Absolute radical concentration measurements in low-pressure H₂/O₂ flames during the combustion of graphite

Absolute CN and CH radical concentrations were determined in situ during the combustion of a graphite substrate in premixed, laminar, low-pressure, H₂/O₂ flames for two different equivalence ratios, φ = 1 and φ = 1.5. For CN measurements, a small amount of NO (1.8%) was added. The graphite substrate reduced the flame temperature in the vicinity of its surface. The CN concentrations were three times higher for the rich flame than for the stoichiometric flame. CH concentrations were slightly higher for the stoichiometric flame than for the rich flame. The observed CH/CN concentration ratio was substantially lower compared to NO-doped low-pressure CH₄/O₂ flames. The obtained quantitative information could serve as a first calibration point for detailed numerical simulations of the burning solid graphite, which are based on the concept of surface elementary reactions. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).