Influence Of Oxygen Content On Combustion Characteristics In The Afterburner

The oxygen content has a significant impact on the combustion performance of the afterburner.As the main combustion chambers of modern aviation engines are developing towards high temperature,high heat capacity,and high efficiency,lower inflow oxygen content of the afterburner will be achieved,which will lead to a substantial reduction in combustion reaction rate and flame propagation speed in the afterburner.This situation poses a challenge to the efficient,stable,and safe operation of aero-engines.Therefore,it is necessary to study the effect of oxygen content on the performance of the afterburner,to provide a reference for highefficient and stable combustion with very little oxygen in the afterburner.In this paper,the steady-state numerical simulation method is implemented to investigate the influence law of inlet flow parameters on fuel atomization characteristics in the afterburner and explore the impact of oxygen content on combustion performance under different inlet flow parameters.Furthermore,transient numerical simulation methods are used to examine the impact of oxygen content on unsteady combustion characteristics under various inlet flow parameters.The main contents of this paper are as follows:(1)In the afterburner,the injection mode,the number,the aperture of nozzles,and the velocity of the nozzle outlet are determined.Through the steady-state numerical simulation method,this paper studies the influence of inflow velocity,temperature,pressure,and oxygen content on the flow field structure and spray characteristics of the afterburner.Accordingly,the results show that with the increase of inlet Mach number and working pressure,the penetration depth of droplets increases,whereas Sauter Mean Diameter(SMD)decreases.And the oil from the nozzle mixes more evenly with the surrounding gas.(2)Through the steady-state numerical simulation method,this paper studies the influence of oxygen content on the hot state field and various performance parameters of the afterburner under varying inflow velocity,temperature and pressure.The results show that when the inlet flow parameter is fixed,the decrease in oxygen content will reduce the flame temperature,and the main reaction area will move towards the combustor outlet,thus reducing the combustion efficiency.With constant oxygen content,an increase in Mach number led to higher heat release intensity within the chamber,while higher working pressure resulted in more even flame spread and improved combustion efficiency.A rise in inlet temperature,however,may lead to reduced combustion efficiency due to high fuel concentration in the recirculation zone.(3)Through transient calculation and simulation method,this paper studied the vortex shedding process under different oxygen content and analyzed the influence mechanism of oxygen content change on flow characteristics.In addition,this paper studied the effect of oxygen content on unsteady combustion characteristics such as vortex structure,flame morphology,exothermic pulsation,and pressure pulsation under different incoming flow parameters.In this study,it is found that the Benard-Von Karman(BVK)instability will cause the flame to fluctuate greatly,leading to the increase in the amplitude of exothermic pulsation and pressure pulsation.Besides,the influence of inlet Mach number,temperature,pressure and oxygen content on BVK instability is nonlinear.