Determination of the burning velocity of gas/dust hybrid mixtures

Abstract

Abstract The laminar flame speed is an essential input for Computational Fluid Dynamics simulation programs aiming to predict the effects of explosions. In this study, an approach to assess fundamental flame propagation properties from the analysis of the flame velocity as a function of its stretching and hydrodynamic instabilities was developed. A numerical tool was developed to analyse videos of propagating flames in order to estimate their unstretched burning velocities. Markstein’s theory, developed for gases and assuming a linear relation between the flame stretch and its speed, was then extended to dust clouds and hybrid mixtures of starch and methane. At first, the approach was validated with pure methane and was extended to pure starch and hybrid mixtures of both compounds. Finally, it appears that hybrid mixtures, especially when the gas concentration is greater than the lower explosive limit, can present a synergetic effect enabling faster flame propagation with regard to pure gas flames. Indeed, the stretching of a gas flame is strongly influenced by the addition of dusts. Nevertheless, for lower gas concentrations and larger dust concentrations called ‘dust-driven regime’, the presence of powders tends to limit the flame velocity to that of the less reactive compound, i.e. the dust.