AbstractThe objective of the present work is to investigate the effect of ethanol fraction on combustion, performance, and emission characteristics of a reactivity controlled compression ignition (RCCI) engine fueled with diesel, cottonseed oil methyl ester (CSME), and hemp oil methyl ester (HOME). The low-reactivity fuel ethanol was injected into the intake manifold using a timed manifold injection system controlled by an electronic control unit, whereas the high-reactivity fuel (diesel, CSME, HOME) was directly injected into the combustion chamber at different injection timings to initiate ignition. The injection timing of 23° crank angle (CA) before top dead center (bTDC) promises a flexible combustion phasing and better results in terms of maximum pressure rise, heat release rate, brake thermal efficiency, and emission characteristics using ethanol as a primary fuel. The RCCI mode of operation with a 20% ethanol premixed ratio resulted in increases in brake thermal efficiency by 28.07%, 10.70%, and 12.34% for diesel, CSME, and HOME at part load (50%), respectively, and 13.22%, 3.09%, 5.92% for the same fuels at full load (100%) conditions owing to uniform mixing and better atomization of fuel particles. The specific fuel consumption decreased by 13.79%, 10.34%, and 8.62% for 20E+80Diesel, 20E+80HOME, 20E+80CSME energy ratios, respectively, at part load conditions and 14.29%, 12.50%, and 10.71% at full load conditions versus the conventional combustion mode. The exhaust gas temperature slightly decreased for 50% and 100% load conditions compared with conventional diesel combustion. A reduction of CO2 emissions was observed for 20E+80Diesel, 20E+80HOME, and 20E+80CSME fuel fractions by 2.37%, 2.06%, and 2.85% respectively, at full load condition compared with neat diesel fuel. While increasing the load in all fuel shares, smoke emissions increased slightly. The low-temperature RCCI combustion strategy achieved a reduction of NOx emissions by up to 18.90% at a full load condition for 20E+80HOME fuel fractions.

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