CO Time-histories Research Articles

High-pressure shock tube study of ethanol oxidation: Ignition delay time and CO time-history measurements

Ethanol oxidation was studied by measuring CO time-histories and ignition delay times behind reflected shockwaves at elevated pressures. In this study, experimental conditions included a temperature range of 960–1580 K, pressure range of 17.8–23.9 atm, and initial fuel concentrations of 6.54% and 0.25% with nitrogen and argon used as bath gasses, respectively. The equivalence ratio for high fuel loading was kept constant at 1.0, and for low fuel loading equivalence ratios were 1.0 and 0.5. For high fuel loading, early heat/energy release was observed in nearly all ignition delay time measurements, indicative of preignition; however, data collected are in good agreement with model predictions. These events are interpreted as a transition from mild to strong ignition. For the low fuel loading cases (ϕ = 1.0 and 0.5), no early heat/energy release was observed. Comparisons of measured CO concentration profiles with the predictions from kinetic mechanisms of Metcalfe et al. (2013), Mittal et al. (2014), and Zhang et al. (2018) were made assuming constant internal energy and volume for the test gas. Such comparisons in addition with performed sensitivity and pathway analyses for CO formation revealed lower temperature sensitivity to the bimolecular reaction of methyl and hydroperoxyl radicals given by CH3 + HO2CH3O + OH, and H-atom abstraction by the hydroperoxyl radical at the alpha site on ethanol given by elementary reaction C2H5OH + HO2sC2H4OH + H2O2. The current study provides important validation targets for ethanol chemical kinetic mechanisms and highlights the benefits of time-history measurements at various temperatures and pressures in a shock tube, which are scare in the literature.

Shock tube investigation of methyl tert butyl ether and methyl tetrahydrofuran high‐temperature kinetics

AbstractThe autoignition and pyrolysis of two C5 ethers, methyl tert butyl ether (MTBE) and 2‐methyltetrahydrofuran (2‐MTHF), are investigated using the shock tube reactor. The experiments are carried out at pressures of 3.5 and 12 atm at temperatures above 1000 K with argon as a diluent gas. By means of direct laser absorption, carbon monoxide time histories and associated chemical kinetic timescales are also determined. It is observed that the competition between ignition and pyrolysis times depends on the temperature and equivalence ratio of the ignition mixture, such that there is a temperature above which pyrolysis predominates oxidative kinetics. This crossover temperature shifts toward higher temperatures for reactive systems with a fixed fuel concentration but higher oxygen content. The resulting experimental observations are also compared with predictions of existing chemical kinetic models from the literature. The results point to differences in chemical reactivity, such that in pyrolysis conditions, the reactivity of the cyclic ether, 2‐MTHF, is generally higher than that of the aliphatic ether, MTBE. While agreement between experimental observations and model predictions is observed under certain conditions, significant variance between observations and predictions is observed under other conditions. With respect to prediction of the pyrolysis time used to capture the global kinetics of pyrolysis, it is observed that the relation of this time to the time needed to attain 90% of the equilibrium CO concentration varies greatly with the result that the models used in this work generally predict a faster initial formation of CO but a much slower approach to the equilibrium concentration. This is thought to arise from the slow transformation of intermediate CH2O and CH2CO to CO. The chemical kinetic models considered in this work are therefore not capable of predicting the CO time histories during pyrolysis.

Methane and Methyl Propanoate High-Temperature Kinetics

The biodiesel surrogate, methyl propanoate (MP), is more reactive than methane. Mixtures of the two can be used to control combustion initiation in various combustion systems. Reported here is a shock tube study of the influence of chemical interactions resulting from mixing the two fuels on observable combustion properties, such as global chemical time scales and species time histories. Experiments are carried out at pressures of about 4, 7.4, and 10 atm covering a temperature window of 1000 to 1500 K. Using direct laser absorption, CO time histories during MP pyrolysis are obtained. The CO absorbance is further used to determine pyrolysis times by means of which the effect of temperature on MP pyrolysis is probed. Reactivity differences are first examined with the fuel concentration maintained at 3% and then with the oxygen concentration fixed at 10%. The evidence of chemical interactions during ignition is observed through a reduction of methane ignition delay times caused by MP addition. The influence...

An experimental, theoretical, and modeling study of the ignition behavior of cyclopentanone

The ignition delay times of cyclopentanone in air were measured using a high pressure shock tube (HPST) and a rapid compression machine (RCM) over the temperature range of 794–1368 K at P = 15 and 30 bar and at equivalence ratios of 0.5, 1.0 and 2.0. To provide more insight into the oxidation of cyclopentanone, CO time-histories during cyclopentanone oxidation in a shock tube at high temperatures and various pressures were also measured. In addition, quantum chemistry calculations have been performed to calculate the reaction rates for the olefin +HȮ2 elimination reactions of fuel peroxyl radical decomposition reactions, which were suggested as critical reaction pathways for the oxidation of cyclopentanone in previous studies. Based on these experimental and theoretical investigations, a detailed kinetic model has been developed and validated using the experimental data. The model has satisfactorily reproduced the ignition delay times in the RCM and shock tube, and CO histories in the shock tube over the wide range of temperature, pressure and equivalence ratio. Rate of production and sensitivity analyses were performed to determine the important reaction pathways and critical reactions that affect the predicted reactivity of cyclopentanone at the condition investigated.

Ignition delay times, laminar flame speeds, and species time-histories in the H2S/CH4 system at atmospheric pressure

Hydrogen sulfide (H2S) composes up to 30% of certain natural-gas resources (“sour gas”) and can considerably alter combustion properties of methane (CH4), but few data on H2S/CH4 are available in the literature. In this work, new shock-tube and laminar flame speed data were obtained to facilitate future model validation. For the shock-tube experiments, a fuel-lean (φ = 0.5) 30/70 H2S/CH4 blend in 99% argon by volume was shock-heated to temperatures between 1538 and 2144 K and pressures near 1 atm. Laser absorption diagnostics at 4.5 and 1.4 µm were employed to measure CO and H2O time-histories, respectively. OH* chemiluminescence profiles were measured using an emission diagnostic at 307 nm. For the laminar flame speed experiments, measurements were carried out in a constant-volume vessel at 295 K and 1 atm for CH4/argon and H2S/CH4/argon (8.25% H2S) mixtures from φ = 0.7 to φ = 1.4. The predictions of several recent chemical kinetics mechanisms were compared to the data, leading to the conclusion that species containing both carbon and sulfur are unimportant for shock-tube conditions but can be quite influential for laminar flames. By combining the modeling efforts of two recent works, a tentative new model is proposed that shows marked improvement over the older models in terms of shock-tube ignition delay times. Flame speed predictions show a discrepancy with the new model but follow general experimental trends. To the best of the authors’ knowledge, this study provides the first shock-tube data and laminar flame speeds measured in the H2S/CH4 system.

Shock Tube/Laser Absorption and Kinetic Modeling Study of Triethyl Phosphate Combustion.

Pyrolysis and oxidation of triethyl phosphate (TEP) were performed in the reflected shock region at temperatures of 1462-1673 K and 1213-1508 K, respectively, and at pressures near 1.3 atm. CO concentration time histories during the experiments were measured using laser absorption spectroscopy at 4580.4 nm. Experimental CO yields were compared with model predictions using the detailed organophosphorus compounds (OPC) incineration mechanism from the Lawrence Livermore National Lab (LLNL). The mechanism significantly underpredicts CO yield in TEP pyrolysis. During TEP oxidation, predicted rate of CO formation was significantly slower than the experimental results. Therefore, a new improved kinetic model for TEP combustion was developed, which was built upon the AramcoMech2.0 mechanism for C0-C2 chemistry and the existing LLNL submechanism for phosphorus chemistry. Thermochemical data of 40 phosphorus (P)-containing species were reevaluated, either using recently published group values for P-containing species or by quantum chemical calculations (CBS-QB3). The new improved model is in better agreement with the experimental CO time histories within the temperature and pressure conditions tested in this study. Sensitivity analysis was used to identify important reactions affecting CO formation, and future experimental/theoretical studies on kinetic parameters of these reactions were suggested to further improve the model. To the best of our knowledge, this is the first study of TEP kinetics in a shock tube under these conditions and the first time-resolved laser-based species time history data during its pyrolysis and oxidation.

Shock Tube and Laser Absorption Study of CH2O Oxidation via Simultaneous Measurements of OH and CO.

The oxidation of Ar-diluted stoichiometric CH2O-O2 mixtures was studied behind reflected shock waves over temperatures of 1332-1685 K, at pressures of about 1.5 atm and initial CH2O mole fractions of 500, 1500, and 5000 ppm. Quantitative and time-resolved concentration histories of OH and CO (at both v″ = 0 and v″ = 1) were measured by narrow-linewidth laser absorption at 306.7 and 4854 nm, respectively. A time delay was observed between the formation of v″ = 0 and v″ = 1 states of CO, suggesting that CO was kinetically generated primarily in the ground state and then collisionally relaxed toward vibrational equilibrium. The measured CO and OH time-histories were used to evaluate the performance of four detailed reaction mechanisms regarding the oxidation chemistry of CH2O. Further analyses of these time-history data have also led to improved determination for the rate constants of two key reactions, namely H + O2 = O + OH (R1) and OH + CO = CO2 + H (R2), as follows: k1 = 8.04 × 1013 exp(-7370 K/T) cm3 mol-1 s-1, k2 = 1.90 × 1012 exp(-2760 K/T) cm3 mol-1 s-1; both expressions are valid over 1428-1685 K and have 1σ uncertainties of approximately ±10%.

CO and H2O Time-Histories in Shock-Heated Blends of Methane and Ethane for Assessment of a Chemical Kinetics Model

Methane and ethane are the two main components of natural gas and typically constitute more than 95% of it. In this study, a mixture of 90% CH4/10% C2H6 diluted in 99% Ar was studied at fuel lean (equiv. ratio = 0.5) conditions, for pressures around 1, 4, and 10 atm. Using laser absorption diagnostics, the time histories of CO and H2O were recorded between 1400 and 1800 K. Water is a final product from combustion, and its formation is a good marker of the completion of the combustion process. Carbon monoxide is an intermediate combustion species, a good marker of incomplete/inefficient combustion, as well as a regulated pollutant for the gas turbine industry. Measurements such as these species time histories are important for validating and assessing chemical kinetics models beyond just ignition delay times and laminar flame speeds. Time-history profiles for these two molecules were compared to a state-of-the-art detailed kinetics mechanism as well as to the well-established GRI 3.0 mechanism. Results show that the H2O profile is accurately reproduced by both models. However, discrepancies are observed for the CO profiles. Under the conditions of this study, the CO profiles typically increase rapidly after an induction time, reach a maximum, and then decrease. This maximum CO mole fraction is often largely over-predicted by the models, whereas the depletion rate of CO past this peak is often over-estimated for pressures above 1 atm.

Combined Ab Initio, Kinetic Modeling, and Shock Tube Study of the Thermal Decomposition of Ethyl Formate.

The potential energy surfaces (PESs) and reaction rate constants of the unimolecular decomposition of ethyl formate (EF) were investigated using high-precision theoretical methods at the CCSD(T)/CBS(T-Q)//M06-2X/6-311++G(d,p) level of theory. The calculated PESs of EF dissociation and molecular decomposition reactions indicate that the intramolecular H-shift to produce formic acid and ethylene is the dominant decomposition pathway. A detailed chemical kinetic mechanism for EF pyrolysis was constructed by incorporating the important reactions of EF and its radicals into an existing mechanism previously developed for small methyl esters. The updated mechanism was first used to reproduce CO, CO2, and H2O concentration time histories during EF pyrolysis in the shock tube reported by Ren et al. [ Ren , W. , Mitchell Spearrin , R. , Davidson , D. F. , and Hanson , R. K. J. Phys. Chem. A 2014 , 118 , 1785 - 1798 ]. The rate of production and sensitivity analyses show that the competing dehydration and decarboxylation channels of the intermediate formic acid control the final product yields of EF pyrolysis. The EF mechanism was further validated against the shock tube data of OH, CO, CO2, and H2O time histories measured during EF oxidation (equivalence ratio Φ = 1.0) at 1331-1615 K and 1.52-1.74 atm. This revised EF mechanism captured all of the species' time histories over the entire temperature range. Such modeling capability was due to the more accurate rate constants of EF reactions determined by high-precision theoretical calculations and a high-fidelity C0-C2 basis mechanism.

Chemical kinetic modeling and shock tube study of methyl propanoate decomposition

The unimolecular decomposition kinetics of methyl propanoate (MP), including the direct C−O/C−C bond fissions and molecular reaction channels, were studied by using high-level ab initio calculations and Rice–Ramsperger–Kassel–Marcus/master equation (RRKM/ME) theory. Four homolytic bond-fission and ten hydrogen transfer reactions of the MP unimolecular decomposition were identified. The phenomenological rate constants were determined using the RRKM/ME theory over a temperature range of 1000−2000K and a pressure range of 0.01atm to the high-pressure limit. At 1atm, the branching ratios show that the dissociation reactions MP ↔ •CH2C(O)OCH3+CH3, MP ↔ CH3OC•(O)+C2H5 and MP ↔ CH3CH2C(O)O•+CH3 dominate MP pyrolysis over the temperature range of 1000−1500K. Our calculated rate constants were adopted in a detailed kinetic model to reproduce the laser-absorption measured CO and CO2 concentration time-histories during the pyrolysis of 0.2% MP/Ar in a shock tube from 1292−1551K and at 1.6atm. The updated mechanism accurately predicted the early-time CO and CO2 formation over the entire temperature range. In particular, our mechanism well reproduced the CO2 time-histories from the early-time formation to the final plateau level.

Shock Tube Measurement for the Dissociation Rate Constant of Acetaldehyde Using Sensitive CO Diagnostics

The rate constant of acetaldehyde thermal dissociation, CH3CHO = CH3 + HCO, was measured behind reflected shock waves at temperatures of 1273-1618 K and pressures near 1.6 and 0.34 atm. The current measurement utilized sensitive CO diagnostics to track the dissociation of CH3CHO via oxygen atom balance and inferred the title rate constant (k1) from CO time histories obtained in pyrolysis experiments of 1000 and 50 ppm of CH3CHO/Ar mixtures. By using dilute test mixtures, the current study successfully suppressed the interferences from secondary reactions and directly determined the title rate constant as k1(1.6 atm) = 1.1 × 10(14) exp(-36 700 K/T) s(-1) over 1273-1618 K and k1(0.34 atm) = 5.5 × 10(12) exp(-32 900 K/T) s(-1) over 1377-1571 K, with 2σ uncertainties of approximately ±30% for both expressions. Example simulations of existing reaction mechanisms updated with the current values of k1 demonstrated substantial improvements with regards to the acetaldehyde pyrolysis chemistry.

Pyrolysis and oxidation of methyl acetate in a shock tube: A multi-species time-history study

High-temperature methyl acetate (MA) pyrolysis and oxidation were studied behind reflected shock waves using laser-absorption species time-history measurements of CO, CO2, OH and H2O. The shock tube experiments with very dilute fuel mixtures covered a temperature range of 1401–1605K for MA pyrolysis (0.2% MA/Ar) and 1423–1674K for MA oxidation (0.4% O2, ϕ=1), and pressures around 1.5atm. The dominant sensitivity of CO2 concentration to MA unimolecular decomposition reactions enabled accurate determination of the rate coefficient and dissociation branching ratio by monitoring the CO2 time-history during MA pyrolysis. A recent kinetic mechanism developed by Yang et al. [13] originally for interpreting flow reactor and low-pressure flame data was adopted to simulate and compare with the current shock tube data. The measured CO and CO2 time-histories during MA pyrolysis were both well-predicted by the modified Yang et al. [13] mechanism. A relatively complete description of MA oxidation behavior was given by measuring CO, CO2, OH and H2O time-histories at the same temperature and pressure (1480K, 1.5atm). A unique two-stage CO2 formation during MA oxidation was clearly observed in the measured CO2 time-histories over the entire temperature range, with the rapid pre-ignition CO2 formation analyzed to be associated with the initial MA dissociation. Despite the overprediction of MA ignition delay times by 18–40% between 1623 and 1423K, the kinetic model successfully captures the plateau levels and the peak values of all the measured species profiles, as well as simulates the characteristic two-stage formation of CO2 observed experimentally.

Mathematical Modeling of a Semibatch Pyrolyser for Sesame Oil Cake

The present study deals with slow pyrolysis of sesame oil cake in an isothermally operated 50 mm diameter and 640 mm long semibatch pyrolyser in the temperature range of 673–1173 K. Under isothermal condition, a lumped parameter model has been used to determine the kinetic parameters for degradation of solid reactant and formation of volatile and char. The iso-conversional kinetics applicable for DAEM (distributed activation energy model) processes have also been determined for pyrolysis of sesame oil cake under nonisothermal conditions based on the thermogravimetric analyses data at different heating rates. The activation energies at different conversion almost follow a Gaussian distribution. On the basis of presently determined lumped kinetic parameters and the literature data for secondary pyrolysis kinetics, a mathematical model has been developed. The model can predict the time histories of unreacted solid, char, CO, H2, CO2, CH4 and condensable pyro-oil. Simulated predictions have been compared with the experimental results satisfactorily.

Experimental and Modeling Study of the Thermal Decomposition of C3–C5 Ethyl Esters Behind Reflected Shock Waves

The thermal decomposition of three ethyl esters, ethyl formate (C3H6O2), ethyl acetate (C4H8O2), and ethyl propanoate (C5H10O2), was studied behind reflected shock waves using laser absorption to measure concentration time-histories of H2O, CO2, and CO. Experimental conditions covered temperatures of 1301-1636 K, pressures of 1.48-1.72 atm, and reactant concentrations of 2000 ppm in argon. Recently developed mid-infrared laser diagnostics for H2O (2.5 μm), CO2 (4.3 μm), and CO (4.6 μm) provide orders-of-magnitude greater detectivity compared to previous near-infrared absorption sensors. The experimental results have highlighted significant differences among these three ethyl esters: negligible CO2 production during ethyl formate pyrolysis, quite slow CO formation rate during ethyl acetate pyrolysis, and nearly equal formation rate of H2O, CO2, and CO during ethyl propanoate pyrolysis. Detailed kinetic modeling was performed to understand the destruction pathways of these three ethyl esters with different alkyl chain lengths. Rate of production and sensitivity analyses were also carried out to interpret the experimental results and to identify the key reactions affecting experimental results.

Shock tube study of methanol, methyl formate pyrolysis: CH3OH and CO time-history measurements

Methanol and methyl formate pyrolysis were studied by measuring CH3OH and CO concentration time-histories behind reflected shock waves. In the study of methanol pyrolysis, experimental conditions covered temperatures of 1266–1707K, pressures of 1.1–2.5atm, and initial fuel concentrations of 1% and 0.2% with argon as the bath gas. Detailed comparisons of CH3OH and CO concentration profiles with the predictions of the detailed kinetic mechanism of Li et al. (2007) [8] were made. Such comparisons combined with sensitivity analysis identified the need to include an additional methanol decomposition channel, CH3OH↔CH2(S)+H2O, into the mechanism. Pathway and sensitivity analyses for methanol decomposition were performed, leading to rate constant recommendations both for CH3OH unimolecular decomposition and H-abstraction reactions with improved model performance. In the study of methyl formate pyrolysis, methanol concentration time-histories were measured at temperatures over the range of 1261–1524K, pressures near 1.5atm, and initial fuel concentrations of 1% with argon as the bath gas. Our current work, and CO time-histories from previous work, indicates that the Dooley et al. (2010) [3] model is able to accurately simulate most species concentrations in shock tube experiments at early times. However, model improvement is still needed to match the CH3OH and CO time-histories at later times. Incorporation of the modified rate constants in the methanol sub-mechanism leads to good predictions of the full methanol time-histories at all temperatures. The kinetic implications of some aspects of the CO time-histories and suggestions for further improving the predictive capabilities of these mechanisms are discussed. The current results are the first quantitative measurements of CH3OH time-histories in shock tube experiments, and hence are a critical step toward understanding of the chemical kinetics of oxygenates.

Multi-species measurements in 2-butanol and i-butanol pyrolysis behind reflected shock waves

The kinetics of 2-butanol and i-butanol pyrolysis were investigated by measuring multi-species time histories using shock tube/laser absorption methods. Species time histories of OH, H2O, C2H4, CO, and CH4 were measured behind reflected shock waves using UV and IR laser absorption during the high-temperature decomposition of 1% butanol/argon mixtures. Initial reflected shock temperatures and pressures for these experiments covered 1270–1640K and 1.3–1.9atm. These are the first multi-species time history measurements in shock tubes for 2-butanol and i-butanol.Production pathways and reaction rate sensitivities for the measured species are analyzed using the recent Sarathy et al. [36] detailed mechanism. It is observed that radical branching in 2-butanol is a highly complicated process with multiple reactions indistinguishably affecting the measured species profiles. However, i-butanol exhibits relatively simple radical branching, and evidence is presented that demonstrates radical branching must be adjusted to favor the iC4H8OH-β channel. Recommendations for i-butanol+H reactions are suggested and significant improvements between measurements and simulations using the Sarathy et al. [36] mechanism are achieved with these revised values.

Shock tube measurements of methane, ethylene and carbon monoxide time-histories in DME pyrolysis

High temperature dimethyl ether (DME) pyrolysis was studied behind reflected shock waves by measuring time-histories of CO, CH4 and C2H4 in mixtures of 0.5%, 1%, and 2% DME in argon respectively. Experiments were conducted at temperatures of 1300–1600K and pressures near 1.5atm. A direct absorption strategy with a fixed wavelength (2193.359cm−1) using a quantum cascade laser (QCL) was used to measure CO concentration time histories. A mid-IR scanned-wavelength laser absorption diagnostic with a difference frequency generation (DFG) laser near 3.43μm was used to measure CH4 concentration time histories. C2H4 was measured using a two-wavelength absorption scheme at 10.532μm and 10.675μm with a CO2 laser. The mechanism of Curran et al. with a constant volume gasdynamic model was used to calculate temperature and pressure profiles and to infer the mole fractions of CO, CH4 and C2H4. The concentration time-histories of CO, CH4 and C2H4 were all found to be strongly sensitive to the DME decomposition rate k1 (CH3OCH3 (+M)→CH3+CH3O (+M)), which was recently measured by Cook et al. at conditions similar to the current work. This measured k1 value was incorporated into two major DME decomposition mechanisms of Curran et al. and Zhao et al. The modified Curran et al. mechanism was found to predict the time histories of CH4 and C2H4 significantly better than the modified Zhao et al. mechanism.

Multi-species time-history measurements during high-temperature acetone and 2-butanone pyrolysis

High-temperature acetone and 2-butanone pyrolysis studies were conducted behind reflected shock waves using five species time-history measurements (ketone, CO, CH3, CH4 and C2H4). Experimental conditions covered temperatures of 1100–1600K at 1.6atm, for mixtures of 0.25–1.5% ketone in argon. During acetone pyrolysis, the CO concentration time-history was found to be strongly sensitive to the acetone dissociation rate constant k1 (CH3COCH3→CH3+CH3CO), and this could be directly determined from the CO time-histories, yielding k1(1.6atm)=2.46×1014exp(−69.3 [kcal/mol]/RT) s−1 with an uncertainty of ±25%. This rate constant is in good agreement with previous shock tube studies from Sato and Hidaka (2000) [3] and Saxena et al. (2009) [4] (within 30%) at temperatures above 1450K, but is at least three times faster than the evaluation from Sato and Hidaka at temperatures below 1250K. Using this revised k1 value with the recent mechanism of Pichon et al. (2009) [5], the simulated profiles during acetone pyrolysis show excellent agreement with all five species time-history measurements. Similarly, the overall 2-butanone decomposition rate constant ktot was inferred from measured 2-butanone time-histories, yielding ktot(1.5atm)=6.08×1013exp(−63.1 [kcal/mol]/RT) s−1 with an uncertainty of ±35%. This rate constant is approximately 30% faster than that proposed by Serinyel et al. (2010) [11] at 1119K, and approximately 100% faster at 1412K. Using the measured 2-butanone and CO time-histories and an O-atom balance analysis, a missing removal pathway for methyl ketene was identified. The rate constant for the decomposition of methyl ketene was assumed to be the same as the value for the ketene decomposition reaction. Using the revised ktot value and adding the methyl ketene decomposition reaction to the Serinyel et al. mechanism, the simulated profiles during 2-butanone pyrolysis show good agreement with the measurements for all five species.

Shock tube measurements of 3-pentanone pyrolysis and oxidation

High-temperature 3-pentanone pyrolysis and oxidation studies were performed behind reflected shock waves using laser-based species time-history measurements (3-pentanone, CH3, CO, C2H4, OH and H2O) and ignition delay time measurements. The overall 3-pentanone decomposition rate coefficient was inferred from the measured 3-pentanone and CH3 time-histories during pyrolysis at temperatures of 1070–1530K and a pressure of 1.6atm., and yielded a mathematical expression for ktot=4.383×1049T−10exp(−44,780/T)s−1 with an uncertainty of ±35% over 1070–1330K. The measured species time-histories and ignition delay times were also compared to simulations from a detailed kinetic mechanism of Serinyel et al. (2010) [14]. The measured ktot was approximately 3.5 times faster than the value used by Serinyel et al. Additionally, the absence of a methyl ketene decomposition reaction was identified as the cause of a deficiency in the O-atom balance of the measured 3-pentanone and CO time-histories. Using the revised overall 3-pentanone decomposition rate coefficient and an additional methyl ketene decomposition pathway, the modified mechanism was able to successfully simulate all six species time-histories, and showed a significant improvement in the predictions of ignition delay times. Finally, a comparison of ignition delay times and OH species time-histories during 3-pentanone, 2-pentanone and acetone oxidation found that 3-pentanone was the most reactive of the three ketones.

Multi-species measurements in 1-butanol pyrolysis behind reflected shock waves

The kinetics of 1-butanol pyrolysis were investigated by measuring multi-species time histories using shock tube/laser absorption methods. Species time histories of OH, H2O, C2H4, CO, and CH4 were measured behind reflected shock waves using UV and IR laser absorption during the high-temperature decomposition of 1% 1-butanol/argon mixtures. Initial reflected shock temperatures and pressures for these experiments covered 1250–1650K and 1.3–1.9atm. Measured OH and H2O time histories are in good agreement with previous experimental studies; measured C2H4, CO, and CH4 time histories are the first reported for this fuel in shock tube experiments.Production pathways and sensitivities for the measured species are analyzed using the recent Sarathy et al. (2012) [37] detailed mechanism. Simulations using this mechanism underpredict H2O, OH, and C2H4 mole fractions, overpredict CH4 mole fractions, and significantly underpredict CO mole fractions at early times. As discussed in past papers and confirmed in this study, the branching ratios of H abstraction rates from 1-butanol, which are not precisely known, can significantly affect H2O time history simulations. These simulations show that H2O is produced primarily through H-atom abstraction from 1-butanol by OH, and therefore H2O time histories are extremely sensitive to 1-butanol decomposition channels that contribute to the OH radical pool. Simulations also show that more C2H4 would be produced by faster decomposition of 1-butanol through several channels that also affect H2O production. Finally, simulations show that CO time histories are strongly sensitive to 1-butanol decomposition into nC3H7 and CH2OH, especially at early times. Evidence is presented that indicates this decomposition pathway is too slow in the simulations by a factor of three to five at conditions of the current study.