Estimating soot primary particle diameter using time-resolved laser-induced incandescence

Time-resolved LII for primary particle size determination is tested using three model carbon blacks. Optical properties change as does the nanostructure upon laser annealing whereas aggregate morphology and primary particle size remain equivalent to the original material, as shown by TEM comparisons. Extraction of primary particle size (dp) values by fitting the time-resolved LII data does not yield a single consistent value for each of the carbon blacks with TEM measured primary particle sizes of 18, 45 and 112 nm. The conductive heat transfer coefficient is shown to differ substantially between these materials, even when normalized for primary particle surface area. Aggregate structure in the form of intra-aggregate connectivity and shielding is suggested as the underlying cause, not presently captured by LII models.