| Micro-energy system has the advantages of small volume,light weight and high energy density,but it has some problems such as relatively large surface area/volume ratio and increased heat loss.Ethanol is a clean energy source.Adding ethanol to diesel can reduce the generation of pollutants.The research on the micro-scale combustion characteristics of ethanol/diesel is of great significance for optimizing the design of micro-scale burners.There are relatively few researches on the characteristics of liquid fuel’s micro-scale combustion flame in domestic and foreign literature.In this paper,ethanol/diesel fuel combustion test is carried out under the micro-scale burner,and then digital image processing technology is used to preprocess the collected flame images and extract relevant information.The fractal characteristics,flame temperature and steady combustion characteristics of ethanol/diesel micro-scale combustion flame were studied and analyzed under different conditions.The main work is as follows:(1)A micro-scale combustion test device was designed and built,and the fuel supply system,combustion system,flame image acquisition system and temperature measurement system were described.The micro-scale flame images of ethanol/diesel under different fuel volume flow,mixing ratio,inner diameter of quartz tube and air flow were obtained by high-speed camera.MATLAB is used to write related preprocessing program to remove noise and segment the acquired flame image.The denoising effects of four denoising methods(mean filtering,median filtering,ideal low-pass filtering and Butterworth low-pass filtering)are compared and analyzed.For the flame image segmentation,the iterative threshold segmentation method is used.The results show that the denoising effect of median filtering is better than the other three methods;the iterative threshold segmentation method can segment the background and image well,and the effect is obvious.After the micro-scale combustion flame image is preprocessed,the structural features are clear,which is convenient for subsequent extraction of relevant indicators.(2)The influence factors and variation rules of flame fractal characteristics of ethanol/diesel micro-scale combustion were studied.The fractal dimension of micro-scale flame images was calculated by using the difference box dimension method,the pixel point coverage method and the fractal dimension of Fourier spectrum,and the comparative analysis was made to select the appropriate calculation method of flame fractal dimension.The variation of fractal dimension with mixing ratio,inner diameter of quartz tube and air flow rate was studied.The results show that the fractal dimension value obtained by the calculation of the Fourier spectrum fractal dimension is better and more suitable for calculating the fractal dimension of micro-scale flame.With the increase of fuel volume flow and air flow,the fractal dimension gradually increases;with the increase of the mixing ratio and the inner diameter of the quartz tube,the fractal dimension gradually decreases;with the increase of air flow,the average fractal dimension gradually increases.(3)The influencing factors and variation rules of flame temperature in ethanol/diesel micro-scale combustion were studied.BP(Back-Propagation),Generalized Regression Neural Network(GRNN)and Support Vector Machine(SVM)were established to predict the flame temperature.The blend ratio B_r,quartz tube inner diameter Q_d,air flow A_f and volume flow V_f is the input parameter,and the flame bottom temperature T_b and the top temperatureT_t are output parameters.Training,prediction,and verification were carried out by using the data of 600 groups of samples collected in the experiment.Choose a suitable prediction model to predict flame temperature for different working conditions.The evaluation index of flame temperature is put forward,and the regularity and influencing factors of top temperature and bottom temperature in different mixing ratios,inner diameter of quartz tube and air flow are analyzed.The results show that the SVM model has higher prediction accuracy than the BP and GRNN model,and is more suitable for predicting micro-scale flame temperature.With the increase of fuel volume flow and air flow,the flame top temperature firstly increases and then decreases;with the increase of the mixing ratio and the inner diameter of the quartz tube,the flame top temperature gradually decreases.With the increase of the fuel volume flow rate and the inner diameter of the quartz tube,the flame bottom temperature gradually decreases;with the increase of the mixing ratio and the air flow rate,the flame bottom temperature gradually increases.(4)The influence factors and variation rules of steady combustion characteristics of ethanol/diesel micro-scale combustion were studied.In view of the research on the characteristics of micro-scale combustion stability,three evaluation indicators of flame aspect ratio,average gray scale and area ratio of high temperature zone are proposed.The variation rules and influencing factors of the evaluation index of the combustion stability characteristic with the mixing ratio,the inner diameter of the quartz tube and the air flow rate are studied.The results show that with the increase of the fuel volume flow rate,the flame aspect ratio gradually increases;with the increase of the mixing ratio,the inner diameter of the quartz tube and the air flow rate,the flame aspect ratio gradually decreases.With the increase of fuel volume flow rate,the average flame gray level gradually increases;with the increase of the blending ratio and the inner diameter of the quartz tube,the average flame gray level gradually decreases;with the increase of air flow rate,the average flame gray level first increases and then reduce.With the increase of fuel volume flow and air flow,area ratio of high temperature zone first increases and then decreases;with the increase of the mixing ratio and the inner diameter of the quartz tube,area ratio of high temperature zone gradually decreases. |
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