A thermodynamic cycle returns a working substance to its initial state. Its net internal-energy change is zero, so the net work output equals net heat input.
The thermal efficiency of a heat engine is the net work output divided by heat input. For a cycle absorbing and rejecting the positive amount ,
The ideal Otto cycle has adiabatic compression, constant-volume heat addition, adiabatic expansion, and constant-volume heat rejection. For an ideal gas with compression ratio and specific-heat ratio ,
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A thermodynamic cycle is a series of processes that involve the transfer of heat and work between a system and its surroundings in a way that the system returns to its initial state at the end of the cycle. In other words, a thermodynamic cycle is a closed loop in which a working substance—typically a gas—undergoes various transformations (such as expansion, compression, heating, and cooling) that cause it to absorb and release energy.