Four Stroke Diesel Engine
- Cycle of operation completed in four strokes of the piston or two revolution of the crankshaft.
1. Suction Stroke
The suction stroke is also called the intake stroke, where inlet valve opens, as a result the piston will suck the air (and not fuel as in case of Petrol Engine) from the intake manifold, filling the cylinder chamber with air and the piston moves down from TDC (top dead center) to BDC (bottom dead center). This movement will increase the volume in the engine cylinder.
2. Compression Stroke
The compression stroke is the process of compressing the air inside the cylinder chamber. As a result there is a narrowing of the cylinder volume. In this condition both the intake valve and exhaust valve are closed, so that the narrowing of the cylinder space will compress the air inside.
Why does the air need to be compressed?
The diesel engine is not equipped with spark plugs, it is because the diesel engine can burn without sparking from the spark plug. This is known as self combustion.
To occur self combustion, the air must be compressed until the temperature rises above the diesel fuel burning point.
3. Expansion Stroke
The combustion step is the main process of the engine. In this process the diesel is fed through the injector into the combustion chamber.
As we discussed already, the air temperature will rise until above of diesel burning point. And when the piston reaches TDC, the air is already in its highest temperature level (exceeding the diesel burning point). In this condition, the diesel injected via injectors, it make the fuel atomized through the injector. As a result, there was a burning that produced expansion power making the downward movement of piston from TDC to BDC.
4. Exhaust Stroke
The exhaust step is the process of removing combustion residual gases from the combustion chamber. This process occurs when the piston returns to TDC after being exposed to the expansion of combustion power.
At this step, the exhaust valve opens so that the upward movement of the piston will push the combustion residual gas to get out into the exhaust manifold.
