Research On Propagation And Stability Of Diffusion Flames Based On Plasma Jet

Due to its excellent performance at high Mach number,scramjet engines are the first choice for hypersonic vehicle propulsion systems.Scramjet engines let the air flow into the combustion chamber at supersonic speed and burn in a supersonic environment.The flow velocity of the combustion chamber is fast and the fuel residence time is short(only milliseconds),making diffusion flame propagation and stable combustion the key to supersonic combustion.problem.At present,the central wall surface ignition technology,center/branch combination oil supply technology,and plasma ignition technology have all been proven to enhance ignition or enhance combustion stability.Therefore,in this paper,based on the ground test and numerical simulation of the scramjet engine combustion chamber,the following research work has been carried out:Using surface tests and numerical simulation techniques,the flame propagation characteristics of plasma enhanced supersonic ignition were studied.Based on the perspective of dynamics,a set of feedback amplification mechanisms were proposed for the propagation and stabilization process of supersonic plasma ignition flame,and the conditions necessary to successfully build this feedback mechanism were determined.Through the simulation calculation of the cold flow field,the pre-combustion flow field is determined to provide favorable conditions for successful ignition and stable combustion.By changing the fuel supply,the main factors affecting the propagation and stability of supersonic plasma ignition diffusion flames are discussed.The results showed that there was a lower limit for the amount of fuel,and if the amount of fuel was too small,the central fire core intensity was too low to achieve stable combustion.The effect of supersonic combustor structure on plasma flame stability was studied using surface tests and numerical simulation techniques.Through the ground ignition and stable combustion test of combustion chambers of different lengths and related numerical simulation calculations,the influence of combustion chamber length on the stability of supersonic combustion is discussed.The results show that there is a lower limit on the length of the supersonic combustion chamber.When the length of the combustion chamber is too short,no pressure rise in the combustion chamber can achieve stable combustion.Increasing the length of the combustion chamber helps to increase the stability of the supersonic combustion,but beyond a certain limit,thesupersonic combustion stability decreases.In addition,increasing the length of the combustion chamber broadens the stable combustion boundary.The effect of fuel distribution ratio on the flame stability of plasma-enhanced supersonic ignition was studied using surface tests and numerical simulations.By changing the combustion equivalence ratio and comparatively analyzing the flow field conditions under different equivalence ratio conditions,the mechanism of the equivalence ratio affecting the combustion performance was determined.By comparing the combustion performance of the combustor under different fuel distribution conditions,the effect of the fuel supply from the center and the support plate on the enhanced combustion was studied.It is determined that increasing the central fuel injection amount and the amount of fuel injected to the support plate have certain gains for enhanced combustion.Comparing the two,the effect of the support plate fuel on the enhanced combustion is stronger.