Effects of gas concentration and obstacle location on overpressure and flame propagation characteristics of hydrocarbon fuel-air explosion in a semi-confined pipe

Abstract

Experiments were conducted in a semi-confined pipe to investigate the effects of obstacle location and gasoline vapor concentration on gasoline-air fuel explosions. The variations of internal overpressure, external overpressure, flame propagation and flame-overpressure coupling relationship were analyzed. The results showed that the internal overpressure histories existed three obvious peaks, and when the obstacle location was set at 0.4 m, the maximum absolute values of overpressure (pmax and pneg), overpressure rise rates ((dp/dt)ave and (dp/dt)max) and the deflagration index (KG) were obtained. Additionally, more than two positive overpressure peaks were observed in the external overpressure histories. The maximum values of external overpressures and overpressure rise rates were obtained at the obstacle location of 0.4 m. For the fuel concentrations of 1.3%, 1.7% and 2.1%, the shortest time to reach pmax appeared at the obstacle location of 0.4 m, 0.2 m and 0.6 m, respectively, while the shortest time to reach (dp/dt)max and the maximum flame propagation speed were obtained for all the fuel concentrations at the obstacle location of 0.2 m. Moreover, a coupling relationship between overpressure and flame propagation was found. It could be deduced that the formation of the positive overpressure peak of the external overpressure might be directly related to the gas explosion inside the pipe and the flow jet caused by the high-speed flame propagation, rather than the external explosion (or secondary explosion) out of the pipe. These results improve our understanding on gas explosion dynamics in a semi-confined space.