Effect Of High Frequency Acoustic Oscillation On Spray Macroscopic Characteristics Of Kerosene And Ethanol

In the development of aero engine and liquid rocket engine,a variety of problems are encountered,notably combustion instability.Combustion instability often occurs inside the combustion chamber of aerospace engine.The problem of combustion instability is one of the most difficult to solve and is also a major factor limiting the performance of aero-engine.High frequency pressure oscillation inside the combustor,categorically those higher than 1000 Hz,can lead severe vibration to engine component and cause significant engine damage in a very short time.Dealing with this problem is one of the main subjects while developing novel rocket engine with superior stability and safety.Fuel atomization and evaporation,one of the controlling processes of combustion rate,is an important mechanism of the combustion instability.To decrease and control the combustion instability,it challenges a deep understanding of the underlying mechanism of fuel atomization and evaporation process.In this paper,acoustic field was established to simulate the pressure oscillation.Transient spray images of ethanol and kerosene were recorded using high-speed camera.The obtained images were processed by MATLAB to extract and analyze the related data.Spatial fuel atomization characteristics was experimentally examined by multi-threshold image processing to analyze the effect of the high frequency acoustic field on the fuel break-up and disintegration,to gain deeper insight into the atomization characteristics of ethanol and kerosene under different conditions.The research on the evaporation characteristics of the fuel shows that the fuel evaporation rate is slow under the experimental back pressure and temperature.Compared with the fuel injection time scale,the characteristic time of evaporation is long,and the effect of the sound field on the fuel evaporation is not obvious.Under the action of unilateral sound field,a certain amount of offset occurred in the fuel spray and the value of spray cone angle changed.At the same time,the existence of sound field has certain effect on the atomization effect of fuel spray.The dispersion of fuel spray in space is more dispersed,especially under the influence of the bilateral sound field,the fuel atomization effect is better.A comparison of the effects of sound field on ethanol and kerosene shows that the presence of sound field has a greater impact on kerosene.This is due to the large kinematic viscosity of kerosene,the slow flow velocity in the tube,the low degree of turbulence development,and the small droplet size of the droplets produced by the first atomization and the second atomization.The moving droplets are slow and the entrainment of the air in the flow field is weak for kerosene and therefore it is susceptible to external disturbance.