Instanteneous measurement of the density distribution at the cross section of a jet is, in particular, very effective to understand direct factors, e.g. scale or uniformity of mixture, which affect the combustion performance. Using laser induced fluorescence, the mixture spreading process of an intermittent unsteady jet flow was measured, and transformed into a visual image of the instantaneous concentration distribution of a jet at its cross section. A quantitative measuring method of the density distribution in a jet was thus established. In thus study, the following effects and problems of the concentration process to get a concentration image from the fluorescence image are discussed: linearity between concentration and fluorescence emission, temperature and the kind of ambient gas effect on fluorescence, induced laser absorption and fluorescence extinction by fluorescence gas.
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