Theory of Radiant and Hypergolic Ignition of Solid Propellants

Abstract

A model is formulated for radiant ignition of a solid propellant, accounting for in-depth absorption of radiation and surface reaction between solid fuel and gaseous oxidizer. Mathematical solutions are obtained in the limit of infinite absorption coefficient. From calculated surface temperature histories, several ignition criteria are compared. Conditions are established under which the choice of ignition criterion influences ignition time; it is shown that ignition times based on constant ignition temperature can be greatly in error at high heating rates. From the dimensionless parametric solutions, dependence of ignition time on oxidizer concentration, pressure and other quantities is extracted. At low pressures and equal solid and gas temperatures, oxidizer mass fraction and pressure affect ignition time only through their effect on oxidizer concentration, but at high pressure or under shock-tube ignition conditions, the additional effect of pressure on transport properties becomes increasingly important. Chemical kinetics constitute the principal factor determining ignition time, while oxidizer diffusion rate imposes a limit on attainment of ignition without significantly affecting ignition time.