Thermal Response and Heat Transfer–Reaction Coupling of HNS Small-Scale Charges during Programmed-Heating Cook-off

Programmed-heating cook-off tests and numerical simulations were conducted to investigate the thermal response of HNS small-scale charges under the coupled effects of charge size, heating rate, and density. The investigated conditions included charge dimensions of Φ 4×4 mm, Φ 5×4 mm, and Φ 5×5 mm, heating rates of 0.5–10.0 K·min -1 , and relative loading densities of 80%–92% TMD. The size and heating-rate effects were examined at a baseline density of 92% TMD, while the density effect was evaluated for Φ 5×4 mm charges at a heating rate of 2.0 K·min -1 .The results show that the ignition temperature increases with heating rate and, at a given heating rate, also increases with charge size. Under fixed charge size and heating rate, the ignition temperature shows a slight increase with increasing density. Kissinger analysis indicates that the Φ 4×4 mm charge is less affected by internal heat transfer, whereas the apparent kinetic parameters of larger charges increase markedly, suggesting a stronger influence of heat transfer-reaction coupling. The numerical model reproduces the measured outer-wall temperature-time curves well and shows that the thermal response evolves through two stages: an early stage dominated by external heat transfer and a later stage with increasing self-heating. Increasing charge size enhances internal thermal lag and raises the pre-ignition central temperature. Increasing density improves early-stage heat transfer but also raises the pre-ignition central temperature in the later stage. These results demonstrate that, within the investigated parameter ranges, the apparent ignition behavior of HNS small-scale charges is governed by the coupled effects of heat transfer and chemical reaction.