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Home > About us > Media > Archived news > 2021 > Mhedine Alicherif defended his PhD "Study of the interaction between non-equilibrium plasmas and detonations : reduction of the cell size and the deflagration-to-detonation transition"
Mhedine Alicherif defended his PhD "Study of the interaction between non-equilibrium plasmas and detonations : reduction of the cell size and the deflagration-to-detonation transition"
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On November 30, 2021, Mhedine Alicherif defended his PhD "Study of the interaction between non-equilibrium plasmas and detonations : reduction of the cell size and the deflagration-to-detonation transition", supervisors Svetlana Starikovskaia (LPP) and Pierre Vidal (Institut Pprime).
Abstract
The thesis presents a study of the interaction between nanosecond non-equilibrium plasma and combustion waves in order to enhance detonability in gaseous mixtures. Two fields of physics with different characteristic times (nanosecond for plasma vs micro/millisecond for combustion) are linked. The aim is to demonstrate the causality between the pre-dissociation of a gas mixture by plasma action and the reduction of characteristic times and lengths of combustion reactions. The work is both experimental and numerical. After literature review on the interests of plasma for combustion. We summarize the basics of the detonation and deflagration phenomena, and the two definitions for detonability: (1) the capacity for a detonation wave to propagate under specific conditions of confinement and (2) the speed for a detonation wave to be established from a flame. The first is linked to the size of the detonation cell characterizing the intrinsic instability of the reaction zone. The second is linked to the length of the deflagration to detonation transition. We provide basic information on nanosecond non-equilibrium plasma and its effect on the dissociation of species in a gas mixture. We further suggest and test a kinetic scheme to understand the effect of plasma in a combustible mixture. The results are used as input parameters in a calculation of the chemical combustion length characterizing the detonation following the ZND model. We realize our experiments in squared- section detonation tubes. In the series of experiments dedicated to the detonation cell, we show that the application of a nanosecond plasma in front of an established detonation front decreases the detonation cell width by a factor 2 in H2:O2:Ar, H2:O2, CH4:H2:O2:Ar et CH4:O2:AR mixtures for initial pressure between 100 and 200 mbar. For the series of experiments dedicated to the DDT, we designed a plasma high-voltage electrode to ignite a deflagration wave. We compare the flame from the plasma ignition to the flame from a classical spark plug. The flame ignited by plasma achieves the detonation regime faster, for shorter distances and for lower pressure for H2:O2 mixtures and for pressure between 200 bar and 600 mbar. For both experiments we characterized the plasma and we particularly cared for the role of the initial pressure (deposited energy and homogeneity). We demonstrate a causality between plasma, induction time and detonability. The study improves the understanding of the role of nanosecond plasma to enhance combustion waves. It underlines the need to adapt plasma setups to detonation phenomenon.
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