Experimental and Numerical Investigation of Stratified Exhaust Gas Recirculation (EGR) in a Spray Guided DI Gasoline Engine

In this paper, results of experimental and numerical investigations of stratified exhaust gas recirculation in a single-cylinder gasoline engine are presented. The engine was operated in spray guided direct injection mode. The radial exhaust gas stratification was achieved by a spatial and temporal separated induction of exhaust gas and fresh air. The spatial separated induction was realized by specially shaped baffles in the inlet port. The temporally separated induction was performed by impulse charge valves, with one for the fresh air and one for the exhaust gas. From various possible strategies for time-dependent induction of fresh air and exhaust gas, three different strategies to stratify the exhaust gas were examined. The first strategy was characterized by a closed left inlet port. Due to the closed inlet port, the swirl motion of both fluids were in the same direction. So mixing effects between both fluids should be minimized. The intake of fresh air was after the intake of exhaust gas. Strategy two and three were characterized by a central induction of fresh air through both inlet ports. The exhaust gas was induced with a swirl motion. At strategy two, the induction of fresh air was before the induction of exhaust gas and at strategy three the temporal induction was vice versa. The in-cylinder flow was investigated using CFD simulation to quantify the distribution of fresh air and exhaust gas in the combustion chamber. These various concepts to stratify the exhaust gas were verified by experiments to evaluate the potential of these concepts to reduce NO_x-emissions.