Research On The Steadiness Of Internal-mixing Twin-fluid Atomization Based On Various Data-processing Methods

In the era of energy saving and emission reduction,improving the fuel efficiency of vehicle engine and reducing vehicle exhaust pollution are the only way for traditional internal combustion engine vehicles to meet the challenges.The internal-mixing two-fluid atomizer can overcome the shortcomings of the traditional atomizer,further optimize the spray effect and improve the combustion of fuel.Improving the steadiness of internal-mixing two-fluid atomization is of great significance for improving engine fuel efficiency,reducing combustion noise and reducing the content of nitrogen oxides in automobile exhaust.The experiment researches and the post-processing technology were combined to analyze the raw testing data.Aiming at the internal-mixing twin-fluid atomizing,various post-processing methods applied on the spray steadiness were systematically studied,which enhanced the understanding of the disciplinary development of spray steadiness.The liquid breakup morphology near the atomizer was captured by high-speed camera,and the steadiness of spray was analyzed by post-processing technology.Through the mean images and root mean square(Root Mean Square,RMS)images analysis of the distribution and variation of liquid in different positions in the fog field can show that the atomization effect is poor when the liquid flow rate is relatively large and air-liquid mass rate(ALR-liquid Mass Rate)is small.However,the liquid breakup has high steadiness and achieves good atomization performance at the large ALR.At the same time,with the increase of ALR,the spray steadiness is getting better and better at different liquid flow rates.The proper orthogonal decomposition POD(Proper Orthogonal Decomposition)technology was used to deal with the spray images recorded by high-speed cameras,and the motion structure from the low modes to the higher modes could be observed in the liquid fracturing process,which helps to analyze the main movement and distribution characteristics of the liquid.By analyzing the feature images,there is obvious swing in the radial direction after the liquid outlet nozzle,and the stability on the left and right sides is different at the large ALR.Along with the increasing of ALR,it can be inferred that there are slug flow and annular flow in the inner part of the injection hole.The movement characteristics of the liquid are more stable under the large liquid flow rate,which is analyzed from the energy composition of the liquid movement structure.Fourier analysis of the average gray level sequence and gray level barycenter sequence in the selected local window were utilized to study the axial and radial pulsation characteristics of liquid out of the nozzle.It is found that the same period pulsation exists in the radial and axial direction after the liquid out of the nozzle,which is related to the antisymmetric characteristics of liquid out of the nozzle.The larger the ALR is,the smaller the characteristic frequency is,the shorter the antisymmetric wavelength is,the smaller the size is,and the better the steadiness of liquid atomization is.Comparing several data processing methods to evaluate the stability and complexity of the diameters of spray liquid drops obtained using the high-frequency sampling model of Malvern Laser Spray-tech,the coefficient of variation was selected as the criterion to evaluate the steadiness and explored the influence of factors on spray steadiness such as different ALR,liquid flow rate and different axial positions.The study found that the stability of small droplets gradually strengthened with the increase of ALR,while the stability of large droplets had the opposite trend.Different liquid flow rates have relatively similar trends on steadiness.Increasing the liquid flow rate would enhance the steadiness of the droplet size,but at the large ALR,the liquid flows have a little of efforts on the particle size steadiness.The liquid fragment images around the 3 centimeters position far from the nozzle exit,had verified the reliability and accuracy of the Malvern Spray-tech that tested in the close nozzle.Meanwhile,with the downstream movement of the liquid outlet nozzle,the steadiness of small droplets in the downstream spray region strengthened but that of large droplets declined.This paper performed that the method of experiment combined with post-processing technology has great potential in atomization research.