Research On The Diffusion And Ignition Characteristics Of Hydrogen Jet

Hydrogen energy is considered to be one of the most important means of replacing traditional fossil energy because of its zero-carbon properties and its wide range of sources,high-efficiency utilization,and green and environmentally friendly clean energy.However,as the substance with the smallest molecular weight in nature,the unique properties of hydrogen have brought attention-grabbing safety risks.The study of the hydrogen jet diffusion process and its ignition characteristics after hydrogen leakage is of great significance for clarifying the safety risks of hydrogen in the use process and formulating hydrogen safety standards and regulations.Aiming at the hydrogen leakage jet scene,this paper uses the research method of experimental observation-numerical simulation-design analysis,and obtains a series of conclusions.Aiming at the problem of hydrogen leakage in common ferrule joints,a physical model of typical pipeline defects was established and a scratch leakage failure mode visualization experiment platform based on the schlieren principle was built;The influence of scratch size,initial pressure and leakage flow rate on the jet shape was studied,and the critical pressure value of the scratch leak jet transition under the test conditions in this paper was 0.15 MPa.When the inlet pressure is greater than 0.15 MPa,the "sweeping tail" turbulent morphology occurs.In order to reduce the volume of combustible gas cloud formed by scratch jet,a subsonic jet computational fluid dynamics(CFD)model was established and calibrated,and the influence of forced convection on reducing the volume of combustible gas cloud was further explored.It is found that when the convective wind speed is 1.5 m/s,the flammable volume of the jet is reduced by 85%,and there will be a marginal effect when the convective wind speed is further increased,and a general method for reducing the volume of the flammable gas cloud of the leaked jet in the hydrogen system is proposed.This part of the work provides methods and data for reducing hydrogen safety risks,and provides a scientific basis for revising hydrogenrelated safety standards and specifications.Aiming at the problem of identifying the ignition boundary in the hydrogen jet process,a hydrogen jet ignition experiment platform was built,and the influence of various factors on the ignition was systematically analyzed.In the spark ignition experiment,by changing the ignition position,ignition energy,ignition frequency and initial pressure,the critical ignition concentration range of the jet produced under the test conditions in this paper is: 15.7% to 53.1%.The hydrogen jet can be ignited by spark ignition(minimum ignition energy is 35 m J)within this concentration range.In the hot surface ignition experiment,the critical ignition temperature of hot surface ignition is620 ℃ under the experimental conditions in this paper.Hot surfaces above this temperature can ignite the jet.The high-pressure under-expanded hydrogen jet CFD model and combustion model were established,and the horizontal axis volume fraction and flame temperature of the high-pressure under-expanded jet were in good agreement with the experimental results,which verified the accuracy of the high-pressure underexpanded hydrogen jet CFD model and combustion model.This part of the work reveals the weight relationship of various factors that affect the occurrence of ignition,and provides method and data support for related experiments and numerical simulation research.In view of the lack of reasonable design of ventilation parameters in the existing hydrogen-related standards,on the basis of the aforementioned hydrogen jet numerical model,the safety issues of hydrogen jets occurring inside the hydrogen production container were explored by means of simulation analysis.The transient and steady-state processes of hydrogen leakage from hydrogen production containers were studied.The dynamic equilibrium analysis of combustible hydrogen cloud was carried out,and the weak ventilation capacity of the ventilation window will lead to the residual combustible gas cloud,and the excessive ventilation capacity of the ventilation window will cause marginal effects.The critical ventilation flow in this research scenario is defined as: the ventilation flow value corresponding to 85% reduction of the combustible gas cloud volume,and the corresponding relationship between the leakage flow and the critical ventilation flow is given.Finally,the harmful effect under the action of dynamic combustible gas cloud was evaluated by TNT explosion equivalent method.This part of the work proposes a ventilation design approach to reduce the volume of flammable hydrogen clouds in confined environments.It can reasonably set ventilation device parameters on the basis of ensuring sufficient reduction of flammable hydrogen clouds,and ultimately provide guidance for the rational design of hydrogen-related ventilation standards and specifications in confined spaces.