Combustion Behavior of Solid Oxidizer/Gaseous Fuel Diffusion Flames

Abstract

The diffusion flame combustion behavior of several solid oxidizers (ammonium nitrate, phase-stabilized ammonium nitrate, ammonium perchlorate, and ammonium dinitramide) in combination with a hydrocarbon fuel (ethylene) was examined. The oxidizers were first analyzed by differential scanning calorimetry, thermal gravimetric analysis, and evolved gas analysis to gain an understanding of their basic decomposition characteristics. Next, an opposed flow burner was used to establish a diffusion flame between the decomposition products of the oxidizer(s) and the fuel. Regression rates of the solid oxidizer were measured by a linear variable displacement transducer as a function of fuel flow rate. Ammonium dinitramide demonstrated the highest linear regression rate characteristics by up to two orders of magnitude, followed by ammonium perchlorate, phase-stabilized ammonium nitrate, and finally ammonium nitrate. When comparing mass burning rates, ammonium perchlorate compares favorably to solid fuels such as hydroxyl-terminated polybutadiene. In addition, the flame zone(s) were imaged via high-speed photography to provide detailed information of flame characteristics. Flame imaging revealed large melt layers and boiling type behavior for ammonium nitrate and phase-stabilized ammonium nitrate as well as droplet ejection from the melt layer. The goal of this study was to gain an understanding of the fundamental combustion behavior of a diffusion flame between a solid oxidizer and a hydrocarbon fuel as a stepping-stone to more complex systems such as reverse hybrid rockets.