Modeling the Energy Release and Burn Rate Characteristics of ZPP Based Initiators

Abstract

Bridge-wire initiators using zirconium potassium perchlorate (ZPP) as pyrotechnic are commonly found in the aerospace, defense, and automotive industries. To measure pyrotechnic output, it is common practice to discharge initiators into small isochoric test vessels and monitor the transient pressure response. The maximum pressures obtained in these tests are usually compared to values determined theoretically based upon a thermochemical analysis. However, an analytical prediction for the rate of pressure increase is problematic because a complete kinetic description of ZPP combustion is impractical; furthermore, the burn rate parameters for ZPP are not reported in the literature. In this research, a previous analytical model describing the energy release characteristic for THPP based initiators is applied to ZPP initiators. ZPP based initiators are discharged into 100 cm 3 test vessels filled with argon at initial pressures ranging between 1.72 and 22.4 MPa. From these experiments the total energy content of the ZPP formulation used in this work is determined to be 5600 J/g. Estimates for the burn rate parameters for ZPP are based upon an earlier model, termed the TPPM, originally developed to describe the transient pressure response of high pressure argon gas environments heated by burning THPP particles. To estimate the burn rate parameters for ZPP a quasi-analytical approach using the TPPM is presented. This approach assumes the initial pressure rise determined from experimental data is proportional to the initial burn frequency which is defined based upon Vielle’s Law. Results from this analysis yield a burn rate exponent (n) and burn rate parameter (A) of approximately 0.47 and 1.94 x 10 -3 cm/ms/MPa n , respectively. These values for the burn rate parameters are used as input in a previously developed model, termed the MTPPM, describing the transient pressure response of argon gas heated by burning pyrotechnic over a wide range of initial pressures. Predictions from the MTPPM using the burn rate parameters of ZPP determined in this research are shown to accurately replicate the measured transient pressures over all initial densities tested. Therefore, the method for predicting burn rate parameters developed in this work can potentially be applied to other pyrotechnic formulations.