A possible radiative model for micronic carbonaceous particle sizing based on time-resolved laser-induced incandescence

A numerical model of time-resolved laser-induced incandescence (TIRE-LII) for different kinds of large carbonaceous particle is developed in this paper. Theoretical temporal LII signals were computed for the following classes of particles: soot, the well known hollow particles called cenospheres (tens of microns) and full carbonaceous particles called by analogy pleospheres (a few microns), pleo- from the Greek pleos (solid). The large carbonaceous particles have a characteristic time for internal gradient dissipation much longer than soot, thus a temperature profile establishes inside them. On the basis of these observations, a spatial time-dependent model for cenospheres and pleospheres was considered, i.e. a system of partial differential equations based on mass and energy balances. The computed LII signals pointed out the sensitivity of the model to the different kinds of particle considered in this paper. The two classes of large carbonaceous particles showed different thermal behaviours. Furthermore, the analysis of the combined effects on the total theoretical LII signal of the different particles highlighted the sensitivity of the time decay of the LII profiles to the mean particle size distributions and to the relative particle number ratios inside the control volume. These results may constitute a basis of a strategy for a comprehensive discrimination between soot and large particles, and for their identification, as in heavy-oil combustion.