Gas Engines

It is based on the proven low speed 4-stroke diesel engine, with only the combustion chamber section converted to a gas engine.

Everything aside from the combustion chamber section has the same structure as conventional engines, so it has the same reliability and durability.

It employs an electric ignition system as a gas mono-fuel combustion engine, and is capable of operating only on gas from startup to high loads.

The gas engine was created with consideration for a simplified structure, where an air-fuel mixture is taken into the cylinder and an electrical ignition system is used to ignite the mixture with a spark plug.

Two spark plugs are provided in each cylinder, so that operation can be continued even in the event that ignition failure occurs with one of them.

In gas engines, various types of control are carried out in order to ensure stable combustion.

In existing diesel engines, only the fuel injection volumes are controlled in accordance with the engine load. In gas engines, however, intake air volumes are also controlled according to the engine load in addition to the fuel injection volumes.

Therefore, two types of valves are installed to adjust the intake air volume - one to bypass the exhaust, and another to bypass the intake air.

Furthermore, under extremely low loads an intake air throttling valve is also provided to adjust the intake air volume in addition to the bypass valves.

Basically, control of the fuel injection volume is carried out by adjusting the gas injection period, but if the gas volume is changed significantly the gas pressure is also controlled.

While gas engines are in operation, the ignition timing is controlled so that the maximum cylinder combustion pressure can be maintained properly at all times. Therefore, pressure gauges are installed in all cylinders to constantly analyze the cylinder pressure while controlling the ignition timing.

Gas is bunkered from the exterior of a vessel to a gas tank, in the form of a low-temperature liquid called LNG.

The LNG is guided from the main gas tank to an evaporator, and after changing to a gaseous state in the evaporator, it is supplied via a buffer tank to the gas engine.

In the left figure, NOx is shown on the horizontal axis and thermal efficiency on the vertical axis. The fuel oil consumption decreases the higher the thermal efficiency.

For the G30(A), the Tier III NOx regulation mode is shown, and for the G30(B) the Tier II NOx regulation mode is shown. In the G30(A) mode, the Tier III NOx regulation is fulfilled while achieving a higher thermal efficiency than the existing LA32 model diesel engine.

Since the Tier III NOx regulation is not applied in the coastal areas of Japan, compliance with the Tier II NOx regulation is sufficient, and under the G30(B) mode even higher thermal efficiency can be achieved.