Flow Reactor Studies and Kinetic Modeling of the Reaction H /O 2 2 M. A. MUELLER, T. J. KIM, R. A. YETTER, F. L. DRYER Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08536 Received 10 June 1998; accepted 20 August 1998 ABSTRACT: Profile measurements of the H 2 /O 2 reaction have been obtained using a variable pressure flow reactor over pressure and temperature ranges of 0.3–15.7 atm and 850–1040 K, respectively. These data span the explosion limit behavior of the system and place significant emphasis on HO 2 and H 2 O 2 kinetics. The explosion limits of dilute H 2 /O 2 /N 2 mixtures extend to higher pressures and temperatures than those previously observed for undiluted H 2 /O 2 mixtures. In addition, the explosion limit data exhibit a marked transition to an extended second limit which runs parallel to the second limit criteria calculated by assuming HO 2 formation to be terminating. The experimental data and modeling results show that the ex- tended second limit remains an important boundary in H 2 /O 2 kinetics. Near this limit, small increases in pressure can result in more than a two order of magnitude reduction in reaction rate. At conditions above the extended second limit, the reaction is characterized by an overall activation energy much higher than in the chain explosive regime. The overall data set, consisting primarily of experimentally measured profiles of H 2 ,O 2 , H 2 O, and temperature, further expand the data base used for comprehensive mechanism de- velopment for the H 2 /O 2 and CO/H 2 O/O 2 systems. Several rate constants recommended in an earlier reaction mechanism have been modified using recently published rate constant data for H + O 2 (+ N 2 ) = HO 2 (+ N 2 ), HO 2 + OH = H 2 O + O 2 , and HO 2 + HO 2 = H 2 O 2 + O 2 . When these new rate constants are incorporated into the reaction mechanism, model predictions are in very good agreement with the experimental data.  1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 113– 125, 1999 INTRODUCTION The hierarchical development of detailed kinetic mechanisms for hydrocarbon oxidation and other complicated reacting systems necessarily begins with the H 2 /O 2 chemistry which plays a prominent role in determining the composition of the radical pool [1]. While the kinetics of the H 2 /O 2 systems have been Correspendence to: F. L. Dryer Contract grant sponsor: Department of Energy, Office of Basic Energy Sciences Contract grant number: SE-FG02-86ER-13503 Contract grant sponsor: Air Force Office of Scientific Research Contract grant number: F49620-93-1-0427  1999 John Wiley & Sons, Inc. CCC 0538-8066/99/020113-13 extensively studied [2,3], reactions involving the for- mation and consumption of HO 2 and H 2 O 2 are com- paratively less understood than the chain-branched re- actions which dominate at low pressures and high temperatures. In a previous paper [4], we presented a moist CO oxidation reaction mechanism incorporating a detailed H 2 /O 2 submechanism developed and vali- dated using high-pressure (2.5 – 15.7 atm) flow reactor data which placed significant emphasis on reactions involving HO 2 and H 2 O 2 [5]. Since that publication, new rate constant data have been published for several important reactions including H + O 2 (+M) = HO 2 (+M) [6,7] and HO 2 + OH = H 2 O + O 2 [8]. In par- ticular, the studies of Bromly et al. [6] and Davidson et al. [7] recommended rate expressions for H + O 2