Concept of Unburning Ratio and Combustion Modeling of ZPP and BKNO₃ in Pyroshock-Reduced Separation Nut

Although BKNO₃ ignited by ZPP is commonly used as an explosive charge for many pyrotechnics, only a limited number of modeling studies can be found in the literature. Thus, recently proposed governing equations for combustion modeling of ZPP are supplemented to simulate the combustion of the BKNO₃ with ZPP. The combustion model was independently validated using CBT results with fixed volume chambers of various sizes. In this process, the concept of the unburning ratio was introduced to correlate the combustion modeling with actual phenomena. The term “unburned” means that some fraction of explosive charge turns into non-reactive solid rather than into combustion products. The model was then coupled with the equations of motion for the internal moving parts of a pyroshock-reduced separation nut. Tests with prototype were performed to validate the coupled model. For accurate verification, the pressure of the expansion chamber and annular chamber and the displacement of the bolt were measured and compared. All measurements are in good agreement with the analysis results obtained from the coupled model. The results validated the generality of the modeling approach for the simulation of the pyroshock-reduced separation nut.