Experimental and numerical study on structure of laminar premixed syngas-air-diluents flames

The structures of laminar premixed syngas-air-diluents flames were obtained at different equivalence ratios (0.6, 0.8, 1.0, 1.2), diluents (N2/CO2), and dilution ratios (3% and 5%) by using OH-PLIF technique. Flame structure was analyzed on the basis of the flow field and species distribution which were calculated with STAR-CD. The results show that high OH distribution shifts towards the outer flame boundary with the increase of equivalence ratio; for lean mixture, the region of high OH radical concentration locates along the conic primary reaction boundary; OH radical concentration at the flame cone tip decreases, and the numerical simulation results show that no leakage occurs at the flame tip; for mixture at stoichiometric ratio, high OH radical concentration appears along the flame front and on the flame surface, meaning the occurrence of a premixed combustion zone and a diffusion combustion zone, and the OH distribution appears to resemble a W shape; due to the effects of diluents N2 and CO2, the laminar burning velocity decreases, leading to the extension of the flame front, and CO2 has a greater impact on the flame structure compared to N2; OH radical concentration decreases along the flame front while increases in the diffusion zone, which means the premixed combustion is weakened while the diffusion combustion is intensified.