On The Influence of Gradient Transports Upon The Burning Velocities of Dust Flames

Abstract

Combining numerics and asymptotic methods in the limit of targe Boltzmann and Zel' (Ze) numbers, we study how the burning speed (U) of rich, adiabaiic dust-flames is aflected by gradient (e.g. turbulent-) transport of heat and species. Depending on the gradient-to-radiative diffusivily ratio η (a Planck number) evaluated in the high-temperature region, two asymptotic regimes are identified and analyzed. η=0(Ze⁻) leads to u(η)ges;u(0), due to reactant spreading by diffusion, whereas η=o(1) and large enough ultimately yields the opposite trend, due to enhanced overall conductive effects. An analytical composite expression of u(η,Ze)which encompasses both effects is provided and allows one to estimate the minimum burning speed; the latter decreases with Ze increasing.

Keywords:

• Flame speed
• two-phase combustion
• radiative transfer
• turbulent transport

Additional information

Notes on contributors

GUY JOULIN

Author to whom the correspondence should be addressed.