Equivalent mass-addition modeling of burning-surface thermal decomposition and numerical study of combustion characteristics of MTV pyrotechnic compositions

Magnesium/Teflon/Viton (MTV) pyrotechnic compositions lack reliable and generally applicable thermal decomposition parameters. Existing numerical simulations often simplify the burning surface using a prescribed velocity inlet, making it difficult to represent the release of mass, momentum, and energy. Therefore, this study proposes an experimental-data-based equivalent mass-addition model that represents burning-surface decomposition using mass, momentum, and energy source terms. The mass source term is constructed from an experimentally fitted burning-rate law, the momentum source term is derived using the near-surface gas density, and the energy source term is obtained through inverse enthalpy calibration. The fitted burning-rate correlation achieved an R ² of 0.9033 and an RMSE of 0.125 mm/s, while the predicted maximum combustion temperatures showed a maximum relative deviation of 2.72% from the experimental values . The validated model is subsequently applied to investigate the effects of flight altitude and Mg content on MTV combustion. Results show that increasing flight altitude suppresses thermal feedback from the burning surface and reduces the burning rate and flame height, whereas jet expansion under low-pressure conditions increases the flow velocity. Increasing Mg content weakens near-surface fluorination heat release and lowers the burning-surface temperature but enhances the burning rate and downstream oxidation heat release, producing burning-surface cooling, downstream heating, and flame elongation. MTV combustion exhibits a spatially partitioned reaction structure, with oxygen-free fluorination dominating near the burning surface and oxygen-involved oxidation dominating farther downstream. Flight altitude and Mg content regulate this spatial competition through environmental and intrinsic formulation effects, respectively, thereby shaping the combustion flow field and product distribution. This study provides an experimentally calibrated equivalent source-term framework for simulating coupled heat and mass transfer in MTV pyrotechnic combustion under sub-atmospheric conditions.