Numerical investigation and experimental validation of aluminized propellant combustion under high pressures: Critical effects of heat feedback

Abstract

Aluminum is a common metal fuel in propellants, but its effects on the burning rate and the underlying mechanism are still unclear. Numerical calculations and temperature measurement experiments were carried out within the pressure range of 0.1–9 MPa, and the effects of the pressure and the ammonium perchlorate (AP) particle size on the combustion characteristics of aluminized propellants were studied. First, based on a two-dimensional micro-scale combustion model of an AP/hydroxyl‑terminated polybutadiene (HTPB) propellant, by considering the “heat sink” effect of aluminum on the burning surface and the chemical reaction of aluminum in the gas phase, a numerical calculation model of heat flux coupled with the steady-state combustion of an aluminized propellant was established. The flame structure of an aluminized propellant obtained by this model conformed to the multi-flame structure and could correctly reflect the influence of the AP particle size and pressure on the burning rate and other combustion characteristics. Subsequently, the influence of radiation heat feedback was further introduced into the model, which greatly improved its accuracy in predicting the burning rate at low pressures of 1–3 MPa. More importantly, the temperature distributions of the propellants were measured using embedded tungsten–rhenium thermocouples, and the flame temperature was obtained by further processing the temperature measurement data according to the thermocouple response characteristics. The temperature measurement results showed that with the increase in the pressure and the decrease in the size of the AP particles, the temperature gradient increased significantly, the flame temperature increased slightly, and the burning rate of the propellant increased. By analyzing how the temperature gradient and the burning rate changed with pressure, it was found that the conduction heat feedback was important to determine the burning rate.