Combustion Characteristics of Aluminum–Water Gelled Composite Propellant

An experimental investigation was conducted to study the combustion characteristics of aluminum and water, gelled using polyacrylamide as gelling agent. These propellants were tested for burn rates and residue in a Crawford bomb. The present study used flakelike aluminum particles with large specific surface area (∼22.5 m2/g) called pyral. Burn rates and residue were measured for oxidizer-to-fuel ratios (O/F) of 0.8, 1, and 1.2. Gelled propellants prepared with pyral had a maximum burn rate of 7.5 mm/s at 60 bar pressure at an O/F of 0.8. However, these propellants had a very large residue of 70–80% of the initial mass. To overcome this, propellants were prepared with pyral, which was mechanically activated with polytetrafluoroethylene. The reduction in residue was mainly attributed to smaller thermal profile depth associated with mechanically activated aluminum and to the higher heat of combustion observed with such propellants. Through careful experimentation, the reason for the residue has been established to be due to heat loss from the sides of the propellant strand. The thermal conductivity and propellant diameter play a vital role in determining the heat loss from the condensed phase and in turn determining burn rates and residue.