OPTIMISATION OF PROCESSING CONDITIONS FOR GEL PROPELLANT PRODUCTION

Abstract

The work of the authors is directed to the most prominent problems concerning production of propellant gels. The main effects on production (gelator concentration, dissolver rotational speed, heating and cooling times, etc.) of hydrocarbon gels are discussed in detail. The experiments were done with 250 ml amounts of Jet A-1 / Thixcin R® gels in a small laboratory dissolver facility. Thixcin R (a ricinolic acid derivative) was chosen as gelator because in comparison to silica or bentonite gellants, it is a combustible organic material and would not change the energy content of the fuel very much. For characterisation and quality control of the gels most of the experiments were done with a double-barrel capillary viscosimeter. The reason for using this instrument instead of a rotational viscosimeter is that the shear rates necessary for gel atomisation in a rocket injector are much higher (> 105/s) than in rotational viscosimeters which have been used by many other authors. Also measurement of extensional viscosity, which plays an important but often ignored role in atomisation, was achieved with this instrument. Several test series were conducted in the laboratory facility. Variation of production temperature within the range of 40 to 60°C showed that the best results could be achieved by keeping the temperature at 50°C. In another test series, the concentration of gelator was varied in the range of 4 to 7% by weight. The results show that at least gelator concentrations of more than 5% and dissolver rotational velocities of 1000 rpm are necessary to get stable gels. The influence of mixing time was investigated in another test series. The results demonstrate that a mixing time not longer than 2.5 hours is sufficient for completion of gel formation. The experiments should be considered as a first step to optimisation of the gel production process.