Reaction rate constants for seven large alkanes + hydroxyl (OH) radicals were measured behind reflected shock waves using OH laser absorption. The alkanes, n-hexane, 2-methyl-pentane, 3-methyl-pentane, 2,2-dimethyl-butane, 2,3-dimethyl-butane, 2-methyl-heptane, and 4-methyl-heptane, were selected to investigate the rates of site-specific H-abstraction by OH at secondary and tertiary carbons. Hydroxyl radicals were monitored using narrow-line-width ring-dye laser absorption of the R1(5) transition of the OH spectrum near 306.7 nm. The high sensitivity of the diagnostic enabled the use of low reactant concentrations and pseudo-first-order kinetics. Rate constants were measured at temperatures ranging from 880 K to 1440 K and pressures near 1.5 atm. High-temperature measurements of the rate constants for OH + n-hexane and OH + 2,2-dimethyl-butane are in agreement with earlier studies, and the rate constants of the five other alkanes with OH, we believe, are the first direct measurements at combustion temperatures. Using these measurements and the site-specific H-abstraction measurements of Sivaramakrishnan and Michael (2009) [1,2], general expressions for three secondary and two tertiary abstraction rates were determined as follows (the subscripts indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon): S20=1.58×10-11exp(-1550K/T)cm3molecule-1s-1(887-1327K)S30=2.37×10-11exp(-1850K/T)cm3molecule-1s-1(887-1327K)S21=4.5×10-12exp(-793.7K/T)cm3molecule-1s-1(833-1440K)T100=2.85×10-11exp(-1138.3K/T)cm3molecule-1s-1(878-1375K)T101=7.16×10-12exp(-993K/T)cm3molecule-1s-1(883-1362K) © 2014 The Combustion Institute.

Ketones are potential biofuel candidates and are also formed as intermediate products during the oxidation of large hydrocarbons or oxygenated fuels, such as alcohols and esters. This paper presents shock tube ignition delay times and OH reaction rates of 2-butanone (C2H5COCH3) and 3-buten-2-one (C2H3COCH3). Ignition delay measurements were carried out over temperatures of 1100-1400K, pressures of 3-6.5atm, and at equivalence ratios (F{cyrillic}) of 0.5 and 1. Ignition delay times were monitored using two different techniques: pressure time history and OH absorption near 306nm. The reaction rates of hydroxyl radicals (OH) with these two ketones were measured over the temperature range of 950-1400K near 1.5atm. The OH profiles were monitored by the narrow-line-width ring-dye laser absorption of the well-characterized R1(5) line in the OH A-X (0, 0) band near 306.69nm. We found that the ignition delay times of 2-butanone and 3-buten-2-one mixtures scale with pressure as P-0.42 and P-0.52, respectively. The ignition delay times of 3-buten-2-one were longer than that of 2-butanone for stoichiometric mixtures, however, for lean mixtures (F{cyrillic}=0.5), 2-butanone had longer ignition delay times. The chemical kinetic mechanism of Serinyel et al. [1] over-predicted the ignition delay times of 2-butanone at all tested conditions, however, the discrepancies were smaller at higher pressures. The mechanism was updated with recent rate measurements to decrease discrepancy with the experimental data. A detailed chemistry for the oxidation of 3-buten-2-one was developed using rate estimation method and reasonable agreements were obtained with the measured ignition delay data. The measured reaction rate of 2-butanone with OH agreed well with the literature data, while we present the first high-temperature measurements for the reaction of OH with 3-buten-2-one. The following Arrhenius expressions are suggested over the temperature range of 950-1450K: kC2H5COCH3+OH=6.78×1013exp(-2534/T)cm3mol-1s-1kC2H3COCH3+OH=4.17×1013exp(-2350/T)cm3mol-1s-1. © 2013 The Combustion Institute.