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Ronald K Hanson - One of the best experts on this subject based on the ideXlab platform.
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measurements of Reflected Shock tunnel freestream nitric oxide temperatures and partial pressure
AIAA Journal, 2021Co-Authors: Julian J Girard, Ronald K Hanson, Joanna Austin, Peter Finch, Christopher L Strand, H. G. HornungAbstract:This paper reports on measurements of freestream nitric oxide (NO) rotational and vibrational temperatures and partial pressures, collected in the Caltech T5 Reflected Shock tunnel. Quantum cascade...
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two temperature collisional radiative modeling of partially ionized o2 ar mixtures over 8000 10 000 k behind Reflected Shock waves
Journal of Physical Chemistry A, 2020Co-Authors: Shengkai Wang, Christopher L Strand, Ronald K HansonAbstract:The collisional excitation kinetics of atomic oxygen was studied behind Reflected Shock waves using tunable diode laser absorption spectroscopy. A test gas mixture of 1% O2/Ar was Shock-heated to t...
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rapid chemiluminescent imaging behind Reflected Shock waves
2017Co-Authors: David F Davidson, M F Campbell, Christopher L Strand, A M Tulgestke, V A Troutman, Victor A Miller, Ronald K HansonAbstract:Current Shock tube combustion experiments generally assume that the test environment behind a Reflected Shock wave is quiescent and that ignition processes progress uniformly over the entire test volume. However, various past investigations, including those based on schlieren data and sidewall imaging [1, 2], have observed nonuniform ignition in certain test regimes. Here, we use both conventional diagnostics (pressure, emission, and laser absorption) and a high-speed chemiluminescent imaging system to investigate the ignition behavior of n-heptane/oxygen/argon in Shock tubes at long test times (greater than 2 ms), in an attempt to map the boundary of uniform and nonuniform ignition behavior in one of our Shock tubes.
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ignition delay times of conventional and alternative fuels behind Reflected Shock waves
Proceedings of the Combustion Institute, 2015Co-Authors: Sijie Li, David F Davidson, Ronald K HansonAbstract:Abstract The auto-ignition characteristics of two distillate jet fuels and fifteen alternative fuels (including fuel blends) were investigated using Shock-tube/laser-absorption methods. Ignition delay times were measured behind Reflected Shock waves over a range of temperatures, 1047–1520 K, and equivalence ratios, 0.25–2.2, in two pressure and mixture regimes: for fuel/air mixtures at 2.07–8.27 atm, and for fuel/4%oxygen(O 2 )/argon(Ar) mixtures at 15.9–44.0 atm. In both pressure ranges, the ignition delay times of the alternative fuels and the blends with conventional fuels were found to be similar to those of conventional fuels but with some small systematic differences manifesting the different fuel types. In particular, for alternative aviation fuels, alcohol-to-jet fuels were found to be generally less reactive than Fischer–Tropsch paraffinic kerosenes or hydro-processed renewable jet fuels. Comparisons were also made of the ignition delay time data with detailed kinetic modeling for selected fuels. These comparisons show that existing multi-component surrogate/mechanism combinations can successfully predict the behavior of these fuels over the conditions studied. For those fuels lacking kinetic models, the current ignition delay time measurements provide useful target data for development and validation of relevant surrogate mixtures and reaction mechanisms.
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hypersonic scramjet testing via diode laser absorption in a Reflected Shock tunnel
Journal of Propulsion and Power, 2014Co-Authors: Ian A Schultz, Ronald K Hanson, Christopher L Strand, Christopher S Goldenstein, Jay B Jeffries, Christopher P GoyneAbstract:A wavelength-multiplexed two-color tunable diode laser absorption spectroscopy sensor probing transitions near 1.4 μm was developed to measure H2O temperature and column density simultaneously across three lines of sight in a ground-based model scramjet combustor. High-enthalpy scramjet conditions equivalent to Mach 10 flight were generated with a Reflected Shock tunnel. The sensor hardware development and optical engineering to overcome noisy combustor conditions, including short test time, beam steering, and mechanical vibration, are discussed. A new scanned-wavelength-modulation spectroscopy technique was used to acquire the complete spectral lineshape while maintaining the high signal-to-noise ratio characteristic of wavelength-modulation spectroscopy measurements. Two combusting flow experiments were conducted, and the results compared with steady-state computational fluid dynamics calculations, with both the simulations and the measurements finding formation of H2O from H2 combustion during the tes...
Eric L Petersen - One of the best experts on this subject based on the ideXlab platform.
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impact of Shock tube facility dependent effects on incident and Reflected Shock conditions over a wide range of pressures and mach numbers
Combustion and Flame, 2020Co-Authors: Damien Nativel, Eric L Petersen, Mustapha Fikri, Sean P Cooper, Timo Lipkowicz, Christof SchulzAbstract:Abstract In real Shock tubes, deviations from the ideal gas-dynamic behavior can affect experiments and complicate data analysis and interpretation. These non-ideal effects depend on the Shock-tube geometry and therefore, results (e.g., ignition delay times) may vary between different experimental facilities. To clarify the influence of geometry and operating procedures, these effects were investigated in four geometrically different Shock tubes located in two laboratories, Texas A&M University and the University of Duisburg-Essen. Incident Shock-wave attenuation and pressure rise (dp*/dt) were measured behind Reflected Shock waves over a 2.1–4.1 Mach number and a 0.1–3.0 MPa post-Reflected-Shock pressure range. A strong influence of the Mach number on dp*/dt was observed for all facilities and conditions, whereas only a slight influence was found for Shock-wave attenuation. Both dp*/dt and attenuation were higher by about a factor of two for the Shock tubes with approximately half the inner diameter (8.0 vs. 16.2 cm). These findings are analyzed through correlations with initial pressure, inner diameter, Mach number, and specific heat ratio. The implication of non-ideal effects on experiments with reactive mixtures and related combustion experiments is discussed. Extreme conditions of dp*/dt were derived from the correlations and used to understand the effects of an equivalent dT*/dt on simulated ignition delay times of two reactive systems (CH4/air and C7H16/air). It was found that smaller Shock-tube diameters with respectively larger dp*/dt show shorter ignition delay times (especially at temperatures below 1000 K for the C7H16/air case). Therefore, the geometry constraints must be considered in simulations through dp*/dt inputs in the chemical kinetics simulation for the extreme cases to account for non-ideal effects.
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ignition delay time and h2o measurements during methanol oxidation behind Reflected Shock waves
Combustion and Flame, 2019Co-Authors: Laura T Pinzon, Olivier Mathieu, Clayton R Mulvihill, Ingmar Schoegl, Eric L PetersenAbstract:Abstract To improve detailed chemical kinetics models, the oxidation of methanol was investigated behind Reflected Shock waves in Shock tubes. Ignition delay times of methanol–air mixtures, with Ar as diluent, were studied between 940 and 1540 K in a heated Shock tube, for pressures up to 14.9 atm and for equivalence ratios of 0.5, 1.0, and 2.0. Water profiles were measured by utilizing a laser absorption technique in the 1350-to-1600-K temperature range, at an average pressure of 1.3 atm and for similar equivalence ratios. The present study shows the ignition delay times of methanol to be in very good agreement with results from the literature (Fieweger et al., 1997), whereas the other conditions have never been investigated before. The ignition delay time data are also in good agreement with modern detailed kinetics mechanisms such as the AramcoMech 3.0 model. The water time-history profiles were modeled using well-known literature mechanisms. Discrepancies were observed between these kinetics mechanisms, and poor predictions were observed for the lower temperatures investigated. Sensitivity and rate-of-production analyses were performed using 3 literature mechanisms (namely, AramcoMech 3.0, Princeton, and JetSurfII). Discrepancies were found among the models when predicting important reactions dominating the oxidation of methanol as well as the rate-of-production of H2O.
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ethanol pyrolysis kinetics using h2o time history measurements behind Reflected Shock waves
Proceedings of the Combustion Institute, 2019Co-Authors: Laura T Pinzon, Olivier Mathieu, Clayton R Mulvihill, Ingmar Schoegl, Eric L PetersenAbstract:Abstract The thermal decomposition of ethanol has been studied under pyrolytic conditions behind Reflected Shock waves in the 1250 to 1677 K temperature range, at an average pressure of 1.31 atm for a mixture highly diluted in Ar. A laser absorption technique was utilized to measure H2O time-histories, and the detailed kinetics mechanism (AramcoMech2.0) was selected among various models from the literature based on its a priori agreement with the experimental data in the present study. Sensitivity and rate-of-production analyses were performed and showed that the C2H5OH→C2H4+ H2O (R1) decomposition pathway is almost the sole reaction contributing to H2O formation at the early times under the present conditions, allowing an a priori direct measurement of its rate coefficient k1. The rate coefficient was determined to be defined as the Arrhenius equation k1 (s−1) = 3.37 × 1011 exp (–27174 K/T), which is in very good agreement with Kiecherer et al. (2015), where k1 was also directly determined under similar conditions. Secondary chemical reactions taking place in the thermal decomposition have very low influence in the H2O formation during the time-frame selected, leading to an uncertainty for k1 of approximately 20%. The full H2O time histories are useful for validating the full ethanol kinetics mechanism for future validation.
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nitromethane ignition behind Reflected Shock waves experimental and numerical study
Fuel, 2016Co-Authors: Olivier Mathieu, Binod Giri, A R Agard, T N Adams, John D Mertens, Eric L PetersenAbstract:Abstract Ignition delay times for nitromethane have been measured behind Reflected Shock waves over wide ranges of temperature (875–1595 K); pressure (2.0–35 atm); equivalence ratio (0.5, 1.0, and 2.0); and dilution (99, 98, 95, and 90% Ar by volume) using a L9 Taguchi array. Emission from excited-state hydroxyl radials (OH ∗ ) was the primary diagnostic for determining the ignition delay times from the experiments. Results showed that nitromethane’s ignition delay time is very sensitive to most of the experimental parameters that were varied. In addition, the OH ∗ profile for nitromethane presents an interesting double feature, with the relative intensity between the two peaks varying greatly depending on the experimental conditions. A detailed chemical kinetics mechanism was assembled from previous work by the authors and from sub-mechanisms from the literature. The latest theoretical work on nitromethane decomposition was used, and the final mechanism satisfactorily reproduces the ignition delay time data from the present study, as well as nitromethane and CH 4 /NOx ignition delay time data available from the literature.
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methane ignition in a Shock tube with high levels of co2 dilution consideration of the Reflected Shock bifurcation
Energy & Fuels, 2015Co-Authors: Joshua W Hargis, Eric L PetersenAbstract:Experiments were performed in a Shock-tube facility to examine experimentally the kinetic effect, if any, of excess amounts of CO2 as part of natural-gas-based fuel–oxidizer mixtures. An important aspect of these experiments was to also observe the role excess amounts of CO2 play in causing nonidealities, particularly Shock bifurcation, in Shock-tube experiments using real (nondilute) fuel–air mixtures. Mixtures were composed of methane fuel at an equivalence ratio of 0.5 to represent a typical natural gas in a modified “air” mixture designed to study the effect of large levels of CO2 dilution. These oxidizer compositions maintained constant levels of O2 while exchanging N2 for CO2 in stages to give oxidizer mixture concentrations ranging from (0.21O2 + 0.79N2) to (0.21O2 + 0.79CO2). Low-pressure and high-pressure (near 1 and 10 atm, respectively) experiments were conducted over an approximate temperature range of 1450 to 1900 K. Results showed that the observed effect of CO2 relating to Reflected-Shock b...
David F Davidson - One of the best experts on this subject based on the ideXlab platform.
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rapid chemiluminescent imaging behind Reflected Shock waves
2017Co-Authors: David F Davidson, M F Campbell, Christopher L Strand, A M Tulgestke, V A Troutman, Victor A Miller, Ronald K HansonAbstract:Current Shock tube combustion experiments generally assume that the test environment behind a Reflected Shock wave is quiescent and that ignition processes progress uniformly over the entire test volume. However, various past investigations, including those based on schlieren data and sidewall imaging [1, 2], have observed nonuniform ignition in certain test regimes. Here, we use both conventional diagnostics (pressure, emission, and laser absorption) and a high-speed chemiluminescent imaging system to investigate the ignition behavior of n-heptane/oxygen/argon in Shock tubes at long test times (greater than 2 ms), in an attempt to map the boundary of uniform and nonuniform ignition behavior in one of our Shock tubes.
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ignition delay times of conventional and alternative fuels behind Reflected Shock waves
Proceedings of the Combustion Institute, 2015Co-Authors: Sijie Li, David F Davidson, Ronald K HansonAbstract:Abstract The auto-ignition characteristics of two distillate jet fuels and fifteen alternative fuels (including fuel blends) were investigated using Shock-tube/laser-absorption methods. Ignition delay times were measured behind Reflected Shock waves over a range of temperatures, 1047–1520 K, and equivalence ratios, 0.25–2.2, in two pressure and mixture regimes: for fuel/air mixtures at 2.07–8.27 atm, and for fuel/4%oxygen(O 2 )/argon(Ar) mixtures at 15.9–44.0 atm. In both pressure ranges, the ignition delay times of the alternative fuels and the blends with conventional fuels were found to be similar to those of conventional fuels but with some small systematic differences manifesting the different fuel types. In particular, for alternative aviation fuels, alcohol-to-jet fuels were found to be generally less reactive than Fischer–Tropsch paraffinic kerosenes or hydro-processed renewable jet fuels. Comparisons were also made of the ignition delay time data with detailed kinetic modeling for selected fuels. These comparisons show that existing multi-component surrogate/mechanism combinations can successfully predict the behavior of these fuels over the conditions studied. For those fuels lacking kinetic models, the current ignition delay time measurements provide useful target data for development and validation of relevant surrogate mixtures and reaction mechanisms.
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pyrolysis study of conventional and alternative fuels behind Reflected Shock waves
Fuel, 2014Co-Authors: Yangye Zhu, David F Davidson, Ronald K HansonAbstract:Abstract Fuel decay time-histories and ethylene time-histories were measured behind Reflected Shock waves for JP-8 and three synthetic aviation fuels (SPK, HRJ-Camelina, and HRJ-Tallow) in 0.2–0.3% fuel/argon mixtures near 7 atm and in the temperature range 1146–1500 K, and F-76 and three synthetic navy fuels (F-76 Blend, DIM, and 103–2) in 0.15–0.3% fuel/argon mixtures near 18 atm and in the temperature range 1234–1376 K. The absorption measurements of fuel decomposition were carried out using a 3.39 μm He–Ne laser, and the overall fuel decomposition rates were inferred from the fuel decay traces. The ethylene measurements were made near 10.5 μm using a CO 2 gas laser, and the peak ethylene yields were inferred for different fuels from the ethylene time-histories. The four aviation fuels show noticeably different overall fuel decomposition rates, while the four navy fuels have overall fuel decomposition rates that are close to each other. The peak ethylene yields for the four aviation fuels match each other well, while the peak ethylene yields for the navy fuels show significant fuel dependences. The current study presents the first species time-history measurements for the synthetic aviation and navy fuels covered, and provides important kinetic targets for surrogate validation and mechanism development.
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Shock tube measurements of ignition delay times for the butanol isomers using the constrained reaction volume strategy
International Journal of Chemical Kinetics, 2014Co-Authors: David F Davidson, Ronald K HansonAbstract:Ignition delay times of sec-, iso-, and tert-butanol were measured behind Reflected Shock waves using both conventional operation and a new constrained-reaction-volume (CRV) strategy. This CRV filling method constrains the volume of reactive gases, thereby producing near-constant-pressure test conditions for Reflected Shock measurements. The initial Reflected Shock conditions cover temperatures ranging from 828 to 1095 K, pressures near 20 atm and an equivalence ratio of 1.0 in air mixtures. Additional data were also collected at 30 atm and at φ = 0.5 for iso-butanol/O2/N2 mixtures. At 20 atm and φ = 1.0, the ignition delay time increases for the isomers in the following order: n-butanol, iso-butanol and sec-butanol, and tert-butanol. Modeling of all collected data using the Vasu and Sarathy (Energy Fuel 2013, 27, 7072–7080) mechanism showed overall good agreement with the experimental data.
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ignition delay times of very low vapor pressure biodiesel surrogates behind Reflected Shock waves
Fuel, 2014Co-Authors: M F Campbell, David F Davidson, Ronald K HansonAbstract:Abstract Ignition delay times for a variety of low-vapor-pressure biodiesel surrogates were measured behind Reflected Shock waves, using an aerosol Shock tube. These fuels included methyl decanoate (C 11 H 22 O 2 ), methyl laurate (C 13 H 26 O 2 ), methyl myristate (C 15 H 30 O 2 ), methyl palmitate (C 17 H 34 O 2 ), and a methyl oleate (C 19 H 36 O 2 )/Fatty Acid Methyl Ester (FAME) blend. Experiments were conducted in 4% oxygen/argon mixtures with the exception of methyl decanoate which was studied in 1% and 21% oxygen/argon blends. Reflected Shock conditions covered initial temperatures from 1026 to 1388 K, pressures of 3.5 and 7.0 atm, and equivalence ratios from 0.3 to 1.4. Arrhenius expressions describing the experimental ignition delay time data are given and compared to those derived from applicable mechanisms available in the literature. Graphical comparisons between experimental data and mechanism predictions are also provided. Experiments of methyl laurate, methyl myristate, and methyl palmitate represent the first Shock tube ignition delay time measurements for these fuels. Finally, experiments with methyl palmitate represent, to the authors’ knowledge, the first neat fuel/oxidizer/diluent gas-phase Shock tube experiments involving a fuel which is a waxy solid at room temperature.
Olivier Mathieu - One of the best experts on this subject based on the ideXlab platform.
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ignition delay time and h2o measurements during methanol oxidation behind Reflected Shock waves
Combustion and Flame, 2019Co-Authors: Laura T Pinzon, Olivier Mathieu, Clayton R Mulvihill, Ingmar Schoegl, Eric L PetersenAbstract:Abstract To improve detailed chemical kinetics models, the oxidation of methanol was investigated behind Reflected Shock waves in Shock tubes. Ignition delay times of methanol–air mixtures, with Ar as diluent, were studied between 940 and 1540 K in a heated Shock tube, for pressures up to 14.9 atm and for equivalence ratios of 0.5, 1.0, and 2.0. Water profiles were measured by utilizing a laser absorption technique in the 1350-to-1600-K temperature range, at an average pressure of 1.3 atm and for similar equivalence ratios. The present study shows the ignition delay times of methanol to be in very good agreement with results from the literature (Fieweger et al., 1997), whereas the other conditions have never been investigated before. The ignition delay time data are also in good agreement with modern detailed kinetics mechanisms such as the AramcoMech 3.0 model. The water time-history profiles were modeled using well-known literature mechanisms. Discrepancies were observed between these kinetics mechanisms, and poor predictions were observed for the lower temperatures investigated. Sensitivity and rate-of-production analyses were performed using 3 literature mechanisms (namely, AramcoMech 3.0, Princeton, and JetSurfII). Discrepancies were found among the models when predicting important reactions dominating the oxidation of methanol as well as the rate-of-production of H2O.
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ethanol pyrolysis kinetics using h2o time history measurements behind Reflected Shock waves
Proceedings of the Combustion Institute, 2019Co-Authors: Laura T Pinzon, Olivier Mathieu, Clayton R Mulvihill, Ingmar Schoegl, Eric L PetersenAbstract:Abstract The thermal decomposition of ethanol has been studied under pyrolytic conditions behind Reflected Shock waves in the 1250 to 1677 K temperature range, at an average pressure of 1.31 atm for a mixture highly diluted in Ar. A laser absorption technique was utilized to measure H2O time-histories, and the detailed kinetics mechanism (AramcoMech2.0) was selected among various models from the literature based on its a priori agreement with the experimental data in the present study. Sensitivity and rate-of-production analyses were performed and showed that the C2H5OH→C2H4+ H2O (R1) decomposition pathway is almost the sole reaction contributing to H2O formation at the early times under the present conditions, allowing an a priori direct measurement of its rate coefficient k1. The rate coefficient was determined to be defined as the Arrhenius equation k1 (s−1) = 3.37 × 1011 exp (–27174 K/T), which is in very good agreement with Kiecherer et al. (2015), where k1 was also directly determined under similar conditions. Secondary chemical reactions taking place in the thermal decomposition have very low influence in the H2O formation during the time-frame selected, leading to an uncertainty for k1 of approximately 20%. The full H2O time histories are useful for validating the full ethanol kinetics mechanism for future validation.
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nitromethane ignition behind Reflected Shock waves experimental and numerical study
Fuel, 2016Co-Authors: Olivier Mathieu, Binod Giri, A R Agard, T N Adams, John D Mertens, Eric L PetersenAbstract:Abstract Ignition delay times for nitromethane have been measured behind Reflected Shock waves over wide ranges of temperature (875–1595 K); pressure (2.0–35 atm); equivalence ratio (0.5, 1.0, and 2.0); and dilution (99, 98, 95, and 90% Ar by volume) using a L9 Taguchi array. Emission from excited-state hydroxyl radials (OH ∗ ) was the primary diagnostic for determining the ignition delay times from the experiments. Results showed that nitromethane’s ignition delay time is very sensitive to most of the experimental parameters that were varied. In addition, the OH ∗ profile for nitromethane presents an interesting double feature, with the relative intensity between the two peaks varying greatly depending on the experimental conditions. A detailed chemical kinetics mechanism was assembled from previous work by the authors and from sub-mechanisms from the literature. The latest theoretical work on nitromethane decomposition was used, and the final mechanism satisfactorily reproduces the ignition delay time data from the present study, as well as nitromethane and CH 4 /NOx ignition delay time data available from the literature.
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ignition delay time measurements behind Reflected Shock waves for a representative coal derived syngas with and without nh3 and h2s impurities
Proceedings of the Combustion Institute, 2015Co-Authors: Olivier Mathieu, Joshua W Hargis, Alejandro Camou, Clayton R Mulvihill, Eric L PetersenAbstract:Abstract The composition of a representative coal-derived syngas was determined by averaging 40 practical coal syngas compositions from the literature and corresponds to a departure from many recent studies which only focus on syngas blends containing just CO and H2. Ignition delay times have been measured behind Reflected Shock waves for this averaged mixture with an equivalence ratio of 0.5 (0.4554% CO/0.3297% H2/0.1032% CO2/0.0172% CH4/0.2407% H2O/0.8538% O2 in 98% Ar (mol.%)) at around 1.7, 13, and 32 atm. The same mixture was also investigated with impurities (200 ppm of NH3 and 50 ppm of H2S). Care was taken when working with the blends containing H2O and NH3 to avoid errors in the Shock-tube composition; direct measurement of the water vapor mole fractions were performed using a tunable diode laser absorption diagnostic near 1.38 μm. The effect of the various constituents on the ignition delay time was also investigated by comparing to results from a baseline mixture (H2/CO/O2/Ar) and results with this baseline mixture with only one of the other constituents of the syngas (i.e., CO2, CH4, H2S). Experimental data were compared with recent detailed kinetics mechanisms from the literature. Results showed that, under the conditions of this study, extending the mixture composition to include realistic concentrations of species beyond just the CO and H2 does not have a very large effect on the ignition delay time for a coal-derived syngas. However, a comparison of this coal-derived syngas with a syngas derived from biomass, tested in an earlier study by the authors, exhibited large differences due to the larger CH4 concentration in the bio-derived syngas. Two chemical kinetic models from the literature were found suitable to reproduce these data over most of the range of mixtures, temperatures, and pressures investigated, namely the mechanisms associated with Galway and with Princeton.
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effects of h2s addition on hydrogen ignition behind Reflected Shock waves experiments and modeling
Combustion and Flame, 2014Co-Authors: Olivier Mathieu, Fiona Deguillaume, Eric L PetersenAbstract:Abstract Hydrogen sulfide is a common impurity that can greatly change the combustion properties of fuels, even when present in small concentrations. However, the combustion chemistry of H2S is still poorly understood, and this lack of understanding subsequently leads to difficulties in the design of emission-control and energy-production processes. During this study, ignition delay times were measured behind Reflected Shock waves for mixtures of 1% H2/1% O2 diluted in Ar and doped with various concentration of H2S (100, 400, and 1600 ppm) over large pressure (around 1.6, 13, and 33 atm) and temperature (1045–1860 K) ranges. Results typically showed a significant increase in the ignition delay time due to the addition of H2S, in some cases by a factor of 4 or more over the baseline mixtures with no H2S. The magnitude of the increase is highly dependent on the temperature and pressure. A detailed chemical kinetics model was developed using recent, up-to-date detailed-kinetics mechanisms from the literature and by changing a few reaction rates within their reported error factor. This updated model predicts well the experimental data obtained during this study and from the Shock-tube literature. However, flow reactor data from the literature were poorly predicted when H2S was a reactant. This study highlights the need for a better estimation of several reaction rates to better predict H2S oxidation chemistry and its effect on fuel combustion. Using the kinetics model for sensitivity analyses, it was determined that the decrease in reactivity in the presence of H2S is because H2S initially reacts before the H2 fuel does, mainly through the reaction H2S + H ⇄ SH + H2, thus taking H atoms away from the main branching reaction H + O2 ⇄ OH + O and inhibiting the ignition process.
J V Michael - One of the best experts on this subject based on the ideXlab platform.
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rate constants for the thermal decomposition of ethanol and its bimolecular reactions with oh and d Reflected Shock tube and theoretical studies
Journal of Physical Chemistry A, 2010Co-Authors: R Sivaramakrishna, J V Michael, Stephe J Klippenstei, Lawrence Harding, Anko RuscicAbstract:The thermal decomposition of ethanol and its reactions with OH and D have been studied with both Shock tube experiments and ab initio transition state theory-based master equation calculations. Dissociation rate constants for ethanol have been measured at high T in Reflected Shock waves using OH optical absorption and high-sensitivity H-atom ARAS detection. The three dissociation processes that are dominant at high T are C2H5OH--> C2H4+H2O (A) -->CH3+CH2OH (B) -->C2H5+OH (C).The rate coefficient for reaction C was measured directly with high sensitivity at 308 nm using a multipass optical White cell. Meanwhile, H-atom ARAS measurements yield the overall rate coefficient and that for the sum of reactions B and C , since H-atoms are instantaneously formed from the decompositions of CH(2)OH and C(2)H(5) into CH(2)O + H and C(2)H(4) + H, respectively. By difference, rate constants for reaction 1 could be obtained. One potential complication is the scavenging of OH by unreacted ethanol in the OH experiments, and therefore, rate constants for OH+C2H5OH-->products (D)were measured using tert-butyl hydroperoxide (tBH) as the thermal source for OH. The present experiments can be represented by the Arrhenius expression k=(2.5+/-0.43) x 10(-11) exp(-911+/-191 K/T) cm3 molecule(-1) s(-1) over the T range 857-1297 K. For completeness, we have also measured the rate coefficient for the reaction of D atoms with ethanol D+C2H5OH-->products (E) whose H analogue is another key reaction in the combustion of ethanol. Over the T range 1054-1359 K, the rate constants from the present experiments can be represented by the Arrhenius expression, k=(3.98+/-0.76) x10(-10) exp(-4494+/-235 K/T) cm3 molecule(-1) s(-1). The high-pressure rate coefficients for reactions B and C were studied with variable reaction coordinate transition state theory employing directly determined CASPT2/cc-pvdz interaction energies. Reactions A , D , and E were studied with conventional transition state theory employing QCISD(T)/CBS energies. For the saddle point in reaction A , additional high-level corrections are evaluated. The predicted reaction exo- and endothermicities are in good agreement with the current Active Thermochemical Tables values. The transition state theory predictions for the microcanonical rate coefficients in ethanol decomposition are incorporated in master equation calculations to yield predictions for the temperature and pressure dependences of reactions A - C . With modest adjustments (<1 kcal/mol) to a few key barrier heights, the present experimental and adjusted theoretical results yield a consistent description of both the decomposition (1-3) and abstraction kinetics (4 and 5). The present results are compared with earlier experimental and theoretical work.
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thermal decomposition of nh2oh and subsequent reactions ab initio transition state theory and Reflected Shock tube experiments
Journal of Physical Chemistry A, 2009Co-Authors: Stephen J Klippenstein, N K Srinivasan, Branko Ruscic, Lawrence B Harding, R Sivaramakrishnan, J V MichaelAbstract:Primary and secondary reactions involved in the thermal decomposition of NH2OH are studied with a combination of Shock tube experiments and transition state theory based theoretical kinetics. This coupled theory and experiment study demonstrates the utility of NH2OH as a high temperature source of OH radicals. The Reflected Shock technique is employed in the determination of OH radical time profiles via multipass electronic absorption spectrometry. O-atoms are searched for with atomic resonance absorption spectrometry. The experiments provide a direct measurement of the rate coefficient, k1, for the thermal decomposition of NH2OH. Secondary rate measurements are obtained for the NH2 + OH (5a) and NH2OH + OH (6a) abstraction reactions. The experimental data are obtained for temperatures in the range from 1355 to 1889 K and are well represented by the respective rate expressions: log[k/(cm3 molecule(-1) s(-1))] = (-10.12 +/- 0.20) + (-6793 +/- 317 K/T) (k1); log[k/(cm3 molecule(-1) s(-1))] = (-10.00 +/- 0.06) + (-879 +/- 101 K/T) (k5a); log[k/(cm3 molecule(-1) s(-1))] = (-9.75 +/- 0.08) + (-1248 +/- 123 K/T) (k6a). Theoretical predictions are made for these rate coefficients as well for the reactions of NH2OH + NH2, NH2OH + NH, NH + OH, NH2 + NH2, NH2 + NH, and NH + NH, each of which could be of secondary importance in NH2OH thermal decomposition. The theoretical analyses employ a combination of ab initio transition state theory and master equation simulations. Comparisons between theory and experiment are made where possible. Modest adjustments of predicted barrier heights (i.e., by 2 kcal/mol or less) generally yield good agreement between theory and experiment. The rate coefficients obtained here should be of utility in modeling NOx in various combustion environments.
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Reflected Shock tube studies of high temperature rate constants for oh no2 ho2 no and oh ho2 h2o o2
Journal of Physical Chemistry A, 2006Co-Authors: N K Srinivasan, J W Sutherland, J V Michael, Branko RuscicAbstract:The motivation for the present study comes from the preceding paper where it is suggested that accepted rate constants for OH + NO2 → NO + HO2 are high by ∼2. This conclusion was based on a reevaluation of heats of formation for HO2, OH, NO, and NO2 using the Active Thermochemical Table (ATcT) approach. The present experiments were performed in C2H5I/NO2 mixtures, using the Reflected Shock tube technique and OH-radical electronic absorption detection (at 308 nm) and using a multipass optical system. Time-dependent profile decays were fitted with a 23-step mechanism, but only OH + NO2, OH + HO2, both HO2 and NO2 dissociations, and the atom molecule reactions, O + NO2 and O + C2H4, contributed to the decay profile. Since all of the reactions except the first two are known with good accuracy, the profiles were fitted by varying only OH + NO2 and OH + HO2. The new ATcT approach was used to evaluate equilibrium constants so that back reactions were accurately taken into account. The combined rate constant from...
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Reflected Shock tube studies of high temperature rate constants for ch3 o2 h2co o2 and oh o2
Journal of Physical Chemistry A, 2005Co-Authors: N K Srinivasan, J W Sutherland, J V MichaelAbstract:The Reflected Shock tube technique with multipass absorption spectrometric detection of OH-radicals at 308 nm, corresponding to a total path length of ∼2.8 m, has been used to study the reaction CH3 + O2 → CH2O + OH. Experiments were performed between 1303 and 2272 K, using ppm quantities of CH3I (methyl source) and 5−10% O2, diluted with Kr as the bath gas at test pressures less than 1 atm. We have also reanalyzed our earlier ARAS measurements for the atomic channel (CH3 + O2 → CH3O + O) and have compared both these results with other earlier studies to derive a rate expression of the Arrhenius form. The derived expressions, in units of cm3 molecule-1 s-1, are k = 3.11 × 10-13 exp(−4953 K/T) over the T-range 1237−2430 K, for the OH-channel, and k = 1.253 × 10-11 exp(−14241K/T) over the T-range 1250−2430 K, for the O-atom channel. Since CH2O is a major product in both reactions, reliable rates for the reaction CH2O + O2 → HCO + HO2 could be derived from [OH]t and [O]t experiments over the T-range 1587−210...
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Reflected Shock tube studies of high temperature rate constants for oh ch4 ch3 h2o and ch3 no2 ch3o no
Journal of Physical Chemistry A, 2005Co-Authors: N K Srinivasan, J W Sutherland, J V MichaelAbstract:The Reflected Shock tube technique with multipass absorption spectrometric detection of OH radicals at 308 nm has been used to study the reactions OH + CH4 → CH3 + H2O and CH3 + NO2 → CH3O + NO. Over the temperature range 840−2025 K, the rate constants for the first reaction can be represented by the Arrhenius expression k = (9.52 ± 1.62) × 10-11 exp[(−4134 ± 222 K)/T] cm3 molecule-1 s-1. Since this reaction is important in both combustion and atmospheric chemistry, there have been many prior investigations with a variety of techniques. The present results extend the temperature range by 500 K and have been combined with the most accurate earlier studies to derive an evaluation over the extended temperature range 195−2025 K. A three-parameter expression describes the rate behavior over this temperature range, k = (1.66 × 10-18)T2.182 exp[(−1231 K)/T] cm3 molecule-1 s-1. Previous theoretical studies are discussed, and the present evaluation is compared to earlier theoretical estimates. Since CH3 radicals a...
