Effect of vent burst pressure on the external overpressure behaviors and flame transients of vented petroleum fuel-air mixture explosion: Small-scale study

A small-scale vented explosion experimental apparatus (0.01 m3) was developed to study the external overpressure and flame dynamics of petroleum fuel-air mixture explosions under various static rupture pressures (PST = 0–100 kPa). Transient data acquisition systems and high-speed cameras were employed to capture the dynamic evolution of multi-directional overpressure and flame behaviors following vent cover rupture. Key parameters, including characteristic overpressure peaks, overpressure rise rates, flame morphology, flame front positions, and flame speeds, were systematically analyzed. The results revealed direction-dependent overpressure mechanisms: axial peaks significantly exceeded radial counterparts, with Δpb monotonically increasing with PST, while Δpun and Δpfv exhibited nonlinear trends due to unburned gas acceleration and flame-turbulence coupling. The overpressure peak induced by residual fuel combustion was exclusively observed in the axial far field. Flame morphology transitioned through three distinct regimes: small scale mushroom-shaped flames (PST = 0–10 kPa), large-scale mushroom-shaped flames (20–30 kPa), and axial jet-dominated flames (≥40 kPa). The Flame Development Dominance Number (FDDN) was used to quantitatively calculate the flame regime, and the results showed that FDDN = 1.0 is the boundary point between mushroom-shaped flames and jet-dominated flames. Spatial analysis demonstrated that directional disparities in overpressure and flame parameters gradually diminished with distance.