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Effect of hydrogen enrichment on combustion characteristics and emissions of a four-stroke gasoline engine | ||
| Al-Qadisiyah Journal for Engineering Sciences | ||
| Articles in Press, Accepted Manuscript, Available Online from 30 July 2026 | ||
| Document Type: Research Paper | ||
| DOI: 10.30772/qjes.2026.172099.2021 | ||
| Author | ||
| Haidar K. Mohammed* | ||
| Department of Mechanical Engineering, College of Engineering, Islamic Azad University, Tehran South Campus, Iran. | ||
| Abstract | ||
| This study experimentally investigates the effect of hydrogen enrichment on combustion characteristics, engine performance, and exhaust emissions of a four-stroke spark-ignition (SI) gasoline engine. A single-cylinder, 0.61-L, air-cooled engine was operated at 2300 rpm under full load with hydrogen blending ratios of 5%, 10%, 15%, and 20% by fuel energy, using unleaded gasoline (RON 95) as the base fuel. Hydrogen was delivered through a dedicated port injector upstream of the intake valve. Peak cylinder pressure increased by 17.6% (4.82 to 5.67 MPa at H20%), and the 10–90% mass-fraction-burn duration decreased by 31.6% (38 to 26 °CA), driven by hydrogen’s high laminar flame speed (237 cm/s) and wide flammability range (4–75 vol%). Brake thermal efficiency peaked at H15% (32.1%, +12.6%), while brake-specific fuel consumption fell by 17.35% at H20%. Combustion stability improved by 60.7%, with COV of IMEP reduced from 2.8% to 1.1%. CO, HC, and CO₂ emissions decreased by 81%, 66.5%, and 25%, respectively, with the average unburned-HC carbon chain length reduced from C₆.₂ to C₃.₁. However, NOx emissions rose by 338.7% due to higher peak combustion temperatures activating the thermal (Zeldovich) mechanism. The optimal blending ratio is 10–15%, balancing efficiency gains against NOx penalties addressable through established aftertreatment strategies. | ||
| Keywords | ||
| Hydrogen enrichment; Gasoline engine; Combustion characteristics; Emissions; Alternative fuels; Dual-fuel; NOx emissions | ||
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