Fuel Tracer Laser-induced Fluorescence for Droplet Liquid-Vapor Visualization
In order to understand the fuel droplet vaporization process in engine cycles, measurements of the local concentration of fuel vapor in high temperature and pressure environments are required. To achieve this, planar laser-induced fluorescence (PLIF) of well-characterized tracer molecules are used to track the local fuel vapor concentration. For many tracer molecules of interest, there is a strong quenching effect of local oxygen. This work aims to control and determine the quenching environment to allow quantitative measurements. For this purpose, a fluid system is designed to vary the amount of dissolved oxygen within the fuel tracer using a pressurized storage vessel. To verify the removal of dissolved oxygen from the tracer molecules, laser-induced measurements of the phosphorescence lifetime of the 'oxygen-free' fuel vapor in nitrogen bath gas is made using the fourth harmonic output of an Nd:YAG laser. A fast-time-gated ICCD camera is used to take images and determine both the fluorescence and phosphorescence lifetimes with this laser excitation. Ultimately, these techniques will allow measurements of fuel concentration at high temperature and pressure conditions during engine cycles through better understanding of the purge requirements for quenching-free measurements.