Investigations on the droplet combustion of gelled mono-and bipropellants

Gelled propellants combine the advantages of solid propellants which do not pour out on leakages with that of liquid propellants which are pumpable and burn well-defined in sprays. There exist only few investigations on the influence of gelling agents on the burning behavior of single burning droplets especially when the droplet is freely moving in a hot atmosphere. The paper describes high-speed spectroscopic and cinematographic investigations on ignited moving gelled droplets of monopropellants under ambient conditions and contacting droplets of bipropellants hovering above a hot plate driven by the Leidenfrost effect. The monopropellants were pure nitromethane and nitromethane/hydrogen peroxide (90% purity) mixtures. Bipropellants consisted of a fuel component like nitromethane, aluminized JP-I, iso-octane and kerosene combined with an oxidizer like hydrogen peroxide, RFNA, high concentrated solutions of ammonium nitrate or ADN in water. Gelling agents were aerosol, guar gum and other mostly commercial chemical ingredients. The flame geometry was characterized using highspeed video and IR-camera techniques. To measure the distribution of temperature, gas components like water, CO2, CO, NO and hydrocarbons of the moving droplets highspeed NIR- and IR-spectrometers with up to 1000 scans per second were applied. The spectra series of a droplet passing the focal point were analyzed by fitting calculated spectra using the data of "NASA-handbook of IR-Radiation" to the experimental data. Local profiles of temperature and of concentration × path length that qualitatively agree well with thermodynamic and chemical kinetic calculations could be achieved by this method. The experimental findings were compared to a simple transient mathematical model describing diffusion controlled combustion of single droplets.