design are similar to those of API 618
Alternative fuel gas supply system Compressor designs employing the for continuous operating process com-
concepts, employing either 2 x 50 % highly reliable labyrinth sealing prin- pression applications.
installed compressors and a separate ciple have been extensively used for
supply line for the GCU, or 1 x 100 % such applications. The challenge for The compressor designation is as follows:
compressor in combination with a BOG the compressor designer of the ME-GI
reliquefaction plant, are currently being application is to extend the delivery 6LP250-5S_1
considered by the market. pressure reliably and efficiently by add- 6 number of cranks
ing additional compression stages to L labyrinth sealing piston,
These alternative concepts are not de- achieve the required engine injection stages 1 to 3
scribed further in this paper. pressure. In doing so, the compressor’s P ring sealing piston,
physical dimensions must consider the stages 4 to 5
restricted space available within the 250 stroke in mm
deck-mounted machinery room. 5 number of stages
S cylinder size reference
1 valve design
A unique compressor construction al-
lows the selection of the best applicable
cylinder sealing system according to
the individual stage operating tempera-
ture and pressure. In this way, a very
high reliability and availability, with low
maintenance, can be achieved.
Oil-free compression, required for the
very cold low pressure stages 1 to 3,
employs the labyrinth sealing principle,
which is well proven over many years
on LPG carriers and at LNG receiving
terminals. The avoidance of mechanical
friction in the contactless labyrinth cylin-
der results in extremely long lifetimes of
sealing components (see Appendix 1).
The high-pressure stages 4 and 5 em-
ploy a conventional API 618 lubricated
cylinder ring sealed compressor tech-
nology (see Fig. 3).
Fig. 2: Basic design concept for two compressor units 100 %, type 6LP250-5S_1
6

7. Labyrinth piston –
oil-free compression Ring piston – lubricated design
Fig. 3: Highly reliable cylinder sealing applied for each compression stage
Six cylinders are mounted on top of a Stage 4/5 Stage 4/5
cooled cooled
vertical arranged crankcase. The double lube lube
acting labyrinth compression stages 1 Pa= 265 bar a Pa= 265 bar a
to 3 are typical of those employed at an
LNG receiving terminal. Stage 1 Stage 3 Stage 2 Stage 1
not cooled cooled cooled not cooled
The single acting stages 4 and 5 are a
design commonly used for compres-
sion of high-pressure hydrocarbon Ps= 1.03 bar a Ps= 1.03 bar
process gases in a refinery application
(Fig. 4).
The two first-stage labyrinth cylinders,
Heat barrier
which are exposed to very low tem- stage 1 only
peratures, are cast in the material
GGGNi35 (Fig. 5). This is a nodular cast
iron material containing 35 % nickel,
also known under the trade name of Ni-
Resist D5.
This alloy simultaneously exhibits re-
markable ductility at low temperatures
and one of the lowest thermal expan-
sion coefficients known in metals.
The corresponding pistons are made
of nickel alloyed cast iron with laminar
graphite. Careful selection of cylinder
materials allows the compressor to be Fig. 4: Main constructional features of the 6LP250-5S compressor
7

8. Cylinder gas nozzie
Valve ports
Fig. 5: Cylinder block
started at ambient temperature condi-
tion and cooled down to BOG tempera-
ture without any special procedures.
Second and third stage labyrinth cylin-
ders operate over a higher temperature
range and are therefore provided with
a cooling jacket. Cylinder materials are
nodular cast iron and grey cast iron re-
spectively.
The oil lubricated high-pressure 4th
and 5th stage cylinders are made from
forged steel and are provided with a
coolant jacket to remove heat of com-
pression.
In view of the smaller compression
volumes and high pressure, the piston
and piston rod for stages 4 and 5 are
integral and manufactured from a single
forged steel material stock. Compres-
sion is single acting with the 4th stage
arranged at the upper end and the 5th
stage at the lower end and arranged in
step design. Piston rod gas leakage of
the 5th stage is recovered to the suc-
tion of the 4th stage (see Fig. 6). Fig. 6: Sectional view of the lubricated cylinder 4th and 5th stage
8

9. Double-acting Capacity Control – Valve
Piston rod guiding labyrinth or ring Unloading
Piston rod guidance is provided
at the lower crank end by a heavy Cylinder
nodular cast iron crosshead an Compression
at the upper end by an additional section, oil-free Capacity control by valve unloading is
or lubricated Packing oil-free
guide bearing . Both these or lubricated extensively employed at LNG terminals
components are oil lubricated and where very large variations in BOG
Heat barrier
water cooled. Distance piece pro- flows are experienced during LNG
vides separation Oil shield transfer from ship to storage tank.
These key guiding elements are
therefore subjected to very little Gulde bearing The capacity of the compressor may
wear. be simply and efficiently reduced to
Piston guide 50 % in one step by the use of valve
Heat barrier system lubricated Crosshead unloaders. The nitrogen actuated un-
The cold first-stage cylinders
loaders (see Fig. 8) are installed on the
are separated from the warm
compressor motion work by Gas-tight casing lower cylinder suction valves and act
means of a special water jacket to unload one half of the double-acting
situated at the lower end of cylinders.
the cylinder block. This jaket
is supplied with a water/glycol
Additional stepless regulation, required
coolant mixture and acts as a
thermal heat barrier. to control a compressor capacity cor-
responding to the rate of boil-off and
Fig. 7: Design principle of vertical gas-tight compressor casing the demand of the engine, is provided
by returning gas from the discharge
to compressor suction by the use of
Motion work – 6LP250-5S bypass valves. The compressor control
system is described in detail later in this
The 6-crank, 250 mm stoke compres- paper.
sor frame is a conventional low speed,
crosshead design typically employed
for continuous operating process du-
ties. The industry design standard for
this compressor type is the American Compressed gas
Petroleum Industry Standard API 618 Cylinder Suction gas
for refinery process application. Valve disc gas nozzle
The forged steel crankshaft and con-
necting rods are supported by heavy
tri-metal, force lubricated main bear- Diaphragm
ings. Oil is supplied by a crankshaft actuator
driven main oil pump. A single distance
piece arranged in the upper frame sec- Valve seat
tion provides separation between the
lubricated motion work and the non-
lubricated compressor cylinders.
The passage of the crankshaft through
the wall of the crankcase is sealed off
N2 control
by a rotating double-sided ring seal
gas inlet/outlet
immersed in oil. Thus, the entire inside
of the frame is integrated into the gas
containing system with no gas leakage Fig. 8: Cylinder mounted suction valve unloader
to the environment (see Fig. 7).
9

10. Compressor System The P&I diagram for the compressor The design of the gas system com-
Engineering – 6LP250-5S gas system is shown in Appendix III. prising piping, pulsation vessels, gas
intercoolers, safety relief valves and ac-
A compressor cannot function correctly Bypass valves are provided over stage cessory components follows industry
and reliably without a well-designed 1, stages 2 to 3, and stages 4 to 5. practices for hydrocarbon process
and engineered external gas system. These valves function to regulate the oil and gas installations.
Static and dynamic mechanical analy- flow of the compressor according to
sis, thermal stress analysis, pulsation the engine set pressure within defined Process duty – compressor
analysis of the compressor and auxiliary system limits. Non-return valves are rating
system consisting of gas piping, pulsa- provided on the suction, side to prevent
tion vessels, gas intercoolers, etc., are gas back-flow to the storage tanks, The sizing of the fuel gas compressor is
standard parts of the compressor sup- between stages 3 and 4, to maintain directly related to the “design” amount
plier’s responsibility. adequate separation between the of nBOG and, therefore, to the capacity
oil-free and the oil lubrication compres- of the LNG carrier.
A pulsation analysis considers upstream sor stages, and at the final discharge
and downstream piping components in from the compressor. The fuel gas system design concept
order to determine the correct sizing of considers compressor operation not
pulsation dampening devices and their Compressor safety only for supplying gas to the ME-GI en-
adequate supporting structure. gine, but also to deliver gas to the gas
Safety relief valves are provided at the combustion unit (GCU) in the event that
The compressor plant is designed to discharge of each compression stage the engine cannot accept any gas.
operate over a wide range of gas suc- to protect the cylinders and gas system
tion temperatures from ambient start- against overpressure. Stage differen- The compressors are therefore rated to
up at +30°C down to −160°C without tial relief valves, where applicable, are handle the maximum amount of natural
any special intervention. installed to prevent compressor exces- BOG defined by the tank system sup-
sive loading. plier and consistent with the design rat-
Each compressor stage is provided ing of GCU.
with an intercooler to control the gas Pressure and temperature instrumenta-
inlet temperature into the following tion for each stage is provided to en- Design nBOG rates are typically in the
stage. The intercooler design is of the sure adequate system monitoring alarm range of 0.135 to 0.15 % per day of
conventional shell and tube type. The and shutdown. Emergency procedures tanker liquid capacity. During steady-
first-stage intercooler is bypassed when allow a safe shutdown, isolation and state loaded voyage, a BOG rate of
the suction temperature falls below set venting of the compressor gas system. 0.10 to 0.12 % may be expected.
limits (approx −80°C).
Carrier capacities in the range 145 to
Table II: Rated process design data for a 210 kcum carrier 260 kcum have been considered, re-
sulting in the definition of 3 alternative
Volume LNG tanker cum 210,000 compressor designs which differ accord-
Max. BOG rate LNG tanker % 0.15 per day and liquid volume ing to frame rating and compressor
speed.
Density of methane liquid at 1.06 bar a kg/m3 427 assumed basis for design
BOG mass flow kg/h 5,600 Rated process design data for a carrier
LNG tank pressure low / high bar a 1.06/1.20 capacity of 210 kcum are as shown in
Temperature BOG low °C −140 during loaded voyage Table II.
Temperature BOG high °C −40 during ballast voyage
The rating for the electric motor driver
Temperature BOG start up °C +30 is determined by the maximum com-
Delivery P to ME-GI pressure low / high bar a 150/265 pressor power required when consider-
Temperature NG delivery to ME-GI °C +45 ing the full operating range of suction
temperatures from + 30 to −140°C and
Compressor shaft power kW 1,600
suction pressures from 1.03 to 1.2 bar a.
Delivery P to GCU bar a 4.0 to 6.5
10

11. ME-GI Gas System Exhaust reciever
Engineering
The ME-GI engine series, in terms of
engine performance (output, speed,
thermal efficiency, exhaust gas amount
and temperature, etc.) is identical to the
Large volume
well-established, type approved ME en- accumelator
gine series. The application potential for Gas valves
the ME engine series therefore also ap-
plies to the ME-GI engine, provided that ELGI valve
gas is available as a main fuel. All ME en-
gines can be offered as ME-GI engines. High pressure
double wall
Cylinder cover with gas pipes
Since the ME system is well known,
the following description of the ME-GI gas valves and PMI
engine design only deals with new or
modified engine components.
Fig. 9 shows one cylinder unit of a
S70ME-GI, with detail of the new modi- Fig. 9: Two-stroke MAN B&W S70ME-GI
fied parts. These comprise gas supply
double-wall piping, gas valve control The GI system also includes: • They act as flexible connections be-
block with internal accumulator on the tween the stiff main pipe system and
(slightly modified) cylinder cover, gas in- • Control and safety system, compris- the engine structure, safeguarding
jection valves and ELGI valve for control ing a hydrocarbon analyser for check- against extra-stresses in the main and
of the injected gas amount. In addition, ing the hydrocarbon content of the air branch pipes caused by the inevitable
there are small modifications to the ex- in the double-wall gas pipes. differences in thermal expansion of
haust gas receiver, and the control and the gas pipe system and the engine
manoeuvring system. The GI control and safety system is desig- structure.
ned to “fail to safe condition”. All failures
Apart from these systems on the en- detected during gas fuel running includ- The buffer tank, containing about 20
gine, the engine and auxiliaries will ing failures of the control system itself, times the injection amount per stroke
comprise some new units. The most will result in a gas fuel Stop/Shut Down, at MCR, also performs two important
important ones, apart from the gas and a change-over to HFO fuel operation. tasks:
supply system, are listed below, and Blow-out and gas-freeing purging of the
the full system is shown in schematic high-pressure gas pipes and the complete • It supplies the gas amount for injec-
form in Appendix IV gas supply system follows. The change- tion at a slight, but predetermined,
over to fuel oil mode is always done with- pressure drop.
The new units are: out any power loss on the engine.
• It forms an important part of the
• Ventilation system, for venting the The high-pressure gas from the com- safety system.
space between the inner and outer pressor-unit flows through the main
pipe of the double-wall piping. pipe via narrow and flexible branch Since the gas supply piping is of com-
pipes to each cylinder’s gas valve block mon rail design, the gas injection valve
• Sealing oil system, delivering sealing and accumulator. These branch pipes must be controlled by an auxiliary control
oil to the gas valves separating the perform two important tasks: oil system. This, in principle, consists of
control oil and the gas. the ME hydraulic control (system) oil sys-
• They separate each cylinder unit from tem and an ELGI valve, supplying high-
• Inert gas system, which enables the rest in terms of gas dynamics, utili- pressure control oil to the gas injection
purging of the gas system on the sing the well-proven design philoso- valve, thereby controlling the timing and
engine with inert gas. phy of the ME engine’s fuel oil system. opening of the gas valve.
11

12. ME-GI Injection System Sealing oil inlet
Sealing oil inlet
Dual fuel operation requires the injection
of both pilot fuel and gas fuel into the
combustion chamber.
Different types of valves are used for
this purpose. Two are fitted for gas
injection and two for pilot fuel. The aux- Cylindercover
Cylinder cover
iliary media required for both fuel and
gas operation are as follows: Connectionto the
Connection to the
ventilatedpipe system
ventilated pipe system
Controloil
Control oil
• High-pressure gas supply
Sealing oil
Sealing oil
Gas inlet
Gas inlet
• Fuel oil supply (pilot oil)
Gas spindle
gas spindle
• Control oil supply for activation
of gas injection valves
• Sealing oil supply.
The gas injection valve design is shown Fig. 10: Gas injection valve – ME-GI engine
in Fig. 10. This valve complies with
traditional design principles of com-
pact design. Gas is admitted to the system, in order to detect any malfunc- on fuel oil, without stopping the engine,
gas injection valve through bores in the tioning of the valve. this can be done. If the demand is pro-
cylinder cover. To prevent gas leakage longed operation on fuel oil, it is recom-
between cylinder cover/gas injection The designs of oil valve will allow oper- mended to change the nozzles and
valve and valve housing/spindle guide, ation solely on fuel oil up to MCR. lf gain an increase in efficiency of around
sealing rings made of temperature and the customer’s demand is for the gas 1% when running at full engine load.
gas resistant material are installed. Any engine to run at any time at 100 % load
gas leakage through the gas sealing
rings will be led through bores in the
gas injection valve and further to space
between the inner and the outer shield Low pressure fuel supply
Gas
pipe of the double-wall gas piping sys-
tem. This leakage will be detected by Fuel return
HC sensors. Injection
Measuring and
limiting device
The gas acts continuously on the valve Pressure booster
(800 - 900 bar)
spindle at a max. pressure of about
Position sensor
250 bar. To prevent gas from entering Bar abs
800
the control oil activating system via the
clearance around the spindle, the ELFI valve
200 bar hydraulic oil. 600 Pilot il pressure
o
spindle is sealed by sealing oil at a Common with
exhaust valve actuator
pressure higher than the gas pressure ELGI valve 400
(25-50 bar higher). Control oil pressure
The system provides:
200
Pressure, timing, rate shaping,
The pilot oil valve is a standard ME fuel main, pre- & post-injection
0
oil valve without any changes, except 0 5 10 15 20 25 30 35 40 45
Deg CA
.
for the nozzle. The fuel oil pressure is
constantly monitored by the GI safety Fig. 11: ME-GI system
12

13. As can be seen in Fig. 11 (GI injection High-Pressure Double- supply pipes to the main supply pipe,
system), the ME-GI injection system Wall Piping and via the suction blower into the at-
consists of two fuel oil valves, two fuel mosphere.
gas valves, ELGI for opening and clos- A common rail (constant pressure) gas
ing of the fuel gas valves, and a FIVA supply system is to be fitted for high- Ventilation air is exhausted to a fire-safe
valve to control (via the fuel oil valve) pressure gas distribution to each valve place. The double-wall piping system
the injected fuel oil profile. Furthermore, block. Gas pipes are designed with is designed so that every part is ven-
it consists of the conventional fuel oil double-walls, with the outer shielding tilated. All joints connected with seal-
pressure booster, which supplies pilot pipe designed so as to prevent gas ings to a high-pressure gas volume are
oil in the dual fuel operation mode. This outflow to the machinery spaces in the being ventilated. Any gas leakage will
fuel oil pressure booster is equipped event of rupture of the inner gas pipe. therefore be led to the ventilated part of
with a pressure sensor to measure the The intervening space, including also the double-wall piping system and be
pilot oil on the high pressure side. As the space around valves, flanges, etc., detected by the HC sensors.
mentioned earlier, this sensor monitors is equipped with separate mech-anical
the functioning of the fuel oil valve. If ventilation with a capacity of approx. 30 The gas pipes on the engine are de-
any deviation from a normal injection air changes per hour. The pressure in signed for 50% higher pressure than
is found, the GI safety system will not the intervening space is below that of the normal working pressure, and are
allow opening for the control oil via the the engine room with the (extractor) fan supported so as to avoid mechanical
ELGI valve. In this event no gas injec- motors placed outside the ventilation vibrations. The gas pipes are further-
tion will take place. ducts. The ventilation inlet air is taken more shielded against heavy items fall-
from a non-hazardous area. ing down, and on the engine side they
Under normal operation where no mal- are placed below the top-gallery. The
functioning of the fuel oil valve is found, Gas pipes are arranged in such a way, pipes are pressure tested at 1.5 times
the fuel gas valve is opened at the cor- see Fig. 12 and Fig 13, that air is suck- the working pressure. The design is to
rect crank angle position, and gas is ed into the double-wall piping system be all-welded, as far as it is practicable,
injected. The gas is supplied directly from around the pipe inlet, from there using flange connections only to the ex-
into an ongoing combustion. Conse- into the branch pipes to the individual tent necessary for servicing purposes.
quently the chance of having unburnt gas valve control blocks, via the branch
gas eventually slipping past the piston
rings and into the scavenge air receiver
is considered to be very low. Monitoring Protective hose Soldered
the scavenge air receiver pressure safe-
guards against such a situation. In the
event of high pressure, the gas mode
is stopped and the engine returns to
burning fuel oil only.
The gas flow to each cylinder during
one cycle will be detected by measur-
ing the pressure drop in the accumu- Bonded seal
lator. By this system, any abnormal Ventilation air
Ventilation air
gas flow, whether due to seized gas
injection valves or blocked gas valves, Fuel Gas flow
Fuel Gas flow
will be detected immediately. The gas
supply will be discontinued and the gas
lines purged with inert gas. Also in this
event, the engine will continue running Ventilation air
Ventilation air Outer pipe High pressure gas
on fuel oil only without any power loss.
Ventilation air High pressure gas pipe
Fig. 12: Branching of gas piping system
13

14. Gas stop
Ventilation air Fuel gas valve
Control air Nitrogen
Cylinder
Control Oil
cover
Purge
valves
Fuel gas
accumulator
volume
One way valve Fuel gas inlet Control oil buffer
volume
Fig. 13: Gas valve control block
The branch piping to the individual
cylinders is designed with adequate
flexibility to cope with the thermal ex-
pansion of the engine from cold to hot
condition. The gas pipe system is also
designed so as to avoid excessive gas
pressure fluctuations during operation.
For the purpose of purging the system
after gas use, the gas pipes are con-
nected to an inert gas system with an
inert gas pressure of 4-8 bar. In the
event of a gas failure, the high-pressure
pipe system is depressurised before
automatic purging. During a normal
gas stop, the automatic purging will be
started after a period of 30 min. Time is
therefore available for a quick re-start in
gas mode.
14

15. Fuel Gas System - When considering compressor control, The main control input for compressor
Control Requirements an important difference between cen- control is the feed pressure Pset re-
trifugal and reciprocating compressors quired by the ME-GI engine. The feed
The primary function of the compres- should be understood. A reciprocating pressure may be set in the range of 150
sor control system is to ensure that the compressor will always deliver the pres- to 265 bar according to the desired en-
required discharge pressure is always sure demanded by the down-stream gine load. If the two ME-GI engines are
available to match the demand of the user, independent of any suction con- operating at different loads, the higher
main propulsion diesel engines. In do- ditions such as temperature, pressure, set pressure is valid for the compressor
ing so, the control system must ade- gas composition, etc. Centrifugal com- control unit.
quately handle the gas supply variables pressors are designed to deliver a cer-
such as tank pressure, BOG rate (laden tain head of gas for a given flow. The If the amount of nBOG is insufficient to
and ballast voyage), gas composition discharge pressure of these compres- satisfy the engine load requirement, and
and gas suction temperature. sors will therefore vary according to the make-up with fBOG is not foreseen, the
gas suction condition. compressor will operate on part load to
If the amount of nBOG decreases, the ensure that the tank pressure remains
compressor must be operated on part This aspect is very important when within specified limits. The ME-GI en-
load to ensure a stable tank pressure, considering transient starting conditions gine will act independently to increase
or forced boil-off gas (fBOG) added to such as suction temperature and pres- the supply of HFO to the engine. Prima-
the gas supply. If the amount of nBOG sure. The 6LP250-5S_1 reciprocating ry regulation of the compressor capac-
increases, resulting in a higher than compressor has a simple and fast start- ity is made with the 1st stage bypass
acceptable tank pressure, the control up procedure. valve, followed by cylinder valve unload-
system must act to send excess gas to ing and if required bypass over stages 2
the gas combustion unit (GCU). Compressor control – to 5. With this sequence, the compres-
6LP250-5S_1 sor is able to operate flexibly over the
Tank pressure changes take place over full capacity range from 100 to 0 %.
a relatively long period of time due to Overall control concept
the large storage volumes involved. If the amount of nBOG is higher than
A fast reaction time of the control sys- Fig. 15 shows a simplified view of the can be burnt in the engine (for example
tem is therefore not required for this compressor process flow sheet. The during early part of the laden voyage)
control variable. system may be effectively divided into resulting in higher than acceptable
a low-pressure section (LP) consisting suction pressure (tank pressure), the
The main control variable for compres- of the cold compression stage 1, and a control system will send excess gas to
sor operation is the feed pressure to the high-pressure section (HP) consisting of the GCU via the side stream of the 1st
ME-GI engine, which may be subject to stages 2 to 5. compression stage.
controlled or instantaneous change. An
adequate control system must be able
to handle such events as part of the Control of gas delivery pressure
General Data for
“normal” operating procedure. Gas Delivery Condition:
Pressure:
Gas pressure Set point (bar)
The required gas delivery pressure var- Nominal 250 bar
ies between 150-265 bar, depending Max. value 300 bar
on the engine load (see Fig. 14 below). Pulsation limit ± 2 bar
Set point tolerance ± 5%
The compressor must also be able Temperature :
Approx. 45 oC
to operate continuously in full recycle
Quality:
mode with 100 % of delivered gas
Condensate free, without oil/water
returned to the suction side of the droplets or mist, similar to the
compressor. In addition, simultaneous PNEUROP recommendation 6611
delivery of gas to the ME-GI engine and ‘‘Air Turbines’’
GCU must be possible.
Engine Load ( % of MCR )
Fig. 14: Gas supply station, guiding specification
15

16. Fig. 15: Simplified flow sheet
In the event of engine shutdown or sud- Pmin suction Prevents under-pressure 1st stage bypass valve, which will open
den change in engine load, the com- in compressor inlet mani- or close until the actual compressor
pressor delivery line must be protected fold - tank vacuum. discharge pressure is equal to the Pset.
against overpressure by opening by- With this method of control, BOG de-
pass valves over the HP section of the Phigh suction Suction manifold high- livery to the ME-GI is regulated without
compressor. pressure - system safety any direct measurement and control of
(GCU) on standby. the delivered mass flow. If none of the
During start-up of the compressor with above control limits are active, the con-
warm nBOG, the temperature con- Pmax suction Initiates action to reduce troller is able to regulate the mass flow
trol valves will operate to direct a flow inlet manifold pressure. in the range from 0 to 100 %.
through an additional gas intercooler
after the 1st compression stage. Pmax Prevents overpressure of The following control limits act to over-
ME-GI feed compressor discharge rule the ME-GI controller setting and
The control concept for the compres- manifold. initiate bypass valve operation:
sor is based on one main control mode
which is called “power saving mode”. A detailed description of operation with- Pmin suction (tank pressure below
This mode of running, which minimises in these control limits is given below. set level)
the use of gas bypass as the primary
method of regulation, operates within Power saving mode The control scenario is falling suction
various well defined control limits. pressure. If the Pmin limit is active, the 1st
Economical regulation of a multi-stage stage recycle valve will not be permitted
The system pressure control limits are compressor is most efficiently executed to close further, thereby preventing fur-
as follows: using gas recycle around the 1st stage ther reduction in suction pressure. If the
of compression. The ME-GI required pressure in the suction line continues
set pressure Pset is therefore taken as to decrease, the recycle valve will open
control input directly to the compressor governed by the Pmin limiter.
16

17. Action of Pressure will fall at the burned simultaneously in the GCU.
ME-GI control compressor discharge No action is taken in the ME-GI control
system: requiring the HFO system.
injection rate to be
increased. Pmax ME-GI feed
fBOG: If a spray cooling or The control scenario is a reduction of
forced vaporizer is the engine load or closure of the ME-GI
installed, it may be supply line downstream of the com-
used for stabilising the pressor. The pressure will rise in the
suction pressure and delivery line. Line overpressure is pre-
thereby increase the vented by a limiter, which acts to direct-
gas mass flow to the ly open the bypass control valve around
engine. Such a sys- stages 2 to 5. As a consequence, the
tem could be activated controller will also open the 1st stage
by the Pmin suction recycle valve.
pressure limit.
The control range of the compressor is
Phigh suction (tank pressure above 0 to 100 % mass flow.
set level)
GCU-only operating mode
The control scenario is increasing suc-
tion pressure due to either reduced The control scenario considers a situa-
engine load (e.g. approaching port, tion where gas injection to the ME-GI is
manoeuvring) or excess nBOG due to not required and tank gas pressure is at
liquid impurities (e.g. N2). the level of Phigh.
The control limiter initiates a manual The nBOG is compressed and delivered
start of the GCU (the GCU is assumed to the GCU by means of a gas take-off
not to be on standby mode during nor- after the 1st stage.
mal voyage).
The following actions are initiated:
There is no action on the compressor
control or the ME-GI control system. • manual start of the GCU
Pmax suction (tank pressure • closing of the bypass valve
too high) around 1st stage
The control scenario is the same as de- • fully opening of the bypass
scribed above, however, it has resulted valves around stages 2-5.
in even higher suction pressure. Action
must now be taken to reduce suction In this mode, the compressor is oper-
pressure by sending gas to the GCU. ating with stages 2-5 in full recycle at a
reduced discharge pressure of approxi-
The high pressure alarm initiates a mately 80 bar. The pressure setting of
manual sequence whereby the 1st the GCU feed valve is set directly by the
stage bypass valve PCV01 is closed GCU in the range 3 to 6 bar a.
and the bypass valve PCV02 to the
GCU is opened. When the changeover There is no action on the ME-GI
is completed, automatic Pset control controller.
is transferred to the GCU control valve
PCV02. The gas amount which can-
not be accepted by the ME-GI will be
17

18. Machinery Room Instal-
lation – 6LP250-5S
The layout of the cargo handling equip-
ment and the design of their supporting
structure presents quite a challenge to
the shipbuilder where space on deck
is always at a premium. In conjunction
with HHI and the compressor maker, an
optimised layout of the fuel gas com-
pressor has been developed.
There are many factors which influence
the compressor plant layout apart from
limited space availability. (See Fig. 16.)
External piping connections, adequate
access for operation and maintenance,
equipment design and manufacturing 15m
codes, plant lifting and installation are 27m
just a few. 34m
The compressor together with acces-
sory items comprising motor drive, Fig. 16: Typical layout of cargo machinery room
auxiliary oil system, vessels, gas cool-
ers, interconnecting piping, etc., are
manufactured as modules requiring
minimum assembly work on the ship
deck. Separate auxiliary systems pro- Compensator E. mortor
vide coolant for the compressor frame
and gas coolers. Discharge
line
If required, a dividing bulkhead may
separate the main motor drive from
the hazardous area in the compressor
room. A compact driveshaft arrange-
ment without bulkhead, using a suitably
designed ex motor, is however pre-
ferred. Platforms and stairways provide
access to the compressor cylinders for
valve maintenance. Piston assemblies
are withdrawn vertically through man-
holes in the roof of the machinery house
(see Fig. 17).
Oil System
Suction line
Fig. 17: Fuel gas compressor with accessories
18

19. Requirements for Cargo Foundation deflection due to ship Major intervention for dismantling and
Machinery Room Support movement must, furthermore, be con- bearing inspection is recommended
Structure sidered in the design of the compressor every 2-3 years.
plant to ensure stress-free piping termi-
Fig. 18 shows details of the compressor nations. Average availability per compressor
base frame footprint and requirement unit is estimated to be 98.5 % with best
for support by the ship structure. Maintenance requirements availability approximately 99.5 %. With
- availability/reliability an installed redundant unit, the com-
Reciprocating compressors, by nature pressor plant availability will be in the
of movement of their rotating parts, The low speed, crosshead type com- region of 99.25 %.
exhibit out-of-balance forces and mo- pressor design 6LP250-5S, like the
ments which must be considered in the ME-GI diesel engine, is designed for Any unscheduled stoppage of the
design of the supporting structure for the life time of the LNG carrier (25 to 30 6LP250-5S compressor will most likely
acceptable machinery vibration levels. years or longer). Routine maintenance be attributable to a mal-function of a
is limited purely to periodic checking in cylinder valve. With the correct valve
As a boundary condition, the structure the machinery room. design and material selection (Burck-
underneath the cargo machinery room hardt uses its own design and manu-
must have adequate weight and stiff- Maintenance intervention for dis- facture plate valves) these events will be
ness to provide a topside vibration level mantling, checking and eventual part very seldom, however a valve failure in
of (approximately) 1.2 - 1.5 mm/s. Sat- replacement is recommended after operation cannot be entirely ruled out.
isfactory vibration levels for compressor each 8,000 hours of operation. Annual
frame and cylinders are 8 and 15 mm/s maintenance interventions will normally LNG boil-off gas is an ideal gas to com-
respectively (values given are rms – root require 50-70 hours work for checking press. The gas is relatively pure and
mean square). and possible replacing of wearing parts. uncontaminated, the gas components
are well defined, and the operating tem-
peratures are stable once “cool-down”
is completed.
These conditions are excellent for long
lifetime of the compressor valves where
an average lifetime expectancy for valve
plates is 16,000 hours. Therefore, we
do not expect any unscheduled inter-
vention per year for valve maintenance.
Such a maintenance intervention will
take approx. 7-9 hours for compressor
shutdown, isolation and valve replace-
ment.
A total unscheduled maintenance in-
tervention time of 25 hours, assuming
8,000 operating hours per year, may be
used for statistical comparison. On this
basis compressor reliability is estimated
at 99.7 %.
Our experience in many installations
shows that no hours are lost for un-
scheduled maintenance. The reliability
of these compressors is therefore com-
Fig. 18: Compressor base frame footprint parable to that of centrifugal compres-
sor types.
19

20. Requirements for Actual Test and Analysis Main Engine Room
Classification of Safety when Operating Safety
on Gas
When entering the LNG market with the The latest investigation, which was
combined two-stroke and reliquefaction The use of gas on a diesel engine calls recently finished, was initiated by a
solution, it was discovered that there for careful attention with regard to number of players in the LNG market
is a big difference in the requirements safety. For this reason, ventilated dou- questioning the use of 250 bar gas in
from operators and classification socie- ble-walled piping is a minimum require- the engine room, which is also located
ties. ment to the transportation of gas to the under the wheel house where the crew
engine. is working and living.
Being used to cooperating with the
classification societies on other com- In addition to hazard considerations Even though the risk of full breakage
mercial ships, the rules and design re- and calculations, it has been necessary happening is considered close to neg-
commendations for the various applica- to carry out tests, two of which were ligible and, in spite of the precautions
tions in the LNG market are new when carried out some years ago before the introduced in the system design, MAN
it comes to diesel engine propulsion. installation and operation of the Chiba Diesel found it necessary to investi-
In regard to safety, the high availability power plant 12K80MC-GI engine in gate the effect of such an accident,
and reliability offered when using the 1994. as the question still remains in part of
two-stroke engines generally fulfil the the industry: what if a double-wall pipe
requirements, but as the delivery and A crack in the double-wall breaks in two and gas is released from
pick up of gas in the terminals is carried inner pipe a full opening and is ignited?
out within a very narrow time window,
redundancy is therefore essential to the The first test was performed by intro- As specialists in the offshore industry,
operators. ducing a crack in the inner pipe to see DNV were commissioned to simulate
if the outer pipe would stay intact. The such a worst case situation, study the
As such, a two-engine ME-GI solution test showed no penetration of the outer consequences, and point to the appro-
is the new choice, with its high effi- pipe, thus it could be concluded that priate countermeasures. DNV’s work
ciency, availability and reliability, as the the double-wall concept lived up to the comprised a CFD (computational fluid
traditional HFO burning engines. expectations. dynamics) simulation of the hazard of
an explosion and subsequent fire, and
Compared with traditional diesel Pressure fluctuation an investigation of the risk of this situa-
operated ships, the operators and ship- tion ever occurring and at what scale.
owners in the LNG industry generally The second test was carried out to
have different goals and demands to investigate the pressure fluctuations in As input for the simulation, the volume
their LNG tankers, and they often apply the relatively long piping from the gas of the engine room space, the position
more strict design criteria than applied compressor to the engine. of major components, the air ventilation
so far by the classification societies. rate, and the location of the gas pipe
By estimation of the necessary buffer and control room were the key input
A Hazid investigation was therefore volume in the piping system, the stroke parameters.
found to be the only way to secure that and injection of gas was calculated to
all situations are taken into account see when safe pressure fluctuations are Realistic gas leakage scenarios were
when using gas for propulsion, and that achieved within given limits for optimal defined, assuming a full breakage of
all necessary precautions have been performance of the engines. The piping the outer pipe and a large or small hole
taken to minimize any risk involved. system has been designed on the basis in the inner fuel pipe. Actions from the
of these calculations. closure of the gas shutdown valves, the
In 2005, HHI shipyard, HHI engine ventilation system and the ventilation
builder, BCA and MAN Diesel therefore conditions prior to and after detec-
worked out a hazard identification study tion are included in the analysis. The
that was conducted by Det Norske Ver- amount of gas in the fuel pipe limits the
itas (DNV), see Appendix V. duration of the leak. Ignition of a leak
causing an explosion or a fire is further-
more factored in, due to possible hot
20

21. spots or electrical equipment that can Simulation Results This new engine room design is based
give sparks in the engine room. on the experience achieved by HHI
The probability of this hazard happen- with their first orders for LNG carriers
Calculations of the leak rate as a func- ing is based on experience from the equipped with 2 x 6S70ME-C and reli-
tion of time, and the ventilation flow offshore industry. quefaction plant. The extra safety that
rates were performed and applied as will be included is listed below:
input to the explosion and fire analyses. Even calculated in the worst case, no
structural damage will occur in the HHI • Double-wall piping is located as
LNG engine room if designed for 1.1 far away as possible from critical
bar over pressure. walls such as the fuel tank walls and
switchboard room walls.
• No areas outside the engine room
will be affected by an explosion. • In case of an engine room fire alarm,
a gas shutdown signal is sent out, the
If this situation is considered to repre- engine room ventilation fans stops,
sent too high a risk, unattended machin- and the air inlet canals are blocked.
ery space during gas operation can be
introduced. Today, most engines and • During gas running it is not possible
equipment are already approved by the to perform any heavy lifting with the
classification societies for this type of engine room crane.
operation.
• A failure of the engine room ventilation
• By insulation, the switchboard room will result in a gas shutdown.
floor can be protected against heat
from any jet fires. • HC sensors are placed in the engine
room, and their position will be based
• No failure of the fuel oil tank structure, on a dispersion analysis made for the
consequently no escalation of fire. purpose of finding the best location
for the sensors.
The above conclusion is made on the
assumption that the GI safety system • The double-wall piping is designed
is fully working. with lyres, so that variation in tem-
peratures from pipes to surroundings
In addition, DNV has arrived at a differ- can be absorbed in the piping.
ent result based on the assumption that
the safety system is not working. On In fact, any level of safety can be
the basic in these results DNV have put achieved on request of the shipowner.
up failure frequencies and developed The safety level request will be achieved
a set of requirements to be followed in in a co-operation between the yard
case a higher level of safety is required. HHI, the engine builder HHI, the classifi-
cation society and MAN Diesel A/S.
After these conclusion made by DNV,
HHI has developed a level for their The report “Dual fuel Concept: Analysis
engine room safety that satisfies the of fires and explosions in engine room”
requirements from the classification so- was made by DNV consulting and can
cieties, and also the requirements that be ordered by contacting MAN Diesel
are expected from the shipowners. A/S, in Copenhagen.
21

22. Engine Operating Modes Gas Main Operating Panel in the control the 30% limit for minimum-fuel mode
room. In this mode, the control system will be challenged taking advantage of
One of the advantages of the ME-GI will allow any ratio between fuel oil and the increased possibilities of the ME fuel
engine is its fuel flexibility, from which gas fuel, with a minimum preset amount valves system to change its injection
an LNG carrier can certainly benefit. of fuel oil to be used. profile, MAN Diesel expects to lower
Burning the boil-off gas with a varia- this 30% load limit for gas use, but for
tion in the heat value is perfect for the The preset minimum amount of fuel oil, now no guaranties can be given.
diesel working principle. At the start of hereafter named pilot oil, to be used
a laden voyage, the natural boil-off gas is in between 5-8% depending on the
holds a large amount of nitrogen and fuel oil quality. Both heavy fuel oil and
the heat value is low. If the boil-off gas marine diesel oil can be used as pilot
is being forced, it can consist of both oil. The min. pilot oil percentage is cal-
ethane and propane, and the heat value culated from 100% engine load, and
could be high. A two-stroke, high-pres- is constant in the load range from 30-
sure gas injection engine is able to burn 100%. Below 30% load MAN Diesel is
those different fuels and also without not able to guarantee a stable gas and
a drop in the thermal efficiency of the pilot oil combustion, when the engine
engine. The control concept comprises reach this lower limit the engine returns
two different fuel modes, see also to Fuel-oil-only mode.
Fig. 19.
Gas fuels correspond to low-sulphur
• fuel-oil-only mode fuels, and for this type of fuel we rec-
ommend the cylinder lube oil TBN40 to
• minimum-fuel mode be used. Very good cylinder condition
with this lube oil was achieved from the
The fuel-oil-only mode is well known gas engine on the Chiba power plant.
from the ME engine. Operating the A heavy fuel oil with a high sulphur con-
engine in this mode can only be done tent requires the cylinder lube oil TBN
on fuel oil. In this mode, the engine is 70. Shipowners intending to run their
considered “gas safe”. If a failure in the engine on high-sulphur fuels for longer
gas system occurs it will result in a gas periods of time are recommended to in-
shutdown and a return to the fuel-oil- stall two lube oil tanks. When changing
only mode and the engine is “gas safe”. to minimum-fuel mode, the change of
lube oil should be carried out as well.
The minimum-fuel mode is developed
for gas operation, and it can only be Players in the market have been fo-
started manually by an operator on the cussed on reducing the exhaust emis-
sions during harbour manoeuvring.
When testing the ME-GI at the MAN
Diesel research centre in Copenhagen,
Fuel 100% Fuel-oil-only mode Fuel 100%
"Minimum fuel" mode
Fuel gas
Fuel oil
Min. Pilot
Fuel oil oil 5-8%
100% load 30% load 100% load
Min load for Min. fuel mode
Fig. 19: Fuel type modes for the ME-GI engines for LNG carriers
22

23. Launching the ME-GI to test the gas engine on the testbed, gas compressor system for the specific
but this is a costly method. Alternatively, LNG carrier. Only in this combination it
As a licensor, MAN Diesel expects a and recommended by MAN Diesel, the will be possible to get a valid test.
time frame of two years from order to compressor and ME-GI operation test
delivery of the first ME-GI on the test- could be made in continuation of the Prior to the gas trial test, the GI system
bed. gas trial. Today, there are different opin- has been tested to ensure that every-
ions among the classification societies, thing is working satisfactory.
In the course of this time, depending and both solutions are possible de-
on the ME-GI engine size chosen, the pending on the choice of classification
engine builder will make the detailed society and arrangement between ship
designs and a final commissioning test owners, yard and engine builder.
on a research engine. This type approv-
al test (TAT) is to be presented to the MAN Diesel A/S has developed a test
classification society and ship owner in philosophy especially for approval of the
question to show that the compressor ME-GI application to LNG carriers, this
and the ME-GI engine is working in all philosophy has so far been approved
the operation modes and conditions. by DNV, GL, LR and ABS, see Table III.
The idea is that the FAT (Factory Ac-
In cooperation with the classifica- ceptance Test) is being performed for
tion society and engine builder, the the ME system like normal, and for the
most optimum solution, i.e. to test the GI system it is performed on board the
compressor and ME-GI engine before LNG carrier as a part of the Gas Trial
delivery to the operator has been con- Test. Thereby, the GI system is tested
sidered and discussed. One solution is in combination with the tailor-made
Table III: MAN B&W ME-GI engines – test and class approval philosophy
MAN Diesel Engine builder Yard Yard Gas trial
Copenhagen testbed Quay trial Sea trial
MAN B&W research TAT of ME-GI con-
engine – 4T50MX trol system and of
or similar suitable gas components.
location Test according to
MBD test program.
Subject to Class ap-
proval.
First ME-GI Test according to: Test according to: Test according to: After loading gas, the
production engine • IACS UR M51 • Yard and Engine • Yard and Engine following tests are to
MBD Factory Builder test pro- Builder test pro- be carried out:
Acceptance Test gram approved gram approved • Acceptance test
program (FAT) for by Class by Class of the complete
ME engines. gas system includ-
ing the main engine.
• Test of the ME-GI
control system ac-
cording to MBD test
program approved
by Class
Second and follow- - do - - do - - do - - do -
ing ME-GI engines
Engine is tested on: Gas and marine Marine diesel oil Marine diesel oil Marine diesel oil Marine diesel Heavy
diesel oil and/or heavy fuel oil and/or heavy fuel oil fuel oil and gas
23