The effects of the hydrogen addition on the HCN profiles in fuel-rich-premixed, burner-stabilized C1–C3 alkane flames

The effects of hydrogen addition on HCN formation and consumption in fuel-rich, burner-stabilized methane, ethane and propane flames are reported. The HCN mole fraction was measured using quartz-microprobe sampling followed by direct absorption spectroscopy. Experiments were performed at equivalence ratio of 1.3, with 0 and 0.2 mole fraction of hydrogen in the fuel. The mass flux through the burner was varied for each mixture. The addition of hydrogen only modestly affects the HCN mole fractions. For the vast majority of the flames studied, the peak HCN fraction decreases by less than 20% upon hydrogen addition. The decrease in HCN fraction is smaller in ethane and propane flames compared to methane flames. Increasing the mass flux, independent of hydrogen fraction, results in a small increase in the HCN peak fraction, a shift of the HCN peak towards the burner and acceleration of the HCN consumption downstream. Burnout of HCN occurs faster in ethane and propane flames than in methane flames. Comparison of the experimental results with computations using two mechanisms for NCN oxidation shows that both mechanisms predict the HCN profiles reasonably well.