RADIATION-AUGMENTED COMBUSTION OF HOMOGENEOUS SOLIDS

The thermal effects of incident radiation on the burning characteristi cs of homogeneous solids are considered and the practical implications of these effects in solid rocket motors are assessed. The applicabili ty of the equivalence principle (equivalence between radiation and ini tial temperature) is investigated experimentally and analytically. Exp erimental steady burning rates asa function of initial temperature and mean radiant flux are presented for a fine ammonium perchlorate (AP) composite propellant which indicate that the equivalence principle is accurate to within experimental error. The equivalence principle is al so assessed analytically by considering the worst case conditions of c ondensed phase controlled burning. For deflagration and pyrolysis of s olids controlled by condensed phase reactions it is shown that a modif ica; tion of Ibiricu and Williams' high activation energy asymptotic b urning rate expression allows consideration of the effect of incident radiation on steady burning rate over a wide range of propellant opaci ties. Numerical simulations are used to verify this modification. Ther mal radiation from combustion gases in typical non-metalized solid roc ket motors is examined using band model calculations. These calculatio ns show that even pure molecular gas radiation (no particles) can reac h near blackbody levels for realistic motor conditions. The effects of thermal radiation on burning rate and temperature sensitivity are als o examined using the equivalence principle. It is shown that differenc es in burning rare and temperature sensitivity between motors and prop ellant strands which in the past have primarily been attributed to ero sive burning, could in some instances be due to thermal gas radiation. The implications of gas radiation on combustion stability are also di scussed. It is shown that radiation may have either a stabilizing or d estabilizing effect, according to the initial temperature dependence o f the temperature sensitivity sigma(p)-(T-0), although in most cases i t is a stabilizing influence.