Otto Cycle

An Otto cycle is an idealized thermodynamic cycle that is taken as a standard of comparison for internal combustion engines. For the purpose of comparison with the other cycle, the air is assumed to be the working substance.

The ideal Otto cycle consists of two constant volume and two reversible adiabatic or isentropic process. 

Process:

• Process (1-2): Reversible adiabatic compression.
• Process (2-3): Constant volume heat addition.
• Process (3-4): Reversible adiabatic expansion.
• Process (4-1): Constant volume heat rejection. 

Heat Supplied = mC_v(T₃-T₂)

Heat Rejected = mC_v(T₄-T₁)

Efficiency:

Note:

• The efficiency of the Otto cycle depends on the compression ratio.
• The efficiency increases with the compression ratio (r). In actual practice r can not be increased beyond a value of 7 or so.