Quantitative two-dimensional fuel vapor concentration measurements in an evaporating diesel spray using the exciplex fluorescence method

Kim, T. Quantitative Two-Dimensional Fuel Vapor Concentration Measurements in an Evaporating Diesel Spray Using the Exciplex Fluorescence Method. University of Wisconsin-Madison, 2001.

To experimentally investigate evaporating sprays under conditions experienced in high-speed direct injection (HSDI) diesel engines, the exciplex (excited state complex) laser-induced fluorescence technique and high-speed natural luminosity cinematography were applied for non-reacting and reacting diesel sprays respectively. A combustion-type spray chamber was developed and provides diesel engine conditions with good repeatability.

A detailed set of calibration experiments were performed in order to quantify the TMPD (tetramethyl-p-phenylene-diamine) fluorescence signal. The effects of pressure and collision partner were found to be negligible. The effect of temperature was found to increase the fluorescent yield up to 600 K, then decrease it for further increases in temperature. An adiabatic mixing model for the estimation of the temperature reduction due to vaporization allowed correction of the temperature effects.

The fuel vapor concentration was integrated and found to agree well with the mass of fuel injected (<10%) when all the liquid fuel was vaporized. Estimation of the uncertainty of the measurements was 21%.

Using a density of 15 kg/m3 the effects of ambient gas temperatures, peak injection pressures and nozzle hole sizes were investigated. Limited experiments were performed at 7.5 kg/m3.

Higher ambient temperatures were shown to produce a wider radial vapor extent with higher equivalence ratios and higher gradients at the edge of the jet. Distributions of the vapor concentration for higher injection pressures showed faster fuel vaporization rates and larger spray head volumes. Lower ambient density or larger hole sizes were shown to provide faster vapor penetration and longer liquid lengths. The effects of the aforementioned parameters on the spray-spreading angle were shown to be transient in nature although as injection progressed the steady values were achieved.

Natural luminosity images were compared with the exciplex image data. As a result, the first detection of the chemiluminescence signals seems to occur in fuel-rich vapor regions near the boundary of the liquid core with an equivalence ratio near 2 and a temperature of approximately 800 K. These conditions were found to be independent of injection pressure and nozzle diameter for the ambient condition 15 kg/m3 and 1000 K.