Effects of Vortex Flow Pancake Hybrid Rocket Engine Operating Parameters on Liquefying Fuel Combustion

Experimental results from the vortex flow pancake hybrid rocket engine implemented at the Space Propulsion Laboratory of Politecnico di Milano are presented. Paraffin-based fuels are tested under quasi-steady and forced transient operating conditions. This preliminary investigation shows a database of more than 30 firings with quasi-steady operating conditions, and 4 runs with oxidizer mass flow rate throttling. The three main engine operating parameters varied in the current research are: (i) the oxidizer mass flow rate, (ii) the combustion chamber height, and (iii) the oxidizer injection velocity. The latter parameter is altered by changing the number of injectors for the oxidizer inlet flow. Throttling is performed on selected fuel formulations. Under the investigated conditions, the quasi-steady tests showed a regression rate decrease for increasing reinforcing polymer mass fraction in the paraffin-based blends. Such a result is due to the augmented viscosity of the melt layer of the formulations as the reinforcing polymer mass fraction increases. At the same time, the regression rate showed no direct dependence on the initial combustion chamber height, while oxidizer injection velocity dependence was identified. Forced transient tests showed an immediate response to throttling for the two investigated fuels.