Shock Tube and Laser Absorption Study of CH2O Oxidation via Simultaneous Measurements of OH and CO

The oxidation of Ar-diluted stoichiometric CH2O-O-2 mixtures was studied behind reflected shock waves over temperatures of 1332-1685 K, at pressures of about 1.5 atm and initial CH2O mole fractions of 500, 1500, and 5000 ppm. Quantitative and time-resolved concentration histories of OH and CO (at both v '' = 0 and v '' = 1) were measured by narrow-linewidth laser absorption at 306.7 and 4854 nm, respectively. A time delay was observed between the formation of v '' = 0 and v '' = 1 states of CO, suggesting that CO was kinetically generated primarily in the ground state and then collisionally relaxed toward vibrational equilibrium. The measured CO and OH time-histories were used to evaluate the performance of four detailed reaction mechanisms regarding the oxidation chemistry of CH2O. Further analyses of these time-history data have also led to improved determination for the rate constants of two key reactions, namely H + O-2 = O + OH (R1) and OH + CO = CO2 + H (R2), as follows: k(1) = 8.04 x 10(13) exp(-7370 K/T) cm(3) mol(-1) s(-1), k(2) = 1.90 x 10(12) exp(-2760 K/T) cm(3) mol(-1) s(-1); both expressions are valid over 1428-1685 K and have 1 sigma uncertainties of approximately +/- 10%.