Soot Formation and Properties from Combustion of Toluene in a Shock Tube

Aromatic organic compounds are commonly found in various fossil fuels and their combustion in engines produces soot that has significant impacts on air quality, human health, and climate. Using toluene as a proxy, we have investigated the formation and properties of soot particles from the combustion of aromatic compounds in a shock tube. Several important properties of the soot particles were measured, including size distributions, effective density, elemental carbon (EC) to organic carbon (OC) ratio, morphology, and optical properties (light absorption, scattering, and single scattering albedo). The dependence of soot properties on combustion temperature and fuel equivalent ratio was explored. Combustion temperature showed significant impacts on particle size distribution, morphology, and EC/OC ratio. In general, higher combustion temperature yielded larger, more fractal soot particles with higher EC content. Soot yield increased as the fuel equivalent ratio increased. Increases in combustion temperature and fuel equivalent ratio enhanced the aerosol light absorption and reduced the single scattering albedo. Compared to propane and diesel fuel, toluene combusted in the shock tube produced significantly more soot at a faster rate and with an earlier soot inception. Our results contribute to a better understanding of the soot formation mechanism and properties, helping to assess climate and environmental impacts from the combustion of fossil fuels.10-2015-->