Droplet Size Measurements in a Diesel Fuel Spray Using a Planer Laser Induced Fluorescence Method

Abstract

This paper presents new technique for the measurement of particle size of dense fuel spray. Much studies had been focused on particle size distribution. And various methods were tried to observe it, for example there were droplet collecting method, molten wax method, direct photography method, fraunhofer diffraction method, image analysis method and recently, the phase-doppler anemometer (PDA) method. But above these methods, problems such as injection pressure limitation and the existence of multiple scattering inside the dense spray remain. In this study, the planer laser induced fluorescence (PLIF) technique was applied to measure the particle mean size and particle size distribution of the diesel fuel spray. The fuel used was n-tridecane mixed with 1 wt% N,N,N',N'­Tetramethylparaphenylenediamine (TMPD). Light source to excite TMPD in the fuel was secondary harmonics of a ruby laser-light sheet. Greatly magnified image of fluorescence from TMPD was taken by a 35 mm still camera with magnified optics, and mean particle size and particle size distribution of the fuel spray were obtained by processing the images of fuel particles magnificently printed on a paper. First, the accuracy of this method was con finned by comparing with PDA' s results for fuel spray particles of an air-assisted gasoline injector. Then, for the diesel spray, the effects of injection velocity, ambient pressure on fuel particle mean size and size distribution were investigated in a high pressure vessel at room temperature. As the results, small size particles increase in the case of higher injection velocity in which particles seem to atomize more actively. At higher ambient pressure condition, mean particle size increases.