Santoro flame: The volume fraction of soot accounting for its morphology & composition

The soot volume fraction, f_v, measured by Santoro and coworkers in an ethylene diffusion flame by light extinction has become a standard for validation of models for soot formation and growth. This f_v, however, has been obtained assuming soot spheres of constant refractive index. As a result, when compared to that measured by microscopy and thermocouple particle densitometry (TPD) at identical conditions it is almost twice as much! This apparent disparity is resolved here by accounting for the detailed fractal-like structure and composition of soot through coupling discrete element modeling with the discrete dipole approximation to invert light extinction data and extract the f_v. This is in good agreement with the f_v from microscopy and TPD pointing out the benefit of accounting for the ramified soot morphology to close the soot mass balance and facilitate comparison of experiments with models for soot formation and growth.