Otto Cycle

The Otto Cycle is a four step cycle where the internal combustion engine converts chemical energy of a fuel into mechanical work. The cycle is as follows:


1. Fuel and air are drawn into each cylinder by the piston’s downward movement.


2. The fuel and air mixture is compressed by the piston moving upward, decreasing the volume of the cylinder.


3. The fuel and air mixture ignites, releasing energy that forces the piston downward. A gasoline engine relies on a spark plug to ignite the gas while a diesel engine compresses the mixture sufficiently so that it auto-ignites.


4. The hot exhaust gases are forced out of the cylinder by the piston moving upward.


The entire processes can be summarized on a graph of pressure versus cylinder volume:

Internal Combustion Engine P-V Diagram

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Authored by: Andrew Kristof