Diesel Engine Proper 2 of 2


Diesel Engine Combustion Chamber

In a diesel engine, the fuel is injected as mist from the injection nozzle and mixed with the air and is ignited and burned. To obtain good combustion, it is necessary for the injected fuel and air to mix well in the combustion chamber.

Direct injection type combustion chamber

In the direct injection type combustion chamber, the main combustion chamber is formed between the cylinder head and piston. This type causes ignition and burning by injecting highly pressurized fuel into the highly compressed, high temperature air. As the construction is simple, the output is high, the heat efficiency is high and the cooling loss is low, the fuel consumption is small and the startability is superior. Therefore, some engines use an intake heater or glow plug although some do not have a preheating system. As the combustion pressure increases, noise and vibration during driving also increase.

Swirl chamber type combustion chamber

This combustion chamber is formed with the spherical swirl chamber including the main combustion chamber. These chambers are connected through the transfer passage. A swirling air flow is produced in the swirl chamber during the compression stroke and most of the fuel is ignited and burned. Then the part of the fuel remaining is burned in the main combustion chamber. In this way, smooth driving can be obtained because the maximum engine speed or combustion pressure can be higher and the engine speed range is wide. However the temperature of the high temperature air inside the swirl chamber lowers as the cylinder head absorbs the heat. Therefore the startability is worse than that of the direct combustion type, which is why a glow plug is used as a preheating system.

Shape of piston head

The upper surface of the piston makes up a part of the combustion chamber, and is specially formed to make turbulence in order to improve the mixture between the air and fuel. The sunken shape of the upper surface of the piston is deeper on the direct injection type. Among them, the troidal type is used the most. The piston of the swirl chamber is shallow because almost all of air-fuel mixture is burned. Some of these types are flat.

Diesel Engine Cylinder Liner

Cylinders are divided into two typesThe linerless type and the type in, which the cylinder liner is inserted in the cylinder block.

(1) Liner type There are two types of cylinder linerThe wet type in, in which the coolant touches the backside directly, and the dry type, which the coolant does not touch directly. The top of the cylinder liner is made to protrude slightly above the top of block. This protrusion (A) prevents gas leaks by sufficiently penetrating the cylinder gasket.

(2) Linerless type The linerless type uses a special alloy cast iron, which is more resistant to wear. The engine is made compact and lightweight by narrowing the bore pitch.


The cylinder block of most of diesel engines is made of cast iron. Recently some engines use an aluminium cylinder block, in which a cylinder liner is inserted.

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