Experimental study on the overpressure variation and flame mode of premixed fuel-air deflagration in a semi-closed enclosure

Abstract

A small scale combustible gas venting explosion experimental system with a volume of 0.002 m3/0.0035 m3 was established, and the venting explosion experiments of ‘petroleum fuel vapor-air mixture’ under various vent sizes were conducted. The characteristics of overpressure and flame parameters under different vent sizes were obtained and the different venting modes were classified. The research results show that the overpressure history of petroleum fuel vapor/air mixture during the venting explosion process could be divided into four types, and four typical overpressure peaks induced by various phenomena were captured. With increasing venting coefficient Kv, the number of overpressure peaks decreases, but the value of overpressures gradually increases. When the value of Kv was relatively small (Kv ≤ 3.329) a ball or mushroom flame cloud was formed in the external field. When the value of Kv was comparatively large (4.560 ≤ Kv), a jet-like flame was formed in the external field. With the increase of the venting coefficient Kv, the internal maximum overpressure peak, the external maximum overpressure peak along vertical direction, the external flame height dimensionless number along the vertical direction and the external flame speed dimensionless number along the vertical direction showed an increasing trend, while the external flame diameter dimensionless number along the horizontal direction and the external flame speed dimensionless number along horizontal direction showed an decreasing trend. If treat ‘the least number of overpressure peaks’ and ‘the external explosion doesn’t occur’ as the ideal state of the venting explosion process, the vent opening needs to be set to ensure that 4.560 ≤ Kv ≤ 8.585.