Compression ratio of an optimized air standard Otto-cycle model

We propose an irreversible simplified model for the air standard Otto thermal cycle. This model takes into account the finite-time evolution of the cycle's compression and power strokes and it considers global losses lumped in a friction like term. The proposed model permits the maximization of quantities such as the power output and the efficiency in terms of the compression ratio r. The optimum r values obtained compare well with standard r values for real Otto engines. Our model leads to loop-shaped power-versus-efficiency curves as is common to almost all real heat engines.