Combustion of Hydroxylammonium Nitrate Based Monopropellants
“Green” monopropellants based on hydroxylammonium nitrate (HAN) are of interest for replacing highly toxic hydrazine in space propulsion systems and for other applications. Further, gelling such propellants may offer additional advantages such as the long-term stability of compositions with added energetic and catalytic particles in suspension. However, the combustion mechanisms of HAN-based monopropellants and the effect of gelling on their combustion characteristics are poorly understood. In the present work, combustion of an aqueous HAN/methanol solution (70.1 wt% HAN and 14.9 wt% methanol) was studied in a strand burner at nitrogen pressures up to 30 MPa. A version gelled with 1 wt% polyacrylamide was also studied under the same conditions. Thermogravimetric analysis, differential scanning calorimetry, and mass spectrometry were used to investigate the reaction mechanisms of both propellants. Combustion experiments of the ungelled mixture revealed an increase in the linear burning rate by over 50 % at 12 – 14 MPa, explained by reaching the critical pressure of the liquid. Other observed pressure dependencies of the burning rate include a decrease at 9 – 12 MPa, a plateau at 14 – 19 MPa, a decrease at 20 MPa, and an increase at 22 – 30 MPa. The strand burner studies further showed that gelling the propellant suppressed the multiple pressure regimes, with a consistent pressure exponent of 1.15 over the tested range of 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.
Mechanical engineering|Chemical engineering|Aerospace engineering
Ferguson, Robert Edwin, "Combustion of Hydroxylammonium Nitrate Based Monopropellants" (2021). ETD Collection for University of Texas, El Paso. AAI28714749.