Evolution characteristics of deflagration wave system and flame acceleration effect of combustible gas in variable-caliber pipelines

Abstract

To understand the deflagration phenomenon of combustible gas in gas pipelines and improve the design of pipeline structural strength, this work adopted the self-developed experimental platform with a length of 12 m and a diameter of 90 mm to simulate the transportation process of urban variable-caliber gas pipelines. Experiments were conducted in a 9.5% methane/air premixed gas environment using a high-voltage ignition system, high-resolution data acquisition system, multiple piezoelectric sensors, fiber-optic flame speed sensors, ultra-high-speed laser schlieren system, and laser texture technology. The effects of blocking ratios of 0.4, 0.6, and 0.8 on the evolution characteristics of the deflagration wave system and the acceleration effect of combustible gas flames were comprehensively investigated. The blocking ratio was varied by placing an annular block somewhere along the pipeline. The results reveal that: (1) As the blocking ratio increased from 0 to 0.8, the pressure peak of the flow field did not appear near the ignition location. Comparing different blocking ratios, 0.4 blocking ratio had the maximum pressure, reaching 302 kPa, 0.6 blocking ratio reached the pressure peak position earliest, and the maximum pressure occurred at 83 times the cross-sectional diameter; (2) The blocking ratio of 0.6 had the most obvious effect on the flame acceleration, it could accelerate nearly three times within a range of 2 m, with a peak velocity of 130 m/s and an acceleration of 829 m/s2; (3) By identifying the laser schlieren image, the flame acceleration process and the coupling relationship between the reflected wave and the flame were able to be clearly understood, and the obtained flame speed was consistent with the measurement speed of the fiber optic sensors. The research results can provide a basis for urban variable-caliber gas pipeline accident prevention and structural design, and provide new ideas for re-understanding the gas deflagration mechanism.