Numerical investigation of the effects of inlet valve closing temperature and exhaust gas recirculation on the performance and emissions of an RCCI engine

In this paper, the effects of inlet valve closing temperature (TIVC) and exhaust gas recirculation (EGR) on the emissions and the performance of a reactivity controlled compression ignition (RCCI) engine have been numerically investigated. The numerical results were obtained for TIVC variations from 293 to 353 K and the EGR variations from 0 to 25%. For this purpose, the natural gas was injected in inlet port as a low reactivity fuel, while the diesel fuel was directly injected in the cylinder as a high reactivity fuel. For the numerical simulation validation, the results were compared to the reference data. The comparison shows that the in-cylinder pressure, rate of heat release (RoHR), soot and nitrogen oxide (NOx) emissions results are in good agreement with the reference data. According to the results, with increasing the EGR, the maximum in-cylinder pressure and also the maximum RoHR will be decreased. Moreover, increasing the EGR can considerably reduce NOx and soot emissions. When EGR increases from 0 to 25%, the NOx emission decreases from 0.47 to 0.02 g kW−1 h−1, while soot decreases from 0.009 to 0.0005 g kW−1 h−1. Also, increasing the TIVC will significantly increase the maximum pressure, RoHR and NOx and soot emissions. When TIVC increases from 293 to 353 k, the NOx emission increases from 0.01 to 0.41 g kW−1 h−1 and also soot from 0.0005 to 0.011 g kW−1 h−1. Finally, the results show that both of the TIVC and the EGR play important roles in controlling the combustion phase of an RCCI engine.