Energy and exergy analyses of hydrogen-fueled spark ignition engine with various air excess ratios and ignition timings

Many studies have been conducted to determine the efficiency and emission of hydrogen internal combustion engines. However, only a few of these investigations have performed exergy analysis (especially when important parameters, such as excess air ratio, vary) based on the second law of thermodynamics. Accordingly, in this study, experiments were conducted on a commercial automotive spark ignition engine. The engine is modified to run on hydrogen as fuel at 1500 rpm with various spark timings and excess air ratios under a wide-open throttle. In addition, zero-dimensional two-zone modeling was conducted by matching and examining the experimental results considering both energy (first law of thermodynamics) and exergy (second law of thermodynamics) analyses. The results indicate that with the same excess air ratio, the trend exergy analysis results, such as increasing exhaust exergy loss and decreasing heat transfer exergy loss by retarding ignition timing, are similar to the energy analysis results. Additionally, irreversibility increased as the spark timing retarded owing to the reduction in combustion temperature caused by prolonged combustion duration. In considering various excess air ratios, the gap between the energy and exergy analysis results was evaluated: the heat transfer exergy loss increased from 27% to 31%, the exhaust exergy loss decreased from 20% to 15%, and irreversibility was maintained at approximately 10%. Irreversibility was maintained because of the offset between the irreversibility increment (due to the decrease in combustion temperature) and decrement (due to the decrease in fuel amount). Moreover, the relationship between the thermo-mechanical exergy rise rate and behavior of each exergy component was examined.