Mitigation of high pressure rise rate by varying IVC timing and EGR rate in an RCCI engine with high premixed fuel ratio

In a reactivity controlled compression ignition (RCCI) engine, when the ratio of premixed low-reactively fuel is high, unacceptable high pressure rise rate (PRR) always occurs. The objective of this study is to find effective ways of mitigating the high PRR in and biodiesel and gasoline fueled RCCI engine. Coupled KIVA4-CHEMKIN code was used to mimic the combustion process of RCCI engine with 70% of premixed gasoline. At first, parametric studies were conducted to investigate the effects of intake valve close (IVC) timing and exhaust gas recirculation (EGR) rate, respectively. Results indicate that delaying IVC timing and increasing EGR rate could mitigate the maximum PRR. Then, a two-stage optimization was undertaken by considering IVC timing and EGR rate at one time. To guide the optimization, contour maps on indicated mean effective pressure (IMEP) and emissions were generated. It was found that high EGR rate with advanced IVC timing would lead to satisfying results. Finally, two optimal cases were identified. Comparing with the cases of varying IVC timing and EGR rate individually, while resulting same acceptable maximum PRR, the optimal cases emit much lower NO, soot and CO emissions, and achieve slightly higher thermal efficiency.