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4-Stroke Engines, Thermodynamics Background Information: Internal combustion engines are the type commonly used in cars today, where the petrol is actually ignited in the cylinder. They are known as 4 stroke, because the process occurs in two cycles (two up strokes, and two down strokes). The piston begins at the top of the cylinder, moving down. The intake valve is opened, and so a mixture of fuel and oxygen is sucked into the cylinder. When the piston reaches the bottom, the valve is closed, and the piston moves up, compressing the mixture until the piston reaches the top. When the piston is at the top, the spark plug fires, igniting the mixture, producing high downward pressure on the piston. This pressure pushes the piston down (this is where the actual work is done by the engine). When the piston reaches the bottom, the exhaust valve is opened and as the piston moves up the exhaust is pushed out. After reaching the top, the exhaust valve is closed, and the intake valve opened (bringing us back to the start). Thermodynamics is used to describe the relationship between heat and work, and the transfer of both in and out of systems.
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