Numerical Study On The Control Of Internal EGR And Its Influence On Gasoline Homogeneous Charge Compression Ignition Combustion

Variable Valve Timing technology is one of the effective methods to control gasoline engine HCCI in a wide range of operation map.The aim of this thesis is to analyze the EGR formation and its influence on HCCI combustion based on the numerical simulation of working process of a GDI engine. In the research, two internal EGR formation strategies, the Exhaust Port Recirculation (EPR) and the Combustion Chamber Recirculation (CCR), were investigated respectively. By numerical simulation, the author studied and compared the effects of each EGR strategy events on ignition phenomena under the same operational condition. Meanwhile, the effects of variable valve timing (VVT) strategies on EGR rate, internal EGR distribution and its influence on combustion performances were studied.For the analysis,I-D simulation tool GT-POWER, and3-D CFD package FIRE for numerical simulation were applied. Numerical simulation results show that early exhaust valve close and exhaust valve open twice strategies not only provide high EGR rate, but also control work fluid temperature distribution effectively. For the control of engine gasoline HCCI combustion, the proper EGR rate of the CCR strategy is about31%-57.5%, while the EPR is about40%-53%. When the engine run from152°CA BTDC to10°CA BTDC, the EGR in-cylinder distribution of the two strategies is increasingly homogeneous. Comparing the two internal EGR formation strategies, the CCR strategy provides more homogeneous EGR distribution than EPR. Both EGR ratio and EGR in-cylinder distribution have important influence on combustion performance.