Vapor Phase Mass Measurements of In-Cylinder Diesel Fuel Sprays

Images of transient, evaporating, diesel fuel sprays were taken inside of an optically accessible engine. The images were converted into vapor mass, equivalence ratio, and temperature contour maps of the spray. The conversion is accomplished using an exciplex fluorescence method. The experiment focused on the period of time between start of injection and the onset of autoignition. Engine operating conditions were varied using three operating parameters. These parameters were: intake temperature, ambient density, and engine speed.

The effects of increasing intake temperature were to create richer, hotter mixtures with increased total vapor mass at autoignition. Increasing ambient density created cooler, leaner mixtures with decreased vapor mass at autoignition. Increasing engine speed showed increased Top Dead Center (TDC) temperature and decreased ignition delay. These effects competed with one another to control the total amount of vapor mass. The dominating effect, either temperature or ignition delay, was found to be a function of engine speed.