Experimental And Numerical Study On The Deflagration To Detonation Transition In Curved Channels

The research of detonation propulsion technology has great significance to the development of power systems.Detonation has now received widespread attention for its advantages of high combustion efficiency,wide range of flying Mach number,and low pollution.This paper refines key scientific issues from the subject of detonation engine,the new power propulsion device,then conducts related basic theoretical research.The experiment using equivalent ratio of ethylene/oxygen was carried out in a 270 ° curved channel,with high-speed photography working as optical capture of the transition from deflagration to detonation;Correspondingly,the numerical method was based on the two–dimensional Navier–Stokes equations solved by WENO scheme and Runge-Kutta,with 35 detailed mechanisms of ethylene/oxygen used for chemical reaction.The main results obtained from the study are as follows:(1)In this paper,experiments and numerical simulations are carried out on the directly ignited curved channel.The flame shape evolution under curvature condition was discussed experimentally.The influence of geometry conditions on detonation characteristics were investigated numerically.The results show that the flame evolution process is the same under different curvature conditions,including four distinctive patterns: spherical flame,finger flame,tongue-like flame,and detonation.For different circular pipes,the DDT distance is proportional to the channel width.The DDT distance in curved channel is shorter than that in straight channel with the same width.(2)In this paper,the numerical study on tongue-like flame formation mechanism was conducted.The tongue-like flame occupies the most time in entire evolution process,which is essential for the transition of deflagration to detonation.The high-speed gas accumulates in the area around flame head,witch getting more concentrated with combustion reaction develops.The fluid was inhibitd by compression effect from outer wall,and promoted by expansion effect from inner wall.The velocity gradient ahead of flame front increases gradually under comprehensive effect.The interaction between accelerating flame-induced and wall generates boundary layer,which thickness grows gradually with the interaction weakening.By analyzing the pressure evolution during the whole process,it can be found that the pressure has increased by 2 times in tongue-like stage,and the detonation initiation occurs after the pressure reaches the peak value.(3)In this paper,detonation initiation was investigated experimentally and numerically.Through experiments,the flame characteristics and relationship between initiation distance and initial pressure were studied experimentally,while flow field evolution and characteristics of pressure development and propagation were investigated numerically,respectively.The results indicated that explosion position keeps the same under different initial pressure,in the same curved channel,moreover,the DDT distance is inversely proportional to initial pressure.The chemical reaction at the detonation position is the most intense,with the highest pressure and temperature.The velocity of outer flame skirt jumps,while the local pressure around explosion position reaches to peak instantly.The pressure wave intensity weakens gradually during propagating towards upstream and downstream.