Numerical Investigation of the Potential of Late Intake Valve Closing (LIVC) Coupled with Double Diesel Direct-Injection Strategy for Meeting High Fuel Efficiency with Ultra-Low Emissions in a Heavy-Duty Reactivity Controlled Compression Ignition (RCCI) Engine at High Load 2019-01-1166

The potential of diesel/gasoline RCCI combustion coupled with late intake valve closing (LIVC) and double direct injection of diesel for meeting high fuel efficiency with ultra-low emissions was investigated in this study. The study was aiming at high load operation in a heavy-duty diesel engine. Based on the reactivity stratification of RCCI combustion, the employment of double injection of diesel fuel provided concentration stratification of the high-reactivity fuel, which is to further realize effective control of the combustion process. Meanwhile, late intake valve closing (LIVC) strategy is introduced to control the maximum in-cylinder pressure and nitrogen oxides (NO_x) emissions. By coupling KIVA-3V code with genetic algorithm (GA), six crucial operating parameters including premix ratio (PR), start of first injection (SOI1), start of second injection (SOI2), mass fraction of the first fuel injection, exhaust gas recirculation (EGR) rate, and intake temperature (T_in) were optimized to realize simultaneous minimization of fuel consumption, NO_x and soot emissions in the present study. The results indicate that the soot emissions and fuel economy can be effectively decreased with the employment of two split fuel injections while the NO_x is maintained under the Euro 6 limit, which demonstrates the potential of double direct-injection strategy for improving the performance of RCCI combustion with LIVC. In the evolution process, the strategies with more separated fuel injections realized by an earlier SOI1 and later SOI2 are preferred to increase the homogeneity of the cylinder charge and reduce the soot emissions. However, the amount of the premixed diesel fuel in the first injection is limited by the peak pressure rise rate (PPRR) constraint. Moreover, the double injection strategy is superior over the single injection strategy in fuel consumption due to the more near-TDC combustion phasing and in reducing the heat transfer due to the shorter combustion duration, whereas the combustion efficiency is deteriorated to some extend due to serious wall impingement with early fuel injection.