Four Stroke Diesel Engine:

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 Four Stroke Diesel Engine: Theory

A four-stroke diesel engine is an internal combustion engine that converts the chemical energy of diesel fuel into mechanical energy. It completes one operating cycle in four piston strokes and two crankshaft revolutions (720°). Unlike a petrol engine, a diesel engine uses compression ignition, so it does not require a spark plug. Only air is drawn into the cylinder during the intake stroke, and diesel fuel is injected at high pressure near the end of the compression stroke.

Working Principle

1. Suction Stroke

During the suction stroke, the inlet valve opens while the exhaust valve remains closed. The piston moves from Top Dead Centre (TDC) to Bottom Dead Centre (BDC), creating a vacuum that draws fresh air into the cylinder.

2. Compression Stroke

Both the inlet and exhaust valves remain closed. The piston moves from BDC to TDC, compressing the air to a very high pressure. This raises the air temperature to about 500°C to 700°C, making it hot enough to ignite diesel fuel automatically.

3. Power Stroke

Near the end of the compression stroke, the fuel injector sprays diesel into the hot compressed air. The fuel ignites instantly due to the high temperature. The expanding gases force the piston from TDC to BDC, producing useful mechanical power. This is the only power-producing stroke.

4. Exhaust Stroke

The exhaust valve opens while the inlet valve remains closed. The piston moves from BDC to TDC, pushing the burnt gases out of the cylinder. After this, the cycle repeats.

Advantages

High fuel efficiency.

Produces high torque at low speeds.

No spark plug or ignition system is required.

Long service life and reliable operation.

Suitable for heavy-duty applications.

Applications

Four-stroke diesel engines are widely used in:

Trucks and buses

Tractors and agricultural machinery

Diesel generators

Ships and marine engines

Construction equipment

Railway locomotives

Conclusion

The four-stroke diesel engine is one of the most efficient and durable internal combustion engines. Its operation consists of Suction, Compression, Power, and Exhaust strokes. The engine produces power through compression ignition, making it ideal for heavy-duty vehicles and industrial applications where fuel economy and reliability are important.

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