An experimental and modeling study of propene oxidation. Part 2: Ignition delay time and flame speed measurements (original) (raw)
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An experimental and kinetic modeling study of propyne and allene oxidation
Proceedings of the Combustion Institute, 2000
New experimental data for propyne and allene oxidation were obtained in a jet-stirred reactor (JSR) in the temperature range 800-1200 K at 1-10 atm for different fuel/oxygen equivalent ratios (0.2-2.0). Experimental data clearly indicate the different oxidation behavior of the two isomers and provide valuable information for extending the simulation capabilities of an already existing comprehensive kinetic scheme. Critical reactions are presented and discussed together with extended comparisons of model predictions with experimental data obtained in the JSR conditions, in the Princeton turbulent flow reactor (PTFR), and in a shock tube at higher temperatures. Finally, the effects on reaction paths of allene addition to a fuel-rich acetylene premixed flame are also discussed. Isomerization reactions proceeding via direct and H addition routes are significant in the oxidation. As a result of H-abstraction reactions, both propyne and allene form the resonantly stabilized propargyl radical. These species are important intermediates in all the combustion processes, and their successive reactions are relevant candidates in explaining the formation of aromatic and polyaromatic species, possible precursors of particulate and soot. The analysis of the mild combustion conditions of the JSR reactor also allows the reliability of the overall kinetic scheme to be extended to the so-called flameless conditions.
Combustion and Flame, 2011
The chemical composition of flames of mixed hydrocarbon-oxygenate fuels was examined systematically for a series of laminar, premixed low-pressure propene-oxygen-argon flames blended with ethanol or dimethyl ether (DME). All flames were established at a carbon-to-oxygen ratio of C/O = 0.5 at 40 mbar. Propene was replaced incrementally by either additive, so that the entire range from pure propene to pure ethanol or pure DME was accessible. Experimental results have been reported previously (J. Wang et al., J. Chem. Phys. A 112 (2008) 9255-9265), including temperature profiles measured with laserinduced fluorescence (LIF) and quantitative mole fraction profiles for a large number of species obtained from molecular-beam mass spectrometry (MBMS), using electron ionization (EI) and vacuum-ultraviolet (VUV) photoionization (PI). The effects of oxygenate addition to the propene base flame were seen to result in interesting differences, especially regarding trends to form aldehydes. The entire flame series is now analyzed with a comprehensive kinetic model that combines the chemistries of propene, ethanol, and DME combustion. The flames of pure fuels are also compared with the predictions of different detailed mechanisms taken from the literature. Quantitative comparison of C 1-to C 6-species from this model with the measurements is provided. Major trends of propene replacement by the oxygenates are reproduced in quantitative agreement with the experiments, enabling a more detailed understanding of the combined reaction sequences in such fuel blends.
Jet-stirred reactor and flame studies of propanal oxidation
Proceedings of the Combustion Institute, 2013
There is a strong drive towards utilizing oxygenated biofuels in blends with existing fossil fuels. Improving the kinetic modeling of the oxidation of these bio-derived oxygenates requires further investigation of their key stable intermediates such as the aldehydes. In this study, an experimental and chemical kinetic modeling investigation of propanal oxidation was carried out. Experiments were conducted in a jet stirred reactor and in counterflow flames over a wide range of equivalence ratios, temperatures, and ambient pressures. Stable species concentration profiles were measured in the jet stirred reactor and laminar flame speeds were measured. A detailed chemical kinetic reaction model was validated using the present experimental results and existing literature data. The model was used also to provide insight into the controlling reaction pathways for propanal oxidation in both the low-and high-temperature kinetic regimes.
Detailed Chemical Kinetic Mechanisms for Hydrocarbon and Oxygenated Hydrocarbon Fuel Combustion
2009
Stricter emissions legislation combined with the need to reduce greenhouse gas emissions drives fundamental research to produce cleaner, more efficient systems. Chemical kinetic mechanisms together with CFD codes are used to design more efficient and clean systems and optimize the operating behaviour of practical combustion devices such as internal combustion engines, gas turbines and other combustion devices. However, in order to validate and produce accurate detailed chemical kinetic mechanisms, a wide range of data is needed, which is normally generated under well-controlled physical conditions of temperature, pressure, fuel/air ratio and dilution. These data include (i) ignition delay times recorded in shock tubes and in rapid compression machines, (ii) speciation data from flow reactors, jet-stirred reactors and flame experiments and (iii) flame measurements of laminar burning velocity. Typically, these mechanisms for hydrocarbon and oxygenated hydrocarbon systems are generated...
Experimental and detailed kinetic model for the oxidation of a Gas to Liquid (GtL) jet fuel
Combustion and Flame, 2014
The kinetics of oxidation, ignition, and combustion of Gas-to-Liquid (GtL) Fischer-Tropsch Synthetic kerosene as well as of a selected GtL-surrogate were studied. New experimental results were obtained using (i) a jet-stirred reactor-species profiles (10 bar, constant mean residence time of 1 s, temperature range 550-1150 K, equivalence ratios φ = 0.5, 1, and 2), (ii) a shock tube-ignition delay time (≈ 16 bar, temperature range 650-1400 K, φ = 0.5 and 1), and (iii) a burner-laminar burning velocity (atmospheric pressure, preheating temperature = 473 K, 1.0 ≤ φ ≤ 1.5). The concentrations of the reactants, stable intermediates, and final products were measured as a function of temperature in the jet-stirred reactor (JSR) using probe sampling followed by on-line Fourier Transformed Infra-Red spectrometry, and gas chromatography analyses (on-line and off-line). Ignition delay times behind reflected shock waves were determined by measuring time-dependent CH* emission at 431 nm. Laminar flame speeds were obtained in a bunsen-type burner by applying the cone angle method. Comparison with the corresponding results for Jet A-1 showed comparable combustion properties. The GtL-fuel oxidation was modeled under these conditions using a detailed chemical kinetic reaction mechanism (8217 reactions vs. 2185 species) and a 3-component model fuel mixture composed of n-decane, iso-octane (2,2,4-trimethyl pentane), and npropylcyclohexane. The model showed good agreement with concentration profiles obtained in a JSR at 10 bar. In the high temperature regime, the model represents well the ignition delay times for the fuel air mixtures investigated; however, the calculated delays are longer than the measurements. It was observed that the ignition behavior of the surrogate fuel is mainly influenced by n-alkanes and not by the addition of iso-alkanes and cyclo-alkanes. The simulated laminar burning velocities were found in excellent agreement with the measurements. No deviation between burning velocity data for the GtL-surrogate and GtL was seen, within the uncertainty range. The presented data on ignition delay times and
A comprehensive experimental and kinetic modeling study of ethylbenzene combustion
Combustion and Flame, 2016
Iso-paraffinic molecular structures larger than seven carbon atoms in chain length are commonly found in conventional petroleum, Fischer-Tropsch (FT), and other alternative hydrocarbon fuels, but little research has been done on their combustion behavior. Recent studies have focused on either mono-methylated alkanes and/or highly branched compounds (e.g., 2,2,4trimethylpentane). In order to better understand the combustion characteristics of real fuels, this study presents new experimental data for the oxidation of 2,5-dimethylhexane under a wide variety of temperature, pressure, and equivalence ratio conditions. This new dataset includes jet stirred reactor speciation, shock tube ignition delay, and rapid compression machine ignition delay, which builds upon recently published data for counterflow flame ignition, extinction, and speciation profiles. The low and high temperature oxidation of 2,5-dimethylhexane has been modeled using a comprehensive chemical kinetic model developed using established reaction rate rules. The agreement between the model and data is presented, along with suggestions for improving model predictions. The importance of propene chemistry is highlighted as critical for correct prediction of high temperature ignition delay. The oxidation behavior of 2,5dimethylhexane is also compared with oxidation behavior of other linear and branched octane isomers, in order to determine the effects of the number of methyl branches on combustion properties. Both experimental data and model predictions indicate that increasing the level of branching decreases fuel reactivity at low and intermediate temperatures. The model is used to elucidate the structural features and reaction pathways responsible for inhibiting the reactivity of 2,5-dimethylhexane.
Detailed Modeling of Low-Temperature Propane Oxidation: 1. The Role of the Propyl + O 2 Reaction
The Journal of Physical Chemistry A, 2010
Accurate description of reactions between propyl radicals and molecular oxygen is an essential prerequisite for modeling of low-temperature propane oxidation because their multiple reaction pathways either accelerate the oxidation process via chain branching or inhibit it by forming relatively stable products. The CBS-QB3 level of theory was used to construct potential energy surfaces for n-C 3 H 7 + O 2 and i-C 3 H 7 + O 2 . Highpressure rate constants were calculated using transition state theory with corrections for tunneling and hindered rotations. These results were used to derive pressure-and temperature-dependent rate constants for the various channels of these reactions under the framework of the Quantum RicesRamspergersKassel (QRRK) and the modified strong collision (MSC) theories. This procedure resulted in a thermodynamically consistent C 3 H 7 + O 2 submechanism, which was either used directly or as part of a larger extended detailed kinetic mechanism to predict the loss of propyl and the product yields of propylene and HO 2 over a wide range of temperatures, pressures, and residence times. The overall good agreement between predicted and experimental data suggests that this reaction subset is reliable and should be able to properly account for the reactions of propyl radicals with O 2 in propane oxidation. It is also demonstrated that for most conditions of practical interest only a small subset of reactions (e.g., isomerization, concerted elimination of HO 2 , and stabilization) controls the oxidation kinetics, which makes it possible to considerably simplify the mechanism. Moreover, we observed strong similarities in the rate coefficients within each reaction class, suggesting the potential for development of relatively simple rate constant estimation rules that could be applied to analogous reactions involving hydrocarbon radicals that are too large to allow accurate detailed electronic structure calculations.
Energy & …, 2010
In the present paper, synchrotron VUV photoionization mass spectrometry is used to study the detailed chemistry of co-flow methane diffusion flames with different dilution ratios. The experimental results constitute a comprehensive characterization of species important for PAH and soot formation under conditions that resemble those of practical flames. In addition to the main C H 8 ) are detected. The laminar, co-flow flames were simulated using an original CFD code based on the operator-splitting technique, specifically conceived to handle large kinetic mechanisms. The detailed kinetic modeling was effectively used to describe and analyze the fuel consumption and the formation of PAH. Experimental measurements and numerical predictions were found to be in satisfactory agreement and showed the relative importance of the C 2 and C 3 mechanisms in the formation of the first aromatics.
A jet-stirred reactor and kinetic modeling study of ethyl propanoate oxidation
Combustion and Flame, 2009
A jet-stirred reactor study of ethyl propanoate, a model biodiesel molecule, has been carried out at 10 atm pressure, using 0.1% fuel at equivalence ratios of 0.3, 0.6, 1.0 and 2.0 and at temperatures in the range 750-1100 K with a constant residence time of 0.7 seconds. Concentration profiles of ethyl propanoate were measured together with those of major intermediates, ethylene, propanoic acid, methane and formaldehyde, and major products, water, carbon dioxide and carbon monoxide. This data was used to further validate a previously published detailed chemical kinetic mechanism, containing 139 species and 790 reversible reactions. It was found that this mechanism required a significant increase in the rate constant of the six-centered unimolecular elimination reaction which produces ethylene and propanoic acid in order to correctly reproduce the measured concentrations of propanoic acid. The revised mechanism was then used to re-simulate shock tube ignition delay data with good agreement observed. Rate of production and sensitivity analyses were carried out under the experimental conditions, highlighting the importance that ethylene chemistry has on the overall reactivity of the system.
Exploring gasoline oxidation chemistry in jet stirred reactors
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Recent decades have seen increasingly restrictive regulations applied to gasoline engines. Gasoline combustion chemistry must be investigated to achieve a better understanding and control of internal combustion engine efficiency and emissions. In this work, several gasoline fuels, namely the FACE (Fuel for Advanced Combustion Engines) gasolines, were selected as targets for oxidation study in jet-stirred reactors (JSR). The study is facilitated by formulating various gasoline surrogate mixtures with known hydrocarbon compositions to represent the real gasolines. Surrogates included binary mixtures of n-heptane and iso-octane, as well as more complex multicomponent mixtures. The oxidation characteristics of FACE gasolines and their surrogates were experimentally examined in JSR-1 and numerically simulated under the following conditions: pressure 1 bar, temperature 500-1050K, residence time 1.0 and 2.0 s, and two equivalence ratios (ϕ=0.5 and 1.0). In the high temperature region, all real fuels and surrogates showed similar oxidation behavior, but in the low temperature region, a fuel's octane number and composition had a significant effect on its JSR oxidation characteristics. Low octane number fuels displayed more low temperature reactivity, while fuels with similar octane number but a larger number of nalkane components were more reactive. A gasoline surrogate kinetic model was examined with FACE gasoline experiments either measured in JSR-2, or taken from previous work under the following conditions: pressure 10 bar, temperature 530-1200K, residence time 0.7s, and three equivalence ratios (ϕ=0.5, 1.0 and 2.0). Comparison between FACE gasoline experimental results with surrogate model predictions showed good agreement, demonstrating considerable potential for surrogate fuel kinetic modeling in engine simulations.