Separate differential equations are solved for soot volume fraction and number density describing their convection and time rates of nucleation, heterogeneous surface growth and oxidation through the respective balance [7].
The soot model quantifies the rate of soot emissions as an outcome of the balance between production and transport of soot particles (forming from large polycyclic aromatic hydrocarbons).
The inception process is controlled by the formation and growth of these ring-formed molecules. Acetylene is set as the soot precursor as it is the key species for the formation of the first aromatic ring.
Soot subsequently grows as the hydrogen abstraction from the hydrocarbon takes place, followed by the addition of an acetylene molecule to the radical-site formed.
When these compounds reach a certain size, they further grow by sticking to each other such that larger clusters develop and eventually evolve as solid particles.
While the growth reactions are temperature-dependant (as the agglomeration rate depends on the frequency of collisions), the oxidation reactions are accelerated by increasing the temperature as well as the O2 and OH concentrations.