Diesel 4 Stroke Cycle

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The four stroke diesel is nearly the same as the petrol four stroke cycle, apart from the very few differences, the whole cycle is explained below.

The first stroke of the diesel four stroke engine is the ‘Induction’ stroke, the same as the petrol four stroke. On this stroke air only is drawn into the combustion chamber, the inlet port is open allowing the air to be drawn in and the exhaust port is closed, so that incoming air cannot escape.

The second stroke of the diesel four stroke engine is called the ‘Compression’ stroke; on this stroke the piston is moving up the cylinder to compress the air that was drawn into the combustion chamber on the induction stroke (above). The exhaust port and inlet port is closed on this stroke to ensure the air is compressed as much as possible. The air that is being compressed gets extremely hot due to the amount of compression it has just undertaken.

The third stroke of the diesel four stroke engine is the ‘Ignition’ (power) stroke. This stroke is one that is very different to that of the petrol four stroke. The fuel is injected by an injector located at the top of the cylinder, which sprays into the highly compressed air, which is hot from the compression. Once the fuel hits the air, because of the amount of heat created by compression, the air and fuel mixture forms a highly combustible mixture and ignites, which forces the piston down the cylinder onto the fourth stroke (below). Both inlet and exhaust ports are closed on this stroke.

The fourth stroke of the diesel four stroke engine is the ‘Exhaust’ stroke; this stroke is the final stroke, which leads back onto the ‘Induction’ stroke. On this stroke the piston is moving back up the cylinder, because of the force, and rotation of the crankshaft. With the exhaust port open and inlet port closed on this stroke, as the piston is moving up the cylinder, it forces the burnt gases out of the cylinder via the exhaust port.

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