Article

A diaphragmless shock tube for high temperature kinetic studies

C. S. E. Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439-4831, USA
Review of Scientific Instruments (Impact Factor: 1.58). 10/2008; DOI: 10.1063/1.2976671
Source: IEEE Xplore

ABSTRACT A novel, diaphragmless shock tube (DFST) has been developed for use in high temperature chemical kinetic studies. The design of the apparatus is presented along with performance data that demonstrate the range and reproducibility of reaction conditions that can be generated. The ability to obtain data in the fall off region, confined to much narrower pressure ranges than can be obtained with a conventional shock tube is shown, and results from laser schlieren densitometry experiments on the unimolecular dissociation of phenyl iodide ( P2=57±9 and 122±7  torr , T2=1250–1804  K ) are presented. These are compared with results similar to those that would be obtained from a classical shock tube and the implications for extrapolation by theoretical methods are discussed. Finally, the use of the DFST with an online mass spectrometer to create reproducible experiments that can be signal averaged to improve signal/noise and the quality of mass peaks is demonstrated; something that is not possible with a conventional shock tube where each experiment has to be considered unique.

0 Bookmarks
 · 
59 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The decomposition of ethyl iodide and subsequent dissociation of ethyl radicals have been investigated behind incident shock waves in a diaphragmless shock tube by laser-schlieren (LS) densitometry (1150–1870 K, 55 ± 2 Torr and 123 ± 3 Torr). The LS density-gradient profiles were simulated assuming that the initial dissociation of C2H5I proceeded by 87% C–I fission and 13% HI elimination. Excellent agreement was found between the simulations and experimental profiles. Rate coefficients for the C–I scission reaction were obtained and show strong falloff. Gorin model RRKM (Rice, Ramsperger, Kassel, and Marcus) calculations are in excellent agreement with the experimental data with E0 = 55.0 kcal/mol, which is in very good agreement with recent thermochemical measurements and evaluations. However, E0 is approximately 2.7 kcal/mol higher than previous estimates. First-order rate coefficients for dissociation of C2H5I were determined to be k55Torr = 8.65 × 1068T−16.65 exp(−37,890/T) s−1, k123Torr = 3.01 × 1069T−16.68 exp(−38,430/T) s−1, k∞ = 2.52 × 1019T−1.01 exp(−28,775/T) s−1. Rates of dissociation for ethyl radicals were also obtained, and these are in very good agreement with theoretical predictions (Miller J. A. and Klippenstein S. J. Phys Chem Chem Phys 2004, 6, 1192–1202). The simulations show that at low temperatures ethyl radicals are consumed through recombination reactions as well as dissociation, whereas at high temperatures, dissociation dominates. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 433–443, 2012
    International Journal of Chemical Kinetics 01/2012; 44(7). · 1.57 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A miniature high repetition rate shock tube with excellent reproducibility has been constructed to facilitate high temperature, high pressure, gas phase experiments at facilities such as synchrotron light sources where space is limited and many experiments need to be averaged to obtain adequate signal levels. The shock tube is designed to generate reaction conditions of T > 600 K, P < 100 bars at a cycle rate of up to 4 Hz. The design of the apparatus is discussed in detail, and data are presented to demonstrate that well-formed shock waves with predictable characteristics are created, repeatably. Two synchrotron-based experiments using this apparatus are also briefly described here, demonstrating the potential of the shock tube for research at synchrotron light sources.
    The Review of scientific instruments 09/2013; 84(9):094102. · 1.58 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The pyrolysis of methyl acetate, 2% and 4% dilute in krypton, was investigated in a diaphragmless shock tube (DFST) using laser schlieren densitometry (LS). Experiments were performed at 122 ± 3 and 63 ± 2 Torr over the temperature range of 1492-2266 K. Master equation models for the four main dissociation paths of methyl acetate based on a prior study by Peukert et al. [S. Peukert, R. Sivaramakrishnan, M. Su and J. Michael, Combust. Flame, 2012, 159, 2312-2323] were refined and formed the basis for simulating the LS experiments. The density gradient profiles from the LS experiments indicate that the initial dissociation proceeds predominantly by breakage of the C-O bond leading ultimately to two methyl radicals and CO2, accounting for 83-88% of the methyl acetate loss over this temperature range. Rate coefficients for dissociation of methyl acetate were satisfactorily simulated with a master equation model, with modelled rate coefficients of k120 Torr = 9.06 × 10(81) × T(-19.07) × exp(-61 600K/T) s(-1), k60 Torr = 3.71 × 10(82) × T(-19.34) × exp(-61 200K/T) s(-1), and of k∞ = 1.97 × 10(30) × T(-3.80) × exp(-47 900K/T) s(-1) for the major channel, based on fitting to 120 Torr and 60 Torr data taken in this study. The model also captures the pressure dependency of methyl acetate dissociation and resolves an earlier discrepancy concerning the mechanism of dissociation of methyl acetate.
    Physical Chemistry Chemical Physics 03/2014; · 4.20 Impact Factor