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Exciplex-based fluorescence was employed for the remote, nonintrusive, instantaneous and point measurements of fuel droplet temperature. A hydrocarbon droplet doped with naphthalene and TMPD was allowed to evaporate in a heated gaseous mixture of oxygen, nitrogen, carbon dioxide and water. The fluorescence emission spectra from a droplet subjected to nitrogen laser excitation were measured with an optical multichannel analyzer. Photographic observation showed that a droplet fluoresced with a green color at room temperature. As the temperature was raised, fluorescence became purple. The ratio of fluorescence emission intensities at two different wavelengths was an appropriate criterion for in situ determination of droplet temperature. Oxygen in the ambient gas was found to be a major quencher for the fluorescence. Droplet velocity relative to the ambient gas did not have an appreciable influence on the fluorescence emission spectra.

Laser Rayleigh scattering was applied for the remote, nonintrusive measurements of the time history of the transient fuel vapor concentration in the combustion chamber which was caused by the timed injection of unleaded regular gasoline, n-Pentane and n-Hexane into the intake port of a motored automotive spark ignition engine. The results denonstrated that the fuel vapor concentration increased with the time elapsed from the start of the fuel injection and reached a peak after which it decreased during the intake stroke. It showed a very slight increase during the compression stroke. It was also revealed that the fuel vapor concentration increased with an increase in the quantity of fuel injected, the engine speed and the fuel injection pressure. It showed a maximum as a function of the fuel injection timing.