Quantitative Vapor Phase Imaging of In-Cylinder Diesel Fuel Sprays

Beckman, M. S. Quantitative Vapor Phase Imaging of In-Cylinder Diesel Fuel Sprays. University of Wisconsin-Madison, 2004.

Images of transient, evaporating, diesel fuel sprays are taken inside of an optically accessible engine. The images are converted into vapor mass, equivalence ratio, and temperature contour maps of the spray. The quantification is accomplished using an exciplex fluorescence method. The method allows the vapor regions of the spray to be imaged separately from the liquid regions of the spray and then converted into mass concentration. The experiment focuses on the ignition delay period of the injection process. This period is the time between start of injection and the beginning of autoignition. The reason for the narrow focus is that the exciplex method does not provide quantitative information beyond the autoignition point.

Information regarding vapor concentration and temperature during the ignition delay period is important for a variety of reasons. These reasons include: Determining factors which affect ignition delay, determining the composition and temperature of the pre-mixed burn, measurement of the total amount of vaporization prior to autoignition, and validation of modeling data. Engine operating conditions are varied using three principle variables. These variables are intake temperature, ambient density, and engine speed. These are variables which are commonly examined in engine research and are easily controlled. In addition to the three variable already mentioned, top dead center temperature and ignition delay are measured but could not be independently varied.

The effect of increasing intake temperature is to reduce ignition delay, increase top dead center temperatures, increase the total amount of vaporization, and decrease the efficiency of the pre-mixed burn. These results are observed at all engine speeds. Increasing ambient density reduces ignition delay, lowers top dead center temperatures, and decreases the amount of vapor mass. No effect of the efficiency of the pre-mixed bun is measured. The effect of increasing ambient density is dependent on the engine speed. Increasing engine speed shows increasing top dead center temperature and decreasing ignition delay. These effects compete with one another to control the total amount of vapor mass. The overriding effect, either temperature or ignition delay, is found to be a function of engine speed.