A Numerical Simulation Study On Mechanisms Of H₂/O₂/N₂ Premixed Flame Propagation

Pulse detonation engine is a new type of propulsive device of aviation. Research on propagation characteristics of premixed flame can effectively shorten the distance of DDT progress, it also expands the PDE application; As an emerging green energy, hydrogen has high calorific value, with no pollution producing. It is significant to study the characteristics of hydrogen premixed flame propagation. Meanwhile, with the development of modern industrial countries, and the widespread using of flammable gas, industrial safety becoming a more important problem. Mine gas explosion and other accidents not only cause a lot of casualties, but also caused huge economic losses to the country. Therefore, study on the characteristics of flame propagation in the pipeline, especially the research of changes of flame structure, play an important role in controlling of the explosion or preventing the occurrences of disasters.In this paper, the standard k-ε turbulence model and the EDC combustion model is used,and the hydrogen-air 9 component 19-step reaction is selected to be the mechanism chemical reaction model in simulating the two-dimensional flame propagation process of hydrogen-air mixture. Then the propagation characteristics of premixed flames is discussed. The main work of this paper consists of following two parts:(1) Study on the propagation process of hydrogen-air mixture in a two-dimensional smooth tube. The first group numerical simulation conditions is: initial pressure P0=1 atm, the mixture equivalence ratio is 1.0, changing the initial temperature T0=300 K, 500 K, 700 K;the second group numerical simulation condition is: the initial pressure P0=1 atm, the initial temperature T0=300 K, changing the mixture equivalence ratio Φ=0.8, 1.0, 1.2, then compare the simulation results with each other. Simulation results show that: as the initial temperature increase, the burning rate of the flame increases, then the flame front speed increases; at the ratio of 1.0 the flame has the highest speed, when the ratio is reduced, the flame propagation speed decreases rapidly, when the ratio increases, the flame front speed steady decline.(2) Study on the propagation process of hydrogen-air mixture in a two-dimensional tube with obstruction. The numerical simulation condition is: the initial pressure P0=1 atm, theinitial temperature T0=300 K, the mixture equivalence ratio Φ=1.0, blocking ratio(BR)=0.5,the distance of the obstacle is also fixed to be S=D. Observe the difference between all the results of the simulations, then compare it with the results in the smooth pipe under the same conditions, in order to analyze the acceleration mechanism of premixed flames. The simulation results showed that: adding obstacles in the flame propagation process can effectively improve the flame propagation speed; number of obstacles affecting the flame acceleration process, two obstacles have better acceleration than a single obstacle.Simulation results indicate the influence trend of flame propagation when the initial temperature, equivalence ratio or obstacle conditions is changing, meanwhile, revealing the underlying causes of such influence. It provides a theoretical basis for Pulse Detonation Engines and hydrogen fuel use, and avoiding gas explosion or other accidents.