Research On Flowing Gas Discharge During Plasma Ignition

Plasma ignition technology uses the special electrical,thermal and chemical effects of gas discharge plasma to enhance the physical and chemical processes of fuel ignition,which is expected to solve the ignition reliability problem of hypersonic scramjets.It is a research hotspot in the field of plasma discharge in recent years.Airflow is ubiquitous in the process of plasma ignition,and the coupling mechanism between airflow and plasma will significantly affect the ignition process of the engine.Forming a stable and continuous plasma ignition source in the airflow inside plasma igniter and avoiding the instability of flowing gas discharge induced by supersonic airflow outside plasma igniter are important challenges for the plasma ignition technology.Therefore,it has important theoretical and practical significance to carry out the research on the influence of the internal and external airflow of the igniter on the plasma discharge characteristics.In order to understand the influence of airflow on the basic process of discharge,the characteristics of flowing gas discharge in plate-to-plate gap flow are experimentally studied.The influence of airflow transport on the discharge memory effect is the main factor to change the discharge characteristics of flowing gas.The airflow transport effect leads to the loss of long-lived active particles and Joule heat generated by the discharge,which increases the parameters of power supply corresponding to the initiating-extinguishing of discharge boundary;The airflow transport effect changes the established positions of the two adjacent discharge micro-discharge channels,so that the discharge filament channels move with the streamline of the vortex flow,and the discharge pattern shows the movement trajectory of the discharge filament channel,which can reflect the basic characteristics of the flow state from laminar flow to turbulent flow.Basic recognize of the effect of airflow on discharge characteristics provides theoretical support for the study of the flow gas discharge problem during subsequent plasma ignition.Aiming at the real characteristics of the flow field distribution inside the plasma igniter,a targeted study on the characteristics of the discharge arc establishment and motion in the flow environment is carried out.Firstly,based on the non-linear characteristics of the flow gas discharge initiation-extinction boundary,a topological geometric analysis of the non-linear law of the discharge initiation-extinction boundary is carried out using Thoms classification theorem,and the dependence of the discharge state on the operation path is found;then,the prediction of the igniter working state is achieved under different plasma ignition operation paths.Secondly,based on the periodic motion characteristics of the discharge arc of the plasma igniter,the influence of the discharge arc motion law on the ablation of the electrode surface is found;and then the spatial distribution and motion law of the discharge arc are changed by regulating the internal vortex flow environment of the igniter to improve the ablation of the electrode surface of the igniter.By studying the discharge characteristics of the flowing gas inside the igniter,a new method is provided for the prediction of the igniter discharge initiation /extinction state and the reduction of the local ablation on the electrode surface.Aiming at the unstable discharge of the igniter induced by the external airflow of the plasma igniter,the experimental study of the discharge characteristics in the external carrying airflow environment is carried out by constructing an external carrying airflow environment at the nozzle of the igniter.The entrained flow holes on both sides of the entrained flow device introduce the external supersonic airflow into the entrained flow cavity,and spatially construct a low-speed vortex flow and a high-speed entrained flow airflow environment.The propagation characteristics of the discharge arc in different airflow environments are analyzed,and it is found that when the discharge arc moved to the vortex flow region or the high-speed entrained flow region,as the airflow changes to a turbulent flow state with disturbances between adjacent flow layers,the discharge arc bends or oscillates,thus increasing the contact area between the fuel and the arc and improving the chance of fuel ignition under the plasma action.Based on the knowledge of the influence of the basic characteristics of the gas flow on the discharge and the discharge characteristics of the airflow inside and outside the igniter,the structure integration,parameter selection and prototype development of a plasma igniter for supersonic combustion chamber are completed.Under the test conditions of simulated flight Ma=6.0,the supersonic kerosene ignition test under the action of plasma is carried out;the plasma igniter induces the fuel to burn and the combustion fills the entire combustion chamber.The internal pressure of the combustion chamber is greatly increased,and the successful ignition of the ramjet under the simulation condition of Ma=6.0 is realized.Furthermore,the feasibility of applying the plasma igniter in supersonic plasma ignition is verified.