Feasibility Study of Paraffin-Based Fuels for Hybrid Rocket Engine Applications

This paper describes a combined analysis performed in pure waxes and paraffin-based mixtures that can be used as solid fuels in hybrid rocket engines. Density measurements of pure waxes were performed using a dilatometer. An experimental facility was set up and, after preliminary measurements and calibration, a repeatable procedure was implemented. The implemented instrumentation setup allowed the measure of density in softening and melting intervals. Mechanical uniaxial tensile tests were performed according to Standard ISO 527-1 on pure macro paraffin and microcrystalline wax and on these waxes doped with stearic acid and graphite; elastic modulus, elongation and maximum stress were calculated. Data indicate that ductile rupture is achievable even on pure tested macro paraffin. Moreover, microcrystalline wax was mixed with a synthetic wax characterized by a higher nominal melting temperature in order to improve the softening point up to higher temperatures without compromising regression rate values. Thermal, rheological, viscosimetric, and ballistic experiments were performed on this new fuel formulation. This new formulation is promising for propulsion applications in wide temperature ranges.