Non-premixed Turbulence Deflagration Characteristics Of Hydrogen/Air Under High Pressure Jet Conditions

Hydrogen energy is a kind of high-efficiency energy source that human beings can obtain from nature.Its combustion process only produces water,which is non-polluting to the environment,has high energy utilization efficiency,and has great potential development value.However,due to the very active chemical properties of hydrogen,once the hydrogen stored at high pressure is leaked,it will spread rapidly,which will lead to combustion and explosion disasters in case of ignition source,resulting in casualties and property losses.Based on the self-established experimental research platform of non-premixed high-pressure hydrogen jet deflagration pipeline and the turbulent flame simulation model,this paper conducts in-depth research and analysis on the flame structure and dynamic propagation characteristics of hydrogen jet deflagration.Firstly,the flame structure and propagation characteristics of the non-premixed deflagration flame of the high-pressure hydrogen jet under the conditions of eight incident pressures in the range of 0.32 MPa-0.52 MPa were analyzed experimentally.When the incident pressure is small,at the initial stage of ignition,the flame spreads rapidly to the right,and the flame is smooth and laminar;as the flame continues to propagate forward,the flame pulsation appears at the front end;when the front end of the flame propagates to the outside of the pipe and contact with the air,the turbulence intensity increases,the pulsation of the front end of the flame is completely disconnected from the rear flame,and a flame intermittent zone appears.When the incident pressure is large,the gas flow rate is higher and the flame jet velocity is larger;the flame presents a general jet flame form without tip pulsation,but due to the limitation of the pipe wall,the flame is "knife shaped".As the jet velocity increases,the diffusion of turbulence between hydrogen and air continues to increase,which has a great impact on the mixing of hydrogen and air,as well as on the rate of chemical reactions.Secondly,the flame structure and propagation characteristics of non-premixed deflagration of high-pressure hydrogen jet were experimentally studied when ignited at different ignition positions(IP0,IP250 and IP500).Under the same ignition position and different incident pressure,the deflagration propagation flame structure of highpressure hydrogen jet presents a similar change law.The ignition position has a significant effect on the structure of the jet flame.Compared with ignition at IP250,when ignited at IP500,the pulsation intensity at the left end of flame is significantly increased,and the phenomenon of flame return is more obvious;when the incident pressure is 0.52 MPa,the flame turbulence intensity increases until tulip flame appears.The velocity of the flame front is largely affected by the incident pressure.At the same ignition position,with the increases of incidence pressure,the time required for the right flame front to reach the rightmost end gradually decreases.When the ignition position is IP250 and IP500,the overall time of the left flame front contacting the left stainlesssteel plate also decreases with the increase of incident pressure.Finally,in order to analyze the coupling oscillation law of flame and turbulence,the non-premix deflagration of high-pressure hydrogen jet was numerically simulated,and the reliability of the simulation was verified by comparing the flame structure and development trend in the experimental results.In the process of non-premixed deflagration propagation of high-pressure hydrogen jet,due to the interaction between pressure shock wave and flow field,a low-pressure zone is formed in the flame.The vortex in the flow field also changes with the change of the low-pressure zone in the pipe.In the initial stage,the hydrogen jet in the pipe is a convex shape in the middle.Then,as the low-pressure zone moves downward gradually,the hydrogen diffusion velocity near the lower wall also increases gradually,and the hydrogen jet in the pipe gradually changes into the shape of middle concave.With the gradual propagation of jet flame,a "knife-shaped" hydrogen/air mixed layer is eventually formed under the combined action of the wall surface and gravity.Through the analysis of the dynamic distribution of vortex and velocity,the process of coupling flame and turbulence is studied,and the positive feedback mechanism of flame turbulence coupling is revealed.In the region with large vorticity,the flame velocity is relatively large,and turbulence can promote the rapid mixing and deflagration of unburned gases with high-temperature gases,thereby accelerating the flame propagation speed.