Characteristics of water-base foam combustion

Abstract

Systematic experimental studies have been carried out to characterize the combustion of water-base foams with various hydrogen- and methane-air mixtures. The dependencies of the combustion wave speed (S) on the expansion ratio of foam (K), concentration of surface-active agent (SAA) in detergent solution, and bubble size of foam have been investigated. The combustion of foams with hydrogen mixtures has been established to be steady state. The effects of unsteadiness arising from combustion of methane foams are due to sound generation in the system and its interaction with the flame. The flame speed in foam with rapidly burning gas mixture has been demonstrated to decrease with decreasing expansion ratio and the foams with slowly burning mixtures have demonstrated to be a non-monotonic function of K, including an anomalous region of increasing flame speed with decreasing K. It has been demonstrated that the increase in both the SAA concentration in a detergent solution and the mean size of foam bubbles have no effect on the form of S(K) dependence but leads, however, to the increase in the flame speed values. The characteristics of foam combustion have been shown to be due to the effects of heat transfer from the gas to foammore » films and aerosol droplets forming upon destruction of foams by a flame front. Taking into account the interphase interaction provided the basis for derivation of a simple model of foam combustion and allowed to predict the flame speed dependences on the controlling parameters. The characteristics of combustion predicted by the model are in fair agreement with experimental data.« less