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A model experimental set-up dedicated to the study of a compressed tumbling motion is presented in this paper. Measurements are obtained by using Laser Doppler Velocimetry and Particle Image Velocimetry in a complementary way. A tumbling motion representative of high tumble research engines develops in the square chamber. We quantify effects of cycle-to-cycle variations on ensemble mean and fluctuating velocity fields at BDC. PIV is shown to be an optimal technique in order to understand the evolution of the confined vortex during the compression stroke. The breaking down of the tumbling vortex is a gradual process and the vortex/wall interaction is proved to be an essential mechanism responsible for abrupt modifications of the flow fields and for the generation of 3D turbulence. A link is made with the present development of tumble control pistons. The problem of turbulence level estimation appears very complex as cyclic variations are enhanced during the breakdown phase.

Characteristics of the in-cylinder air motion in Diesel engine has been investigated owing to Particle Imagery Velocimetry (PIV). Measurements have been performed in a full transparent engine, respecting real diesel engine geometry configuration (in particular high compression ratio). Two different piston shapes have been studied: flat and bowl-in-piston. A first paper (2003-01-3083, Pittsburgh congress October 2003) describes experimental set up which allowed to obtain very high quality measurements until the Top Dead Centre (TDC), and presents results of Diesel internal aerodynamics flow based on mean averaged velocity fields [1]. The present paper shows the second part of this study and is focused on turbulence evolution from intake to exhaust phases.

Reducing pollutant emissions of passenger car is one of the main task of manufacturers. One way to reduce emission is to operate SI engine in lean combustion with natural gas. The objectives of this work are, to investigate differences between natural gas and gasoline exhaust emissions and combustion, and then, to show the accuracy of a zero-dimensional two zones thermodynamic model for NOx predictions. Data are acquired in a 4 cylinders bi-fuel engine. With natural gasl, SI engine operates at lower ratio than gasoline leading to a reduce in NOx emission. The thermodynamic model calculates NOx emissions and time burning duration from the cylinder pressure. Typical difference between natural gas and gasoline have been found: With natural gas flame ignition duration decreases and flame propagation duration increases. An improvement of NOx formation model have been developed by locking into account cycle to cycle cylinder pressure in.