A parametric numerical study of nanothermite pellet combustion under laser ablation and thermal nonequilibrium

Nanothermites are advanced energetic materials with a broad range of potential applications. The development of continuum-scale models for the combustion of consolidated nanothermite pellets is essential for practical utilization. However, comprehensive modeling approaches that accurately capture the relevant combustion phenomena remain limited. In particular, laser-induced ablation during ignition and thermal nonequilibrium among different phases can significantly influence both ignition delay and reaction-wave propagation, yet these factors are often neglected or insufficiently addressed. This work extends a state-of-the-art continuum-scale framework by incorporating a simplified ablation model and by introducing thermal nonequilibrium with two distinct couplings to the global reaction kinetics. Parametric investigations reveal that ablation notably delays ignition in low-porosity pellets; in contrast, the convective heat transfer that arises in high-porosity pellets compensates for ablation-induced heat loss, rendering ablation effects less critical in these cases. Further, depending on how the reaction kinetics couple to the solid or gas temperature, flame propagation may be predominantly driven by either conductive heat transfer (solid-phase dominated) or convective transport (gas-phase dominated). Particularly, the combined effects of superadiabatic heating and convection can lead to flame propagation speeds that are up to an order of magnitude higher, which may help explain part of the previously reported discrepancies between numerical predictions and experimental burn rates.