Self-sustained combustion propagation mechanism and critical thresholds of Al/PTFE composite under laser ignition

• Al/PTFE combustion shows three stages: ignition, surface spread, self-sustained. • Minimum ignition energy is theoretically derived as a criterion for reliable ignition. • Surface flame spread is driven by preferential heat diffusion and is validated experimentally. • A self-sustained combustion model reveals the key role of Al size and content. • Predicted threshold Al content agrees well with experimental data across sizes. In this study, a systematic experimental investigation and theoretical analysis are conducted on the self-sustained combustion process of Al/PTFE (aluminum/polytetrafluoroethylene) composite under laser ignition. The entire combustion process is divided into three stages: laser ignition, flame front propagation, and self-sustained combustion. First, the minimum ignition energy required for initiating combustion was theoretically derived, from which the critical parameters of laser power and irradiation duration ensuring reliable ignition were obtained. Second, the post-ignition flame spreading behavior on the specimen surface was analyzed. Theoretical derivation demonstrated that the surface heat spread exceeds the heat conduction rate into the material interior, leading to preferential and rapid surface propagation, this result was strongly consistent with experimental observations. Finally, a self-sustained combustion model describing the continuous combustion of the entire specimen from the surface to the interior was established. The model revealed the critical role of Al particle size and content in maintaining self-sustained combustion. Based on the model, the minimum Al content required for achieving self-sustained combustion at different particle sizes was predicted, and the predictions were validated by experimental data. This work provides a theoretical basis and predictive tool for the design and performance regulation of Al/PTFE reactive composites.