Numerical Simulation Of Hydrogen/Air Combustion And Explosion Characteristics In Confined Space

With the gradual depletion of fossil fuels,hydrogen,as an ideal fuel,can be used as fuel and material in many fields such as heating,transportation and industry.However,hydrogen is an explosive gas,and the chemical reaction is extremely fast during combustion,and it can react violently in the concentration range of 4%-75% when contacting with very low ignition energy,which makes hydrogen have more serious explosion risk than other hydrocarbon fuels.If the pressure is not released in time in the confined space,the flame will accelerate combustion and turn into detonation,which will become a major potential safety accident.Therefore,studying the effect of explosion venting conditions and tube struture on the explosion characteristics of combustible premixed gas has certain theoretical and engineering value for further revealing the evolution law of premixed gas combustion and explosion parameters and improve explosion safety prevention and control technology.In this paper,the numerical simulation of the combustion and explosion characteristics of hydrogen / air in confined space is carried out by CFD.LES model and zimont combustion model are used in the calculation.After verifying the effectiveness of the model.The flame propagation of premixed gas is studied by change pipe structure and the venting conditions.The flame propagation velocity,pressure were analyzed by the coupling of flame structure and flow field in the pipe.The main results are as follows:(1)The flame propagation process of premixed gas in a square tube with a length of 6m,the positions of the explosion vents are 1,2,3,4,and 5m respectively,and compared with a closed pipe.The results show that the vent position and the relative position of the flame front will affect the flame propagation velocity and the overpressure.When the vent is in the middle of the pipe,the pressure relief effect is better and the flame propagation velocity and overpressure decrease greatly due to the large pressure gradient formed in the pipe.In a pipeline with large length diameter ratio,setting reasonable vent position can reduce the explosion risk.(2)The flame propagation characteristics of premixed gas in a 6 m square tube with 2,3,4m venting position and 0.1,0.3,0.5 and 0.7 MPa respectively were studied.The results show that compared with the influence of the broken membrane pressure and the position of the vent on the flame propagation characteristics,the effect of the broken membrane pressure is more significant,and explosion hazard can be effectively reduced by premature pressure relief.When the pressure in the tube reaches the broken membrane pressure,the explosion relief port in the tube will open,which will affect the air flow in the tube,and effectively reduce the extreme value of velocity and the peak value of overpressure under various working conditions,thus affecting the flame propagation characteristics in the tube.(3)The flame propagation characteristics of premixed gas in straight pipe,90 ° bend pipe and T-shaped bifurcated pipe were studied in a 5.5m closed pipe.The results show that there is a good consistency between velocity and pressure in the three tube strutures.The flame propagation process have changed because of the abrupt structure of the pipeline.Compared of three pipe structures,The peak velocity and explosion overpressure in T-shaped bifurcation tube are the highest,while 90 ° The peak velocity and explosion overpressure in the elbow are the lowest.At the same time,the rate of pressure rise reflects the variation characteristics of overpressure.Among them,the variation range of pressure rise rate in T-shape is the largest,which indicates that the combustion rate in the pipe has the largest variation range.(4)The flame propagation chartacteristics of premixed gas in straight pipe,90 ° bend pipe and T-shaped bifurcated pipe were studied in a 5.5m long open circular pipe.The results show that the peak velocity and the peak overpressure are opposite state in each pipe structure.In the three strutures of pipe,the velocity increases gradually and reaches the peak at the end of the pipe,but the pressure does not reach the peak at the end of the pipe due to the air flow relief.The flame development process can be reflected by the changes of flame structure and flow field.There is no tulip flame structure in the straight tube and T-shaped bifurcated tube.In the 90 ° bend,there is only one tulip structure in the tube because of the structure and the obstruction of the tube.It shows that the closure of the end or the obstruction of the air flow in the tube is the necessary condition for the formation of tulip structure.