Combustion of Gelled HAN/Methanol/Water Propellants

Abstract

Monopropellants based on hydroxylammonium nitrate (HAN) are a low-toxic, high-performance alternative to hydrazine in space propulsion systems. Gelling such propellants may offer additional advantages such as the longterm stability of compositions with added energetic and catalytic particles in suspension. However, the effect of gelling on the combustion characteristics and mechanisms of HAN-based propellants is not well understood. In the present work, an aqueous HAN/methanol solution (70.1 wt% HAN and 14.9 wt% methanol) was gelled with 1 wt% polyacrylamide in an acoustic mixer. Combustion of the obtained gel was studied in a strand burner at nitrogen pressures up to 30 MPa. Thermogravimetric analysis, differential scanning calorimetry, and mass spectrometry were used to investigate the reaction mechanisms in the HAN/methanol/ water solutions with and without polyacrylamide. The strand burner tests have shown that gelling suppressed the multiple pressure regimes observed in previous studies of the HAN-based propellants, with a consistent pressure exponent of 1.15 � 0.05 over the tested pressure range 4-30 MPa. Thermoanalytical testing of the gelled mixture indicates there is no chemical interaction between the gellant and the HAN decomposition, and the effect of gelling on the combustion of HAN/methanol/water propellants is hydrodynamic in nature.