EVALUATION OF A LABORATORY-SCALE HYBRID ROCKET ENGINE'S PERFORMANCE

An investigation of the performance of Ryerson University's prototype laboratory-scale hybrid rocket engine is undertaken in the present study. The evaluation is primarily based on two experimental firings of this engine-one employing low-density polyethylene as the solid fuel and the other employing paraffin wax. Gaseous oxygen is the oxidizer in both cases. The principal test data collected are the firing's head-end pressure/time and thrust/time profiles. A cutaway view of the respective fuel grain at the end of the firing is also an important piece of experimental information. A quasi-steady internal ballistic simulation program is used to compare the predicted numerical results with the experimental test data in order to develop a better understanding of the engine's performance behavior. Factors such as fuel surface roughness, fuel decomposition temperature under non-combustive ablation (when beyond the nominal stoichiometric length limit), and burning fuel surface temperature are among the performance elements of interest that are incorporated into the simulation model and evaluated for their respective influence on the engine's performance. To some degree, the comparisons between the experimental and numerically predicted results indicate some qualitative agreement but less so in other respects. The main differences can likely be attributed to the following undesirable experimental factors: a non-constant, subsonic oxidizer delivery; an overly intense and prolonged ignition process (using steel wool positioned at the head end); and in the case of the paraffin engine firing, an inordinate propensity for the soft paraffin wax to be ejected uncombusted from the combustion chamber.