The effect of pressure and oxygen concentration on the ignition and combustion of aluminum-magnesium fuel-rich propellant

In order to better understand how future candidate solid propellants may affect combustion characteristics in ramjet motor, the aluminum-magnesium fuel-rich propellant was tested on a sealed high-pressure laser ignition platform. The laser ignition experimental device was designed and built, then the ignition and combustion characteristics of aluminum-magnesium fuel-rich propellant under different pressures and oxygen concentrations in environment gas were studied. The comprehensive impacts of pressure and oxygen concentration on ignition delay time and burning rate were appraised. The results displayed that the ignition delay time was decreased with the increase of pressure and oxygen concentration. The effect of pressure on ignition delay time was weaker than oxygen concentration. The impact of oxygen concentration on ignition was very complex. When the oxygen concentration of environment gas was less than that of the oxidizing gas from the propellant pyrolysis products, the ignition gas phase reaction occurred in the dispersion region of the solid propellant pyrolysis product, the initial flame was close to the propellant surface. In contrast, when the oxygen concentration was larger than the pyrolysis oxidizing gas, the ignition gas phase reaction occurred in the diffusion zone of the propellant pyrolysis products and the environment gas, the initial flame appeared far from the propellant surface. The burning rate of aluminum-magnesium fuel-rich propellant increased with the increase of pressure and oxygen concentration, where their effect on burning rate is accord with B-number theory. Comparing the experimental measurements with an analytical model, the results showed good consistency. The function of oxygen concentration and pressure could explain the effect on burning rate and ignition delay time, because pressure and oxygen concentration were favorable for the heat transfer, radiation and convection from the flame. The function of the combined influences of pressure and oxygen concentration on burning rate was established by a power law fitting. The good fitting is consistent with the experimental measurements, and shows that the scaling is valid for a full range of pressure and oxygen concentration tests to predict burning rate.