Controlling Parameters for Fuel Regression Rate of Swirling-oxidizer-flow-type Hybrid Rocket Engine

Abstract

In the swirling-oxidizer-flow-type hybrid rocket engine with front head injection, the local fuel regression rates at the leading edge of the grain were considerably larger than those in the real region. The regression rate behaviors in both regions could not be expressed by the conventional hybrid combustion formula using the oxidizer mass flux based on the grain port area. In this paper, the authors reviewed much of our experimental data on fuel regression rate behavior obtained previously and carried out additional experiments for polypropylene grain under the following various experimental conditions with the geometric swirl number for the gaseous oxygen injector of 19.4 and 32.3, a grain length of 600 and 1000 mm, an average oxygen mass flux Goave of up to about 200 kg/(m 2 -s), a combustion chamber pressure of up to about 4MPa, and a burning time of up to about 25 s. The review and the additional experiment showed that the local fuel regression rates were substantially independent of the grain port area in the leading edge region, but they depended on the area in the rear region. The parameters which determined the fuel regression rate were derived from the experimental findings; in the leading edge region of the grain, the fuel regression rates were controlled by the velocity of the swirling oxygen wall jet along the grain, that is, the oxygen mass flow rate and the swirl intensity of the oxygen injector. In the rear region, the modified oxygen mass flux of the grain port adding the tangential velocity component and the increase in the burning port was more appropriate for arranging the fuel regression rates.