Effects of Exhaust Gas Recirculation and Boost Pressure on Reactivity Controlled Compression Ignition Engine at High Load Operating Conditions

Abstract

Reactivity controlled compression ignition (RCCI) at engine high load operating condi tions is investigated in this study. The effects of exhaust gas recirculation (EGR) andboost pressure on RCCI combustion were studied by using a multidimensional computa tional fluid dynamics (CFD) code. The model was first compared with a previous CFD model, which has been validated against steady-state experimental data of gasoline-diesel RCCI in a multicylinder light duty engine. An RCCI piston with a com pression ratio of 15:1 was then proposed to improve the combustion and emissions at high load. The simulation results showed that 18 bar indicated mean effective pressure (IMEP) could be achieved with gasoline-diesel RCCI at an EGR rate of 35% and equivalence ratio of 0.96, while the peak pressure rise rate (PPRR) and engine combustion effi ciency could both be controlled at reasonable levels. Simulations using both early and late direct-injection (Dl) of diesel fuel showed that RCCI combustion at high load is very sensitive to variations o f the EGR amount. Higher IMEP is obtained by using early diesel injection, and it is less sensitive to EGR variation compared to late diesel injection. Reduced unburned hydrocarbon (HC), carbon monoxide (CO), soot and slightly more nitrogen oxides (NO,) emissions were seen for early diesel injection. HC, CO, and soot emissions were found to be more sensitive to EGR variation at late diesel injection tim ings. However, there was little difference in terms of peak pressure (PP), efficiencies, PPRR. and phasing under varying EGR rates. The effect of boost pressure on RCC! at high load operating conditions was also studied at different EGR rates. It was found that combustion and emissions were improved, and the sensitivity of the combustion and emis sion to EGR was reduced with higher boost pressures. In addition, cases with similar combustion phasing and reasonable PPRR were analyzed by using an experimentally validated GT-Power model. The results indicated that although higher IMEP was gener ated at higher boost pressures, the brake mean effective pressure (BMEP) was similar compared to that obtained with lower boost pressures due to higher pumping losses

A detail simulation of reactivity controlled compression ignition combustion strategy in a heavy-duty diesel engine run on natural gas/diesel fuel

“…A number of experimental and computational works have been carried out by researchers in the field of the RCCI using a wide variety of fuel combinations, such as gasoline–diesel fuel, ethanol–diesel fuel, gasoline–biodiesel, gasoline–gasoline with an improved cetane number. 14–46…”

Complex analysis of combustion and emission parameters of bio‐renewable fuel mixtures in dual‐fuel mode

“…This effect is achieved by the reduced temperature inside the cylinder. A reduced in‐cylinder temperature results from EGR thermal effects and dilution 75 . The fact that the temperature inside the cylinder is lower causes lower production of emissions.…”

Progress and recent trends in reactivity-controlled compression ignition engines

“…Studies are currently ongoing to explore factors that affect the ability to achieve RCCI combustion over a wide range of speed and load points. 221 The effects of piston bowl design, piston material, CR and injection strategy are being considered. Optimization work at light loads is recommended to improve the combustion efficiency and to reduce HC and CO emissions of high-speed RCCI engines.…”