The flow field behaviours of under-expansion jet flame in premixed hydrogen/air explosion venting

Abstract

The short chemical reaction time and high heat release of hydrogen fuel make a fine propulsion performance. Hydrogen is recognized as an excellent new resource. However, the inherent hazard of combustion and explosion should not be ignored. In this paper, the formation of the under-expansion jet flame (UEJF) of premixed hydrogen/air in explosion venting was simulated by ANSYS Fluent, and the wave system structures of the UEJF were systematically analyzed. The changes of pressure, Mach number, and main gas mass fraction distribution in the formation of the UEJF structures were described. The results indicated that the pressure difference at the outlet of explosion venting tube induced the intersection of expansion wave and reflected wave, and the formation of an obvious negative pressure area in the flow field. Meanwhile, alternating changes of the pressure in the jet center area propagated forward with the flame, resulting in the generation of UEJF. The fluxion of airflow at the outlet of explosion venting tube can be regarded as Prandtl-Meyer flow. The expansion angle was a positive correlation to the Mach number and the pressure ratio of the internal and external of the explosion venting tube. The distribution of H2O, O2, and –OH on the Mach disk revealed that the residual hydrogen reacted with O2 to produce secondary or multiple explosions. Therefore, the attention and research on the hazard of the under-expansion jet field should be strengthened.