Impact of EGR direct injection in a spark-ignition engine using CFD

Exhaust gas recirculation (EGR) is widely implemented in internal combustion engines to reduce pollutant emissions. The traditional way of introducing EGR is by creating a homogeneous air-exhaust gas mixture in the engine intake system. This paper proposes a novel technique of EGR based on the direct injection of exhaust gases into the cylinder. Such an approach can create exhaust gas stratification which offers benefits compared to the traditional technique. To gain insight of the consequence of the novel approach, 3D-CFD numerical simulations were employed. Results showed a high velocity EGR jet, emanating from the three EGR inlets, which crosses the cylinder and hits the junction piston-cylinder liner on the opposite side. The jet then continued its course creating a clear stratification of EGR inside the cylinder along the liner surface. Moreover, simulation results suggested a direct advantage of the proposed approach, as a significant increase of turbulence was observed and it persisted up to spark timing when compared to a homogeneous EGR approach, with the net consequence of a faster burning rate for the stratified approach. Overall, the results show that the proposed approach modifies the in-cylinder flow and turbulence intensity, which in turn changes the flame development.