PAH formation characteristics of hydrogen-enriched methane diffusion flames

Soot emission remain undesirable and a source of major health concern for the environment and human beings. It is also a major source of PM10 and has been shown to be toxic, mutagenic and cancerous when inhaled for a long time. These lethal effects are due to adsorbed polycyclic aromatic hydrocarbons (PAHs) on the soot surface which double as important precursors to the formation of soot particles. Hence, an understanding of the formation characteristics of PAH is imperative to effectively limit its formation and hence reduce soot. In this study, an experimental methodology to analyse the formation characteristics of PAH in an inverse diffusion methane-air-H2 flame utilising simultaneous planar laser induced fluorescence imaging of PAH and hydroxyl radical (OH) is presented. Additionally, same fuel mixture combinations were simulated for a 1-D opposed-jet laminar non-premixed flame to allow comparison between experimental results and computational results. Qualitative PAH intensity values from experiment were observed to increase as the height above burner (HAB) increased. However, a strong reduction was observed in both PAH intensity values and PAH concentration for the experimental and simulated results respectively with increasing hydrogen addition. Similarity in the magnitude of PAH reduction between experiment and simulated values was observed with heights closer to the burner lip. The reduction in acetylene and propargyl concentrations, and reduced H-abstraction rates, which minimised the availability of active sites for PAH growth is implicated for the reduction in PAH with H2 addition. This PAH experimental methodology is suitable for any diffusion flame fuel/air mixture PAH analysis.

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