Combustion mechanisms of nitramine-based propellants with additives

Abstract

Propellants containing HMX and an energetic binder have a very pressure sensitive burning rate law. Modifications of the burning rate and of the pressure exponent may be obtained by adding lead salts or ammonium perchlorate (AP) to the propellant. In the first case, the additive effect is related to the possibility for the binder to produce efficient finely divided carbon near the combustion surface. In the second case, the effect results from an interaction between AP flame oxygen and binder flame products. This interaction is observed between 20 and 300 bars. Its importance depends on the AP particle size. In parallel with this experimental study, an interpretative combustion model has been developed. This model is based on a sequential combustion concept and allows one to correlate the experimental results and especially the dependence of the burning rate on the HMX mass ratio. Nomenclature A = pre-exponential factor cp = heat capacity D = diameter E = activation energy / = mass fraction M - mass NJ = number of particle of size / in a unit volume | Qc = heat balance in the condensed phase, cal/g rb = burning rate V = volume £ = volumic fraction p = specific mass 0 = heat flux transferred from gas to condensed phase Subscripts