Performance analysis and optimization of an M100 automotive methanol engine based on a finite-time thermodynamic Otto cycle model

Abstract This study develops an irreversible Otto-cycle model for neat methanol engines within the framework of finite-time thermodynamics. Standard temperature-dependent thermophysical data for each species were used to determine process-specific effective heat capacities and heat-capacity ratios for the methanol–air charge and corresponding ideal combustion products. The calculated power output and thermal efficiency were compared with published performance data for methanol engines, and the maximum relative deviations remained below 10% throughout the investigated speed range. The model was subsequently used to evaluate the cycle-level effects of key design and operating parameters, including the compression ratio and the cycle temperature ratio. The results indicate that richer mixtures and lower friction losses contribute positively to overall thermodynamic performance. In addition, reducing the heat-transfer coefficient from 2.8 to 2.2 W/K increases the maximum ecological function from 0.43 to 1.67 kW, highlighting the importance of suppressing irreversible heat dissipation. Single-objective optimization further reveals pronounced trade-offs among performance indicators. Achieving a maximum thermal efficiency of 41.78% limits the corresponding output power to 15.48 kW. Overall, the results quantitatively characterize the influence of the investigated parameters on the performance of the irreversible M100 Otto-cycle model within the prescribed assumptions.