Research on the Effect of Bend Geometry on the Explosion Characteristics of Air–Light Hydrocarbon Mixing Gas in Pipelines

This study examines how pipe bends affect the explosion behavior of premixed air–light hydrocarbon mixtures. We aim to provide a basis for safer pipeline design and explosion risk reduction in industrial systems that include bends. We used a combined experimental and computational approach: high-fidelity explosion experiments together with large eddy simulation (LES). First, we conducted baseline tests in a straight pipe with premixed gases at different equivalence ratios to find the ratio that gives the highest peak explosion pressure. We then systematically varied the double-elbow configuration, testing seven complementary angle pairs: 30°/150°, 45°/135°, 60°/120°, 90°/90°, 120°/60°, 135°/45°, and 150°/30°. By tracking flame morphology, maximum overpressure, overpressure rise rate, and flame speed, we identified how bend geometry couples with explosion dynamics. The results show that bend angle strongly influences wall-induced compression, but the effect on peak overpressure is non-monotonic due to competing mechanisms: pressure wave reflection reinforces the flame at symmetric angles, while flow dissipation weakens it in highly asymmetric configurations. Peak overpressure reaches its highest value at the symmetric 90–90° arrangement, exceeding the straight-pipe baseline by 66%. However, the largest flame surface area and fastest propagation occur in configurations with large angle differences. The maximum pressure rise rate, by contrast, increases steadily with bend angle. Flame speed increases substantially in elbow configurations, driven by stronger turbulent mixing from flow separation and vortex shedding. The 150–30° and 90–90° configurations produce the highest speeds (~100 m/s), whereas the 30–150° arrangement yields a smaller enhancement due to weak initial turbulence. Downstream of the bend, flame morphology distorts significantly: both wrinkling intensity and total flame surface area grow with bend angle, which increases the reaction rate and overall explosion intensity. These findings offer quantitative guidance for optimizing explosion prevention, positioning ignition sources, and assessing risk in bent industrial piping.