Ignition mechanism and laws of explosion-driven thermal field and fuel dispersion flow

As an advanced form of conventional explosive energy, fuel mists react with ambient oxygen and can deliver high energy density. In fuel–air explosive (FAE) devices, the central detonation generates high pressure and high temperature: the former drives rapid fuel dispersion, whereas the latter can ignite the evolving fuel–air mixture during dispersion, leading to premature ignition and reduced effective cloud energy utilization. Premature ignition during dispersion involves strongly coupled unsteady processes, including flow, turbulence, heat and mass transfer, droplet-field evolution, and chemical reactions. In this study, numerical simulations together with experimental validation are employed to identify the critical conditions for premature ignition in a typical explosion-driven dispersion configuration and to elucidate the underlying physico-chemical mechanisms. The results show that ignition activity preferentially appears near the upper and lower ends of the device in the early stage, and then migrates toward the ±45° directions relative to the X-axis (defined as 0°) in the middle stage, consistent with the evolving temperature and mixing fields. For a 2 kg propylene-oxide FAE device, no premature-ignition occurs at a central charge ratio of 1.0%, whereas ratios of 2.0% or higher lead to sustained premature ignition. A central charge ratio of 1.5% is identified as the critical condition, with additional cases at 1.25% and 1.75% used to bracket this boundary. This critical boundary can be interpreted by an ignition-in-motion rate-competition criterion, Da = R_A/R_critical≈1; within the present single-step framework, the associated effective critical reaction-rate level is about 0.5 kgmol/m³s. The present results provide a baseline for the studied configuration under controlled ambient conditions. For a 2.0% central charge ratio, premature ignition initiates at the upper edge of the cloud, where the local fuel concentration is about 300 g/m³ and the explosion-driven temperature at the ignition site is about 1146 K. Novelty and significance statement Significance: Premature-ignition is a critical bottleneck limiting the energy efficiency of fuel-air explosive (FAE) systems. A fundamental understanding of this process is essential for optimizing FAE design to overcome incomplete energy release and maximize performance, providing a basis for developing more advanced energetic systems. Novelty: Moving beyond previous work limited to static parameters, this study reveals the fundamental cause of premature-ignition. It is the first to elucidate the dynamic, multi-field coupling between an evolving high-temperature field and a transient fuel cloud, establishing a previously unreported transient ignition mechanism.