NOx emission characteristics of partially premixed laminar flames of H2/CO/CO2 mixtures

NOx emission indices were experimentally measured for partially premixed laminar flames of five different H2/CO/CO2 fuels over a wide range of equivalence ratios. Through those fuels, the effects of H2/CO ratio and CO2 concentration on NOx emissions, flame appearance, visible flame height and flame temperature are presented. EINOx values increase when 1.0 ≤ Φ ≤ 1.6, then remain near the highest value, before decreasing slowly when 3.85 ≤ Φ ≤ ∞. The increase of the CO2 concentration reduces the EINOx for the whole range of equivalence ratios, while the increase in the H2/CO ratio reduces the EINOx when Φ ≤ 2.0 and is inconsequential for richer mixtures. The variation in flame temperatures approximates EINOx trends. The variation of flame color from blue to orange when the H2/CO ratio is increased might be explained by higher CO levels in by-product combustion.