Development of laboratory-scale gel propulsion technology

Selected gel propellants and simulants were formulated, prepared, rheologically characterized, and tested in the first phase of a program to develop gel-propulsion technology infrastructure. Hydrazine-based fuels, gelled with polysaccharides, were characterized as shear-thinning pseudoplastic fluids with low-shear yield stress (τ y i e l d ), whereas inhibited red-fuming nitric acid (IRFNA) and hydrogen peroxide oxidizers, gelled with silica, were characterized as yield thixotropic fluids with significant τ y i e l d . Safe storage and handling procedures were established. A laboratory-scale experimental setup was used to hot fire successfully a small 100-N nominal thrust rocket engine with selected hypergolic neat-liquid and gelled bipropellant combinations. One-element pentad-type injectors were utilized in the tests to inject the propellants into the combustion chamber. Continuous tests of up to 25-s firing duration and multipulse operations of up to 20 cycles of 0.1-s on/0.5-s off were successfully conducted with gelled-hydrazine/IRFNA bipropellants. Neat-liquid and gelled mono-methyl hydrazine/IRFNA bipropellants were also tested. The combustion pressure ranged between 20 and 35 bars. Experimental characteristic velocity, c* e x p , was determined as a function of the oxidizer-to-fuel (O/F) mass flow rate ratio. Maximum c* efficiency of more than 95 and about 90% was obtained in continuous firings for the neat-liquid and gelled hydrazine/IRFNA, respectively. In both cases, the maximum c* e x p values were obtained at higher O/F ratios than those that yield maximum theoretical c*.