A comprehensive study on CH 2O oxidation kinetics

Abstract

Results of calculations based on a detailed chemical mechanism for the oxidation of formaldehyde are compared with data from a variety of experimental conditions: flow reactor, shock tube, static reactor, and a lean flame. The range of conditions spans temperatures from 773 to 2500 K, equivalence ratios from pure pyrolysis to very fuel-lean and pressures from 0.3 to 1.5 atm. New experimental results from the oxidation of formaldehyde in flow reactors at 1095 K are reported. The original model, based on reaction rate constants obtained in the literature, was modified based on comparisons of calculated and experimental results. Recommended changes were guided by extensive sensitivity and flux analysis for each case, as well as on the current knowledge of uncertainties in reaction rate constant values. The comprehensive mechanistic features of formaldehyde oxidation at low and high temperatures are discussed. The results of the analysis reveal the key role of HO 2 radicals up to temperatures around 1100 K, through the cycle HCO + O 2 → CO + HO 2, CH 2O + HO 2 → HCO + H 2O 2 and H 2O 2 + M → OH + OH + M. Shock tube data are revisited using more recent rate constants to verify the model. Finally, the competition between formyl radical reactions HCO + M → H + CO + M and HCO + O 2 → CO + HO 2, which determines the rate of production of H radicals, was found to be the primary controlling factor in the evolution of lean formaldehyde flames. A matrix of influences of the most important reaction rates on the calculated parameters for the different experimental conditions summarizes the conclusions.