Study of Geometrical Parameter Influence on Air/EGR Mixing

The present work deals with the understanding and optimisation of air-EGR mixture phenomena since EGR strategy already showed its benefits on combustion and particularly on NOx emissions. Such benefits can be only observed with an accurate regulation system limiting EGR cylinder-to-cylinder maldistribution, otherwise a risk of opposite effect may appears (no NOx reduction with increasing of particulate emission).

Given the complexity to get EGR cylinder-to-cylinder distributions on « real » engine working conditions and to understand mixing process which occurs upstream cylinder head, a simplify bench has been built in co-operation with the Institute of Fluid Mechanics from Toulouse (IMFT) in order to characterise Air/EGR mixing owing to optical diagnostic (PIV, PLIF). EGR cylinder-to-cylinder distribution is also measured by a thermal method.

In order to improve knowledge on mixing process and to create a data base for further 3D unsteady CFD simulations, parametrical study was carried out concerning EGR rate, camshaft speed (600 rpm, 1200 rpm and 1500rpm) and geometrical parameters. Classification of studied configurations and analysis of their influence on mixture in manifold (somewhere representative of cylinder-to-cylinder distribution) is then proposed.