Performance comparison between two different injector configurations in a hybrid rocket

Mass flux and pressure are usually considered the main parameters affecting the fuel regression rate in hybrid rockets, whereas the influence of the oxidiser injector is often neglected. Nevertheless, in some specific configurations, even in conventional hybrids, a noticeable dependence of regression rate on oxidiser injection modes has been found. Gaseous oxygen and polyethylene fuel cylindrical grains were burned. Results from the firing tests conducted with a conical axial injector of the oxidiser are discussed. That configuration provides highly stable combustion so it is considered very interesting and, hence, deserving of an in-depth analysis. A comparison to the results obtained with a radial injector is drawn in terms of average and instantaneous regression rate, fuel consumption profiles, and combustion efficiency and stability. The radial injector, at the same mass flux and pressure, produces lower regression rate, high pressure oscillations and worse combustion efficiency.