Which types of processes are involved in an ideal Otto combustion cycle?

In an ideal Otto combustion cycle, the processes involved can be characterized by two constant volume processes and two isentropic processes. The Otto cycle consists of four stages typically represented on a pressure-volume (P-V) diagram.

The first stage is the compression process, which is adiabatic (isentropic) and occurs as the piston moves upwards in the cylinder, compressing the fuel-air mixture. Since this process is adiabatic, there is no heat exchange with the surroundings, and the temperature and pressure of the mixture rise significantly.

Following the compression, the second stage is a constant volume process, where combustion occurs. At this point, the spark plug ignites the compressed fuel-air mixture, resulting in a rapid increase in pressure and temperature at a constant volume since the combustion takes place within the confines of the cylinder.

Once combustion is complete, the third stage is another isentropic expansion process, where the high-pressure gases expand, driving the piston down and performing work on the crankshaft. This expansion is also adiabatic, meaning that the gas does not exchange heat with its surroundings during this phase.

Finally, the fourth process is another constant volume process as the exhaust gases are expelled from the cylinder after the expansion. In this stage,