Interactions turbulence-combustion lors des explosions de mélanges hybrides vapeurs/poussières - Combustion-turbulence interactions in hybrid mixtures flames - Université de Lorraine Access content directly
Journal Articles Récents Progrès en Génie des Procédés Year : 2011

Interactions turbulence-combustion lors des explosions de mélanges hybrides vapeurs/poussières - Combustion-turbulence interactions in hybrid mixtures flames

Abstract

Gas/dust explosions have been studied for years, but very few researches have been carried out on the hydrodynamic behavior of such flames. However, recently, the specific behaviors of such mixtures as regard to their ignition sensitivity and explosion severity have been demonstrated. Experiments have shown that concentration of gas/vapours as low as 1% vol. causes a significant decrease of the minimum ignition energy and induces changes in the rate-limiting step of the combustion reaction. They also confirmed that a hybrid mixture explosion is possible even when both dust and vapour concentrations are respectively lower than their minimum explosion concentration and lower explosivity limit. Addition of small amounts of gaseous compounds has also a strong effect on the explosion severity and could lead to explosivities of hybrid mixtures, which could be greater than those of the pure compounds themselves. This work also focuses on the effect of combustion/turbulence interactions on the flame propagation in hybrid mixtures. As regard to gaseous mixtures, the presence of particles strongly modifies the turbulence level, bringing new hydrodynamic instabilities. The impact of flame stretching on the flame velocity has also been studied. Two parameters of hybrid mixtures methane/wheat starch and hexane/sunflower oilcakes have notably been determined for: S u °, the fundamental unstretched burning velocity (ranging between 22 and 36 cm.s-1) and L, the Markstein length (from 0.2 to 1.9 mm). This study allows the determination of specific means of prevention and protection for such mixtures.
De nombreuses études ont été entreprises sur les explosions de poussière alors que les travaux concernant les explosions de mélanges solide/gaz ou vapeur (mélanges hybrides) sont plus rares. Nos expériences ont montré d'une part que l'explosion d'un mélange hybride est possible même quand la concentration en poudre et la concentration en vapeur sont respectivement inférieures à la concentration minimale explosive (CME) et à la limite inférieure explosive (LIE), et d'autre part, que les mélanges hybrides peuvent avoir une sensibilité à l'inflammation très élevée comparée à celle de la poussière seule. De même la sévérité des explosions peut être exacerbée en présence de mélanges hybrides en particulier pour ce qui est de la vitesse maximale d'accroissement de la pression. Si la détermination des paramètres de sévérité reste empirique et imprécise, une autre approche plus fondamentale basée sur l'analyse des vitesses de flamme est néanmoins possible. Les effets de la courbure et de l'étirement sur la structure du front de flamme, et donc sur sa vitesse de propagation, ont été étudiés expérimentalement en exploitant les images obtenues à l'aide d'une caméra à haute définition. Deux grandeurs caractéristiques des mélanges méthane/amidon et hexane/tournesol ont donc été déterminées : S u °, la vitesse fondamentale à étirement nul (comprise entre 22 et 36 cm.s-1) et L, la longueur de Markstein (entre 0,2 et 1,9 mm). Ces tests permettent de comparer les stabilités des flammes de mélanges hybrides par rapport à celles des composés purs et démontrent leur comportement particulier. Ils soulignent aussi la nécessité d'utiliser des moyens de prévention et de protection spécifiques pour ce type de mélanges et de les dimensionner. Mots-clés : Mélange hybride, explosions de poussières, étirement, longueur de Markstein. Abstract Gas/dust explosions have been studied for years, but very few researches have been carried out on the hydrodynamic behavior of such flames. However, recently, the specific behaviors of such mixtures as regard to their ignition sensitivity and explosion severity have been demonstrated. Experiments have shown that concentration of gas/vapours as low as 1% vol. causes a significant decrease of the minimum ignition energy and induces changes in the rate-limiting step of the combustion reaction. They also confirmed that a hybrid mixture explosion is possible even when both dust and vapour concentrations are respectively lower than their minimum explosion concentration and lower explosivity limit. Addition of small amounts of gaseous compounds has also a strong effect on the explosion severity and could lead to explosivities of hybrid mixtures, which could be greater than those of the pure compounds themselves. This work also focuses on the effect of combustion/turbulence interactions on the flame propagation in hybrid mixtures. As regard to gaseous mixtures, the presence of particles strongly modifies the turbulence level, bringing new hydrodynamic instabilities. The impact of flame stretching on the flame velocity has also been studied. Two parameters of hybrid mixtures methane/wheat starch and hexane/sunflower oilcakes have notably been determined for: S u °, the fundamental unstretched burning velocity (ranging between 22 and 36 cm.s-1) and L, the Markstein length (from 0.2 to 1.9 mm). This study allows the determination of specific means of prevention and protection for such mixtures.
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Dates and versions

hal-01925947 , version 1 (18-11-2018)

Identifiers

  • HAL Id : hal-01925947 , version 1

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Khalili Imad, Dufaud Olivier, Perrin Laurent, Nicolas Cuervo, Laurent André. Interactions turbulence-combustion lors des explosions de mélanges hybrides vapeurs/poussières - Combustion-turbulence interactions in hybrid mixtures flames. Récents Progrès en Génie des Procédés, 2011, pp.1-6. ⟨hal-01925947⟩
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