Study On The Initiation And Propagation Characteristics Of Detonation Wave In Millimeter-scale Tubes

With the increasing requirements for power system,detonation combustion has attracted more and more attention due to its advantages such as high expansion ratio,high combustion efficiency and less pollution.By studying detonation phenomenon,we can not only avoid the disadvantages caused by deflagration and detonation,but also make effective use of them.In order to study the deflagration-to-detonation transition and propagation characteristics of detonation waves in capillary tubes,the experiment is conducted in four tubes with length of1930mm and diameters of 0.5mm,1mm,2mm,and 4mm.The high-speed digital camera is used to imaging the flame propagation of C₃H₈+5O₂?C₂H₄+3O₂?2C₂H₂+5O₂+7Ar at initial pressure range from 10 to 100kPa.The main results can be concluded to the following aspects:1.In this paper,the process of the deflagration to detonation transition in various capillary tubes include:premix ignition,flame acceleration,deflagration-to-detonation transition,detonation propagation.2.Area divergence causes?different relationship between run-up distance and the initial pressure or the tube diameter in the capillary tubes.The run-up distance can be expressed aslinear relationship with d at the lower pressure less than 60 kPa,however,a relatively stable variation range of L_DDTDT is found to be about 100²00 mm when the initial pressure is greater than 60 kPa.Since the relative distance L_DDT/d in the capillary tubes is bigger than that in macro-tube,a formula used to predict L_DDT/d in macro-tube cannot be applied in micro-tube.For a given tube diameter,the run-up distance can be expressed as inverse relationship with the initial pressure in both capillary and macro-tubes.The critical value used for discriminating the DDT model in micro-and macro-tube was obtained by researching the effect of the boundary layer thickness on DDT distance.3.The propagation modes of detonation waves obtained in this paper include stable propagation mode,gallop detonation mode,and"stuttering"detonation mode.The detonation wave's stable propagation velocity oscillates around the theoretical C-J velocity,and the velocity does not change much.Galloping detonation undergoes a cycle of overdriven,degeneration,failure,and re-initiation."Stuttering"detonation has obvious speed attenuation.These two modes belong to the unstable propagation modes of detonation waves.Extinguishing and back propagation is an unstable propagation phenomenon observed in this experiment.4.When the detonation wave propagates steadily in the millimeter diameter tubes,the detonation wave has a velocity loss due to the influence of the boundary layer of the pipe wall.When the initial pressure is constant,the detonation wave propagates steadily with the increase of the diameter The velocity deficit is getting smaller and smaller.When the pipe diameter is fixed,as the initial pressure increases,the velocity deficit becomes smaller and smaller.In this paper,the actual value of the steady propagation velocity deficit of the detonation wave of C₂H₄+3O₂ premixed gas has good agreement with the theoretical value.5.In millimeter-scale smooth tubes,the propagation limit of detonation waves is related to the tube diameter and initial pressure and the types of premixed gas.