Effect of Numerical Configuration on Predicted EGR Cylinder-to-Cylinder Dispersion

Exhaust Gas Recirculation (EGR) is employed widely in compression-ignited engines and currently under consideration for being implemented into spark-ignited engines. EGR cylinder-to-cylinder dispersion is one of the features of such engines that developers are challenged to abate, because low EGR rates increase NOx emissions and excessive EGR rates can produce a significant amount of particulate matter. Taking into account the complex geometries of some automotive manifolds, the treatment of this topic through 3D computational fluid-dynamics (CFD) simulations seems mandatory to study the transport phenomena in a proper way. The main objective of this work is the analysis of the influence of the numerical setup main parameters (mesh, time-step size, turbulence modeling) in a CFD URANS simulation of an automotive engine intake manifold in the EGR distribution. To achieve this objective, it is necessary in the first place to develop a 1D model of the considered engine so as to get the transient boundary conditions for the CFD simulations in the studied operating points. This 1D model will be developed and calibrated with different experimental measurements. After that, the 3D CFD URANS simulations will be carried out, aiming to predict the dispersion on the EGR rate swallowed by the different cylinders of the engine. Different studies of mesh sensitivity and time step will be useful to set an optimal numerical configuration of the setup, and the effects of turbulence submodels will be assessed too. All the obtained results will be validated by comparing average and instantaneous results against experimental data. An important aspect of this work is the analysis and assessment of mixing between the air and EGR streams, and its important role in the EGR dispersion.