Variable Pressure Flow Reactor Research Articles

Comparative Kinetic Analysis of Ethane Pyrolysis at 0.1 and 2.0 MPa

Understanding the pyrolysis of ethane over an extended pressure range can help improve the understanding of the pressure dependence of pyrolysis of higher alkanes. For this work, a variable pressure flow reactor was operated at 1073 K at pressures of 0.1 and 2.0 MPa to gain insight into the effect of pressure on the rate of ethane decomposition and formation of the major products and deposit precursors, such as benzene and toluene. Ethane conversion was achieved by sweeping through residence times over a range from 0.2 to 6 s at 0.1 MPa and from 2 to 30 s at 2.0 MPa. The results showed that, at higher pressure, more ethane is converted to benzene and toluene, species that readily lead to deposit formation; additionally, at an elevated pressure, the selectivity of hydrogen, ethylene, and methane is significantly affected. The experimental results were compared to several chemical kinetic mechanisms to gauge the performance of the mechanisms under the various test conditions. A mechanistic analysis showed that the variation in the selectivity of the products as a result of pressure was in large part due to the shift in the kinetics of ethyl radicals: unimolecular β-scission dominated at lower pressures, while bimolecular addition and abstraction reactions become important at high pressures.

Investigation of n-pentane pyrolysis at elevated temperatures and pressures in a variable pressure flow reactor

Thermally cracking fuel in a fuel processing facility or undergoing pyrolysis in the anode channel of a fuel cell can lead to coke deposition. The formation of coke occurs via chemical kinetic pathways that are largely dependent on poly aromatic hydrocarbons (PAHs). The formation of PAH⿿s largely depends on species which include ethylene, acetylene, butadiene, benzene and toluene. Pentane is a relatively simple structure for modeling purposes, yet large enough that it produces some of the relevant chemistry of real fuels. Experiments were conducted in a newly designed variable pressure flow reactor (VPFR) built to process both liquid and gaseous reactants at pressures to 4.0MPa and temperatures to 1373K. The VPFR was initially validated via ethane pyrolysis experiments and comparing the results with existing literature data. Pentane experiments were done over a range of temperatures (923⿿1073K), pressures (1⿿2.0MPa) and residence times (30ms⿿40s). The product selectivity appeared to be greatest influenced by pressure and level of fuel conversion. Pressure increases ethylene production but has an inverse effect on ethane production. Soot precursors appeared at higher levels of conversion. The results of the experiments were compared to an existing chemical kinetic mechanism with good agreement.

Predicting the global combustion behaviors of petroleum-derived and alternative jet fuels by simple fuel property measurements

Pre-vaporized global combustion behaviors of a petroleum-derived jet fuel (JP-8), five alternative jet fuels (Shell SPK, Sasol IPK, HRJ Camelina, HRJ Tallow, and Gevo ATJ), and five 50/50 (liquid volume) blends of JP-8/alternative fuels are experimentally examined and compared. Three experiments are performed to investigate the gas-phase combustion behaviors of the tested fuel samples: (1) global oxidative species profiles in a variable pressure flow reactor, (2) diffusion flame extinction in a counterflow burner, and (3) premixed flame initiation in a heated spherical combustion chamber. Multivariate linear regression methods have been applied to investigate the sensitivities of pre-vaporized global combustion behaviors to individual combustion property targets of the fuels, including Derived Cetane Number (DCN), H/C ratio, mean molecular weight, and smoke point. As a proof of concept for fuel screening tool based on the standardized fuel property measurements, a “combustion property target (CPT) index” based upon this regression analysis is found to show promise as a rapid means to evaluate the global pre-vaporized combustion behaviors of the tested fuel samples against each other as well as the spectrum of JP-8 fuels found in use. The present work suggests the applicability of such a methodology not only as an expeditious fuel screening tool for assessing the fully pre-vaporized, kinetically coupled behaviors of emerging alternative jet fuel candidates, but further supports the use of combustion property targets in developing kinetic models that are specific to each real fuel.

An experimental and kinetic modeling study of n-dodecane pyrolysis and oxidation

The current study investigates n-dodecane (n-C12H26) pyrolysis and oxidation kinetics in the temperature regime of 1000–1300 K in the Stanford Variable Pressure Flow Reactor facility. The reactor environment is vitiated and the experiments were conducted at atmospheric pressure. Species time history data were collected for n-dodecane and oxygen, as well as for 12 intermediate and product species over a span of 1–40 ms residence times using real time gas chromatography. The experimental data were compared against the predictions of four detailed kinetic models. The results showed that the fuel oxidation proceeds through an early pyrolytic stage where the fuel breaks down into smaller hydrocarbon fragments, including mostly C2–4 alkenes, and a late oxidation stage where the fragments oxidize to CO. The kinetic models were observed to diverge notably in their predictions from one another. Sensitivity and flux analysis identified the cause of the divergences to differences in the small hydrocarbon chemistry modeling. Finally, the flow reactor data were used to demonstrate how model uncertainty minimization can improve model predictions. It is shown that after uncertainty minimization against a selected set of n-dodecane combustion data, the predictions of the resulting optimized model are improved notably for all existing n-dodecane data sets tested, including those of the current flow reactor study that were not part of the optimization target list.

Decomposition Studies of Isopropanol in a Variable Pressure Flow Reactor

Abstract Alternatives to traditional petroleum derived transportation fuels, particularly alcohols, have been investigated increasingly over the last 5 years. Isopropanol has received little attention despite bridging the gap between smaller alcohols (methanol and ethanol) and the next generation alcohols (butyl alcohols) to be used in transportation fuels. Previous studies have shown that decomposition reactions that dehydrate are important in the high-temperature oxidation of alcohols. Here we report new data on the dehydration reaction for isopropanol (iC3H7OH → C3H6 + H2O) in a Variable Pressure Flow Reactor at 12.5 atm pressure and temperatures from 976–1000 K. Pyrolysis experiments are performed in the presence of a radical trapper (1,3,5 trimethyl benzene or toluene) to inhibit secondary reactions of radicals with the fuel and product species. The recommended rate constant for the dehydration reaction is determined using an indirect method along with Latin Hypercube sampling to estimate uncertainties. Comparison of the rate constant data to previous works show that the reaction is considerably more rapid than the high level theoretical predictions of Bui et al. (Bui et al., J. Chem. Phys., 2002). The dehydration reaction rate for isopropanol is well described by k = 8.52 × 106 T 2.12 exp (− 30, 667/T) with an estimated uncertainty of σ ln A 2 = 0.0195. The C–C bond fission reaction is also investigated, but the insensitivity of the decomposition data to this reaction results in an uncertainty in the determined rate constants to approximately 2 orders of magnitude. Theoretical estimates lie within these experimental uncertainties.

An experimental and modeling study of propene oxidation. Part 1: Speciation measurements in jet-stirred and flow reactors

Propene is a significant component of Liquefied Petroleum Gas (LPG) and an intermediate in the combustion of higher order hydrocarbons. To better understand the combustion characteristics of propene, this study and its companion paper present new experimental data from jet-stirred (JSR) and flow reactors (Part I) and ignition delay time and flame speed experiments (Part II).Species profiles from JSR experiments are presented and were obtained at near-atmospheric pressure over a temperature range of 800–1100K and for equivalence ratios from φ=0.64 to 2.19. The new JSR data were obtained at lower dilution levels and temperatures than previously published. Also reported are species profiles from two high-pressure flow reactor facilities: the Princeton Variable Pressure Flow Reactor (VPFR) and the High Pressure Laminar Flow Reactor (HPLFR). The VPFR experiments were conducted at pressures of 6–12.5atm, in the temperature range 843–1020K and at equivalence ratios of 0.7–1.3. The HPLFR experiments were conducted at 15atm, at a temperature of 800K and at equivalence ratios of 0.35–1.25. The flow reactor data is at higher pressures and lower temperatures than existing data in the literature.A detailed chemical kinetic mechanism has been simultaneously developed to describe the combustion of propene under the experimental conditions described above. Important reactions highlighted via flux and sensitivity analyses include: hydrogen atom abstraction from propene by molecular oxygen, hydroxyl, and hydroperoxyl radicals; allyl–allyl radical recombination; the reaction between allyl and hydroperoxyl radicals; and the reactions of 1- and 2-propenyl radicals with molecular oxygen. The current mechanism accurately predicts the combustion characteristics of propene across the range of experimental conditions presented in this study, from jet-stirred and flow reactors and for ignition delay times and flame speed measurements presented in Part II. In comparison to a previous mechanism, AramcoMech 1.3, the current mechanism results in much improved performance, which highlights the importance of the new experimental data in constraining the important reactions.

Dehydration Rate Measurements for tertiary-Butanol in a Variable Pressure Flow Reactor

Fundamentally, the dehydration reaction of tertiary-butanol is frequently used as an internal standard for relative rate studies of other decomposition reactions. We report here a study using radical trappers to isolate this path in tertiary-butanol pyrolysis experiments conducted in the Princeton variable pressure flow reactor between 658 and 980 K. A novel technique that determines the rate constant value by applying a global least-squares fit incorporating all experimental species (tertiary-butanol, isobutene, and water) evolution data is developed and applied to yield six rate constant values at two reaction pressures (6.1 and 18 atm) and at temperatures between 949 and 980 K. Data from previously reported studies are reanalyzed to evaluate their "absolute" uncertainties, and new Arrhenius parameters are derived based upon the present and previous measurements. The recommended rate constant (uncertainties) for the dehydration reaction is k = 2.88(0.91) × 10(7)T(2.21(0.10)) s(-1) exp(-62.4(0.9) kcal mol(-1)/RT). The new correlation is in excellent agreement with other independent experimental and theoretical studies appearing in the literature.

Development of a new skeletal mechanism for n-decane oxidation under engine-relevant conditions based on a decoupling methodology

A new skeletal mechanism for n-decane oxidation was developed based on a decoupling methodology with the special emphasis on the engine-relevant operating conditions from low to high temperature at high pressure. With the decoupling methodology, an extremely simplified model for C2–C10 was used to simulate the oxidation of heavy hydrocarbons for prediction of the ignition characteristics, while the mechanism of H2/CO/C1 was considered in details for providing accurate information of laminar flame speed and extinction strain rate. The new skeletal n-decane oxidation mechanism consists of 40 species and 141 reactions. Extensive validations of the present mechanism were performed by comparing with the experimental data available in the literature on n-decane oxidation, including ignition delay in shock tube and rapid compression machine, species concentrations in jet-stirred reactor and variable pressure flow reactor in wide ranges of temperature (550–1800K), pressure (1–80bar) and equivalence ratio (0.5–2). Moreover, the experimental data on the profiles of species concentration, laminar flame speed and extinction strain rate in premixed flame and counterflow flame was also being used in the validations. Finally, the skeletal n-decane mechanism was applied to predict the combustion and emissions of premixed charge compression ignition (PCCI) engines by using the multi-dimensional simulation. Overall, the current prediction from the present mechanism shows a good agreement with the experimental measurements, which indicates the potential of the decoupling methodology for the development of oxidation mechanism for heavy alkanes.

The combustion kinetics of a synthetic paraffinic jet aviation fuel and a fundamentally formulated, experimentally validated surrogate fuel

A surrogate fuel is formulated in an a priori manner through a combustion property matching technique to emulate the gas phase chemical kinetic combustion phenomena of S-8 POSF 4734, an alternative aviation fuel derived from natural gas via the Fischer–Tropsch process. A fundamental concept is described which identifies n-dodecane and iso-octane as being appropriate surrogate fuel components for the non-aromatic synthetic fuels. The performance of the formulated 51.9/48.1mole % n-dodecane/iso-octane mixture as a surrogate for the target real fuel is evaluated by the measurement of a series of combustion phenomena exhibited by both fuels including:(1)The oxidative reactivity of stoichiometric mixtures of each fuel in O2/N2 at 12.5atm and 500–1050K, for a residence time of 1.8s at a fixed carbon content of 0.3% using a variable pressure flow reactor.(2)The autoignition behavior of stoichiometric mixtures of each fuel in air at compressed conditions of 667–1223K and ∼20atm by the reflected shock technique.(3)The strained extinction limits of diffusion flames of each fuel at 1atm.The performance of available kinetic models for n-dodecane/iso-octane mixtures is evaluated by analysis of their computations of this experimental data. Furthermore, the impact of oxidation kinetics unique to the mono methylated alkanes which are the dominant molecular structure in synthetic fuels is examined by an experimental study involving the formulation of an n-decane/iso-octane mixture as a surrogate fuel for 2-methyl heptane, a proposed model molecule for such real fuel components.

The experimental evaluation of a methodology for surrogate fuel formulation to emulate gas phase combustion kinetic phenomena

A methodology for the formulation of surrogate fuels for the emulation of real fuel gas phase combustion kinetic phenomena pertinent to gas turbine combustion is described and tested. A mixture of n-dodecane/iso-octane/1,3,5-trimethylbenzene/n-propylbenzene is formulated in a predictive manner to exhibit the same gas phase combustion phenomena of a target Jet-A fuel by the sharing of fundamentally significant combustion property targets in addition to a prescribed commonality of chemical kinetically controlling intermediate species. The appropriateness of the surrogate formulation technique is demonstrated by the experimental measurement of various gas phase combustion kinetic phenomena of the proposed surrogate mixture and of the target Jet-A fuel:(1)A variable pressure flow reactor is used to chart the chemical reactivity of a stoichiometric mixture of surrogate fuel/O2/N2 at 12.5atm and 500–1000K, for a residence time of 1.8s at a fixed carbon content of 0.3%.(2)The autoignition behavior of stoichiometric mixtures of surrogate fuel in air is measured with a shock tube at 667–1223K at ∼20atm and also with a rapid compression machine at 645–714K at compressed pressures of 21.7atm.(3)Detailed measurements of the intermediate species formed in the high temperature oxidation of the target fuel and in the oxidation of the surrogate fuel are performed with a shock tube for reaction times of 1.23–3.53ms at 18–35atm and 901–1760K for 0.0808/0.158/0.1187mole% mixtures of C/H/O2.(4)The laminar burning velocity and strain extinction limits of premixed mixtures of surrogate fuel in O2/N2 are determined by the counter flow twin flame technique. These phenomena are also determined for premixed mixtures of the target fuel and for a previously proposed surrogate fuel composed of n-decane/iso-octane/toluene in O2/N2.(5)The high temperature chemical reactivity and chemical kinetic–molecular diffusion coupling of the surrogate fuel is evaluated by measurement of the strained extinction limits of diffusion flames.(6)The propensity of surrogate and real fuel to form soot is tested by laser extinction measurements of the soot volume fractions formed by each fuel in a wick-fed laminar flame diffusion burner as a function of the radial distance of each flame.These experimental data are compared to those previously reported at identical conditions for the target Jet-A fuel and for a similar n-decane/iso-octane/toluene surrogate fuel. A conceptual theory of real fuel oxidation is proposed and the similarity of the exhibited combustion phenomena of all three fuels is analyzed and interpreted in this context in order to (a) further evaluate the proposed strategy to surrogate fuel formulation and the appropriateness of the proposed theory to real fuel oxidation, (b) evaluate the appropriateness of the proposed n-dodecane/iso-octane/1,3,5-trimethylbenzene/n-propylbenzene mixture as a surrogate fuel for the target Jet-A fuel, and (c) to provide direction for the development of a tractable numerical modeling framework to compute real fuel multiphase combustion phenomena.

A chemical kinetic study of tertiary-butanol in a flow reactor and a counterflow diffusion flame

The combustion chemistry of tertiary-butanol is studied experimentally in a high pressure flow reactor and in counterflow diffusion flames. Princeton Variable Pressure Flow Reactor results show that t-butanol does not exhibit low temperature chemistry, and thus has no negative temperature coefficient behavior under the studied conditions. The onset of gas phase chemistry at high pressure occurs at ∼780 K. Over the temperature range of 780–950 K, t-butanol primarily reacts through hydrogen abstraction − alkyl or alkoxy radical beta-scission pathways to form methyl and propen-2-ol, which likely tautomerizes in the sampling system to form acetone. A species sampling study of a t-butanol counterflow diffusion flame reveals that the high temperature consumption routes of t-butanol lead to the stable intermediates isobutene, acetone, and methane, with isobutene existing in the highest concentrations. The extinction limits of t-butanol, isobutene, acetone, and methane diffusion flames are also reported. On a transport-weighted enthalpy basis, t-butanol extinguishes more readily than any of its primary intermediates, signifying that it is kinetically less resistant to extinction than the products of its initial reactions. Numerical simulation of these t-butanol flames reveals that the isobutene and acetone chemistry sub-models significantly affect the computed extinction limits. Improvement in the current understanding of isobutene oxidation kinetics, in particular, appears necessary to developing reliable kinetic models for t-butanol combustion.

A detailed experimental and kinetic modeling study of n-decane oxidation at elevated pressures

The oxidation of n-decane/oxygen/nitrogen is studied at stoichiometric conditions of 1000 ppm fuel in the Princeton variable pressure flow reactor at temperatures of 520–830 K and pressures of 8 and 12.5 atm. The overall oxidative reactivity of n-decane is observed in detail to show low temperature, negative temperature coefficient (NTC) and hot ignition regimes. Detailed temporal speciation studies are performed at reactor initial temperatures of 533 K and 740 K at 12.5 atm pressure and 830 K at 8 atm pressure. Significant amounts of large olefins are produced at 830 K, at conditions of transition from NTC to hot ignition behavior. The predictions using available chemical kinetic models for n-decane oxidation are compared against each other and the experiments. Only the kinetic models of Westbrook et al., Ranzi et al., and Biet et al. capture the NTC behavior exhibited by n-decane. However, each of these models yields varying disparities in the mechanistic predictions of major intermediate species, including ethylene and formaldehyde. Analyses of the Westbrook et al. model are compared with the new data. The predicted double-peaked species yield of ethylene, a behavior not found for the other models or in the experimental observations results from deficiencies in the C 2 chemistry. Mechanistic validation information about fuel oxidation chemistry is also provided by the measurement of various larger carbon number alkene isomers at 830 K and 8 atm. The modeling analysis suggests that in addition to n-alkyl beta-scission chemistry, alkyl peroxy radical chemistry contributes significantly to the formation of these alkenes. Specific reaction pathways and rate constants which affect the computation of these observations are discussed.

A jet fuel surrogate formulated by real fuel properties

An implicit methodology based on chemical group theory to formulate a jet aviation fuel surrogate by the measurements of several combustion related fuel properties is tested. The empirical formula and derived cetane number of an actual aviation fuel, POSF 4658, have been determined. A three component surrogate fuel for POSF 4658 has been formulated by constraining a mixture of n-decane, iso-octane and toluene to reproduce the hydrogen/carbon ratio and derived cetane number of the target fuel. The validity of the proposed surrogate is evaluated by experimental measurement of select combustion properties of POSF 4658, and the POSF 4658 surrogate. (1) A variable pressure flow reactor has been used to chart the chemical reactivity of stoichiometric mixtures of POSF 4658/O 2/N 2 and POSF 4658 surrogate/O 2/N 2 at 12.5 atm and 500–1000 K, fixing the carbon content at 0.3% for both mixtures. (2) The high temperature chemical reactivity and chemical kinetic–molecular diffusion coupling of POSF 4658 and POSF 4658 surrogate have been evaluated by measurement of the strained extinction limit of diffusion flames. (3) The autoignition behavior of POSF 4658 and POSF 4658 surrogate has been measured with a shock tube at 674–1222 K and with a rapid compression machine at 645–714 K for stoichiometric mixtures of fuel in air at pressures close to 20 atm. The flow reactor study shows that the character and extent of chemical reactivity of both fuels at low temperature (500–675 K) and high temperature (900 K+) are extremely similar. Slight differences in the transition from the end of the negative temperature coefficient regime to hot ignition are observed. The diffusion flame strained extinction limits of the fuels are observed to be indistinguishable when compared on a molar basis. Ignition delay measurements also show that POSF 4658 exhibits NTC behavior. Moreover, the ignition delays of both fuels are also extremely similar over the temperature range studied in both shock tube and rapid compression machine experiments. A chemical kinetic model is constructed and utilized to interpret the experimental observations and provides a rationale as to why the real fuel and surrogate fuel exhibit such similar reactivity.

A high‐temperature chemical kinetic model for primary reference fuels

AbstractA chemical kinetic mechanism has been developed to describe the high‐temperature oxidation and pyrolysis of n‐heptane, iso‐octane, and their mixtures. An approach previously developed by this laboratory was used here to partially reduce the mechanism while maintaining a desired level of detailed reaction information. The relevant mechanism involves 107 species undergoing 723 reactions and has been validated against an extensive set of experimental data gathered from the literature that includes shock tube ignition delay measurements, premixed laminar‐burning velocities, variable pressure flow reactor, and jet‐stirred reactor species profiles. The modeled experiments treat dynamic systems with pressures up to 15 atm, temperatures above 950 K, and equivalence ratios less than approximately 2.5. Given the stringent and comprehensive set of experimental conditions against which the model is tested, remarkably good agreement is obtained between experimental and model results. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 399–414, 2007

A comprehensive kinetic mechanism for CO, CH2O, and CH3OH combustion

AbstractNew experimental profiles of stable species concentrations are reported for formaldehyde oxidation in a variable pressure flow reactor at initial temperatures of 850–950 K and at constant pressures ranging from 1.5 to 6.0 atm. These data, along with other data published in the literature and a previous comprehensive chemical kinetic model for methanol oxidation, are used to hierarchically develop an updated mechanism for CO/H2O/H2/O2, CH2O, and CH3OH oxidation. Important modifications include recent revisions for the hydrogen–oxygen submechanism (Li et al., Int J Chem Kinet 2004, 36, 565), an updated submechanism for methanol reactions, and kinetic and thermochemical parameter modifications based upon recently published information. New rate constant correlations are recommended for CO + OH = CO2 + H (R23) and HCO + M = H + CO + M (R24), motivated by a new identification of the temperatures over which these rate constants most affect laminar flame speed predictions (Zhao et al., Int J Chem Kinet 2005, 37, 282). The new weighted least‐squares fit of literature experimental data for (R23) yields k23 = 2.23 × 105T1.89exp(583/T) cm3/mol/s and reflects significantly lower rate constant values at low and intermediate temperatures in comparison to another recently recommended correlation and theoretical predictions. The weighted least‐squares fit of literature results for (R24) yields k24 = 4.75 × 1011T0.66exp(−7485/T) cm3/mol/s, which predicts values within uncertainties of both prior and new (Friedrichs et al., Phys Chem Chem Phys 2002, 4, 5778; DeSain et al., Chem Phys Lett 2001, 347, 79) measurements. Use of either of the data correlations reported in Friedrichs et al. (2002) and DeSain et al. (2001) for this reaction significantly degrades laminar flame speed predictions for oxygenated fuels as well as for other hydrocarbons. The present C1/O2 mechanism compares favorably against a wide range of experimental conditions for laminar premixed flame speed, shock tube ignition delay, and flow reactor species time history data at each level of hierarchical development. Very good agreement of the model predictions with all of the experimental measurements is demonstrated. © 2007 Wiley Periodicals, Inc. 39: 109–136, 2007

A wide-ranging kinetic modeling study of methyl butanoate combustion

A detailed chemical kinetic model has been used to study methyl butanoate (a model compound for biodiesel fuels) oxidation over a wide range of conditions. New experimental results obtained in a jet stirred reactor (JSR) at 0.101 MPa, Φ = 1.13 and 800 < T (K) < 1350 were obtained and used to test and modify an earlier model. In addition, new experimental data generated in an opposed-flow diffusion flame at 0.101 MPa and in the Princeton variable pressure flow reactor (VPFR) at 1.266 MPa, 0.35 < Φ < 1.5 and 500 < T (K) < 900 are presented and compared against the revised model. The numerical model consists of 295 chemical species and 1498 chemical reactions and gives a good description of the data. Experimentally, the oxidation of methyl butanoate shows very little low temperature and negative temperature coefficient behaviour, with hot ignition occurring at about 800 K. Modeling results show similar diminished low temperature oxidation character, but reasonably reproduce hot ignition behaviour found in the VPFR. At higher temperature conditions, the model well describes the intermediate species found in the jet stirred reactor and in opposed flow diffusion flame experiments.

Experimental and Numerical Studies of Ethanol Decomposition Reactions

Ethanol pyrolysis experiments at 1.7−3.0 atm and 1045−1080 K were performed in the presence of radical trappers using a variable pressure flow reactor. Stable species time histories were determined using continuous sampling, on-line Fourier transform infrared spectrometry, and off-line gas chromatography. The rate constant k1 of the molecular decomposition reaction, C2H5OH → C2H4 + H2O (R1), was determined experimentally. The obtained result agrees very well with extrapolation of the recent shock-tube data of Herzler et al.1 The multichannel unimolecular decomposition of ethanol was also investigated theoretically on the basis of RRKM/master equation calculations. The effects of the hindered rotations in C2H5OH and quantum tunneling on the molecular decomposition reaction were taken into account. The reaction R1 was found to be strongly dependent on temperature and the dominant channel over the range of temperatures 300−2500 K at 1 atm. The calculated k1 is in excellent agreement with the recent theoretical work of Tsang2 as well as with the experimental measurements of Herzler et al.1 and the present data. The influence of tunneling on the shape of the falloff is discussed. In addition, the RRKM/master equation results were fit to modified Arrhenius expressions to facilitate chemical kinetic modeling applications of the results.

Ethanol pyrolysis experiments in a variable pressure flow reactor

AbstractExperimental profiles of stable species concentrations are reported for pyrolysis of ethanol in a variable‐pressure flow reactor at initial temperatures near 950 K and at constant pressures ranging from 3 to 12 atm. We present a new technique for comparison of model predictions with experimental observations in order to overcome the problem that time shifting of zero‐dimensional modeling results cannot accommodate the memory effects resulting from phenomena that occur in the mixing–diffuser region in the experiments. Using this new technique, comparison of the experiments with the recent ethanol kinetic model of Marinov shows that the model underestimates the fuel consumption rate and the yields of H2O and C2H4, the main products of ethanol decomposition, as well as CH3HCO and CH4, species related to abstraction channels. Both decomposition and abstraction reactions require significant modifications to improve detailed modeling of ethanol pyrolysis at the conditions of the reported experiments. © 2001 John Wiley &amp; Sons, Inc. Int J Chem Kinet 33: 859–867, 2001

Initial Observations of Ketene in Flow Reactor Kinetic Studies

Variable Pressure Flow Reactor (VPFR) experiments were conducted for ethene/methane mixtures utilizing both FTIR analyses of extracted gas samples and

The reaction kinetics of dimethyl ether. II: Low‐temperature oxidation in flow reactors

Dimethyl ether oxidation has been studied in a variable-pressure flow reactor over an initial reactor temperature range of 550–850 K, in the pressure range 12–18 atm, at equivalence ratios of 0.7 ≤ ϕ ≤ 4.2, with nitrogen diluent of approximately 98.5%. On-line extraction sampling in conjunction with FTIR, NDIR (for CO and CO2), and electrochemical (for O2) analyses were performed to quantify species at specific locations along the axis of the turbulent flow reactor. Product species concentrations were correlated against residence time (at constant inlet temperature) and against temperature (at fixed mean residence time) in the reactor. Formic acid was observed as a major intermediate of dimethyl ether oxidation at low temperatures. The experimental species-evolution profiles were compared to the predictions of a previously published detailed kinetic mechanism [1]. This mechanism did not predict the formation of formic acid. In the current study we have included chemistry leading to formic acid formation (and oxidation). This new chemistry is discussed and is able to reproduce the experimental observations with good accuracy. In addition, this model is able to reproduce low-temperature kinetic data obtained in a jet-stirred reactor [2] and the shock-tube results of Pfahl et al. [3] © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 741–759, 2000