Flame structures and burning rate characteristics of CMDB propellants

Abstract

Flame structures and burning rate characteristics of composite modified double-base (CMDB) propellants are studied by photographic observations and temperature profile measurements of the combustion zones. The oxidizers studied for CMDB propellants were various particle sizes and concentrations of AP (ammonium perchlorate) and HMX (cyclotetramethylene-tetranitramine), each of which has a different reaction scheme. AP particles decompose at the burning surface and diffuse into the decomposition gas of the DB (double-base propellant) matrix in the fizz and dark zones. The diffusing decomposition gases shift in equivalence ratio toward stoichiometric and produce an AP/DB luminous flame of increased reaction rate and flame temperature. Increased temperature gradient in the fizz zone and large temperature fluctuations in the dark zone were observed. The increased temperature gradient increases the heat feedback from the gas phase to the burning surface, and increases the burning rate. On the other hand, HMX particles in CMDB propellants gasify at the burning surface, but the flame structure and the temperature profile in the fizz and dark zones are not altered. The burning rate was slightly decreased by the addition of HMX. Based on the experimental observations, simplified burning rate models' were presented. The models describe fairly well the observed effects, of the concentration and particle size of oxidizers on burning rate characteristics.