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Operational Information

The 4 Stroke Dual Fuel Engine

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BasicsThe 2 Stroke

EngineThe 4 Stroke

EngineOperatio

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course special precautions in the piping of the gas into the engine room have to be observed.

team turbine plant is not very efficient: about 29% for main propulsion and about 25% for electrical generation.

ur stroke diesel engines which can burn gas or diesel fuel (known as Duel Fuel or DF engines) have been around in

ed installations for some time. These engines are now being adapted for use in merchant vessels, notably LNG carrihough some gasfield supply vessels have been built with dual fuel engines. MAN B&W have developed a two strok

ine which will run on gas.

e efficiency of the diesel engine in the dual fuel concept approaches 50%. When installed as part of the diesel electr

pulsion plant (for economic, practical and redundancy purposes) the efficiency overall is about 43% due to losses in

rnators, transformers, converters, motors and shafting. However the efficiency far exceeds that of the steam turbinent.

e principle of the plant is outlined above. The gas boil off is pressurised to about 5.5 bar by compressors and is then

ted to about 30C. The gas is then piped to the engines, where it is injected into the intake air before the air enters t

inders. Ignition is by pilot injection of diesel fuel.

e first diesel electric LNG carrier is the Gaz de France at 74 000 m3 She is powered by 4 Wartsila 6L50DF engines

eloping 5700kW at 514rpm. Under normal operation she runs 3 out of the 4 engines giving a service speed of 16 kn

hough with all 4 engines running she can achieve 28.5 knots.

e energy consumption of the engines when burning gas is quoted as the Brake Specific Energy Consumption (BSEC

the Wartsila 50DF engine it is given as 7410kJ/kWh (about 48.5% efficiency). This means that each engine willsume 1 013 688MJ of energy in 24 hours. This means that at the lower boil off figure of 0.1%/day given above, the

y enough gas to meet the requirements for 1 engine. To meet the need to run all the engines, some of the cargo is fo

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boil off (F-BOG) This is more economical than running the engines on diesel fuel. On ballast passage the engines ca

her be run on diesel fuel or LNG retained on board specifically for burning in the engines. It is possible to modify thines to burn heavy fuel oil by adjustments to the fuel pump timing and fuel injection equipment, although the use o

vy fuel will require a change in the type of lubricating oil to a High Duty oil.

EL SYSTEM

sel Supply

ere are two fuel supply systems: one for pilot fuel when the engine is running on gas, the other for back up operatio

sel fuel. The pilot fuel is supplied at 900 bar from a common rail supplied by an engine driven variable delivery rad

ton type pump. The timing and duration of the pilot injection is electronically controlled.

operation on diesel fuel, standard type cam driven fuel injection pumps are used injecting through standard designing loaded fuel injectors.

e injectors are twin needle valve units. The smaller needle is used for the electronically controlled pilot injection, an

ger needle for when running on diesel fuel.

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s Supply

The photos opposite and below shows t

gas regulating unit.In the foreground of the picture opposit

the manual Isolating valve (with the red

handle)

No 1 is the filter

No 2 is the flow meterNo 3 is the gas regulator unit

No 4 are the shut off valves

No 5 is a venting valve (1 of 3)

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Gas Regulating Unit

e gas supply is filtered and then goes through a pressure regulator, the output of which is dependent on engine load rgy content of the gas, but is a maximum of 4 bar. The system also incorporates necessary shut of and venting valv

ety purposes. The gas is then piped to the engine by a large diameter double wall common rail system with each cyling an individual feed to a gas admission valve.

INCIPLE OF OPERATION

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e engine runs on the lean burn principle. This means that the air to fuel ratio is high (about 2.1:1). An advantage is tengine will produce low NOx emissions (

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intaining the correct air fuel ratio over the operating

ge of the engine is essential to prevent knocking andsfiring and to keep emissions low.

s is achieved by an engine controlled waste gate which

passes some of the exhaust gas around thebocharger.

View of Engine Showing Waste Gate

FETY

In case the boil off gas cannot be used by the engines,

there is no reliquefaction plant, there must be analternative way of disposing of it. To do this a Gas

Combustion Unit or Thermal Oxidiser is installed in t

ships funnel.

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View of V12 engine showing gas manifold and emergency gas venting valve actuator

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e safety considerations are similar to those for an LNG steamship. A leak of methane into the machinery space coul

se a devastating explosion. To prevent this, the gas is led through a double skinned pipe fitted with a flame arrestor

et to the supply manifold, an extraction system and gas detector. There must be sufficient flexibility in the pipes tovent fatigue failure due to oscilliation of the engine. An extraction fan from a hood above the engine is also fitted w

detection system. Leakage of gas will trip the gas master valve (the engine will automatically change over to diese

ration) and the BOG will be diverted to and burnt in the Thermal Oxidiser. The gas pipe system will also be fitted w

ogen inerting system which will operate to purge through if gas is detected.

CS require that the following safety requirements must be met:

Only oil fuel is to be used when starting the engine.

Only oil fuel is, in principle, to be used when the operation of an engine is unstable, and/or during

manoeuvring and port operations.

In case of shut-off of the gas fuel supply, the engines are to be capable of continuous operation by oil fueonly.

Crankcase relief valves are to be fitted in way of each crankthrow. The construction and operating pressu

the relief valves are to be determined considering explosions due to gas leaks.

Explosion relief valves or other appropriate protection system against explosion are to be provided in the

exhaust, scavenge and air inlet manifolds. The exhaust gas pipes from Dual Fuel engines are not to be connected to the exhaust pipes of other enginsystems.

Starting air branch pipes to each cylinder are to be provided with effective flame arresters.

Flame arresters are to be provided at the inlet to the gas supply manifold for the engine.

Arrangements are to be made so that the gas supply to the engine can be shut-off manually from the starting plaor any other control position.

a trunk piston type engine is used as as Dual Fuel engine, the crankcase is to be protected by the following

asures:

Ventilation is to be provided to prevent the accumulation of leaked gas, the outlet for which is to be led t

safe location in the open through flame arrester.

Gas detecting or equivalent equipment. (It is recommended that means for automatic injection of inert gato be provided).

Oil mist detector.

e engine must be designed to stop before the gas concentration detected by the gas detectors specified reaches 60% wer flammable limit.

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a cross-head type engine is used as a Dual Fuel engine:

The crankcase is to be protected by oil mist detector or bearing temperature detector.

Gas detecting or equivalent equipment is to be provided for piston underside space of cross-head type en

e engine must be designed to stop before the gas concentration detected by the gas detectors specified reaches 60%

wer flammable limit.

Also The 2 Stroke Dual Fuel Engine

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