Shock-induced ignition of hydrogen gas during accidental or technical opening of high-pressure tanks

This paper is devoted to the numerical and experimental investigation of hydrogen self-ignition as a result of the formation of a primary shock wave in front of a cold expanding hydrogen gas jet. Temperature increase, as a result of this shock wave, leads to the ignition of the hydrogen–air mixture formed on the contact surface. The required condition for hydrogen self-ignition is to maintain the high temperature in the area for a time long enough for hydrogen and air to mix and inflammation to take place.

Calculations of the self-ignition of a hydrogen jet are based on a physicochemical model involving the gas-dynamic transport of a viscous gas, the kinetics of hydrogen oxidation, the multi-component diffusion, and the heat exchange. We found that the reservoir pressure range, when a shock wave formed in the air during depressurization, has sufficient intensity to produce self-ignition of the hydrogen–air mixture formed at the front of a jet of compressed hydrogen. We present an analysis of the initial conditions (the hydrogen pressure inside the vessel, the temperature of the compressed hydrogen and the surrounding air, and the diameter of the hole through which the jet was emitted), which leads to combustion.     

Mechanisms of high-pressure hydrogen gas self-ignition in tubes

This paper describes a numerical and experimental investigation of hydrogen self-ignition occurring as a result of the formation of a shock wave. The shock wave is formed in front of high-pressure hydrogen gas propagating in a tube. The ignition of the hydrogen–air mixture occurs at the contact surface of the hydrogen and oxidant mixture and is due to the temperature increase produced as a result of the shock wave. The required condition for self-ignition is to maintain the high temperature in the mixture for a time long enough for inflammation to take place. The experimental technique employed was based on a high-pressure chamber pressurized with hydrogen, to the point of a burst disk operating to discharge pressurized hydrogen into a tube of cylindrical or rectangular cross section containing air. A physicochemical model involving gas-dynamic transport of a viscous gas, detailed kinetics of hydrogen oxidation and heat exchange in the laminar approach was used for calculations of high-pressure hydrogen self-ignition. The reservoir pressure range, when a shock wave is formed in the air that has sufficient intensity to produce self-ignition of the hydrogen–air mixture, is found. An analysis of governing physical phenomena based on the experimental and numerical results of the initial conditions (the hydrogen pressure inside the vessel, and the shape of the tube in which the hydrogen was discharged) and physical mechanisms that lead to combustion is presented.