Investigation on unconfined hydrogen cloud explosion with external turbulence

Fully understanding the coupling mechanism between the enhancement of explosion overpressure and flame acceleration is a prerequisite for assessing hydrogen cloud explosion overpressure. In this research, unconfined fan-stirred hydrogen explosion experiments were performed to study the effects of flame instability and external turbulence on flame propagation and overpressure characteristics. The results showed that the combination of the external turbulence and the flame instability could result in great flame acceleration and explosion overpressure enhancement. For the intensity of external turbulence considered in this study, the combustion regimes were all in the flamelet zone. With the increase of the external turbulence intensity, the flame gradually got accelerated, and the explosion overpressure got enhanced. A theoretical prediction model for the upper and lower limit of the maximum overpressure was proposed, which fully accounted for flame instability, external turbulence, and flame-induced turbulence. It provides a conservative evaluation for hydrogen cloud explosion. • Fan-stirred hydrogen explosion experiment was performed in unconfined cubic space. • Flame acceleration due to flame instability and external turbulence were analyzed. • Explosion characteristics with and without external turbulence were analyzed. • Theoretical prediction model of limit of peak explosion overpressure was proposed.