Combustion improvement and emission reduction through control of ethanol ratio and intake air temperature in reactivity controlled compression ignition combustion engine

Highlights: • Diesel/ethanol RCCI combustion simultaneously reduces NOx and PM. • The IMEP_net increases as the ethanol supplied ratio increases for early injection. • RCCI combustion increases the thermal efficiency with reduction in the heat transfer and exhaust losses. • The increase in the intake air temperature retards the optimal injection timing. • The higher the intake air temperature, the higher the increase in the diesel supply ratio. -- Abstract: The reactivity controlled compression ignition (RCCI) combustion has the potential to simultaneously reduce the NO_X and PM emissions and maintain combustion performance even when injection timing is advanced. Because intake air temperature is an important factor affecting the reactivity of fuels, it is necessary to study optimized fuel supply ratios according to the intake air temperature. Therefore, the purpose of this study was to analyze combustion and exhaust characteristics in relation to the fuel supply ratio, injection timing, and intake air temperature. In this study, ethanol was injected into an intake port; increasing the ethanol supplied ratio increased the ignition delay. Thus, the net indicated mean effective pressure (IMEP_net), compared with conventional diesel combustion, increased from 4.14 to 4.90 bar for the advanced injection timing (BTDC 27°). In addition, because the combustion period was lengthened and combustion temperature lowered, the NO_X emission decreased (19.1 → 2.7 g/kWh); however, the THC (1.1 → 2.5 g/kWh) and CO (5.2 → 10.1 g/kWh) emissions increased. Moreover, burning an homogeneous mixture of ethanol decreased the particulate matter emission from 74 to 45 μg/m³. However, under high intake air temperature conditions, the effect of ethanol ratio on ignition delay was small. Therefore, the injection timing at which the maximum IMEP_net occurred was retarded. In addition, as the intake air temperature increased, the THC and CO emissions decreased and that of NO_X increased.