Quantitative Analysis of Fuel Vapor Concentration in Diesel Spray by Exciplex Fluorescence Method 970796
An unsteady single spray of n-tridecane which was mixed with a small quantity of exciplex - forming dopants, that is naphthalene and TMPD, was impinged on a flat wall surface with high temperature of 550 K at a normal angle. These experiments were carried out in a quiescent N2 atmosphere with high temperature of 700 K and high pressure of 2.5 MPa. It was possible to generate the fluorescence emissions from the vapor and liquid phases in this spray, when a laser light sheet from a Nd:YAG laser was passing through the cross section of the spray containing its central axis. Then, clear 2 - D images of vapor and liquid phases in the spray were acquired simultaneously by this method. And, the vapor concentration was analyzed quantitatively by applying Lambert - Beer's law to the measured TMPD monomer fluorescence intensity from vapor phase, and by correcting the intensity for the effect of the quenching process due to the ambient temperature and fuel concentration. The experimental parameters are the impinging distance from the injector to the wall surface and the elapsed time from injection start. As a result, it is found that thermal decomposition of TMPD as a vapor tracer does not occur even in this high temperature field within a short time period, such as 80 ms. And, the fluorescence emission from the vapor phase decreases with increasing ambient temperature and vapor concentration. The change in vapor concentration with radial distance from the spray axis and the temporal change in fuel vapor mass and volume are discussed in detail. Moreover it is found that the process of the mixture formation depends on the impinging distance.