3-D Numerical Study of Turbulent Mixing of Intake Air and Exhaust Gas in a Low Pressure EGR System

A 3-D numerical study of turbulent mixing characteristics of air and exhaust gas in a low pressure EGR system (LP-EGR) has been performed under typical operating conditions. There are two objectives of this study. The first objective of the study is to understand and quantify the effects of following factors on mixing quality of exhaust gas and intake air: a) Rate of generation and dissipation of turbulence in the near mixing zone. b) Swirl induced due to formation of counter rotating vortex pairs (CVPs). c) Impingement of the EGR jet on the opposite wall of the intake manifold. The second objective of this study is to understand mixing quality with respect to pressure drop. Under typical conditions, on the low pressure side of the turbocharger, the pressure drop available to ensure required mass flow rate of EGR into the intake air is minimal. Hence, different EGR inlet configurations have been modeled to calculate the mixing quality along with the pressure drops. Some of configurations that have been studied are the effect of varying the diameter of EGR inlet tube, varying the insertion of EGR inlet tube into the intake air duct, angular injection, mixing elbow, multi-point EGR injection, EGR tube with multiple nozzles, venturi configuration, EGR flow control valve at EGR inlet etc. The above mixers have been compared by plotting respective mixing quality vs. EGR-side pressure drop and air-side pressure drop on a 3-D scatter plot at various operating conditions of the engine. One of the important conclusions of the study is that, in the range of operating conditions considered, a simple T-Junction like configuration, which generates maximum local turbulence and allows uninhibited formation and propagation of counter rotating vortex pairs, provides the best mixing quality with the least pressure drop.