Second-law analysis of an ideal Otto cycle

The system input and output exergy at each portion of an ideal Otto cycle, as well as the process effectiveness, are calculated for compression ratios of 3.0:9.0 and air/fuel equivalence ratios of 0.25:1.0. For comparison, the energy-based efficiencies are also calculated. It was found that both effectiveness and efficiency increase with compression ratio and with air-to-fuel ratio (but at different rates), and that the effectiveness does not vary much when the air-to-fuel ratio increases above 200%. It was also shown that exergy analysis represents the losses in the cycle, such as in the combustion and exhaust processes, much more realistically than the conventional first-law analysis and serves as a good guide for cycle improvements. Several recommendations are made in that direction.