Concentration Profiles Of Stable Species Research Articles

An experimental and modeling study of ethylene–air combustion over a wide temperature range

Ethylene is an important intermediate during oxidation and pyrolysis process of higher hydrocarbons, and also serves as a fuel under practical engines. An experimental and modeling study is performed to investigate the combustion chemistry of ethylene–air mixtures under a wide range of conditions. The shock tube experiments are conducted at pressures of 1, 4, 10 and 19 atm with equivalence ratios of 0.5, 1.0 and 2.0 to determine the ignition delay times by measuring the emission signal of excited methylidyne (CH*). The ignition data under 10 and 19 atm both span a wide temperature range varying from a low temperature of 721 K to a high temperature of 1320 K. No typical negative-temperature-coefficient is observed, but the ignition at low temperatures is much shorter than the extrapolation at high temperatures. Simulations are performed and compared to the experiments using contemporary core models with consideration of a linear pressure rise of 3% /ms, but no simulation could predict the ignition trend under low-to-intermediate temperatures. Therefore, a detailed model of ethylene oxidation is proposed based on AramcoMech2.0 in the present work.The modeling behavior at high temperatures is improved by revision of addition reaction between ethylene and oxygen atom (C2H4+Ӧ). The modeling behavior at the region of low-to-intermediate temperatures is improved by detailed updating of β-hydroxyethyl oxidation (PĊ2H4OH+O2). The effect of reactions at the potential energy surface of C2H4+HȮ2 and Ċ2H5+O2 is determined, and the second oxygen addition (Ċ2H4OOH+O2) is added into current model. The present model is extensively validated by ignition delay times, concentration profiles of stable species in jet-stirred reactors and laminar flame speed under various test conditions. Sensitivity analyses are carried out to identify the dominant reactions during the auto-ignition process and laminar premixed flame propagation. Additional simulations are performed to investigate the effect of model modifications on predictions of ethane and ethanol oxidation. The present model slightly promotes the low-temperature ignition of both ethane and ethanol, and its prediction on the concentration profiles of some stable species is also improved. The proposed model of ethylene oxidation can be used as a cornerstone to develop models of larger hydrocarbon fuels.

Experimental and Modeling Study of the Oxidation of Two Branched Aldehydes in a Jet-Stirred Reactor: 2-Methylbutanal and 3-Methylbutanal

Aldehydes, especially formaldehyde and acetaldehyde, are common intermediates in the oxidation of many hydrocarbons and biofuels. Alcohols are known to produce important quantities of aldehydes. This work describes the oxidation of 2-methylbutanal and 3-methylbutanal (isopentanal) at both low and high temperatures. The former aldehyde is a main intermediate in 2-methylbutanol oxidation while the latter in isopentanol oxidation. Experiments were conducted in a jet-stirred reactor (JSR) at a pressure of 10 atm, for equivalence ratios of 0.35, 0.5, 1, 2, and 4 and over the temperature range 500–1200 K. The mean residence time was kept constant (700 ms). Concentration profiles of stable species were measured using gas chromatography and Fourier transform infrared spectroscopy. A detailed chemical kinetic mechanism including oxidation of various hydrocarbon and oxygenated fuels was extended to include the oxidation chemistry of both aldehydes; the resulting mechanism was used to simulate the present experiments. Both aldehydes showed negative temperature coefficient behavior in lean mixtures mainly due to the production of sec- and isobutyl radicals from 2- and 3-methylpentanal oxidation, respectively.

An experimental and modeling study of n-octanol combustion

This study presents the first investigation on the combustion chemistry of n-octanol, a long chain alcohol. Ignition delay times were determined experimentally in a high-pressure shock tube, and stable species concentration profiles were obtained in a jet stirred reactor for a range of initial conditions. A detailed kinetic model was developed to describe the oxidation of n-octanol at both low and high temperatures, and the model shows good agreement with the present dataset. The fuel’s combustion characteristics are compared to those of n-alkanes and to short chain alcohols to illustrate the effects of the hydroxyl moiety and the carbon chain length on important combustion properties. Finally, the results are discussed in detail.

Experimental and kinetic modeling study of trans-2-butene oxidation in a jet-stirred reactor and a combustion bomb

Butenes are intermediates ubiquitously formed by decomposition and oxidation of larger hydrocarbons (e.g. alkanes) or alcohols present in conventional or reformulated fuels. This study provides new complementary data for the oxidation of trans-2-butene. The oxidation of trans-2-butene was studied for measuring stable species concentration profiles during the oxidation of the fuel at atmospheric pressure, over a range of equivalence ratios (0.5⩽φ⩽2), and temperatures (900–1450K). A combustion bomb apparatus was used to determine laminar flame velocities of trans-2-butene in air at 1atm, 300K, and for equivalence ratios of 0.8–1.4. The oxidation of trans-2-butene was simulated under these experimental conditions using an extended detail chemical kinetic reaction mechanism (201 species involved in 1788 reactions). This mechanism is based on a previously proposed scheme for the oxidation of hydrocarbons. Good agreement with experimental data presented in this article was obtained which significantly improves kinetic modeling ability. The structure of a trans-2-butene premixed low pressure flat flame recently published was also successfully modeled. Sensitivity and reaction pathways analyses were performed to get insights into the processes involved in the oxidation of trans-2-butene.

Experimental Study of Tetralin Oxidation and Kinetic Modeling of Its Pyrolysis and Oxidation

Tetralin is the simplest polycyclic naphtheno-aromatic hydrocarbon found in liquid fuels (e.g., jet fuels, diesel). It is also produced by the pyrolysis and oxidation of decalin. To get a better understanding of tetralin combustion characteristics, new oxidation experiments were performed in a jet-stirred reactor, and the results are reported here. For the first time, stable species concentration profiles were measured at 1 and 10 atm over a range of equivalence ratios (φ = 0.5–1.5) and temperatures (790–1400 K). The oxidation of tetralin under these conditions was simulated using a semidetailed kinetic reaction scheme (∼10 000 reactions and ∼400 species) deriving from a chemical kinetic model proposed earlier for the oxidation of decalin over a wide range of conditions (jet-stirred reactor, plug-flow reactor, and shock-tube). The proposed kinetic model shows reasonable agreement with the present measurements. It can also be used to represent tetralin pyrolysis based on a variety of results available in t...

Experimental realization and characterization of unstretched planar one-dimensional diffusion flames

A burner configuration that allows the creation of nearly unstretched one-dimensional diffusion flames has recently been introduced. This paper presents the first detailed characterization of flames produced in such a burner to assess how well they approach the idealized one-dimensional configuration, which is used extensively for the development of theoretical models for diffusion flame stability. Particular emphasis is directed at quantifying the remaining inhomogeneities in the burner, such as residual flame stretch or variations in the boundary conditions, and identifying possible means to minimize them. Measurements made include the velocity field, stable species concentration profiles and temperature distribution throughout the burning chamber. Additionally, the flame position in the burner is determined as a function of mixture strength, reactant transport properties and bulk flow velocity. All the measurements are found to be in good agreement with a simplified one-dimensional flame model. However, the boundary conditions and their physical location have to be determined experimentally on both sides of the flame, which complicates comparison with results from theoretical and numerical models. Despite these limitations, we conclude that this new burner type provides a good experimental approximation of the one-dimensional idealized construct.

Experimental and kinetic modeling study of 1-hexanol combustion in an opposed-flow diffusion flame

Biofuels are of particular interest as they have the potential to reduce our dependence on petroleum-derived fuels and the levels of greenhouse gas emissions from transportation. 1-Hexanol is a promising renewable long chain alcohol that can be used in conventional fuel blends or as a cosolvent for biodiesel mixtures. However, the fundamental combustion properties of 1-hexanol have not been fully characterized in the literature. Thus, new experimental results, consisting of temperature and concentration profiles of stable species were obtained for the oxidation of 1-hexanol generated in an opposed-flow diffusion flame at 0.101MPa. This experimental data were compared to the predicted values of a detailed chemical kinetic mechanism proposed in the literature to study the combustion of 1-hexanol.This mechanism consists of 361 chemical species and 2687 chemical reactions (most of them reversible). Reaction pathway and sensitivity analyses were performed to interpret the results. In addition, improvements were investigated to optimize the proposed mechanism.

Experimental and Detailed Kinetic Modeling Study of Ethyl Pentanoate (Ethyl Valerate) Oxidation in a Jet Stirred Reactor and Laminar Burning Velocities in a Spherical Combustion Chamber

To improve our understanding of the combustion characteristics of ethyl pentanoate, a possible second generation biofuel, new experimental data were acquired for its oxidation kinetics in two complementary experiments. In a JSR (jet stirred reactor), concentration profiles of stable species were measured at 10 atm over a range of conditions (equivalence ratios of 0.6, 1, 2, fuel initial concentration of 1000 ppm, and temperatures between 560 to 1160 K). In a spherical combustion chamber, unstretched laminar burning velocities of ethyl pentanoate–air mixtures were measured at different pressures and temperatures and for equivalence ratios in the range 0.7–1.4. The oxidation of ethyl pentanoate was modeled using a new detailed kinetic reaction scheme (2719 reactions, 522 species). The chemical kinetic mechanism proposed here yielded good agreement with the present data. To interpret the results, reactions flux and sensitivity analyses were carried out.

Jet-stirred reactor and flame studies of propanal oxidation

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.

Experimental and semi-detailed kinetic modeling study of decalin oxidation and pyrolysis over a wide range of conditions

Decalin is the simplest polycyclic alkane (polynaphtenic hydrocarbon) found in liquid fuels (jet fuels, Diesel). In order to better understand the combustion characteristics of decalin, this study provides new experimental data for its oxidation in a jet-stirred reactor. For the first time, stable species concentration profiles were measured in a jet-stirred reactor at a constant mean residence time of 0.1s and 0.5s at respectively 1 and 10atm, over a range of equivalence ratios (ϕ=0.5–1.5) and temperatures (750–1350K). The oxidation of decalin under these experimental conditions was modeled using a semi-detailed chemical kinetic reaction mechanism (11,000 reactions involving 360 species) derived from a previously proposed scheme for the ignition of the same fuel in a shock-tube. The proposed mechanism that includes both low- and high-temperature chemistry shows reasonably good agreement with the present experimental data set. It can also represent well decalin pyrolysis and oxidation data available in the literature. Reaction path analyses and sensitivity analyses were conducted to interpret the results.

Experimental and Detailed Kinetic Modeling Study of Isoamyl Alcohol (Isopentanol) Oxidation in a Jet-Stirred Reactor at Elevated Pressure

Isoamyl alcohol (isopentanol or 3-methylbutan-1-ol) that can be biologically produced is among the possible alcohols usable as an alternative fuel in internal combustion engines. It has a higher energy density than smaller alcohols (ca. 28.5 MJ/L, as compared to ca. 21 MJ/L for ethanol and 27 MJ/L for 1-butanol). It is less hydroscopic than ethanol and mixes better with hydrocarbons. To better understand the combustion characteristics of that alcohol, new experimental data were obtained for its kinetics of oxidation in a jet-stirred reactor (JSR). Concentration profiles of stable species were measured in a JSR at 10 atm over a range of equivalence ratios (0.35−4) and temperatures (530−1220 K). The oxidation of isopentanol was modeled using an extended detailed chemical kinetic reaction mechanism (2170 reactions involving 419 species) derived from a previously proposed scheme for the oxidation of a variety of fuels. The proposed mechanism shows good agreement with the present experimental data. Reaction pa...

Experimental and Detailed Kinetic Modeling Study of the Oxidation of 1-Propanol in a Pressurized Jet-Stirred Reactor (JSR) and a Combustion Bomb

New experimental results were obtained to better characterize and understand the oxidation and combustion of 1-propanol, which is a renewable alcohol usable as an alternative to petrol-derived gasoline. A pressurized jet-stirred reactor (JSR) was used to measure concentration profiles of stable species (reactants, intermediates, and final products) at 10 atm, over a range of temperatures (T = 770–1190 K) and equivalence ratios (φ = 0.35–2). A combustion bomb was used to measure burning velocities of 1-propanol/air mixtures at pressures of P = 1–10 bar and T = 423 K, over a range of equivalence ratios (0.7 ≤ φ ≤ 1.4) and at 1 bar for temperatures in the range of 323–473 K. The effects of total pressure and temperature on burning velocity were determined under stoichiometric conditions. The oxidation of 1-propanol under these conditions was modeled using a detailed chemical kinetic scheme taken from the literature and a kinetic scheme of ours was extended to the oxidation of 1-propanol. The computational re...

2-Propanol Oxidation in a Pressurized Jet-Stirred Reactor (JSR) and Combustion Bomb: Experimental and Detailed Kinetic Modeling Study

2-Propanol is a renewable alcohol usable as an alternative to petrol-derived gasoline, for which new experimental data for its oxidation and combustion were obtained to better characterize and understand its combustion. Concentration profiles of stable species (reactants, intermediates, and final products) were measured in a pressurized jet-stirred reactor (JSR) over the temperature range of 770−1190 K and for equivalence ratios in the range of 0.35−4. Flame speeds of 2-propanol/air mixtures were measured at 1−10 bar and 423 K, over a range of equivalence ratios (0.7−1.5). The effect of the total pressure on the flame speed was determined for stoichiometric 2-propanol/air flames. The oxidation of 2-propanol in these experimental conditions was modeled using a detailed chemical kinetic reaction mechanism recently proposed for 2-propanol ignition. The kinetic mechanism showed reasonably good agreement with the present experimental data. Reaction path analyses and sensitivity analyses were performed to interpret the results.

Experimental and Detailed Kinetic Modeling Study of 1-Hexanol Oxidation in a Pressurized Jet-Stirred Reactor and a Combustion Bomb

1-Hexanol is among the promising renewable long-chain alcohols usable as an alternative to petrol-derived gasoline and diesel fuels. To better understand the combustion characteristics of 1-hexanol, new experimental data for the oxidation and combustion of 1-hexanol were obtained. Stable species concentration profiles were measured in a jet stirred reactor (JSR) at 10 atm over a range of equivalence ratios and temperatures. Burning velocities of 1-hexanol/air mixtures were measured at 1−10 bar and 423 K, over a range of equivalence ratios. The effect of total pressure on flame speed was determined. The oxidation of 1-hexanol in these experimental conditions was modeled using an extended detailed chemical kinetic reaction mechanism (2977 reactions involving 600 species). The proposed mechanism shows good agreement with the present experimental data. Reaction path analyses and sensitivity analyses were performed to interpret the results.

A study of low-pressure premixed ethylene flame with and without ethanol using photoionization mass spectrometry and modeling

In order to investigate the influence of ethanol on the process of forming precursors of polyaromatic hydrocarbons (PAH) and soot in ethylene flame, the measurement results and the 1 D numerical modeling results of the concentration profiles of stable species, as well as of radicals in premixed burner-stabilized flame of the fuel-rich mixture of ethylene/ethanol/oxygen/argon at the pressure of 30torr are presented and compared. Rich ethylene flame was chosen as the base flame. The measurements were made using molecular beam mass spectrometry with tunable synchrotron photoionization. The concentration of benzene and propargyl radicals, the main PAH precursors, was found to be lower in the flame of the ethylene/ethanol fuel mixture than in the pure ethylene flame. The main reaction pathways leading to benzene formation in ethylene flame containing ethanol and without it were analyzed.

Experimental and kinetic modeling of methyl octanoate oxidation in an opposed-flow diffusion flame and a jet-stirred reactor

New experimental results, consisting of concentration profiles of stable species as a function of temperature, were obtained for the oxidation of methyl octanoate in a jet-stirred reactor (JSR) at 0.101MPa, 0.5<φ<2 and 800<T (K)<1350. In addition, new experimental data, consisting of concentration profiles of stable species as a function of distance from fuel port, generated in an opposed-flow diffusion flame at 0.101MPa are presented. A detailed chemical kinetic model was developed to study the oxidation of methyl octanoate (CAS 111-11-5), a model compound for biodiesel fuels, under the present conditions. The kinetic model consists of 383 chemical species and 2781 chemical reactions (most of them reversible). Experimentally, the oxidation of methyl octanoate in the JSR at atmospheric pressure does not show low temperature and negative temperature coefficient behavior, whereas hot ignition occurs at about 800K. The present modeling results are in reasonably good agreement with the experimental data, describing the intermediate species measured in the jet-stirred reactor and in opposed-flow diffusion flame experiments.

Experimental and detailed kinetic modeling study of 1-pentanol oxidation in a JSR and combustion in a bomb

1-Pentanol is among the possible alcohols usable as an alternative to conventional gasoline and diesel fuels. In order to better understand the combustion characteristics of 1-pentanol, this study presents new experimental data for 1-pentanol in two complementary experimental configurations. Stable species concentration profiles were measured in a jet-stirred reactor (JSR) at 10atm over a range of equivalence ratios and temperatures. Laminar flame speeds of 1-pentanol-air premixed laminar flame were measured at 1atm and 423K for equivalence ratios of 0.7–1.4. The oxidation of 1-pentanol in these experimental configurations was modeled using an extended detailed chemical kinetic reaction mechanism (2099 reactions involving 261 species) derived from a previously proposed scheme for the oxidation of methanol-, ethanol-, and 1-butanol-based fuels. The proposed mechanism shows good agreement with the present experimental data. Reaction path analyses were conducted to interpret the JSR results.

Application of molecular beam mass spectrometry in studying the structure of a diffusive counterflow flame of CH 4/N 2 and O 2/N 2 doped with trimethylphosphate

The applicability of molecular beam mass spectrometry (MBMS) in studying the structure of counterflow flames has been tested by investigating a counterflow flame of CH 4/N 2 and O 2/N 2. The thermal structure of the flame was examined using a microthermocouple; the concentration profiles of such stable species as CH 4, O 2, and CO 2 were measured by sampling with a microprobe and MBMS at various positions. The microprobe did not disturb the flame. However, the sonic probe, when inserted into the flame transverse to the burner axis to measure the centerline concentration profiles, produced a significant disturbance of the flame. But no such disturbance was observed when the tip of the sonic probe was located at the periphery of the burner. Good agreement was obtained between the concentration profiles of stable species, as measured using a microprobe and a sonic probe at the periphery of the burner. To verify the applicability of MBMS for detecting radicals and other labile species in a counterflow flame, the concentration profiles of H, OH, and the main phosphorus-bearing species in the counterflow flame doped with trimethylphosphate (TMP) were measured by MBMS at the periphery of the burner and compared with results of modeling using the OPPDIF code and a mechanism for the combustion of TMP, tested previously in premixed flames of methane and oxygen with TMP as an additive. Good agreement was obtained between the measured and simulated concentration profiles for the reagents, as well as for the final and intermediate products with relatively high molecular weights (PO, PO 2, HOPO, HOPO 2). The measured concentration profiles of species with low molecular weights (H 2O, CO 2, OH, H) were found to be broader than the calculated ones—in fact, the lower the molecular weight, the wider was the profile. This is probably due to a real flame not being one-dimensional.

Experimental study of the structure of a rich premixed 1,3-butadiene/CH4/O2/Ar flame

The structure of a laminar rich premixed 1,3-butadiene/CH4/O2/Ar flame has been investigated, 1,3-butadiene, methane, oxygen, and argon mole fractions being 0.033, 0.2073, 0.3315, and 0.4280, respectively, for an equivalence ratio of 1.80. The flame has been stabilized on a burner at a pressure of 6.7 kPa. The concentration profiles of stable species have been measured by gas chromatography after sampling with a quartz probe. The quantified species include carbon monoxide and dioxide, methane, oxygen, hydrogen, ethane, ethylene, acetylene, propyne, allene, propene, cyclopropane, 1,3-butadiene, butenes, 1-butyne, vinylacetylene, diacetylene, C5 compounds, benzene, and toluene. The temperature distribution in the flame has also been measured.

Experimental investigation of methanol and ethanol flames in nonuniform flows

Experimental studies are conducted on extinction and autoignition of methanol and ethanol flames in laminar, nonuniform flows. Two flame types are considered: nonpremixed and premixed. The studies are performed in the counterflow configuration. The burner used in the experiments is made up of two ducts. Studies in the nonpremixed configuration are carried out by injecting a stream comprised of fuel vapors and nitrogen from one duct, and a stream of air from the other duct. In the premixed configuration a premixed-reactant stream made up of fuel vapors, air, and nitrogen, is injected from one duct, and a nitrogen stream from the other duct. Numerical calculations are performed using detailed chemistry at conditions corresponding to those used in the experiments. For the nonpremixed systems considered here, the calculated values of the critical conditions of extinction agree well with experimental data. At given values of the strain rate and temperature of the fuel stream, the calculated temperature of the oxidizer stream at autoignition is found to be higher than the measured values. In the premixed configuration the strain rate at extinction is measured for various values of the equivalence ratio of the mixture in the premixed-reactant stream, ϕ 1. The value of ϕ 1, at which the calculated extinction strain rate is the highest, is found to be larger than the value of ϕ 1 at which the measured extinction strain rate is the highest. Sensitivity analysis is carried out to test the influence of various elementary reactions on critical conditions of extinction. The structure of a nonpremixed methanol flame is investigated. Concentration profiles of stable species and temperature profiles are measured. The flame structure is calculated using detailed chemistry. The results of numerical calculations agree well with experimental data.