Determination of rate coefficients for reactions of formaldehyde pyrolysis and oxidation in the gas phase

Seven mixtures of formaldehyde and oxygen diluted in argon were studied behind reflected shock waves at temperatures from 1340 to 2270 K and pressures from 0.7 to 2.5 atm. Mixture compositions covered a range from pure pyrolysis to lean oxidation at a stoichiometric ratio of 0.17. The progress of reaction was monitored by laser absorption of CO molecules. Experimental rates of CO formation were found to be 80% higher, in the case of pyrolysis, and 30% lower, under lean oxidation, than those predicted by the current reaction model, GRI-Mech 1.2. The collected experimental data were subjected to extensive detailed chemical kinetics analysis, including optimization with the solution mapping technique. The analysis identified a strong correlation between two rate constants. Assuming a recent literature expression for one of them produced k(-1a) = 2.66 x 10(24)T(-2.57)e(-215/T) cm(6) mol(-2) s(-1) for the reaction H + HCO + M --> CH2O + M. A new expression was developed for the reaction HO2 + CH2O --> HCO + H2O2, k(6) = 4.11 x 10(4)T(2.5)e(-5136/T) cm(3) mol(-1) s(-1), by fitting the present and literature results. With these modifications, the new reaction model provides good agreement with our experimental data and an acceptable agreement with most literature experimental observations.