Experimental Study On Characteristics Of Aviation Kerosene Atomization

Liquid fuel spray provides the foundation of the two-phase combustion in the engines.Macro characteristics like penetration tip,spray cone angle,spray projected area and entrained air,and micro characteristics like diameter of droplets,spatial distribution of droplets' diameters,i.e.SMD(Sauter mean diameter)and droplet velocities,play important roles for the combustion performance,components profile,temperature profile,soot,emission and so on.Aviation kerosene is widely applied in aero-space fields,meanwhile,aviation kerosene could be the fuel for the direct injection piston engine and is also treated as a substitution fuel in the diesel engine.As a liquid fuel,aviation kerosene undergoes the internal flow,the primary breakup and the secondary breakup,then forms smaller droplets and the ignitable mixture with the ambient air,thereafter combustion occurs.It's valuable and significate to analyze the aviation kerosene spray process since it provides the foundation of the two-phase combustion in the aero engine combustor,liquid rocket thrust and internal-combustion engine.The main targets of this research are listed as follows:(1)An experimental platform is established with high-speed Schlieren photography.This platform consists of common-rail system,high-speed camera,Schlieren light path,ambient pressure generator and high pressure constant volume vessel with some auxiliary measuring equipment.The high pressure constant volume vessel is mounted with inner insulators and heaters to adjust the ambient temperature.All the raw experimental images captured by the high-speed camera are the targets of the further analysis.(2)The algorithms to detect macro characteristics in the raw experimental images are designed and implemented.The images under room-temperature which contain none-variable background noises and the images under high-temperature which contain variable background noises are analyzed with BEG(Background-Edge detection-Gray tolerance)algorithm and BEGU(Background-Edge detection-Gray tolerance-Union)algorithm respectively.The key idea of the former algorithm is the comparison between the pixel's gray value in the experimental image after SOI(Start of Injection)and the same-located pixel's gray value in the background image before SOI one by one.Every point is processed according to the gray value difference.On the basis of BEG algorithm,an extra step named union is required to erase all those noises by connecting all the connected none-background pixels into respective point-set and then erasing all the noisy point-sets by the predefined principles.After that,an temporary target image containing only spray(gray is less than 255)and white background(gray is 255)is generated for the detection of macro characteristics like penetration tip,projected spray area,three kinds of spray cone angles,penetration tip velocity,light intensity of spray and so on.On the basis of the algorithms mentioned above,a software named "SchlierenDataAnalyzer" is designed and implemented including two versions of core algorithms handling the images under the room-temperature environments and the several temperature environments respectively with pure Pascal language.All the images in this study are analyzed and handled with this software,which can detect the macro characteristics like penetration tip,projected spray area,three kinds of spray cone angles,penetration tip velocity and light intensity of spray and so on.(3)The aviation kerosene spray experiments under room-temperature environment are conducted.In this experiment,the aviation kerosene temperature is 300K,the ambient temperature is 300K too,the ambient pressure ranges from 1.4MPa to 5.6MPa and the injection pressure contains 70MPa,80MPa,90MPa and 100MPa.80 conditions including 5 repetitive experimental conditions are achieved.To measure the repeatability of penetration tip,20 tests per repetitive condition are carried out.Through analysis,it's found that under the room-temperature,after 0.2ms,the penetration tip is repeatable to ±7%.On the basis of Hiroyasu and Arai's correlation,a new modified correlation is proposed to predict the penetration tip of aviation kerosene spray which provides a higher accuracy than Hiroyasu and Arai's correlation and Dent's correlation in comparison with the experimental data.Then spray projected area,spray cone angle,penetration tip velocities and entrained air are discussed respectively.(4)The aviation kerosene spray experiments at different ambient temperature are carried out.The high pressure constant volume vessel is mounted with inner insulators and heaters to adjust the ambient temperature.In these experiments,the aviation kerosene temperatures include 285K/300K,the ambient temperatures include 300K,343K and 423K,the ambient pressure ranges from 1.4MPa to 4.8MPa and the injection pressure stays 70MPa throughout all the experiments.Fourteen conditions including five repetitive experimental conditions are achieved.To measure the repeatability of penetration tip,10-20 tests per repetitive condition are carried out.Through analysis,it's found that at high temperature,after 0.5ms,the penetration tip is repeatable to ±10%while at low temperature,the penetration tip is repeatable to ±7%after 0.2ms.On the basis of Dent's correlation,a new modified correlation with the correction of ambient temperature is proposed to predict the penetration tip of aviation kerosene spray.The new modified correlation predicts the trend of the aviation kerosene spray penetration tip better than Hiroyasu and Arai's correlation and Dent's correlation at low temperature and predicts more accurately the penetration tip of aviation kerosene spray at high temperatures in comparison with the experimental data.Then spray projected area,spray cone angle and entrained air are discussed respectively.