Characterization of the Performance of Paraffin / LiAlH4 Solid Fuels in a Hybrid Rocket System

This investigation examined the burning characteristics of paraffin-based solid-fuel grains doped with various additive percentages (up to 28%) of lithium aluminum hydride (LiAlH4). In addition, the test sequence included examination of a paraffin-wax based fuel formulation containing 10% triethylaluminum and another formulation containing 10% diisobutylaluminum hydride. The fuel grains were cast into paper phenolic tubes and then tested in a cartridge-loaded hybrid rocket system. It was found that under similar test conditions, increased LiAlH4 additive increased the overall chamber pressure throughout the duration of the test, caused by an increase in the ratio of flame temperature to the molecular weight of the products. Due to deposits of unburned and unreacted fuel in downstream sections of the hybrid rocket motor, an accurate correlation between increased additive percentage and regression rate was not able to be found. It was determined that a new set of fuel grain formulations with changes to the overall fuel matrix (e.g., higher melting point wax) and/or changes to the energetic additive particles (e.g., reduced particle size) will allow for more accurate regression rate calculations and more favorable combustion characteristics. Despite the necessary modifications to the fuel formulations, the results from this series of tests showed that nearly all these solid-fuel formulations burned similarly. Qualitative comparisons of each type of fuel formulation proved to be a beneficial method for improving the solid-fuel formulations for future tests for hybrid rocket motor applications.