气候变化导致森林火灾形势加剧, 存在危害生物多样性、威胁人类居住带等潜在风险, 防火和灭火工作责任重大。风力灭火机在中国复杂地形林火扑救工作中被广泛应用, 但在实际工作中存在发动机易过热问题, 导致风量减少, 燃烧抑制效率降低。因此, 该研究通过流体尺度自适应模拟(scale adaptive simulation, SAS)研究了高速空气射流与正庚烷池火相互作用时的气相燃烧抑制机制; 通过与大涡模拟的对比验证了SAS的可靠性, 克服了传统大涡模拟在网格分辨率上的限制, 成功模拟了火焰—气流的相互作用过程, 预测误差保持在±15%以内。参数研究结果表明, 射流速度是影响火焰抑制效果的主导因素, 射流可通过动能驱动可燃气体稀释, 导致流场不稳定化。当气流速率超过50 m/s时, 可在0.2 s内实现气相燃烧终止; 相比之下, 温度变化的影响可忽略不计。该研究结论可用于风力灭火机在实际森林灭火场景中的优化设计, 推进野火抑制策略的逐步完善。

Objective: Forest fires play a crucial role in the replacement of plant communities. However, climate change may significantly affect tree regeneration after severe wildfires, transform ecosystems and cause huge economic losses. Pneumatic fire extinguishers have become the primary portable firefighting equipment in China's mountainous and roadless regions due to their high mobility and simple operation. However, prolonged operation often leads to engine overheating, which reduces rotational speed, resulting in lower jet velocity, increased air outlet temperatures, and decreased firefighting efficiency. Extensive studies examine the interactions between air flow and gas-phase combustion, but mainly focus on the effects of ambient wind on pool fire combustion. The understanding of their dynamic mechanisms during engine overheating, which causes reduced air jet velocity and elevated air flow temperature, is still poorly understood. To address these gaps, this study numerically investigates the suppression effect of high-speed air jets from pneumatic fire extinguishers on gas-phase combustion, aiming to provide methodological references and data support for optimizing pneumatic fire extinguisher design and improving pneumatic firefighting strategies. Methods: This study employed the scale-adaptive simulation (SAS) turbulence model and eddy dissipation model to simulate the gas-phase combustion of n-heptane pool fires under the influence of air jets. The SAS turbulence model, based on the modifications of the k-L turbulence equation, blends the advantages of the Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulation (LES) models. It can dynamically adjust its turbulence length scale to balance the modeling and resolution of turbulence stress transport. In this study, the SAS turbulence model was used to simulate n-heptane pool fires in air jets. The oil pan height was increased by 100 mm to minimize the gap between the simulation and experimental results. The simulation of high-speed jet interaction with gas-phase combustion involves two methods: computational domain coupling of the pneumatic fire extinguisher and n-heptane combustion for data transfer, and boundary condition transfer from the fan outlet to serve as the jet inlet conditions in the n-heptane combustion computational domain. For computational efficiency, the second method was chosen. The stable n-heptane gas-phase combustion simulation results were used as the initial flow field, and the RANS results at the fan outlet (average velocity of approximately 80 m/s) were extracted and implanted into the interaction computational domain inlet. Results: The height increases of the oil pan improved model accuracy, keeping the SAS temperature error within an acceptable range. Results showed that high-speed airflow effectively suppressed gas-phase combustion. As the jet velocity increased, the flame shape underwent remarkable changes. At low velocities, the flame maintained a stable and continuous structure within a concentrated combustion area. However, as the velocity of the jet exceeded a certain threshold, it strongly impacted and disrupted the flame, which was stretched, distorted and ultimately extinguished. Furthermore, within the studied range, changes in the jet temperature had minimal impact on the gas-phase combustion of n-heptane. Regardless of the temperature, the flame structure and combustion efficiency remained similar at the same jet velocity. This is likely because physical dilution of the jet masks the sensitivity of the gas-phase combustion rate to the temperature. When the jet velocity dominates, minor temperature fluctuations cannot significantly alter the combustion process. Conclusions: This study presents a simulation approach for analyzing gas-phase combustion suppression of n-heptane pool fires using high-speed airflow. The key findings are as follows: (1) jet velocity is the dominant factor in flame suppression. As the velocity increases, the kinetic energy of a jet increases, effectively diluting combustible gases and disturbing the flow field. This hinders fuel-oxidizer mixing and leads to flame breakup and suppression. However, increased jet velocities may cause fuel splashing in actual firefighting, so an optimal jet velocity range needs to be determined. (2) Within the studied range, the jet temperature exerts minimal impact on combustion. At the same velocity, jets with different temperatures produce similar flame structures and efficiencies, thus indicating that temperature regulation is not critical for suppression under these conditions. (3) The SAS turbulence model is effective for simulating air jet-gas-phase combustion interactions as it balances computational accuracy and cost, outperforming the RANS and LES models. Thus, it is suitable for further firefighting simulation studies. Overall, this study provides simulation methods and data references for optimizing pneumatic fire extinguishers. Future studies should focus more on combustion suppression effects under complex conditions and refine simulation methods to better suit actual firefighting scenarios.