A comparative study on gasoline/diesel-fueled RCCI combustion at different premixed ratios and high-EGR diesel CI combustion in an IC engine under low load conditions

Abstract

Low temperature combustion concepts in internal combustion engines have arisen as one of the solutions that reduce NOx and particulate emissions without a fuel consumption penalty. Among the combustion concepts, reactivity controlled compression ignition (RCCI) has the potential of being able to be achieved in a wider operating range than other low temperature concepts. On the other hand, exhaust gas recirculation (EGR) use in diesel-compression ignition (CI) engines is an effective way to reduce NOx emission. This study experimentally investigated the high-EGR CI fueled with diesel and gasoline/diesel fueled RCCI combustion modes in terms of combustion, performance, and emission at fixed energy inputs corresponding to low load conditions for different engine speeds. In RCCI combustion mode, different premixed ratios were also tested to determine their effects. The results show that CA50 locations in all high-EGR CI combustion occurred later than those of RCCI modes, which led to late peak pressure occurrence. By considering heat release rate curve characteristics, the controlled combustion phase emerged at the highest premixed ratio in RCCI as in the high-EGR CI combustion. RCCI combustion showed an improvement in smoke emissions, and the maximum improvement was attained by about 86%. In RCCI combustion, nitrogen oxide (NO) emissions at 2000 rpm engine speeds are significantly lower than that in high-EGR CI whereas the increasing premixed ratio at 1500 and 1750 rpm led NO emission to increase. Besides, RCCI combustion with the highest premixed ratios resulted in slightly higher brake thermal efficiencies (BTE). The maximum difference in BTE values was obtained by about 3.0% in favor of RCCI combustion.