Quantitative Measurement of Droplets and Vapor Concentration Distributions in Diesel Sprays by Processing UV and Visible Images 2001-01-1294

In order to measure the droplets and vapor concentration inside a fuel spray, a dual-wavelength laser absorption-scattering technique was developed using the second harmonic (532nm) and the fourth harmonic (266nm) of a Nd:YAG laser and using dimethylnaphthalene as the test fuel. The investigation results show that dimethylnaphthalene, which has physical properties similar to diesel fuel, is almost transparent to visible light near 532nm and is a strong absorber of ultraviolet light near 266nm. Based on this result, the vapor concentration in a fuel spray can be determined by the two separate measurements: a transmission measurement at a non-absorbing wavelength to detect the droplets optical thickness and a transmission measurement at an absorbing wavelength to detect the joint vapor and droplets optical thickness. The droplets density can be determined by extinction imaging through the transmission at the non-absorbing wavelength. Based on this technique, the distributions of droplets and vapor concentration in diesel sprays, which were injected into an atmosphere of high-temperature (833K) and high-pressure (4.1MPa) nitrogen, were imaged and quantitatively analyzed. The experimental results show that this imaging technique is a promising diagnostics to simultaneously obtain quantitative information on droplets and vapor concentration in a fuel spray.