Comportements dynamiques de la détonation dans des compositions gazeuses non-uniformes

Abstract : Our study is an experimental and numerical work on the dynamical behaviours of detonation waves in non-uniformly distributed premixed gases with composition gradients parallel to the direction of the detonation propagation. The study aims at improving the understanding of the complex phenomena involved in the combustion chambers of pulsed or rotating detonation engine (PDE, RDE) and after accidental leaks of fuels. We first remind the context of our study, the phenomenology of gaseous detonation and the previous works on detonation propagation in non-uniform compositions. We then describe the experimental set-up that we have designed in order to meet the constraint of a controlled generation of composition gradients in a 50⇥50 mm2 square-section, 665-mm length test chamber, and the diagnoses that we have implemented : oxygen probes, fast pressure transducers, carbon-sooted plates and ultrafast Schlieren and chemiluminescence spectroscopy. Next, we present the results of our experiments in mixtures of propane or ethane and oxygen with initial pressure and temperature 200 mbar and 290 K, respectively. We have considered monotonic distributions, with decreasing equivalence ratio, and non- monotonic distributions, with decreasing then increasing equivalence ratio. In the monotonic distributions, we have identified two types of detonation quenching, one sudden, with a shock-flame decoupling, for the steeper gradients, the other progressive, with a transition through marginal modes of detonation propagation, for the weaker gradients. We have proposed and validated criteria for detonation, based on the characteristic scales of the problem. We have demonstrated, for these monotonic distributions, the ability of numerical simulations with detailed schemes of chemical kinetics to represent our experimental observations, through a collaboration with Keio University. In the non-monotonic distributions, we have identified super-critical, critical and sub-critical behaviours, depending on whether the detonation is transmitted or not from the domain where the equivalence ratio decreases to that where it increases. In particular, we have identified the re-initiation conditions for a detonation that was quenched in the domain of decreasing equivalence ratio. Our study stresses the interest for future works to consider non-uniform distributions of mixtures comprising burnt gases and fresh reactants, and, consequently, non-uniform distributions of temperature. It also stresses the need for performing optical diagnoses and numerical capacities and for detailed schemes of chemical kinetics adapted to the high pressures and temperatures characterizing detonation dynamics.
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Stéphane Boulal. Comportements dynamiques de la détonation dans des compositions gazeuses non-uniformes. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2017. Français. ⟨NNT : 2017ESMA0004⟩. ⟨tel-01508647⟩

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