Ground-expreimental Study On The Technology Of Tri-electrode Plasma Ignition

When an aircraft flies under high-altitude and high-speed condition,the volume of ignition kernel induced by traditional ignition technology is small.The small ignition kernel will be annihilation quickly due to bad condition,and leads to ignition defeat,and ignition becomes unreliable.For the challenge of unreliable ignition,tri-electrode plasma ignition technology was proposed,which induced the formation of the large volume ignition kernel by enlarging the size of discharge channel,and by shortening the induction time of ignition kernel by improving the electron temperature and electron density.The development of the tri-electrode igniter was carried out initially.The fundamental structure and discharge method of the tri-electrode plasma igniter was proposed based on the plasma torch igniter;The structure design of the igniter was carried out,and by designing or choosing the flow velocity of igniter working gas,nozzle structure,electrode structure and excitation method,the flow field design of the igniter and excitation coupling design of the tri-electrode was completed;by numerical simulation,the aerodynamic and electrical properties of the igniter were analyzed;finally,the sample of the igniter was developed.The ground electrical experimental bench was designed to investigate the working characteristic of the igniter.Firstly,by analyzing the typical discharge parameters of the igniter,the effects of the excitation parameters and electrode spacing on plasma heat and electric temperature was studied;secondly,by analyzing the image and power of the igniter discharge,the effect of the excitation parameters and electrode spacing on the discharge channel size and power density of the igniter was studied;then,by fitting line,the electrode density was compared with or without tri-electrode excitation,as well as under different discharge spacing;finally,the ablations of the nozzle and electrode were compared with or without tri-electrode excitation,as well as under different discharge spacing.By carrying out the ground ignition experiment on the constant volume combustion experimental bench,the effect of the igniter parameters on the ignition process was studied.Firstly,the no-working gas tri-electrode plasma ignition experiment was carried out,and the development of ignition kernel with or without tri-electrode excitation was compared,and the reason why the tri-electrode igniter accelerates the development of ignition kernel was analyzed;the effect of the electrode spacing and excitation voltage on the development of ignition kernel was analyzed.Then,the jet tri-electrode plasma ignition experiment was carried out,and the effect of electrode spacing,excitation current and excitation voltage on the flame appearance time and the development of ignition kernel were analyzed,and the experimental results were explained by combining the experimental phenomenon with the igniter working characteristics;the effect of the excitation voltage and excitation current on the development of ignition kernel was compared,and a high efficiency method to accelerate the development of ignition kernel was pointed out.By designing tri-electrode plasma igniter,and carrying out the experimental study of the igniter working characteristics,this paper achieved the goals of enlarging the size of discharge channel and improving plasma electron temperature and electron density;under the electrodes condition defined by this paper,compared with plasma torch igniter,tri-electrode plasma igniter enlarged the discharge channel size by a factor of 14 at most,and improved the electron temperature by 34.8%,as well as electron density by 5.15% at most.When this igniter was applied to ignition experiment,which shortened the flame appearance time successfully,and enlarged the ignition kernel,and proved the ability of the tri-electrode plasma igniter to enlarge the size of ignition kernel,and improve the ignition reliability;in the jet plasma ignition experiment,compared with no tri-electrode excitation,the flame appearance time was shortened by 49.6ms at most with tri-electrode excitation;in the no-working gas plasma ignition experiment,compared with no tri-electrode excitation,the initial ignition kernel size was enlarged by 70% at most.