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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.

Characteristics of the in-cylinder air motion in Diesel engine has been investigated by PIV from intake to exhaust phase. This paper presents the methodology used to perform in cylinder aerodynamics measurements (PIV) using a Renault tansparent single cylinder engine in motored conditions. Measurements have been achieved with exact engine geometry configuration (high compression ratio) even at top dead center (TDC). Two different configurations have been studied: flat and bowl-in-piston. First results, which are high quality, demonstrate that swirl is better centred with bowl-in-piston than flat piston. Nevertheless, swirl still remain dissymetrical. Its evolution during compression measured on experimental engine is close to theory. Finally, squish phenomena is visualized and its intensity appears to be weaker than theory.

Internal flow have a great contribution to the performance of internal combustion engines. A study of the modification of a model GDI tumbling flow is proposed in this paper. The first part gives an overview of the current works concerning in-cylinder flow. Our experiment generates and compress a tumbling vortex during one cycle. The experiment will be described as well as injection calibration. Indeed, It is not possible to use an industrial spray injector in our experiment since velocities in our chamber are lower than in cylinders. Furthermore, our flow is non reactive, the only vaporization would be due to the compression. We decide to use a gas injector. A non dimensional parameter comparing the angular momentum brought by the spray to the initial angular momentum of the tumble structure will be derived in the paper. This non dimensional parameter is useful to define and to analyse our model experiments while being sure to be relevant as engine situation is concerned.

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.

The present work is dedicated to the study of air-natural gas mixing in a model intake manifold for Natural Gas Spark ignition engine. A configuration of continuous Natural Gas injection is considered. The fuel injection located upstream the intake valve is submitted to a time varying crossflow with high acceleration and deceleration levels. A physical analysis is developed and presented. Relevant new non-dimensional numbers are established for the engine situation. With this analysis, we compute a critical diameter of injection that characterizes the sensitivity of the jet to the pulsed transverse flow. Experiment is used to check these predictions. Schlieren technique is applied in a test section to obtain instantaneous images of the injection jet phased in the engine cycle. We visualize the global behavior of the jet and consequently the mixing in the intake manifold.

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.