The internal combustion engine
When a fossil fuel or a high-energy fuel such as petrol or diesel is ignited in a small enclosed space a large amount of energy is released. When fuels like this burn they use the four-stroke combustion cycle or the otto cycle. The four parts of the cycles are...
- Induction Stroke
- Compression Stroke
- Combustion Stroke
- Exhaust Stroke
Most engines contain between four and twelve cyclinders and these allow the smooth rotation of the engine during the cycle. The four strokes of the internal combustion engine are always in the same order, induction, compression, combustion and then exhaust. This in turn means that the piston moves up and down twice in any one cycle in the cylinder. These strokes produce two revolutions of the crankshaft and this process continues to repeat during the operation of the engine.
Internal combustion engine
On the induction stroke, the inlet valve opens. The piston moves downwards and a mixture of air and vapourised fuel is injected or pushed by atmospheric pressure into the cylinder through the inlet valve port. As the piston begins to move up again the inlet valve closes along with the exhaust valve ensuring the cylinder is sealed. As the piston moves upwards, the air/fuel is compressed hereby increasing the pressure in the cylinder and also the temperature.
As the piston reaches the top of the cylinder there is an electrical discharge through the spark plug. The spark ignites the air/fuel mixture. The mixture combusts and the cylinder pressure increases to a higher level. This high pressure forces the piston back down the cylinder. The force on the piston is now transmitted down through a connecting rod to the crankshaft. The crankshaft is rotated due to tyhis force.
As the piston reaches the bottom of the cylinder for the second time the exhaust valve opens. As the piston moves upwards again on the exhaust stroke, it forces the molecules of the combusted gases through the exhaust port. As the piston reaches the top of the cylinder for a second time the exhaust valve closes and the inlet valve opens.