Effects of Al content and particle size on the combustion characteristic of hydrogen peroxide gel and micron-aluminum mixtures

As a novel green and high-performance propellants, H2O2/H2O/Al propellants have the potential to solve the pollution problem faced by composite solid propellants while maintaining high performance. However, the drawback that it cannot be ignited at a low oxidizer-to-fuel weight ratio (O/F) and a low pressure hinders its further development. Fortunately, this ignition defect was addressed by the mixture of hydrogen peroxide gel and micron-Al in our recent work. In this paper, the effects of Al content and particle size on the combustion characteristic of burning surface propagation and combustion products of the mixture were investigated. Combustion experiments were conducted in a windowed pressure vessel, using mixtures with three mixing ratios (fuel-lean, stoichiometric, and fuel-rich) and Al particle diameters between 1 and 12 mu m. The burning surface propagation was captured by a high-speed camera. The particle size distribution, component, and morphology of combustion products were characterized by laser particle size analyzer, X-ray powder diffraction, and scanning electron microscopy, respectively. And it is the first time that the combustion properties of H2O2/H2O/Al propellants (including H2O/Al propellants) are studied from the prospective of particle size distribution of combustion products. Results showed that with the decrease of Al content and the increase of particle diameter, the combustion intensity of the mixture decreased, resulting in the agglomeration of melted Al droplets on the burning surface. When the Al content was decreased to O/F = 1.7, Al particles in the mixture were no longer further oxidized in the process of combustion. When the Al particle diameter was increased to 7-10 mu m, burning rates of the mixture at O/F = 1.7-1.1 tended to be stable. The combustion of mixtures containing 3-7 mu m was kinetically controlled. From the prospective of variable burning rate and efficient combustion, the appropriate Al content in the mixture was O/F = 1.7-1.1, and the Al particle diameter should be kept within 1-7 mu m.