Ignition and combustion of [formula omitted] alloy particles in O 2 at high pressures

Abstract

The ignition and combustion of Al, Mg, and Al Mg alloy particles in 99% O 2 1% N 2 mixtures is investigated at high temperatures and pressures for rocket engine applications. The 20-μm particles contain 0, 5, 10, 20, 40, 60, 80, and 100 wt.% Mg alloyed with Al, and are ignited in oxygen using the reflected shock in a single-pulse shock tube near the endwall. Using this technique, the ignition delay and combustion times of the particles are measured at temperatures up to 3250 K as a function of Mg content for oxygen pressures of 8.5, 17, and 34 atm. An ignition model is developed that employs a simple lumped capacitance energy equation and temperature and pressure dependent particle and gas properties. Good agreement is achieved between the measured and predicted trends in the ignition delay times. For the particles investigated, the contribution of heterogeneous reaction to the heating of the particle is found to be significant at lower temperatures, but may be neglected at gas temperatures above 3000 K. As little as 10% Mg reduces the ignition delay time substantially at all pressures tested. The particle ignition delay times decrease with increasing Mg content, and this reduction becomes less pronounced as oxidizer temperature and pressure are increased.