Interaction entre un jet et un tourbillon compressé. Etude expérimentale de l'aérodynamique et de mélange

Abstract : The transient in-cylinder flow field and mixing that take place during compression stroke of an internal combustion engine cylinder are a key factor for the optimisation of the engine as well as pollutant emissions. This work was performed in a frame of a collaborative project between engine manufacturers (PSA, Renault) and CNRS and was supported by ADEME. An existing experimental set-up has been used but improved with an adapted injection system. We have gathered a large database of the injection and compression stroke. Imaging Laser techniques are used to study the interaction between spray and aerodynamic in a model situation of a engine cylinder. The study will answer if this interaction alter the transport properties of the large-scale rotating flow in a view to realize a vertical charge stratification. We focus here on the mechanical interactions between the spray and the internal flow. Then a model round jet has been injected respecting a non dimensional analysis in order to be representative of the real engine configuration. Two kind of injection axis have been set up in order to study the influence of the tumbling cross flow in the angular momentum jet transfer. Experiments have been carried out to measure velocity field (PIV) and mixture field (PLIF) in the symmetry plane of the chamber during injection and compression strokes. For quantitative measurements of acetone fluorescence, both the absorption coefficient and the fluorescence yield must be determined under reference conditions. This measurements provides a better understanding of energy transfer between jet and large scale motion as well as of the modification of the disruption of the tumbling flow during compression. The mean kinetic energy is transferred to turbulence with a short time scale during the injection. Then dissipation process occurs during the whole compression stroke thus leading to a lower level of fluctuating kinetic energy at the end of compression than without injection. This result is very important as far the combustion is concerned. Finally, we have proposed to use a global approach of the Proper Orthogonal Decomposition in order to get a common base for the whole compression stroke. Fields interpolation has been done using a linear interpolation since this latter minimise the energy lost. The POD analysis confirms the energy transfer activated by the injection and gives some good perspectives of this approach in the analysis of internal unsteady turbulent flow.
Keywords : mixing
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Julien Moreau. Interaction entre un jet et un tourbillon compressé. Etude expérimentale de l'aérodynamique et de mélange. Dynamique des Fluides [physics.flu-dyn]. Institut National Polytechnique de Toulouse - INPT, 2003. Français. ⟨tel-00007174⟩

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