Fuel Regression Rate Behavior for Various Fuels in Swirling-Oxidizer-Flow-Type Hybrid Rocket Engines

Abstract

In order to clarify the overall and local fuel regression rate behavior of hybrid combustion in swirling oxidizer flow, burning tests of the swirling-oxidizer-flow-type hybrid rocket engine were conducted using PP , PMMA and WAX fuel grains. The experiments showed that for all fuels, the relation between the time-averaged overall fuel regression rate, over r& , and the intermediate oxygen mass flux, Goitm, was expressed by a conventional hybrid regression rate formula such as over r& = aGoitm n . The values of a and n differed according to the fuel type. The n values implied that the combustion in the PMMA grains occurred by the diffusion-limited combustion mechanism, and that the gas-phase reaction rate of PP was slower than that of PMMA. For PP grains, the n values at the grain leading edge were smaller than those at the rear grain region. While the local fuel regression rate, loc r& , at the rear region decreased slightly with increasing the burning time tb, loc r& at the leading edge was independent of tb. These results suggested that the combustion mechanisms at the leading edge and the rear region differed.