Radiation heat transfer in particle-laden gaseous flame: Flame acceleration and triggering detonation

Abstract

In this study we examine influence of the radiation heat transfer on the combustion regimes in the mixture, formed by suspension of fine inert particles in hydrogen gas. The gaseous phase is assumed to be transparent for the thermal radiation, while the radiant heat absorbed by the particles is then lost by conduction to the surrounding gas. The particles and gas ahead of the flame is assumed to be heated by radiation from the original flame. It is shown that the maximum temperature increase due to the radiation preheating becomes larger for a flame with lower velocity. For a flame with small enough velocity temperature of the radiation preheating may exceed the crossover temperature, so that the radiation heat transfer may become a dominant mechanism of the flame propagation. In the case of non-uniform distribution of particles, the temperature gradient formed due to the radiation preheating can initiate either deflagration or detonation ahead of the original flame via the Zel'dovich's gradient mechanism. The initiated combustion regime ignited in the preheat zone ahead of the flame depends on the radiation absorption length and on the steepness of the formed temperature gradient. Scenario of the detonation triggering via the temperature gradient mechanism formed due to the radiation preheating is plausible explanation of the transition to detonation in Supernovae Type Ia explosion.

Control of radiative heat transfer in high-temperature environments via radiative trapping—Part I: Theoretical analysis applied to pressurized oxy-combustion

“…The wall heat flux decreases accordingly based on Eq. (10). A comparison between the exact solution obtained by Eq.…”

“…Without appropriate control, the resulting heat flux would be well above the acceptable levels for reactor wall materials. Radiation from particles may also result in fast preheating of particles and gas, affecting ignition and flame propagation in premixed systems [10,11]. Thus, the thermal radiation in high temperature combustion systems involving particle-laden flows is of particular concern [2,3].…”

Multipoint radiation induced ignition of dust explosions: turbulent clustering of particles and increased transparency

“…where U f is the flame velocity, σT 4 b is the black-body radiative flux, ρ g is the mass density of gaseous mixture, c p and c v are specific heats of particles and gas phase, respectively [39]. The increase in temperature of the radiatively heated particles and gas mixture ahead of the flame depends on the time, L a /U f , required for the advancing flame to catch-up the radiatively heated particles ahead of the flame front.…”

“…Figures 1 and 2 show representative examples of the time evolution of the gas temperature and the corresponding increase of the flame velocity computed for the hydrogen-oxygen ( Figure 1), and methane-air ( Figure 2) flames propagating through the particle laden mixtures with uniformly distributed particles for the radiation absorption length, L a = 1 cm. The numerical simulations were performed in a way similar as it was done in [39,40] for a planar flame propagating in a particle-laden combustible gas mixture. The governing equations for the gaseous phase are the one-dimensional, time-dependent, multispecies reactive Navier-Stokes equations including the effects of compressibility, molecular diffusion, thermal conduction, viscosity and detailed chemical kinetics for the reactive species, production of radicals, energy release and heat transfer between the particles and the gas.…”

Mechanism of unconfined dust explosions: Turbulent clustering and radiation-induced ignition

“…As a flame propagates through a dust cloud of evenly dispersed particles it consumes the unburned fuel before the gas temperature will have risen to the ignition level, so radiation cannot become a dominant process of the heat transfer [13].…”