On the Burning Rate of Carbon Monoxide

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Abstract
Burning velocity measurements of the CO–O2–N2–H2O system were made with the flat-flame burner technique. The plan of experimentation was to vary the H2O content, the equivalence ratio, and the pressure, while holding the flame temperature constant by controlling the proportion of N2 in the mixture. The results could be represented empirically by the relation: vu2=3.8×106(CO)u(H2O)u0.5(P/Patmos)−0.24e−11 130/Tb,where vu is burning velocity (cm/sec), (CO)u and (H2O)u are mole fractions in the unburned gas, P is pressure, and Tb is burned-gas temperature. The Zeldovich, Frank-Kamenetsky, and Semenov equation was used to obtain an ``over-all'' activation energy (20 kcal) and frequency factor for the process, and the CO oxidation rate in this type of flame was then compared with the rate at which the CO forming as an intermediate in a lean hydrocarbon-air flame is oxidized in the downstream portion of such a flame. The comparison showed that, at comparable conditions, the CO oxidized 5.6 times as fast in the CO flame as in the hydrocarbon flame. Temperature traverses in hydrocarbon-air flames to which large proportions of H2O have been added showed the rate of CO oxidation to be slightly increased thereby. Equilibrium concentrations of the species H, OH, and O in the burned gases were calculated for a variety of CO–O2–N2–H2O mixtures, all at the same flame temperature, and correlations with burning velocity were sought. The square of the burning velocity was found to be directly proportional to (OH)b(CO)b0.72; alternatively, the group (H)b(O2)b0.136 gave equally good correlation. A third successful grouping was [(H)b+0.15(OH)b]½. The writers are not convinced that correlations of this type reveal the burning mechanism.

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