Impact of intake air pressure and temperature on performance and hydrogen knock limit in a spark-ignition engine using Hydrogen-Gasoline blends

The primary objective of this study is to investigate the effects of varying intake air pressure and temperature on the performance and hydrogen knock limit of a spark-ignition engine. The experiments were conducted using pure gasoline and a hydrogen-gasoline blend at a constant speed of 1000 rpm, a throttle position of 50 %, and a fixed gasoline injection quantity of 6 mg per cycle. The hydrogen flow rate was incrementally increased in steps of 2 L per minute until the knock onset was observed. Intake air pressure was varied from 100 kPa to 112 kPa, while intake air temperature was adjusted from room temperature to 65 °C. The results indicated that brake thermal efficiency decreased from 10.43 % to 3.28 % with an increase in intake air pressure but increased to 15.26 % with a rise in intake air temperature. Combustion analysis revealed that peak in-cylinder pressure decreased from 22.77 bar to 21.22 bar with higher intake air pressure but increased to 25.69 bar with elevated intake air temperature. Additionally, carbon monoxide emissions decreased, whereas carbon dioxide and nitrogen oxide emissions increased with higher intake air temperature. In contrast, increasing intake air pressure exhibited the opposite trend. Cyclic variations were found to increase with intake air pressure and decrease with intake air temperature, with the coefficient of variation for peak pressure remaining below 10 % in all test cases. Engine performance improved with the addition of hydrogen to the fuel mixture. At a hydrogen flow rate of 8 L per minute, the average in-cylinder temperature, carbon dioxide emissions, and nitrogen oxide emissions were 884.34 °C, 7.2 %, and 172 ppm, respectively. Moreover, increasing intake air pressure and retarding spark timing raised the hydrogen knock limit to 14 and 18 L per minute, respectively, compared to the original limit of 8 L per minute. However, an increase in intake air temperature reduced the hydrogen knock limit to 6 L per minute.