Numerical Study On The Process Of Detonation Wave Initiated By Multi Point Jets Based On Elementary Chemical Reaction

Detonation is a combustion method with high efficiency.A pulse detonation engine（PDE）is a new propulsion system which owns great potential to be the mainly propulsion system in the future.The combustion process in the PDE completed by detonation wave has many advantages,such as the constant volume combustion process and self-pressurization.In this way,PDE had been widely researched for several decades.However,there are still some difficult hasn’t been overcome completely,and how to initiate the detonation wave rapidly in a short distance is one of these difficult.The present mainly method of detonation initiation is deflagration to detonation transfer（DDT）process and there are several techniques can be used to shorten the DDT process.The method of hot jets initiation owns evidently advantages.This paper mainly addressed the effects of layout method,number and the interaction of hot jets on the detonation initiation process by numerical simulation.The reaction model of 8 species and 19 steps of H2/Air was used in the simulation and 2 steps and5 species model of C₃H₈/O₂/N₂ has been used.At first,the detonation process in a detonation tube by two hot jets tubes was studied by 2D simulation,where the inner diameter of the detonation tube was 30mm and the inner diameter of jets tubes were both 10mm.The effects of the distance from the first jet tube to the left end of the detonation tube（L1）and the distance between two jets tubes（L2）on the detonation initiation process were studied in detail.The results showed that the detonation jets would developed into a sphere wave in the detonation tube with a decreasing process of pressure and temperature.The time of the jets wave reflected on the left end wall and the time of the interaction of two jets was influenced by these two distances,respectively.Then the time of high pressure points generated from the wave interaction（the first type hot spot）and reflection（the second type hot spots）was influenced,and then the DDT process and the parameter of detonation wave were influenced.The results showed that the best detonation initiation performance was obtained at L1=L2=10mm.Besides,the effect of inner diameter of detonation tube on the detonation initiation was investigated.The results showed that the increasing of the diameter would increase the time of attenuation of detonation jets and the time of the generation of the hot spots,and then the increasing of diameter would cause the increasing of the time and distance of DDT.The process of detonation initiated by low-speed jets was investigated.The results showed that the length difference of two jets tubes among a certain range was tolerated to initiate the detonation wave.The hot jets interlaced arranged at both sides of the detonation tube have better detonation initiation performance compared to the jets against to each other.The number of jets influenced the time of DDT more evidently.The structure of axial hot jet accelerated by several sections in which the flame jets from the interval of accelerated section was designed and the performance of detonation initiation of this structure was investigated by simulation.The results showed that the length of the accelerated section effected the process of flame accelerating evidently,and the best performance of flame accelerating was obtained at the section length l=12mm.The effect of the intense of hot jet on the performance of the detonation initiation of the structure was also investigated and the result showed that the detonation wave can be initiated by intense hot jet in a shorter distance and time compared to the structure of transverse tubes.At last,the effect of the detonation tube diameter and the number of hot jet tubes on the performance of detonation initiation of different detonable mixture was investigated by 3D simulation.The result showed that the diffraction phenomenon of detonation jets was more evidently in the 3D spatial.The interaction process of detonation jets was similar to the situation of 2D.The effect of the wall on the detonation initiation process would be weakened while the number of hot jets tubes increased and the performance of detonation initiation of detonable mixture improved.