Simulation of Deterrent Concentration Decrease at the Surface and its Spatial Concentration during Propellant Storage

摘要

Surface modification of the double base propellant grains is used to moderate their burning rate by application of coating agent (deterrent) which decreases the rate of this undesired process. Two important factors related to the deterrent presence have significant impact on the ballistic performance of the propellant: (i) the rate of decrease of the deterrent concentration on the propellant surface and (ii) the rate of its migration into the interior of the propellant grains. Both parameters continuously change during aging (propellant storage) what may significantly influence the period of time during which the ballistic requirements of propellants are fulfilled. As the determination of the deterrent concentration on the surface and its migration rate are often difficult, expensive and time-consuming, the development of the simulation tools of above processes seems to be of great importance. The present study presents the results of the simulation of deterrent (Dibutylphtalate) diffusion in double base propellant (K05810). The simulation was based on the experimental data in which the temperature dependence of the diffusion coefficients D was determined isothermally at three temperatures. The space concentration profiles C(x,t) of deterrent, used afterwards for calculation of the diffusion coefficient parameters expressed by Arrhenius-type dependence, were collected at 65, 70 and 75°C during 63, 27 and 14 days, respectively. After determination of the deterrent concentration decrease at the surface and the temperature dependence of the diffusion coefficient D, it was possible to simulate the deterrent spatial concentration in propellant under any, arbitrarily chosen temperature profile such as oscillatory temperature mode, real atmospheric temperature profiles or under temperature mode corresponding to atmospheric changes according to STANAG 2895 [1]. The simulations were done using the AKTS-SML software [2]. The described simulation method allows an accurate prediction of the shelf-life of propellants under any storage conditions.