Experimental investigation of the axial oxidizer injectors geometry on a 1-kN paraffin-fueled hybrid rocket motor

Abstract

The showerhead is the most common type of injector used in hybrid rocket motors due to its design and manufacture simplicity. The main drawback of the showerheads (SH) is the relatively low performance in terms of combustion efficiency because of the poor atomization of the liquid oxidizer. This study investigates the problem to enrich the technical literature by presenting detailed experimental data on showerhead injectors by a series of static firing tests using a 1-kN lab-scale hybrid rocket, applying four kinds of showerhead injectors, named SH1 (benchmark), SH2, SH3, and SH4. They differ from each other by the number, distribution, and dimension of the orifice elements. Main performance parameters such as fuel regression rate, specific impulse, and combustion efficiency are experimentally obtained.Two different series of tests were carried out. At first, the influence of SH injector geometries was studied. The injectors SH2, SH3, and SH4 were used under the same initial conditions, and the results were compared with SH1. In the second set of tests, the SH4 injector was chosen, and the effects of the fuel grain initial port diameter were investigated. Using the data obtained in the second battery of tests was possible to determine the influence of the fuel port diameter on the motor efficiency and establish the regression rate law of nitrous oxidizer/paraffin-based fuel for this specific configuration.