The effect of hydrogen addition to rich stabilized methane/air flames

In this paper we examined the effect of hydrogen addition on the formation and consumption of HCN and C2H2 in rich premixed CH4/air mixtures. The HCN measurements show that the HCN mole fraction decreases substantially with increasing hydrogen content in the fuel mixture. This decrease significantly exceeds the reduction in HCN expected from the dilution of the hydrocarbon fuel and nitrogen when hydrogen is added to the mixture, suggesting that addition of hydrogen affects the flame structure related to the formation of HCN. Large differences have been observed between HCN measurements and calculations based on several mechanisms. The addition of 23 % hydrogen to methane results in only a marginal reduction of the measured C2H2 concentration for the flames measured, suggesting that hydrogen addition does not have any significant effect on the flame processes responsible for C2H2 formation/consumption in CH4/air flames. Substantial disagreement is found between the experimental and numerical calculations of C2H2 based on the GRI 3.0 mechanism. Increasing the rate coefficient of the reaction C2H2 + OH → CH2CO +H resulted in good agreement between measured and calculated C2H2 profiles for all flames studied. Good agreement is found for the calculated C2H2 peak concentrations using Konnov_05; however the C2H2 oxidation rate in the post flame zone is substantially over predicted for all flames measured