1996-10-01

Modeling the Effects of EGR Inhomogeneities Induced by Intake Systems in a Four-Valve Engine 961959

The purpose of this study is to determine if inhomogeneous mixing of EGR and fresh air in the intake ports can lead to a specific spatial distribution of burnt gases in the combustion chamber before ignition. To achieve this goal, several three dimensional computations of a multi-valve, spark ignited engine with a dual intake ports are performed. We study the effect of engine speed (1500 and 3000 rpm), the effect of flow structure and turbulence (one and two operating intake valves) and the effect of the EGR intake technology (in the plenum or in each intake runner).
Three dimensional computations are performed with a new version of the KMB code. Numerical improvements (iterative solver. convection scheme …), new sub-models (turbulence, beat transfer and law of the wall), as well as a multi-block strategy with mesh refinement algorithm were developed and implemented in the code. These improvements allow complicated geometries to be modeled. In the present case, it allows having a more refined mesh where the air and EGR mixture is very heterogeneous.
Initial and boundary conditions are obtained from a ID code for which the complete engine, with four cylinders, intake and exhaust systems are taken into account.
Calculations show that burnt gases stratification is slightly more important when increasing the engine speed. We find a more homogeneous field of burnt gases with a single operating intake valve. Introducing EGR by each intake runner of the engine seems to induce a more homogeneous mixture in the cylinder before ignition.

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