Effects of particle size and mixture composition on propulsive performance of gelled and refrigerated aluminum-liquid oxidizer propellants

Abstract

The propulsive performance of aluminum-liquid oxidizer mixtures is studied using an Eulerian-Eulerian multiphase Computational Fluid Dynamics model. The simulations are performed to capture the high-speed multiphase flow dynamics in a lab-scale rocket motor and predict the propulsive performance parameters. The focus of the study is to examine the effects of particle size and mixture composition on key performance parameters such as chamber pressure, thrust, characteristic velocity, and specific impulse. For nano-aluminum and water propellants, the chamber pressure and thrust increase significantly with decreasing particle diameter; a dp^-1.6 correlation is observed. The specific impulse increases with decreasing particle size due to the reduction in two-phase flow losses. However, when the particle size is decreased below 50 nm, a reduction in the specific impulse is observed due to the increase in the oxide content in the particles. The effect of mixture composition is studied by varying the equivalence ratio and H2O2 concentration in the oxidizer. Decreasing the equivalence ratio from 0.943 to 0.71 and increasing the H2O2 concentration in the oxidizer from 0 to 25 % increased the peak chamber pressure and peak thrust due to the increase in the propellant burning rates. However, the characteristic velocity and specific impulse are not as strongly affected. Modifying the pH of water also increases the peak chamber pressure and peak thrust without altering the specific impulse significantly. Overall, the computed specific impulses are in the range of 130-175 s, substantially lower than the ideal theoretical specific impulse, thereby highlighting excessive two-phase flow losses for these propellants.