4.2.6.c Working stroke
Third stroke. Operating stroke 
When the piston is at TDC, and the mixture, which is compressed and heated to a high temperature, is in the combustion chamber, a discharge occurs between the electrodes of the spark plug, which ignites the fuel. The air-fuel mixture in the process of combustion releases gases that are heated to 800 °C. A high pressure is created, under the action of which the piston moves downward, pushing the crankshaft. The whole process continues until BDC. In diesel engines, fuel is injected into the cylinder with compressed air, heated to an extremely high temperature, which ignites spontaneously.
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