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It is now well established that highly turbulent flows in engines are responsible for cycle-to-cycle aerodynamic variations particularly in cylinder. These dispersions may lead to macroscopic changes in flow pattern from one cycle to another one, which are quite different from “true turbulence” (in fact small scale turbulent fluctuations) used to optimize combustion. It is of a great importance to decrease these variations which may effect reliability of combustion concept and particularly when looking to decrease idle engine speed. The difficulty in separating “true turbulence” from cyclic variations is that there is no limit between two kinds of fluctuations. To analyze aerodynamic, PIV is well adapted to study these phenomena and is now currently used in development process, allowing to measure instantaneous aerodynamics field to determine for instance vortex center position for each cycle.

Previous studies of in-cylinder heat transfers give numerous approaches of heat losses modelling principally compression and expansion strokes. These simulation methods are discussed showing that their accuracy during the intake stroke is neglected. Since most of the modern engines use strong structured air motion during the intake and compression strokes to both reduce consumption and reach different emissions levels targets, one may focus on in-cylinder aerodynamics and convective heat transfer coupling. The experimental velocity data acquired allow us to get an in-depth understanding of the spatial and temporal gradients of measured heat transfers in the cylinder of an internal combustion engine. Two different experimental methods have been used to investigate the in-cylinder air motion. First, near wall flow has been studied using two component local time-resolved Laser Doppler Anemometry (LDA).

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.

This paper deals with the problem of complex engine part analysis. It presents an original approach based on the use of X-ray Computed Tomography scan digitizing method. In comparison with classical digitizing method, Computed Tomography method proves to be the only solution in the case of complex parts with internal areas. A validation example for which the precision of the method is estimated, is proposed. At last, the potential of the method is illustrated through the complex example of an engine head cooling circuit for which a computational CFD calculation is made.