Effects of Hydrogen Enrichment and Ignition Timing on Combustion Characteristics and Performance of an M30-Fueled Spark-Ignition Engine

Abstract This study experimentally investigates the effects of hydrogen enrichment and ignition timing (IG) variation on combustion and performance of a single-cylinder spark-ignition engine fueled with M30 (30% methanol, 70% gasoline by volume) at 1500 rpm and 50% load. Hydrogen was introduced into the intake manifold with its energy share varied from 10% to 40%, while IG was adjusted accordingly. Increasing hydrogen energy shares (HES) significantly accelerated combustion due to hydrogen's high flame speed and low ignition energy, leading to steeper pressure rise and advanced combustion phasing. Peak in-cylinder pressure increased by approximately 9 bar, and combustion duration shortened by 15–20% as the hydrogen energy share rose from 10% to 30%. A clear trade-off was observed, whereby moderate hydrogen enrichment (20–30% HES) enhanced the indicated thermal efficiency to around 25%, reduced specific fuel consumption by up to 21%, and increased indicated mean effective pressure to a maximum of 5.54 bar. Beyond 30% HES, air displacement effects began to limit performance gains. Overall, hydrogen enrichment between 20% and 30% HES, combined with IG between 18 deg crank angle (CA) and 24 deg CA before top dead center (BTDC), provided the best balance of combustion efficiency, work output, and knock resistance. These findings demonstrate the potential of hydrogen–methanol–gasoline tri-fuel operation as a practical strategy for improving efficiency and emissions in spark-ignition engines.