MAIN DIESEL GENERATOR ENGINES
There are four main diesel generator engines fitted. The No.2, No.3 and No.4
engines are Wärtsilä 12V50DF, capable of producing 11,700kW when
operating on fuel gas or fuel oil, while the No.1 engine is a Wärtsilä 6L50DF,
capable of producing 5,850kW when operating on fuel gas or fuel oil.
All four engines have been designed to run on either Boil-off Gas (BOG) from
the cargo tanks or Heavy Fuel Oil (HFO) from the fuel oil service tanks.
Even though the two fuels have different densities and calorific values, the
engines can run equally well on either BOG or HFO and can deliver the same
maximum power output on either fuel. The engines can be switched from one
fuel to the other while operating on load and without any interruption to the
power supply.
Apart from the number of cylinders and the in-line or V configuration, the
engines are identical in operation and in parts such as pistons, valves, injectors,
etc.
The fitting of six and twelve cylinder engines allows for flexibility in the
choice of operating engines to suit power demand.
The Wärtsilä Engine Control System (WECS) supervises and controls the
engine safety, speed, fuel regulation and other engine related automated issues.
The burning of fuel gas produces many safety issues and these require special
consideration in the design and operation of the engine. Separate liquid fuel
and gaseous fuel systems are required, and because of the very low ignition
point of natural gas, it is necessary to inject a small amount of MGO as pilot
fuel to produce a flame to ignite the gas in the cylinder.
Gas is directed into the cylinder with the combustion air during the piston
suction stroke and this gas/air mixture is then compressed, being ignited by the
pilot flame. The injection timing of the pilot fuel must be precisely controlled to
produce the flame for gas ignition at exactly the right time. The gas ignites and
burns in exactly the same way that combustion of liquid fuel in a conventional
diesel engine produces power.
Operation
As the 12V50DF and 6L50DF engines are both made by Wärtsilä and are the
same in many respects, the descriptions that follow apply to both types unless
otherwise stated.
The engines drive directly coupled alternators which supply electricity for use
by all of the ship’s systems including the main propulsion. The propulsion
uses two electric motors to drive a fixed pitch propeller through a reduction
gearbox.
The engines can be operated in fuel mode or fuel gas mode. They cannot
operate in dual fuel mode using fuel gas and fuel oil, apart from the use of pilot
MGO when operating in gas mode.
Fuel Mode
In fuel mode, the engine works just like a normal diesel engine, utilising a
conventional jerk-type fuel pump and fuel injector for each cylinder. The fuel
injection pumps are driven by the camshaft and the fuel injector operates in the
normal manner. Each fuel injector however, contains a pilot fuel injector which
operates when the engine is running in fuel gas mode.
Fuel Gas Mode
In fuel gas mode, the engines run as lean burn engines according to the Otto
cycle. Boil-off gas from the cargo tanks is used as the fuel and this boil-off gas
is heated and compressed to a pressure of 0.51MPa at the inlet to the engine.
A gas valve is located at each cylinder air inlet pipe and this opens during the
piston suction stroke to allow gas into the air stream to the engine cylinder. The
gas valve opening period is regulated by the engine control system so that the
correct fuel gas/air mixture is obtained for the operating load and for correct
cylinder combustion. The gas mixes with the air during the suction stroke of
the piston and this homogeneous mix is compressed during the compression
stroke.
Natural gas has a very low ignition point and requires a high temperature
to cause ignition. This fact allows the gas to be mixed with the air during
induction and enables the gas/air mixture to be compressed, but it means an
ignition system is required. Ignition of the gas/air mixture is by means of a
pilot flame. A small amount of diesel, in the form of pilot fuel, is injected
with the correct timing so that it burns at the time when ignition of the gas/air
mixture is required. The MGO will ignite in the same way as MGO injected
into a conventional diesel engine because the compression temperature is
above the ignition temperature of the MGO.
The pilot injection system uses as little as 1% of nominal fuel energy input, the
main energy release being due to combustion of the gas. The pilot fuel injector
is located in the main fuel injector, but the pilot fuel system is separate from
the main fuel system and comprises an engine-driven pilot fuel pump which
supplies fuel to the pilot injectors via a common rail system. A knock sensor
is located at each cylinder, and if knocking is detected, the control system
modifies the timing of the pilot injection to eliminate the knocking.
Here is the working of dual fuel diesel engine on lng carrier. I want to make a video how the engine works and how it powers the ship propeller. Generate a video
