Otto cycle
![Pressure-Volume diagram](/Images/godic/202501/31/P-V_Otto_cycle.svg0254.png")
![Temperature-Entropy diagram
The idealized diagrams of a four-stroke Otto cycle
Both diagrams:
the intake (A) stroke is performed by an isobaric expansion, followed by an adiabatic
compression (B) stroke. Through the combustion of fuel, heat is added in a constant volume (isochoric process) process, followed by an adiabatic expansion process power (C)
stroke. The cycle is closed by the exhaust (D) stroke, characterized by isochoric cooling and isentropic compression processes.](/Images/godic/202501/31/Otto20254.png")
![](/Images/godic/202501/31/OTTO_CYCLE0254.png")
An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines.
The Otto cycle is a description of what happens to a mass of gas as it is subjected to changes of pressure, temperature, volume, addition of heat, and removal of heat. The mass of gas that is subjected to those changes is called the system. The system, in this case, is defined to be the fluid (gas) within the cylinder. By describing the changes that take place within the system, it will also describe in inverse, the system's effect on the environment. In the case of the Otto cycle, the effect will be to produce enough net work from the system so as to propel an automobile and its occupants in the environment.