Instantaneous Regression Rate Determination of a Cylindrical X-Ray Transparent Hybrid Rocket Motor

Abstract

The determination of the solid fuel regression rate is one of the key steps in hybrid rocket combustion studies. Historically, there is lack of direct regression rate measurements for validation of theoretical models. In practice most mass-burning rates were determined by the net burned mass divided by the test duration that yields an average rate. However, this method does not capture the instantaneous regression behavior. To achieve this, a newly designed X-Ray Transparent Center-perforated (XTC) hybrid rocket motor system has been fabricated and tested to provide the ability to measure the instantaneous solid fuel regression rate using a high-powered real-time X-ray radiography system. Tests have been conducted using hydroxyl-terminated polybutadiene (HTPB) as the baseline solid-fuel formulation. The solid-fuel regression rate can be enhanced by the addition of energetic metal powders. Tests have been conducted using a 13% Silberline aluminum flakes solid fuel formulation in order to evaluate a metalized fuel with the X-ray radiography system. The capability of the visual analysis system to capture instantaneous X-ray radiography images has been demonstrated. Time variations of port dimensions have shown good comparison with calculated regression results from developed numerical code. Differences in recovered fuel burning surfaces were observed from SEM photographs. Large surface roughness, exhibited on the burned surfaces of fuels containing nano-sized aluminum particles, indicates high potential for introducing stronger heat feedback to substrate of solid-fuel and enhance burning rate.