Optical Measurements of Soot Size and Number Density in a Spray-Atomized, Swirl-Stabilized Combustor

In-flame optical measurements of soot particulates in a turbulent, recirculating (i.e., complex flow) model laboratory combustor are described. A nonintrusive optical probe based on large-angle (60 and 20 deg) intensity ratio scattering was used to yield a point measurement of soot particulate in the size range of 0.08 to 0.38 μm. A shale-derived JP-8 stock, isooctane, and mixtures of isooctane with various ring and aromatic compounds blended to yield the smoke point of the JP-8 stock were separately injected as a liquid spray through a twin-fluid atomizer. One blend was also introduced prevaporized through a hollow-cone nozzle. The addition of ring compounds to the base isooctane as well as operation on JP-8 increased the amount of soot produced, although the total amount of soot produced depended on fuel type for those fuels of equivalent smoke point. The spatial distribution of soot as well as the amount produced was found to be sensitive to nozzle atomization quality and injection momentum. The amount of soot produced was reduced by a reduction in fuel loading. However, injection of fuel in a prevaporized state both increased the amount of soot produced and changed spatially the region over which soot was distributed. Scanning electron micrographs of extracted samples established that the optical technique resolved the large particle wing of the soot size distribution.