Abstract

THEBA, R; VEALE, KL  and  BEMONT, CP. Development of a combustion visualisation hybrid rocket motor. R&D j. (Matieland, Online) [online]. 2017, vol.33, pp.97-104. ISSN 2309-8988.

The Phoenix Hybrid Sounding Rocket Programme in the University of KwaZulu-Natal's Mechanical Engineering department has so far only utilised pure paraffin wax and nitrous oxide as the propellant combination in their hybrid rockets. Knowledge of regression rate behaviour is required for the design and performance characterisation of hybrid rocket propulsion systems. The regression rate is the rate at which the fuel recedes in the direction perpendicular to the burning fuel surface. A hybrid slab motor was purpose designed for regression rate analysis. Optimum oxidiser-to-fuel (O/F) ratios obtained from literature and NASA CEA were used with interpolation to define the fuel grain dimensions, and the oxidiser and fuel mass flow rates. The slab motor, with windows for direct regression rate visualisation, was designed based on these parameters. It was manufactured from a combination of brass and stainless steel for structural rigidity, thermal properties and material compatibility with nitrous oxide. The design also includes a compact feed system used to supercharge the nitrous oxide run tank, while minimising pressure losses. The motor was designed to accommodate both pure and aluminised fuel grains. From literature, aluminium additives in the fuel have been shown to increase the regression rate of the system. Different regression rate measurement techniques, discussed in this paper, will be implemented to obtain the relevant data. These include visualisation of the regression process and obtaining the mass flow rate data over the burn time. The pre and post combustion grain volumes will also be significant here in order to calculate the regression rate. The regression rate data obtainedfrom these investigations are imperative in the improvement of future launch vehicles in the Phoenix Programme.

Keywords : Metallised; Aluminised; O/F ratio; Paraffin wax; Regression rate.

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