Abstract
This paper deals with the understanding and optimisation of air-EGR mixture since EGR strategy has already shown its benefits on combustion and particularly on NOx emissions. Such benefits need indeed an accurate regulation system limiting EGR rate cylinder-to-cylinder dispersion with which invert effects may appear (no NOx reduction with increasing of particulate emission). In development process, simulation is more and more used. But before this step, a precise description of physic must be available, first to understand phenomena and to calibrate simulation tools, and secondary owing to visualisation. In that aim, Renault has built a bench in cooperation with IMFT to characterise air-EGR mixture phenomena by optical diagnostics such as PIV, PLIF, Mie scattering Tomography. Then 3D unsteady CFD simulations were carried out. It is shown in this paper that our CFD methodology leads to good agreements between PIV/PLIF fields and CFD results, as well as on EGR cylinder-to-cylinder distribution, allowing to use it to propose first recommendations.