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Étude numérique de la dynamique de combustion dans un brûleur diphasique turbulent à deux étages

Abstract : The increasingly stringent environmental standards imposed on air transport are pushing manufacturers to upgrade the existing combustion chambers. To reduce pollutant emissions, lean, premixed and pre-evaporated combustion is an interesting alternative. This technology, however, can lead to a less stable flame and can generate combustion instabilities harmful to the engine. In order to improve control over such combustion systems, multi-stage burners provide additional flexibility through the distribution of fuel between the different injection systems, and thus influence the position of the flame or the burning regime. The BIMER experimental bench has been specially developed in the EM2C laboratory to study this solution. It has been designed to be representative of a real aviation engine and to reproduce its essential characteristics : a two-stage configuration, preheated air and liquid fuel are used. It nevertheless operates at atmospheric pressure and develops a high thermal power at the laboratory scale. The burner consists of two radial swirlers : the pilot stage in which the liquid fuel is injected in the form of a hollow cone, and the multipoint stage where the mixture of fuel and air is favored by a multipoint injection, thanks to ten jets of fuel injected transversely to the air flow. Experimental studies have shown the key role of the fuel distribution, and without modifying the power developed, the existence of a hysteresis cycle : several archetypes of flames can be stabilized, depending on the flow, spray or history of the flame. The objective of this thesis is to complete the experimental data and understanding of poor, premixed and pre-vaporized flame stabilization processes in staged burner using two-phase reactive large-eddy simulations. This numerical approach is applied to the BIMER bench with the AVBP code. Successive simulations, ranging from pure pilot injection to purely multipoint injection, and vice versa, have made it possible to trace the hysteresis cycle observed experimentally. An original tri-stable operating point was encountered numerically for fuel injection cases in the pilot stage alone, with three distinct flame shapes being observed for this single injection condition. The comparison to the experimental results for the operating points for which validation data are available shows a good agreement between the calculation and the experiment for different stages. An original analysis in the composition space shows the combustion regimes observed in these three cases, confirming the different stabilization scenarios. The two transitions of flame shapes observed experimentally are finally presented and analyzed.
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Benoit Cheneau. Étude numérique de la dynamique de combustion dans un brûleur diphasique turbulent à deux étages. Génie des procédés. Université Paris Saclay (COmUE), 2019. Français. ⟨NNT : 2019SACLC021⟩. ⟨tel-02882370⟩

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