Reactivity-Controlled Compression Ignition Engine Mode of Operation With Quaternary Fuel Blends

Abstract The decarbonization of heavy-duty engines demands advanced multi-fuel strategies that enhance efficiency while adhering to stringent pollution regulations. The present numerical study investigates quaternary blends of diesel, natural gas, hydrogen, and ethanol in a dual-fuel single-cylinder heavy-duty engine utilizing ansys forte, three-dimensional simulation software, at a compression ratio of 16.25:1, an engine speed of 1750 rpm, and an engine load of 11.24 bar. The results demonstrated that substituting hydrogen (H2) for up to 20% of the gaseous fuel energy share enhanced flame propagation, reduced combustion duration by approximately 40%, increased indicated thermal efficiency by 16.47%, and decreased fuel consumption by 18%, while significantly elevating nitrogen oxide emissions (NOx). The incorporation of ethanol mitigated the drawback. Moderate substitution (5–20%) of ethanol resulted in a 29–38.8% reduction in NOx emissions, whilst higher levels (>30%) attained reductions surpassing 90%, combined with nearly complete elimination of unburned hydrocarbons. Two optimized quaternary blends, adhering to the reactivity-controlled compression ignition combustion mode with only 5% diesel; D5E20NG55 + 20% H2 and D5E50NG25 + 20% H2—exhibited improved indicated efficiencies ranging from 7.2% to 17.2% relative to the baseline fuel, while regulating soot generation, thereby illustrating the viability of ultra-low diesel operations. The timing of diesel injection was critical because a slight advance (10–16 deg before top dead center) resulted in a thermal efficiency enhancement of 5–14% while effectively managing the nitrogen oxide–soot tradeoff. The results emphasize the synergistic role of hydrogen and ethanol in facilitating low-carbon, high-efficiency heavy-duty engines, with injection phasing as the critical control variable.