Effects of combustion efficiency on an Otto cycle

This paper explains how the combustion efficiency influence the performance of an irreversible Otto cycle under conditions of varying fuel-air ratio. The irreversibility of Otto cycle comes exclusively from the expansion and compression processes. It is assumed that some fraction of the fuel's chemical energy cannot be fully released inside the engine because of incomplete combustion. Amount of the released energy from fuel into the cylinder restricts the compression ratio. Thermal efficiency - work curves cannot have a closed loop shape because of the relationships between the fuel energy, air-fuel mass ratio, combustion efficiency, maximum temperature and heat losses.