The burning rate of hydroxylammonium nitrate-based liquid propellants

Abstract

To improve the understanding of the physical processes which occur during the combustion of liquid propellants (LP), a strand burner was used to study hydroxylammonium nitrate-based LP flames. From observations of the combustion of LP in such an arrangement, much has been deduced of the physical processes that occur during LP ignition and combustion. Combustion experiments were performed in which mixtures of the salts hydroxylammonium nitrate (HAN) and triethanolammonium nitrate (TEAN) in water were ignited by an electric discharge in a vessel at pressures of up to 30 MPa. The mixtures were contained in a strand burner that permitted visual observation of LP combustion at nearly constant pressure. Images of the combustion were obtained through windows, in the pressure vessel by backlit photography, at a framing rate of 60 frames per second, with an exposure time of 100 microseconds. These images clearly showed the movement of a liquid-gas interface and a bright flame during LP combustion. Results of experiments conducted during turbulent combustion are: (1) the combustion of HAN-based LP occurs in two stages in which the liquid phase decomposition of HAN is followed by the decomposition of TEAN, (2) the turbulent combustion rate of LP 1846 decreases with increasing pressure. This variation of apparent burning rate with pressure, a result which is not seen in single component propellant combustion, is attributed to changes in the stability of the liquid-gas interface with pressure, and (3) a model of the combustion of HAN-based liquid propellants as it occurs in bulk has been presented, showing the reaction sequence of the components of HAN-based liquid propellants.