Experimental And Numerical Simulation Study Of Spray Process Of N-decane Using Pressure-swirl Nozzle In Aero-engine

The fuel in the aero-engine enters the combustion chamber and is ignited by the ignition device after being atomized into droplets through the nozzle.This process provides energy for the operation of the aero-engine.Pressure-swirl nozzles are often used for fuel injection in turbofan engines.Therefore,it is particularly necessary to study the spray characteristics of pressure-swirl nozzles.This thesis briefly introduces the design and implementation of an experimental pressure-swirl nozzle spray platform.In the experiment part,n-decane was used as the surrogate fuel of aviation kerosene.A specific pressure-swirl nozzle used in aviation turbofan engine was selected to perform spray experiment under different practical operating conditions such as injection pressures,ambient pressures and ambient temperatures.Optical diagnostic measurements were conducted through backlight illumination technology and schlieren imaging technology.The spray image was taken by a high-speed camera and the macro characteristics such as spray pattern and jet structure were qualitatively analyzed.A MATLAB algorithm was developed for image processing to extract and make quantitative analysis of macro spray characteristics such as spray cone angle and break-up length of liquid film.The experimental results show that the maximum spray cone angle of the nozzle is 87° with the growth of injection pressure and the nozzle cannot work properly while the environment pressure reaches 1.75 MPa.This work also reveals that increased ambient pressure promotes atomization by increasing aerodynamic forces and increased ambient temperature promotes it by decreasing viscous force and surface tension of liquid film.Both of them promotes atomization.Then the VOF spray one-way coupling method was used to numerically simulate the entire spray process from the nozzle internal flow to the break up and atomization of liquid film.According to the results of numerical simulation,the cross section of nozzle orifice was divided into three parts.The gas phase region near the center with the irrotational flow,the liquid phase region performs the rotary centrifugal flow near the wall and the transition region formed by the entrainment between the two phases.The average effective liquid film thickness,filtered by the influence of the gas phase volume,obtained by calculating the axial velocity and the gas phase volume fraction,increases and then remains constant with increasing back pressure.It is found that the VOF spray one-way coupling method has high accuracy for the prediction of macro spray characteristics such as spray cone angle and break-up length of liquid film.This paper analyzes the changes of macro spray characteristics under different environmental conditions through experiments,and provides theoretical guidance for the design of the combustion chamber of an aviation turbofan engine,the governing of injection pressure and the organization of ambient airflow in practical engineering.Meanwhile,the numerical simulation using nozzle internal flow and the spray process coupling method is applied and a preliminary exploration is provided,which provides a new way for studying the entire process of spray evolution and development of pressure-swirl nozzle.