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chapter 5 turbulent diffusion flames - FedOA

chapter 5 turbulent diffusion flames - FedOA

Rx4 Ri + H2 => Ai + H

Rx4 Ri + H2 => Ai + H Rx5 Ri + H2O => Ai + OH Rx6 Ri + C2H2 => Ak + H Rx7 Ri + Aj => Ai+j + H Rx8 Ri + Rj => Ai +j Rx9 Ri + H => Ai Rx10 Ai + OH => Ak + HCO Rx11 Ri + O2 => Ak + 2CO Here Ai is an aromatic compound having a molecular mass corresponding to the ith class of compounds and Ri is its radical. The rate constants are determined by using the Arrhenius formulation multiplied by a size dependent factor and a collision efficiency set to unity, except for the coagulation reactions [35]. Coagulation The aromatics growth process can occur by formation of molecular clusters from collision of molecular compounds. The interaction energy is due to van der Waals forces. Small molecular mass aromatics may exhibit low interaction energy and as molecular mass increases interaction energy increases and the coagulation efficiency becomes more effective. The model of D’Alessio et al. [24], for premixed flame coagulation, is applied. For particles around 1 nm diameter the coagulation efficiency is about 1E–4 increasing to unity for particles around 10 nm diameter (Fig. 1.5). Fig. 1.4 Size depending coagulation efficiency [24]. 26

In summary the complete scheme is made up of the gas-phase and particle phase schemes detailed previously [17-35] and added to the GRI mechanism [9]. There are 26 sections each containing the compound and its radical, starting with C12 and increasing by a constant factor of two. The diameter range is 1 nm – 200 nm. The largest sizes are to ensure that the series does not artificially truncate the solution. Reactions are balanced on carbon number; a sectional reaction generally results in two product classes proportioned to satisfy carbon element balance, but hydrogen element is not strictly balanced. The particle phase sectional combinations generate about 1850 reactions. 27

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