Opposed-flow Diffusion Flames Research Articles

Studies of Opposed Flow Diffusion Flames with Solid-gas Interface— I. Experimental Measurements of Ammonium Perchlorate-Hydrocarbon Systems

Abstract To examine the gas-kinetics parameters pertinent to the flame reactions of ammonium perchlorate (AP) based propellants we have employed the heterogeneous opposed flow diffusion flame (HOFD). In this combustion system a diffusion flame is formed in the stagnation region between a gaseous stream of fuel and an opposing stream of oxidizer originating at the solid surface of A P. With increasing fuel flux the steady-state mass flux of AP reaches a value at which the kinetics of reaction limit the consumption of reactants. This limiting condition provides information on the gas phase kinetic parameters of the combustion system. Both the composition of the solid oxidizer and the gaseous fuels were varied in ( The experimental studies. The effect of different catalysts and solid fuels on the burning rate characteristics of the solid phase were examined. A number of gaseous hydrocarbon fuels were used . Based on the results kinetic expressions are derived for the overall combustion progress in the diffusion flame of solid propellants based on AP.

Diffusion controlled combustion of polymers

A theoretical and experimental study of polymer combustion in an opposed flow diffusion flame (OFDF) is presented. An algebraic formula is derived, expressing the burning rate as a function of the fluid mechanic and thermodynamic variables. A polymer sample feed system has been developed which continuously positions the burning polymer surface within ±0.01 mm of a given set point, allowing accurate regression rate and detailed solid and gas phase flame structure measurements. Regression rate measurements of twelve commercial polymers as a function of oxygen concentration and oxidizer flowrate are reported. From these measurements and the theory, values of the Spalding transfer number, B , are derived and can serve as a useful flammability index for these materials. The OFDF technique also provides a quantitative method for evaluating the effectiveness of flame retardants. Solid and gas phase temperature profiles for charring and non-charring polymers under various oxygen concentrations and oxidizer flow conditions indicate markedly different chemical reaction mechanisms for charring and non-charring polymers.

A model relating extinction of the opposed-flow diffusion flame to reaction kinetics

A theoretical analysis is developed for the extinction of a homogeneous counterflow diffusion flame due to limitations in the reaction kinetics. With increasing mass flux of reactants into the diffusion flame a maximum in the consumption rate of fuel and oxidizer in the reaction zone occurs. The analysis shows that experimental measurements of the extinction conditions (“apparent flame strengths”) can be used to evaluate quantitatively such kinetic parameters as the overall activation energy, the pre-exponential Arrhenius term, and the order of reaction. The theoretical model is applied to the propane-oxygen-nitrogen system, for which an activation energy of 21 ± 2 kcal/mole is calculated on the basis of experimental flame extinction data.