On the inclusion of preferential diffusion effects for PAH tabulation in turbulent non-premixed ethylene/air sooting flames

Soot is an unwelcome by-product of combustion that not only raises public health issues but also plays a role in climate change and, more practically, deteriorates engine performances. Although critical for the design of low-soot burners, the numerical prediction of soot phenomena remains a challenge. Among other, one major difficulty is linked to the numerous chemical species involved in the chemistry of gaseous soot precursors (PAHs). In this paper, an improved modeling methodology is proposed to describe PAHs, which relaxes standard assumptions on transport properties and number of PAHs, two aspects which play a major role on the PAH evolution. To do so, a hybrid method has been developed, coupling semi-detailed chemistry integration for the accurate flame structure description, with pre-tabulated quantities issued from prior simple calculations for gaseous soot precursors modeling. In addition the classical flamelet approach has been extended to account for non-unity Lewis numbers. The proposed modeling approach is first validated against laminar counter flow diffusion ethylene/air flames and then applied to a 3D turbulent non-premixed ethylene/air combustor operated at Cambridge University. Comparison with measurements confirm the validity of the approach for the prediction of PAH.