Research On Deflagration To Detonation Transition Characteristics And Mechanism Of Gas-phase Propane

Detonation combustion has gradually become the research hotspot in the power energy field because of its advantages in self pressurization,small entropy and fast heat release.The compatibility between the gas turbine and the detonation combustion will greatly improve the cycle thermal efficiency,which is expected to break the current technical bottleneck of gas turbine.However,there are still many problems before the engineering application of detonation combustion technology.Among them,how to achieve reliable and efficient detonation initiation is the primary problem and the key for the application of detonation combustion.Deflagration to detonation transition is the most potential mode of detonation initiation.The exploration of its characteristics is the main way to further understand detonation initiation,and also points out the research direction of the enhancement of detonation performance.Some critical parameters such as initial conditions,ignition conditions,and structural parameters of detonation tube are very sensitive to deflagration to detonation process,therefore the mechanism and discussion of these parameters are greatly significant to enhancement of detonation initiation.Propane is a common,economical and clean fuel,which has the advantages of high activity and easy storage.It has a wide application prospect in the detonation combustion.In this paper,we use propane as the research object.In order to explore the macro characteristics and evolution law of deflagration to detonation transition process,reveal the detailed mechanism of flame propagation and detonation transition,and clarify the main ways to strengthen deflagration to detonation,we have studied the effects of typical parameters on the deflagration to detonation transition process by methods of experiment and numerical simulation.This paper aims to provide a new design idea for the research and development of detonation combustion high-efficiency initiation equipment,and lay a theoretical foundation for the application of detonation combustion technology.The specific work is as follows:(1)In order to explore the macroscopic characteristics and evolution rules of the deflagration to detonation transition process for propane fuel,this paper designs and builds experiment system for deflagration to detonation transition process.The experimental tube length is 1500 mm and the diameter is 40 mm.The effects of oxygen content,equivalent ratio and initial pressure on deflagration to detonation transition characteristics are researched experimentally.The changing rules of deflagration to detonation transition distance,detonation velocity and detonaton cell size are obtained under different conditions.The results show that the decrease of oxygen content will lead to different homogeneity of detonation cell structure,and even the angle of detonation cell changes from the sharp angle to the smooth angle.(2)In order to reveal the enhancement mechanism of plasma ignition on promoting deflagration to detonation transition,this paper compares experimentally the deflagration to detonation transition processes under spark plug ignition and plasma ignition.Based on the experimental study of the evolution law of the flame core and the characteristics of the turbulence,it is found that the plasma ignition not only increases the ignition energy and the duration of the flame core,but also increases the area of the flame core by 60 times the spark plug.The flame core has a jet velocity of 10.33m/s.With the increase of plasma ignition energy from 2J to 9J,the area of flame core formed by different plasma generators increases by 3 to 12 times,which further enhances the thermal effect and thermal jet effect,so the deflagration to detonation process is strengthened.(3)After understanding the macroscopic characteristics and evolution law of deflagration to detonation transition,the internal mechanism of flame propagation and detonation transition during deflagration to detonation transition was investigated in detail by numerical simulation due to the constraints of experimental conditions detail.In order to promote the initial development of flame,a comparative study is carried out by changing the first obstacle position from 60 mm to160mm and the ignition position from 0mm～60mm away from the left closed end.It is found that the initial flame development was the most sufficient when the first obstacle position was 100 mm and the ignition position was 10 mm away from the the left closed end,which reduces the obstruction effect of the wall boundary layer and strengthens the promoting effect of the reflection wave formed on the closed end,so the process of deflagration to detonation transition is strengthened.(4)Based on the study of the first obstacle position and ignition position,the deflagration to detonation transition process under obstacles with spacing of 10mm～160mm and blockage ratio of 0～0.9 is studied by numerical simulation method.The results show that when the distance between adjacent obstacles is equal to diameter of the detonation tube pipe and the blockage ratio is between 0.6～0.8,the strengthened effect of obstacles on the deflagration to detonation transition process reaches the best.Moreover,the mechanism and regular of strengthening flame propagation and deflagration to detonation transition are proposed.(5)In order to further strengthen the deflagration to detonation transition,combined with the research on the parameters of obstacles,the study on the enhancement mechanism of precombustion tube on detonation initiation is carried out.The research results show that the precombustion flame is a high intensity turbulent flame with the jet velocity of 220m/s and the pressure of 0.96 MPa,so as to rapidly develop the flame and strengthen the deflagration to detonation transition.Based on the optimization study of the precombustion flame,the ignition position on the sidewall of the precombustion tube is proposed,which reduces the formation time of the precombustion flame by 52.94%,and significantly strengthens the deflagration to detonation transition process in the detonation tube.The detonation initiation time is shortened by 36.56%,and the initiation distance is reduced by 12.86%.