Abstract

Spectrally resolved emission measurements and multiwavelength extinction measurements are used to probe diesel fuel sprays at temperatures of 700-950 K and pressures of 20-30 atm. The emission measurements are performed by using a 12-element infrared spectrometer that operates in the 6-12 μm wavelength range and is sampled at 125 kHz. These measurements are performed in the near-tip region of a diesel injector, where the optical thickness in visible and ultraviolet wavelengths is a major barrier to traditional measurements. The spectrally resolved emission measurements can be used to identify sooting zones within the fuel spray by means of the characteristic spectral signature of soot at flame temperatures. In addition, molecular radiators are clearly present in both oxidizing and pyrolyzing sprays. The spatial resolution of these measurements is 1.2 mm at the spray centerline. A multiwavelength, coaxial extinction measurement in the near-tip region of the spray has also been demonstrated. The outputs from a CO₂ laser (9.2μm), an Nd:Yag laser (1.06μm), and a He-Ne laser (0.633μm) were aligned and focused to a beam size of 0.25 mm at the spray centerline. The ratio of these extinction measurements is a function of droplet size and is relatively insensitive to optical depth (transmissivity of the spray in the visible region was typically below 50%). Droplet diameters were observed to be approximately 6μm in the near-tip region of the spray.

© 1990 Optical Society of America