Sensibilité d'un écoulement de rouleau compressé et des variations cycle à cycle associées à des paramètres de remplissage moteur

Abstract : This experimental work concerns a sensitivity study of the in-cylinder flow in aspark-ignition engine and of the cycle to cycle variations (CCV) by comparing three variationsof boundary conditions related to the optimisation of air filling conditions. In the reference case, the three dimensional tumble flow is characterized during the intake and compression phases. A earlier intake cam phase increases the mass flow rate at inlet valves and amplifiesthe fluctuations immediately after the start of intake phase. The tumble ratio is much lowerat mid-compression phase. The fluctuating energy at top dead center is reduced. A longerengine stroke leads, at the end of compression phase, to a shift of mean flow and to a verydistinct evolution of the fluctuating velocity, due to the different confinement from the pointof view of the engine internal flow. Finally, the modification of intake duct design changes theflow intensity and reorganizes in depth the flow structure. Moreover, to describe the transfer into turbulence, two methodologies of classification in groups of flow structures, by spatial correlation then by clustering, are proposed. A phase-averaged analysis of the statistics of group content and inter-group transitions shows that CCV can be associated with different sets of trajectories during the second half of the compression phase. The conditional statistics are computed to analyse the data in each group, which leads to a triple decomposition. It is important to point out that this more accurate evaluation of CCV is applicable to very large sets of experimental or numerical data.
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Yujun Cao. Sensibilité d'un écoulement de rouleau compressé et des variations cycle à cycle associées à des paramètres de remplissage moteur. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2014. Français. ⟨NNT : 2014ESMA0020⟩. ⟨tel-01127619⟩

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