Otto cycle

An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical spark ignition reciprocating piston engine, the
thermodynamic cycle most commonly found in automobile engines.
The processes are described by
Process 1-2 is an isentropic compression of the air as the piston moves from bottom dead centre (BDC) to top dead centre (TDC).
Process 2-3 is a constant-volume heat transfer to the air from an external source while the piston is at top dead centre. This process is
intended to represent the ignition of the fuel-air mixture and the subsequent rapid burning.
Process 3-4 is an isentropic expansion (power stroke).
Process 4-1 completes the cycle by a constant-volume process in which heat is rejected from the air while the piston is a bottom dead centre.