Synergetic effect of hydrogen enrichment on diesel engine fueled using corn oil methyl ester — Performance, emission and combustion characteristics

This study investigates the synergetic effects of hydrogen enrichment at volumetric flow rates of 6 and 12 litres per minute (LPM) on a direct injection (DI) diesel engine fueled with a 20% corn oil methyl ester biodiesel blend (COME20), with a focus on thermal performance, emission, combustion, and second-law thermodynamic characteristics. Corn oil methyl ester was synthesized via a two-step acid–base transesterification process, achieving 98% conversion efficiency. Experimental results demonstrate that hydrogen induction through the air intake manifold substantially augments brake thermal efficiency (BTE) and combustion quality while simultaneously reducing hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO2[jls-end-space/]), and smoke opacity emissions. At maximum engine load, BTE reached 35.5% and 36.2% for COME20 with 6 and 12 LPM hydrogen, respectively, surpassing both conventional diesel (33.5%) and COME20 alone (30.8%). Brake-specific fuel consumption was reduced to 0.23 and 0.22 kg/kWh for the 6 and 12 LPM hydrogen flow with COME20 biodiesel, compared to 0.26 kg/kWh for diesel and 0.29 kg/kWh for COME20. CO and smoke opacity were reduced by averages of 20.47% and 43.55%, respectively, at 12 LPM relative to COME20. Exergy efficiency improved from 30% (COME20) to 37% (COME20 + 12 LPM), with exergy destruction declining from 56% to 46%. The sustainability index increased from 1.41 for COME20 to 1.59 for COME20 + 12 LPM, confirming enhanced thermodynamic and environmental viability. However, nitrogen oxide (NOx) emissions increased by up to 10.05% over COME20 at full load due to elevated adiabatic flame temperatures, highlighting a key trade-off that necessitates mitigation strategies such as exhaust gas recirculation (EGR).