Nondestructive Mapping of Hybrid Rocket Fuel Grains

Abstract

The regression rates of solid fuels used in hybrid rocket motors are a critical parameter in the design and development of hybrid propulsion systems. Currently, it is difficult to measure fuel geometries accurately, thus causing difficulties in accurately describing regression rates, especially for smaller scale systems. Nondestructive techniques can solve this problem, as it is not necessary to get tooling into the ports. An apparatus that maps the fuel grain employing an immersed ultrasound transducer has been manufactured; its results will be the primary focus of this study. The full geometry of the fuel grains can be generated pre and post fire, which may lead to greater understanding of the way hybrid rocket fuels burn. Furthermore, previously undetectable defects, such as cracks and voids, may be identified. The study found that the method used to cast the fuel grains, spin casting causes thinning in wall thickness on average of 11.3% with a standard deviation of 1.2% from the end to the middle of the fuel grain. The generated data can further validate proposed analytical solutions (Cantwell, 2014) to the regression rate equations (Marxman and Gilbert, 1963) associated with hybrid rocket propulsion systems.

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