Combustion characteristics of AP/HTPB propellants with burning rate modifiers

Abstract

Fe2O3, copper chromite catalyst (CC), LiF, and CaCO3 are the four burning rate modifying additives considered in this study. A wide variety of subatmospheric flames are observed for the propellants with additives. Under subatmospheric pressures a dark zone is present; this zone becomes thicker at lower pressure and with finer ammonium perchlorate (AP) particles. A smoldering surface without a gas-phase flame is noted for the additive Fe2O3. From the smoke deposits, obtained from the subatmospheric burning of propellants with burning rate enhancers, it is shown that the breakdown of heavy fuel molecules is better with finer AP particles. The low-pressure deflagration limit is reduced by the addition of Fe2O3 or CC and increased by the addition of LiF or CaCO3. In the presence of LiF or CaCO3, above certain additive concentration levels, reduction in AP particle size is found to depress the burning rate further. LiF, below certain concentration levels, acts as a burning rate enhancer up to a certain pressure and as a depressant thereafter. The type of additive influences the pressure at which the shape of burning AP surface changes from convex to concave and also the pressure at which the AP surface recesses relative to the mean surface.