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: 1.61). 10/2008; 79(9):094103 - 094103-6. DOI: 10.1063/1.2976671
Source: IEEE Xplore


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.

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    ABSTRACT: Vibrational relaxation and dissociation of CH(3)I, 2-20% in krypton, have been investigated behind incident shock waves in a diaphragmless shock tube at 20, 66, 148, and 280 Torr and 630-2200 K by laser schlieren densitometry. The effective collision energy obtained from the vibrational relaxation experiments has a small, positive temperature dependence, DeltaE(down) = 63 x (T/298)(0.56) cm(-1). First-order rate coefficients for dissociation of CH(3)I show a strong pressure dependence and are close to the low-pressure limit. Restricted-rotor Gorin model RRKM calculations fit the experimental results very well with DeltaE(down) = 378 x (T/298)(0.457) cm(-1). The secondary chemistry of this reaction system is dominated by reactions of methyl radicals and the reaction of the H atom with CH(3)I. The results of the decomposition experiments are very well simulated with a model that incorporates methyl recombination and reactions of methylene. Second-order rate coefficients for ethane dissociation to two methyl radicals were derived from the experiments and yield k = (4.50 +/- 0.50) x 10(17) exp(-32709/T) cm(3) mol(-1) s(-1), in good agreement with previous measurements. Rate coefficients for H + CH(3)I were also obtained and give k = (7.50 +/- 1.0) x 10(13) exp(-601/T) cm(3) mol(-1) s(-1), in reasonable agreement with a previous experimental value.
    The Journal of Physical Chemistry A 08/2009; 113(29):8307-17. DOI:10.1021/jp903336u · 2.69 Impact Factor
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    ABSTRACT: The dissociation of diacetyl dilute in krypton has been studied in a shock tube using laser schlieren densitometry at 1200-1800 K and reaction pressures of 55 +/- 2, 120 +/- 3, and 225 +/- 5 Torr. The experimentally determined rate coefficients show falloff and an ab initio/Master Equation/VRC-TST analysis was used to determine pressure-dependent rate coefficient expressions that are in good agreement with the experimental data. From the theoretical calculations k(infinity)(T) = 5.029 x 10(19) (T/298 K)(-3.40) exp(-37665/T) s(-1) for 300 < T < 2000 K. The laser schlieren profiles were simulated using a model for methyl recombination with appropriate additions for diacetyl. From the simulations rate coefficients were determined for CH(3) + CH(3) = C(2)H(6) and CH(3) + C(4)H(6)O(2) = CH(3)CO + CH(2)CO + CH(4) (k(T) = 2.818T(4.00) exp(-5737/T) cm(3) mol(-1) s(-1)). Excellent agreement is found between the simulations and experimental profiles, and Troe type parameters have been calculated for the dissociation of diacetyl and the recombination of methyl radicals.
    The Journal of Physical Chemistry A 08/2009; 113(29):8318-26. DOI:10.1021/jp903716f · 2.69 Impact Factor
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    ABSTRACT: A combination of experiment and theory is applied to the self-reaction kinetics of phenyl radicals. The dissociation of phenyl iodide is observed with both time-of-flight mass spectrometry, TOF-MS, and laser schlieren, LS, diagnostics coupled to a diaphragmless shock tube for temperatures ranging from 1276 to 1853 K. The LS experiments were performed at pressures of 22 +/- 2, 54 +/- 7, and 122 +/- 6 Torr, and the TOF-MS experiments were performed at pressures in the range 500-700 Torr. These observations are sensitive to both the dissociation of phenyl iodide and to the subsequent self-reaction of the phenyl radicals. The experimental observations indicate that both these reactions are more complicated than previously assumed. The phenyl iodide dissociation yields approximately 6% C(6)H(4) + HI in addition to the major and commonly assumed C(6)H(5) + I channel. The self-reaction of phenyl radicals does not proceed solely by recombination, but also through disproportionation to benzene + o-/m-/p-benzynes, with comparable rate coefficients for both. The various channels in the self-reaction of phenyl radicals are studied with ab initio transition state theory based master equation calculations. These calculations elucidate the complex nature of the C(6)H(5) self-reaction and are consistent with the experimental observations. The theoretical predictions are used as a guide in the development of a model for the phenyl iodide pyrolysis that accurately reproduces the observed laser schlieren profiles over the full range of the observations.
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