Part 2:Application to Combustion-Generated Soot Aerosols as a Function of Fuel Equivalence Ratio Particle Morphology and Density Characterization by Combined Mobility and Aerodynamic Diameter Measurements.

摘要

Composition,shape factor,size,and fractal dimension of soot aerosol particles generated in a propane/O_2 flame were determined as a function of the fuel equivalence ratio (phi).Soot particles were first size-selected by a differential mobility analyzer (DMA) and then analyzed by an Aerodyne aerosol mass spectrometer (AMS).The DMA provides particles of known mobility diameter (d_m).The AMS quantitatively measures the mass spectrum of the nonrefrac-tory components of the particles and also provides the vacuum aerodynamic diameter (d_(va)) corresponding to the particles of known mobility diameter.The measured d_m,d_(va),and nonrefractory composition are used in a system of equations based on the formulation presented in the companion article to estimate the particle dynamic shape factor,total mass,and black carbon (BC) content.Fractal dimension was estimated based on the mass-mobility relationship.Two types of soot particles were observed depending on the fuel equivalence ratio.Type 1:for phi 4 (high propane/O_2),d_(va) was linearly proportional to d_m.Analysis of the governing equations showed that these particles were nearly spherical (likely compact aggregates),with a dynamic shape factor of 1.1 (versus 1 for a sphere) and a fractal dimension of 2.95 (3 for a sphere).These particles were composed of about 50 PAH,45 BC,and 5 aliphatic hydrocarbons (particle density=1.50 g/cm~3).These results help interpret some measurements obtained in recent field studies.