Explosion propagation in inert porous media

Abstract

Porous media are often used in flame arresters because of the high surface area to volume ratio that is required for flame quenching. However, if the flame is not quenched, the flow obstruction within the porous media can promote explosion escalation, which is a well-known phenomenon in obstacle-laden channels. There are many parallels between explosion propagation through porous media and obstacle-laden channels. In both cases, the obstructions play a duel role. On the one hand, the obstruction enhances explosion propagation through an early shear-driven turbulence production mechanism and then later by shock-flame interactions that occur from lead shock reflections. On the other hand, the presence of an obstruction can suppress explosion propagation through momentum and heat losses, which both impede the unburned gas flow and extract energy from the expanding combustion products. In obstacle-laden channels, there are well-defined propagation regimes that are easily distinguished by abrupt changes in velocity. In porous media, the propagation regimes are not as distinguishable. In porous media the entire flamefront is affected, and the effects of heat loss, turbulence and compressibility are smoothly blended over most of the propagation velocity range. At low subsonic propagation speeds, heat loss to the porous media dominates, whereas at higher supersonic speeds turbulence and compressibility are important. This blending of the important phenomena results in no clear transition in propagation mechanism that is characterized by an abrupt change in propagation velocity. This is especially true for propagation velocities above the speed of sound where many experiments performed with fuel-air mixtures show a smooth increase in the propagation velocity with mixture reactivity up to the theoretical detonation wave velocity.

Combustion wave propagation through a bank of cross-flow cylinders

“…Consideration must be taken for phenomena that are influenced by the smaller scale of the experiment, e.g., in the experiment the flame and detonation wave thickness is closer to the cylinder gap spacing, and flame instabilities could be suppressed due to the small gap spacing. The phenomenon observed in the experiment can also be considered a two-dimensional representation of explosion front propagation through a porous medium [17].…”

Effect of Metal Foam Mesh on Flame Propagation of Biomass-Derived Gas in a Half-Open Duct

“…The results show that aluminum silicate wool is a kind of fibrous porous material with a high specific surface area. Ciccarelli 29 found that explosion in porous media transmission channels and obstacles of explosion propagation have many similarities. On the one hand, the obstacles through the early shear-driven turbulence generation mechanism and then through the lead impact shock wave reflection flame interaction enhanced the explosion propagation.…”

Experimental Investigation of the Flame Propagation and Flashback Behavior of a Green Propellant Consisting of N2O and C2H4

“…(4) Quenching in circular ducts Spalding [35] made a few assumptions about the reaction behavior and calculated a critical Peclet of 60.5 for quenching in ducts, while Zel'dovich found the critical Peclet number to be approximately 65 [28]. For porous materials the critical Peclet number seems to be in a range of ± 50% regarding the theoretical value of 60.5 [36,37]. Despite the wide range of experimentally and numerically derived Peclet numbers, the quenching diameter generally scales with a characteristic flame length scale δ L .…”