Effects of fuel structure on soot precursors in a laminar co-flow flame

The goal of this work is to aid in understanding the effects of fuel molecular structure on the spatial development of polycyclic aromatic hydrocarbons (PAH), or soot precursors, in an axisymmetric, co-flow, laminar flame configuration at atmospheric pressure. Two fuels with varying molecular structure are investigated: iso-octane/n-dodecane mixture and m-xylene/n-dodecane mixture. The flames investigated are non-premixed and rich premixed (jet equivalence ratio of 6) flames, and the total carbon flow rate is kept constant to facilitate comparison between fuels. A laser-induced fluorescence technique is used to obtain spatially-resolved PAH in the jet flames. The PAH are identified into two classes: single/two ring aromatics (small) and molecules having three/four rings (large). The experimental results indicate that the level of aromatics for m-xylene/n-dodecane fuel is higher compared to isooctane/n-dodecane fuel. The comparison of PAH in non-premixed and premixed flames show significant differences in the spatial development of PAH along the downstream direction. These results are compared to initial simulation results and a methodology for using the PAH-LIF technique for validating soot models in laminar jet flames is proposed.