| Popis: |
This study aims to improve a technique for measuring fuel distributions, e.g. mixture fraction and droplet sizes, in evaporating and mixing (two-phase) fuel sprays. The technique is based on planar laserinduced fluorescence of acetone, used as a surrogate fuel. Previous work investigated the use of signal level to discriminate against liquid acetone droplets bigger than a critical size. However, droplet streaks were observed. To determine the cause of the streaks, time decay experiments of the signal were conducted and. indicate that acetone phosphorescence is the cause. The phosphorescence lifetime and the phosphorescence to fluorescence ratio for the spray were determined and are similar to that of the vapor (in the absence of oxygen). Further measurements of bulk liquid acetone found widely different values for the phosphorescence lifetime and P/F ratio based on the exposure of the liquid acetone to oxygen. A method is suggested for simultaneous droplet size and vapor mixture fraction measurements. It utilizes two images acquired with a short delay. The first (short exposure) image captures the vapor and liquid fluorescence, and the second (long exposure) image measures the liquid phosphorescence. There is also some difference in the spectral content of the liquid fluorescence and phosphorescence The phosphorescence streaks also have the potential to provide some droplet velocity information. |
