Hydrogen leakage from hydrogen-powered trains in tunnels can create severe deflagration hazards if ignited. Although hydrogen deflagration behavior in confined spaces has been studied, flame propagation and deflagration characteristics of non-uniformly premixed hydrogen in train-in-tunnel scenarios remain insufficiently understood. Based on a 1:70 reduced-scale model, experiments investigate the flame propagation and deflagration characteristics of non-uniformly premixed hydrogen under different relative ignition delays ( Δt ), ignition positions, and carriage numbers. The results indicated that increasing Δt weakened flame propagation and pressure response, with the strongest attenuation occurring at small Δt . For a fixed amount of hydrogen released in a tunnel, a greater dispersion distance/time generally causes a lower average hydrogen concentration, thereby reducing deflagration severity. Additional carriages enhanced obstacle-induced acceleration within the tested configuration. Pressure response showed a clear downstream accumulation along flame propagation direction. These findings provide trend-level experimental evidence for understanding hydrogen deflagration hazards in rail transit systems.
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Wu et al. (2026) studied this question.
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