Determination of Spray Droplet Size by Wavelet Analysis of Interferometric Images

Issues are brought to light in the optimization of combustion processes of fuel, depending on the spraying capability of rocket and aircraft engine nozzles. Using the example of the flame of a fuel-injection nozzle, the problem of determining the size of droplets of spray of an optically transparent fluid by the IPI method, based on the analysis of interferometric images of the particles, was studied. A method is proposed for analysis of the IPI image of a drop using a continuous wavelet transform. The spatial distribution of wavelet coefficients was used for the introduction of an integrated measurement, analogous to the spectral density of a signal. The reliability of the estimated sizes of droplets was verified from the results of processing glistening images that are obtained by the direct optical GPT method on focused images of droplets. The focused images and interferometric images of droplets are taken simultaneously. The sizes of droplets obtained by the IPI method and processed with the aid of wavelet and Fourier transforms were compared with the data of the GPT method. It was shown that the wavelet transform application substantially reduces the frequency of occurrence of systematic error of the determination of size, which is most characteristic for large droplets. It was established that the false maxima causing systematic error in the Fourier spectrum were caused by the occurrence of distortions on the boundary of the interferometric image of a drop. It was shown that it is possible to remove these distortions from the basic maximum in the neighborhood of the center of a drop by means of wavelet transform.