A combined optical diagnostic based on ultraviolet absorption and planar laser-induced fluorescence for quantification of vapor concentration distributions in fuel sprays

A UA-PLIF (Ultraviolet-absorption combined planar laser-induced-fluorescence) optical diagnostic is proposed for two-dimensional quantitative measurements on vapor concentration distributions in evaporated fuel sprays. The idea is to establish an optical system to enable calibrating PLIF measurement in situ using the vapor mass determined by line-of-sight measurement of UA. The imaging system consists of UA (central absorption wavelength of 266 nm) and PLIF (central fluorescence wavelength of 430 nm) optical sub-systems. Since the vapor mass measured by UA is quantitative, measurements of vapor concentration distributions by PLIF can be calibrated in situ based on their geometrical and physical corresponding relationship. The feasibility of UA-PLIF has been verified through an experiment of a completely evaporated fuel spray under the ambient temperature of 573 K and ambient pressure of 1.0 MPa. Acetone was chosen to be the single-component test fuel due to its strong fluorescent band near 430 nm and appropriate absorption characteristic near 266 nm. It was found that the uncertainties due to incident light absorption in the optical path of the PLIF system and the light intensity profile of PLIF laser sheet can be well minimized by an iteration algorithm of optimization. An index named CCR (Consistency of concentration ratio), which is used to describe the accuracy of the measurement results, decreases from 0.343 to 0.108, indicating that the accuracy of PLIF measurement results can be effectively improved by more than 3-times when applying this combined diagnostic.