Experimental and numerical investigations on the condensed combustion products of Mg-based solid fuels

Abstract

The exploration of condensed combustion products (CCPs) is essential to reveal the ignition, combustion, and infrared radiation mechanisms of Mg-based (Magnesium/polytetrafluoroethylene/Viton) solid fuels that have been considerably employed in the field of aerospace. Systematic experiments and numerical simulations are performed with the physicochemical properties (including morphology, element distribution, phase composition and particle size distribution) and flow field distribution characteristics of CCPs, respectively. The effects of formulation and pressure on the combustion behaviors of pyrotechnic compositions are thoroughly investigated based on thermal analysis measurements, laser ignition, optical diagnosis and CCPs collection. The results demonstrated that the major solid products for all cases are MgF2 agglomerates and MgO smoke oxide particles (SOPs). Increasing the Mg content in the formulation is simultaneously beneficial for the reduction of large agglomerates and SOPs. As the pressure is decreased from 0.1 MPa to 0.02 MPa, the volume weighted mean diameter of CCPs increases significantly due to the decrease in burning rate. The numerical model established in this paper better approximates the realistic combustion process by coupling the heterogeneous condensation reactions, and is adopted to predict the distribution of CCPs in the combustion flow field under different experimental conditions. Numerical results reveal that the MgF2 is mainly distributed in the anaerobic combustion core zone immediately above the burning surface, while MgO is located in the peripheral aerobic combustion diffusion zone. The negative pressure environment has more profound influence on the oxidation reaction of Mg than fluorination reaction. The scientific findings are expected to facilitate the development of more complete combustion and infrared radiation models, while theoretically providing in-depth guidance for the increasing military and civilian application of Mg-based solid fuels.