Experimental and modeling studies of C2H4/O2/Ar, C2H4/methylal/O2/Ar and C2H4/ethylal/O2/Ar rich flames and the effect of oxygenated additives

The addition of dimethoxymethane (DMM or methylal) and diethoxymethane (DEM or ethylal) to a rich ethylene/oxygen/argon flame has been investigated by measuring the depletion of soot precursors. Three rich premixed ethylene/oxygen/argon (with and without added methylal or ethylal) flat flames have been stabilized at low-pressure (50 mbar) on a Spalding–Botha type burner with the same equivalence ratio of 2.50. Identification and monitoring of signal intensity profiles of species within the flames have been carried out by using molecular beam mass spectrometry (M.B.M.S.). The replacement of some C₂H₄ by C₃H₈O₂ or C₅H₁₂O₂ is responsible for a decrease of the maximum mole fractions of the detected intermediate species. This phenomenon is noticeable for C₂–C₄ intermediates and becomes more effective for C₅–C₁₀ species, mainly when C₃H₈O₂ added.A new kinetic model has been elaborated and contains 546 reactions and 107 chemical species in order to simulate the three investigated flames: C₂H₄/O₂/Ar, C₂H₄/DMM/O₂/Ar and C₂H₄/DEM/O₂/Ar. The reaction mechanism well reproduces experimental mole fraction profiles of major and intermediate species, and underlines the effect of methylal and ethylal addition on species concentration profiles for these flames.     

Structure of atmospheric-pressure fuel-rich premixed ethylene flame with and without ethanol

Effect of ethanol (EtOH) addition to unburnt gas mixture on the species pool in a fuel-rich flat, premixed, laminar ethylene flame at atmospheric pressure is studied experimentally and by chemical kinetic modeling. Mole fraction profiles as a function of height above burner of various stable and labile species including reactants, major products and intermediates (C₁–C₄ hydrocarbons) are measured using molecular beam mass spectrometry with electron ionization in C₂H₄/O₂/Ar and C₂H₄/EtOH/O₂/Ar flames. The experimental profiles are compared with those calculated using three different chemical kinetic mechanisms. Performances and deficiencies of the mechanisms are discussed. An analysis of the mechanisms is carried out in order to identify the reason of the ethanol effect on the mole fraction of propargyl, the main precursor of benzene. A modification of some mechanisms in order to improve their capability to predict acetylene and diacetylene mole fraction profiles is proposed.     

Soot surface oxidation in hydrocarbon/air diffusion flames at atmospheric pressure

Soot surface oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round fuel jets burning in co-flowing dry air considering acetylene-nitrogen, ethylene, propylene-nitrogen, propane and acetylene-benzene-nitrogen in the fuel stream. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N₂, H₂O, H₂, O₂, CO, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈, and C₆H₆) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by deconvoluted Li/LiOH atomic absorption and flow velocities by laser velocimetry. For present test conditions, it was found that soot surface oxidation rates were not affected by fuel type, that direct rates of soot surface oxidation by O₂ estimated from Nagle and Strickland-Constable (1962) were small compared to observed soot surface oxidation rates because soot surface oxidation was completed near the flame sheet where O₂ concentrations were less than 3% by volume, and that soot surface oxidation rates were described by the OH soot surface oxidation mechanism with a collision efficiency of 0.14 and an uncertainty (95% confidence) of ±0.04 when allowing for direct soot surface oxidation by O₂, which is in reasonably good agreement with earlier observations of soot surface oxidation rates in both premixed and diffusion flames at atmospheric pressure.     

Isomer-specific combustion chemistry in allene and propyne flames

A combined experimental and modeling study is performed to clarify the isomer-specific combustion chemistry in flames fueled by the C₃H₄ isomers allene and propyne. To this end, mole fraction profiles of several flame species in stoichiometric allene (propyne)/O₂/Ar flames are analyzed by means of a chemical kinetic model. The premixed flames are stabilized on a flat-flame burner under a reduced pressure of 25 Torr (=33.3 mbar). Quantitative species profiles are determined by flame-sampling molecular-beam mass spectrometry, and the isomer-specific flame compositions are unraveled by employing photoionization with tunable vacuum-ultraviolet synchrotron radiation. The temperature profiles are measured by OH laser-induced fluorescence. Experimental and modeled mole fraction profiles of selected flame species are discussed with respect to the isomer-specific combustion chemistry in both flames. The emphasis is put on main reaction pathways of fuel consumption, of allene and propyne isomerization, and of isomer-specific formation of C₆ aromatic species. The present model includes the latest theoretical rate coefficients for reactions on a C₃H₅ potential [J.A. Miller, J.P. Senosiain, S.J. Klippenstein, Y. Georgievskii, J. Phys. Chem. A 112 (2008) 9429-9438] and for the propargyl recombination reactions [Y. Georgievskii, S.J. Klippenstein, J.A. Miller, Phys. Chem. Chem. Phys. 9 (2007) 4259-4268]. Larger peak mole fractions of propargyl, allyl, and benzene are observed in the allene flame than in the propyne flame. In these flames virtually all of the benzene is formed by the propargyl recombination reaction.     

Multiple benzene-formation paths in a fuel-rich cyclohexane flame

Detailed data and modeling of cyclohexane flames establish that a mixture of pathways contributes to benzene formation and that this mixture changes with stoichiometry. Mole-fraction profiles are mapped for more than 40 species in a fuel-rich, premixed flat flame (? = 2.0, cyclohexane/O₂/30% Ar, 30 Torr, 50.0 cm/s) using molecular-beam mass spectrometry with VUV-photoionization at the Advanced Light Source of the Lawrence Berkeley National Laboratory. The use of a newly constructed set of reactions leads to an excellent simulation of this flame and an earlier stoichiometric flame (M.E. Law et al., Proc. Combust. Inst. 31 (2007) 565–573), permitting analysis of the contributing mechanistic pathways. Under stoichiometric conditions, benzene formation is found to be dominated by stepwise dehydrogenation of the six-membered ring with cyclohexadienyl ? benzene + H being the final step. This finding is in accordance with recent literature. Dehydrogenation of the six-membered ring is also found to be a dominant benzene-formation route under fuel-rich conditions, at which H₂ elimination from 1,3-cyclohexadiene contributes even more than cyclohexadienyl decomposition. Furthermore, at the fuel-rich condition, additional reactions make contributions, including the direct route via 2C₃H₃ ? benzene and more importantly the H-assisted isomerization of fulvene formed from i-/n-C₄H₅ + C₂H₂, C₃H₃ + allyl, and C₃H₃ + C₃H₃. Smaller contributions towards benzene formation arise from C₄H₃ + C₂H₃, 1,3-C₄H₆ + C₂H₃, and potentially via n-C₄H₅ + C₂H₂. This diversity of pathways is shown to result nominally from the temperature and the concentrations of benzene precursors present in the benzene-formation zone, which are ultimately due to the feed stoichiometry.     

Rich methane premixed laminar flames doped with light unsaturated hydrocarbons: I. Allene and propyne

The structure of three laminar premixed rich flames has been investigated: a pure methane flame and two methane flames doped by allene and propyne, respectively. The gases of the three flames contain 20.9% (molar) of methane and 33.4% of oxygen, corresponding to an equivalence ratio of 1.25 for the pure methane flame. In both doped flames, 2.49% of C₃H₄ was added, corresponding to a ratio C₃H₄/CH₄ of 12% and an equivalence ratio of 1.55. The three flames have been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant, with a gas velocity at the burner of 36 cm/s at 333 K. The concentration profiles of stable species were measured by gas chromatography after sampling with a quartz microprobe. Quantified species included carbon monoxide and dioxide, methane, oxygen, hydrogen, ethane, ethylene, acetylene, propyne, allene, propene, propane, 1,2-butadiene, 1,3-butadiene, 1-butene, isobutene, 1-butyne, vinylacetylene, and benzene. The temperature was measured using a PtRh (6%)-PtRh (30%) thermocouple settled inside the enclosure and ranged from 700 K close to the burner up to 1850 K. In order to model these new results, some improvements have been made to a mechanism previously developed in our laboratory for the reactions of C₃-C₄ unsaturated hydrocarbons. The main reaction pathways of consumption of allene and propyne and of formation of C₆ aromatic species have been derived from flow rate analyses.     

Computational and experimental study of the effects of adding dimethyl ether and ethanol to nonpremixed ethylene/air flames

Two sets of axisymmetric laminar coflow flames, each consisting of ethylene/air nonpremixed flames with various amounts (up to 10%) of either dimethyl ether (CH₃-O-CH₃) or ethanol (CH₃-CH₂-OH) added to the fuel stream, have been examined both computationally and experimentally. Computationally, the local rectangular refinement method, which incorporates Newton's method, is used to solve the fully coupled nonlinear conservation equations on solution-adaptive grids for each flame in two spatial dimensions. The numerical model includes C6 chemical kinetic mechanisms with up to 59 species, detailed transport, and an optically thin radiation submodel. Experimentally, thermocouples are used to measure gas temperatures, and mass spectrometry is used to determine concentrations of over 35 species along the flame centerline. Computational results are examined throughout each flame, and validation of the model occurs through comparison with centerline measurements. Very good agreement is observed for temperature, major species, and several minor species. As the level of additive is increased, temperatures, some major species (CO₂, C₂H₂), flame lengths, and residence times are essentially unchanged. However, peak centerline concentrations of benzene (C₆H₆) increase, and this increase is largest when dimethyl ether is the additive. Computational and experimental results support the hypothesis that the dominant pathway to C₆H₆ formation begins with the oxygenates decomposing into methyl radical (CH₃), which combines with C2 species to form propargyl (C₃H₃), which reacts with itself to form C₆H₆.     

An experimental and numerical investigation of n-heptane/air counterflow partially premixed flames and emission of NOx and PAH species

An experimental and numerical investigation of counterflow prevaporized partially premixed n-heptane flames is reported. The major objective is to provide well-resolved experimental data regarding the detailed structure and emission characteristics of these flames, including profiles of C₁-C₆, and aromatic species (benzene and toluene) that play an important role in soot formation. n-Heptane is considered a surrogate for liquid hydrocarbon fuels used in many propulsion and power generation systems. A counterflow geometry is employed, since it provides a nearly one-dimensional flat flame that facilitates both detailed measurements and simulations using comprehensive chemistry and transport models. The measurements are compared with predictions using a detailed n-heptane oxidation mechanism that includes the chemistry of NO_x and PAH formation. The reaction mechanism was synergistically improved using pathway analysis and measured benzene profiles and then used to characterize the effects of partial premixing and strain rate on the flame structure and the production of NO_x and soot precursors. Measurements and predictions exhibit excellent agreement for temperature and major species profiles (N₂, O₂, n-C₇H₁₆, CO₂, CO, H₂), and reasonably good agreement for intermediate (CH₄, C₂H₄, C₂H₂, C₃H_x) and higher hydrocarbon species (C₄H₈, C₄H₆, C₄H₄, C₄H₂, C₅H₁₀, C₆H₁₂) and aromatic species (toluene and benzene). Both the measurements and predictions also indicate the existence of two partially premixed regimes; a double flame regime for ?<5.0, characterized by spatially separated rich premixed and nonpremixed reaction zones, and a merged flame regime for ?>5.0. The NO_x and soot precursor emissions exhibit strong dependence on partial premixing and strain rate in the first regime and relatively weak dependence in the second regime. At higher levels of partial premixing, NO_x emission is increased due to increased residence time and higher peak temperature. In contrast, the emissions of acetylene and PAH species are reduced by partial premixing because their peak locations move away from the stagnation plane, resulting in lower residence time, and the increased amount of oxygen in the system drives the reactions to the oxidation pathways. The effects of partial premixing and strain rate on the production of PAH species become progressively stronger as the number of aromatic rings increases.     

Numerical and experimental study of ethanol combustion and oxidation in laminar premixed flames and in jet-stirred reactor

The main objectives of this research consist in achieving both experimental and numerical studies of the combustion and oxidation of ethanol. Experimental mole fraction profiles of chemical species (stable, radical, and intermediates) were measured in three C₂H₅OH/O₂/Ar flat premixed flames stabilized at low pressure (50 mbar) and with equivalence ratios equal to 0.75, 1, and 1.25, respectively. The experimental setup used to determine the structure of one-dimensional laminar premixed flames consists of a molecular beam mass spectrometer system (MBMS) combined with electron impact ionization (EI). The oxidation of ethanol was also experimentally studied using a fused silica jet-stirred reactor (JSR). Experiments were performed in the temperature range 890–1250 K, at 1 atm, at four equivalence ratios equal to 0.25, 0.5, 1, and 2 and with an initial fuel concentration of 2000 ppm.A kinetic study was conducted in order to simulate all experimental data measured. It enabled building a kinetic mechanism by thoroughly reviewing the available literature and by taking into account specificities of the two kinds of experiments performed. Validity of the mechanism was also checked against experimental results previously published (ethanol oxidation in a JSR at 10 atm, ignition in a shock tube, combustion in premixed, partially-premixed, and non-premixed flames). This mechanism ensures a reasonably good modelling of the combustion and oxidation of ethanol over the wide range of experimental conditions investigated.     

An experimental study of fuel-rich 1,3-pentadiene and acetylene/propene flames

Fuel-rich laminar premixed flat flames of an acetylene/propene (1:1) mixture and of 1,3-pentadiene were investigated at 50 mbar in order to compare their flame chemistries for identical C/H (0.625) and C/O (0.77) ratios; under these conditions, observed differences in the reaction pathways should be related to fuel structure. Concentrations of the most important species for benzene formation were obtained by molecular beam mass spectrometry (MBMS). Temperature was measured with laser-induced fluorescence (LIF) of seeded NO. The burnt gas temperatures in both flames were similar with maximum values of 2250 K and 2100 K, respectively. The data were analyzed with respect to the formation of C₆ species, in particular to that of benzene as a key species in the soot formation mechanism. As a consequence of different fuel-specific primary decomposition reactions, the two flames show a strikingly different pattern of intermediate compounds, enhancing different possible benzene formation pathways. Relative reaction flows were also calculated from the experimental results which confirm this observation; however, large uncertainties in some important rate coefficients are noted. While the C₃H₃ recombination reaction contributes an important fraction of benzene formed in each flame, the contribution of e.g. C₄H₅ + C₂H₂ cannot be overlooked in the 1,3-pentadiene flame, C₄H₅ being an important pyrolysis product of 1,3-pentadiene. The present results can also be compared to those obtained under similar conditions in pure acetylene and pure propene flames as well as in flames burning further C₅ fuels including 1-pentene and cyclopentene. The consistent data sets provided here as part of this series of systematic investigations should be valuable for testing flame models that include the fuel-rich chemistry of higher hydrocarbons.     

Prediction of the liftoff,blowout and blowoff stability limits of pure hydrogen and hydrogen/hydrocarbon mixture jet flames

The paper presents experimental studies of the liftoff and blowout stability parameters of pure hydrogen, hydrogen/propane and hydrogen/methane jet flames using a 2 mm burner. Carbon dioxide and Argon gas were also used in the study for the comparison with hydrocarbon fuel. Comparisons of the stability of H₂/C₃H₈, H₂/CH₄ and H₂/CO₂ flames showed that H₂/C₃H₈ produced the highest liftoff height and H₂/CH₄ required highest liftoff, blowoff and blowout velocities. The non-dimensional analysis of liftoff height was used to correlate liftoff data of H₂, H₂/C₃H₈, H₂/CO₂, C₃H₈ and H₂/Ar jet flames tested in the 2 mm burner. The suitability of extending the empirical correlations based on hydrocarbon flames to both hydrogen and hydrogen/hydrocarbon flames was examined.     

Numerical study on CH4 laminar premixed flames for combustion characteristics in the oxidant atmospheres of N2/CO2/H2O/Ar-O2

The freely-propagating laminar premixed flames of CH₄–N₂/CO₂/H₂O/Ar-O₂ mixtures were conducted with the PREMIX code. The effects of the equivalence ratio and various oxidant atmospheres on the basic combustion characteristics were analyzed with the initial pressure and temperature of 1 atm and 398 K, respectively, O₂ content in the oxidant of 21%. The chemical reaction mechanism GRI-Mech 3.0 was chosen to determine the effects of the oxidant atmospheres of N₂/O₂, CO₂/O₂, H₂O/O₂, and Ar/O₂ on the adiabatic flame temperature, laminar burning velocity, flame structure, free radicals, intermediate species, net heat release rate and specific heat of the fuel/oxidant mixtures. The numerical results show that the maximum adiabatic flame temperatures and laminar burning velocities are at Ar/O₂ atmosphere. The mole fractions of CO and H₂ increased fastest at CO₂/O₂ atmosphere and H₂O/O₂, respectively. The mole fractions of CH₃ and H follow the order Ar/O₂> N₂/O₂>H₂O/O₂>CO₂/O₂. In addition, for 4 oxidant atmospheres, the peak mole fraction of C₂H₂ is following the order H₂O/O₂>Ar/O₂>N₂/O₂>CO₂/O₂ and the net heat release rate is following the order Ar/O₂>N₂/O₂>H₂O/O₂>CO₂/O₂ for all equivalence ratios.     

Effects of dimethyl methylphosphonate on premixed methane flames

The impact of dimethyl methylphosphonate (DMMP) was studied in a premixed methane/oxygen/N₂-Ar flame in a flat flame burner slightly under atmospheric pressure at two different equivalence ratios: rich and slightly lean. CH₄, CO, CO₂, CH₂O, CH₃OH, C₂H₆, C₂H₄, and C₂H₂ profiles were obtained with a Fourier Transform Infrared (FTIR) spectrometer. Gas samples, analyzed in the FTIR, were extracted from the reaction zone using a quartz microprobe with choked flow at its orifice. Temperature profiles were obtained by measuring the probe flow rate through the choked orifice. Flame calculations were performed with two existing detailed chemical kinetic mechanisms for organophosphorus combustion. DMMP addition caused all profiles except that of CH₃OH to move further away from the burner surface, which can be interpreted as a consequence of a reduction in the adiabatic flame speed. Experimentally, the magnitude of the shift was 50% greater for the near-stoichiometric flame than for the rich flame. Experimental CH₃OH profiles were four to seven times higher in the doped flames than in the undoped ones. The magnitude of this effect is not predicted in the calculations, suggesting a need for further mechanism development. Otherwise, the two mechanisms are reasonably successful in predicting the effects of DMMP on the flame.     

Photofragmentation laser-induced fluorescence imaging in premixed flames

Two-dimensional measurements of primarily hydroperoxyl radicals (HO₂) are, for the first time, demonstrated in flames. The measurements are performed in different Bunsen-type premixed flames (H₂/O₂, CH₄/O₂, and CH₄/air) using photofragmentation laser-induced fluorescence (PF-LIF). Photofragmentation is done by laser radiation at 266 nm, and the generated OH photofragments are probed through fluorescence induced by a laser tuned to the Q₁(5) transition at 282.75 nm. The signal due to naturally occurring OH radicals, recorded by having the photolysis laser blocked, is subtracted, providing an image that reflects the concentration of OH fragments generated by photolysis, and hence the presence of primarily HO₂, but also smaller contributions from H₂O₂ and, for the methane flames, CH₃O₂. For the methane flames the measured radial profiles of OH photofragments and natural OH agree well with corresponding profiles calculated for laminar, one-dimensional, premixed flames using CHEMKIN-II with the Konnov detailed C/H/N/O reaction mechanism. An interfering signal contribution is observed in the product zone of the methane flames. It is concluded that the major source for the interference is most likely hot CO₂, from which O atoms are produced by photolysis, and OH is rapidly formed as the O atoms react with H₂O and H₂. This conclusion is supported by the fact that the interference is absent for the hydrogen flame, but appears when CO₂ is seeded into the flame. Another strong indication is that the Konnov mechanism predicts a similar buildup of OH after photolysis.     

Experimental and modeling study of the effects of adding oxygenated fuels to premixed n-heptane flames

The effects of methanol, dimethoxymethane (DMM), and dimethylcarbonate (DMC) on laminar premixed low pressure (30 Torr) n-heptane flames were investigated by using synchrotron photoionization and molecular-beam mass spectrometry (PI–MBMS) techniques. The overall C/O ratio was maintained constant (0.507) and the equivalence ratio was kept around 1.6 for all the tested flames. The composition of unburned mixtures was adjusted such that the post-flame temperatures were nearly equivalent for all the test conditions. Mole fraction profiles of major and intermediate species were derived and compared among the flames. Parallel computations were performed based on a modified model, and the predicted concentrations of flame species agree reasonably well with the measured results. Early production of CO₂ was observed in the DMC-doped flame. Reaction flux analysis suggested that it was caused by the decomposition of CH₃OCO radical, DMC molecule and CH₃OCOO radical. As oxygenated fuels were added, the concentrations of most C₁C₅ hydrocarbon intermediates were reduced while that of benzene (C₆H₆) also decreased apparently, and the extent of benzene reduction showed little difference among the oxygenate-doped flames. Reaction flux analysis indicated that, in all the tested flames, the primary pathway leading from small aliphatics to C₆H₆ was through C₃ + C₃ reactions, including the self-recombination reaction of propargyl radical (C₃H₃) and the cross reaction between C₃H₃ and allyl radical (a-C₃H₅). Considering that the temperatures of the tested flames were almost equivalent, the reduction of C₆H₆ concentration when doped with oxygenated fuels should be resulted from the reduced concentrations of its precursors. Furthermore, concentrations of certain oxygenated intermediates were also examined. The concentration of formaldehyde (CH₂O) was found to increase when flames were doped with oxygenated fuels, while those of acetaldehyde (CH₃CHO) and vinyl alcohol (C₂H₃OH) were nearly equivalent for all the flames. Methyl formate (CH₃OCHO) was detected only in the DMM-doped flame, which was attributed to the efficient CH₃OCHO formation pathway through the decomposition of CH₃OCHOCH₃ radical in the flame.     

On the effect of molecular and hydrocarbon-bonded hydrogen on carbon particle formation in C3O2 pyrolysis behind shock waves

The effect of H₂ and C₂H₂ addition on particle formation in the pyrolysis of C₃O₂/Ar mixtures was studied behind reflected shock waves. An existing reaction mechanism for the pyrolysis of highly-diluted C₃O₂ in argon was expanded to conditions with higher C₃O₂ concentrations (up to 33 volume%) at elevated pressures and high temperatures and was validated against experimental data. The simulations for the gas-phase chemistry were performed with the program CHEMKIN. The heterogeneous particle formation was modeled by post-processing using the program PREDICI relying on the Galerkin method. It was found that in C₃O₂/H₂/Ar pyrolysis, the induction times and rate constants of particle formation do not differ significantly from those of pure C₃O₂/Ar pyrolysis. However, the presence of H₂ reduced the particle volume fraction, the mean diameter of particles, the particle number density, and the maximum temperature rise of the mixture. Hydrocarbon-bonded hydrogen in C₃O₂/C₂H₂/Ar pyrolysis caused significantly increased induction times for particle formation, decreased particle volume fractions, and decreased temperature rises. The different reaction channels for carbon particle formation were identified in view of the role of hydrogen. An alternating reaction channel including C₂ species played an important role in forming polycyclic aromatic hydrocarbons (PAH) in the mixtures.     

Effect of the equivalence ratio on the concentration of CH4/NO2/O2 combustion products

A chemical kinetic model for determining the mole fractions of stable and intermediate species for CH₄/NO₂/O₂ flames is developed. The model involves 30 different species in 101 chemical elementary reactions. The mole fractions of the species are plotted as a function of the distance from the surface of the burner. The effects of the equivalence ratio on the concentrations of CO, CO₂, N₂, NH₂, OH, H₂O, NO and NO₂ for lean CH₄/NO₂/O₂ flames in the post flame zone at 50 Torr are obtained. The flames are flat, laminar, one dimensional and premixed. The calculated concentration profiles as a function of the equivalence ratio and distance from the surface of the burner are compared with the experimental data. The comparison indicates that the kinetics of the flames are reasonably described by the developed model. The mole fraction of N₂, NH₂, OH, H₂O, CO₂ and CO increase while the mole fractions of NO and NO₂ decrease by increasing the equivalence ratio for lean flames. Copyright © 1999 John Wiley & Sons, Ltd.     

Ethanol flame structure investigated by molecular beam mass spectrometry

The oxidation of ethanol was studied in low-pressure, premixed flat flames using molecular beam mass spectrometry (MBMS) in combination with electron impact ionization (EI) and resonance-enhanced multiphoton ionization (REMPI). Flame temperature profiles were measured by laser-induced fluorescence (LIF) of seeded NO. Two ethanol/oxygen/argon flames with stoichiometries of ?=1.00 and ?=2.57 were investigated at 50 mbar by EI-MBMS. Profiles of a variety of stable and radical species were measured as a function of height above the burner. The benzene profile in the fuel-rich ethanol flame was obtained by REMPI-MBMS. The same technique was used to determine the dependence of the benzene concentration on the ethanol/propene ratio in low-pressure flames with blended fuels (propene/ethanol/oxygen/argon). The C/O ratio of all blends was kept constant at C/O=0.773 or C/O=0.600. Ethanol addition ranged from 0 to 15% for flames with C/O=0.773, and from 0 to 100% for flames with C/O=0.600. In both data sets, a decrease of the benzene concentration with increasing ethanol percentage was observed. Qualitative information on some other aromatic species with higher mass was also obtained.     

Hydrogen production from ethanol decomposition by microwave plasma TIAGO torch

This paper describes the study of molecular hydrogen production from ethanol decomposition by argon microwave TIAGO discharge in air ambiance at atmospheric pressure. In order to estimate the influence of the experimental conditions on the hydrogen production, a wide range of Ar flows, input powers and ethanol flows were tested. The simultaneous use of emission spectroscopy and mass spectrometry techniques allowed us to gain knowledge about the mechanisms which lead to the obtaining of hydrogen and other by-products (C₂H₂, C(s) …) at the plasma exit. Results showed a great capability of TIAGO discharges to withstand ethanol introduction as well as an almost complete ethanol decomposition (higher than 99.6%) with high hydrogen selectivity; argon and ethanol flows were found to be the key parameters in the by-products formation.     

Partial oxidation of ethanol using a non-equilibrium plasma

Partial oxidation of ethanol with air was carried out in a pulsed discharge plasma reactor at low temperature and atmospheric pressure. Effects of O₂:ethanol ratio, ethanol flow rate, and discharge current were investigated. H₂ and CO are the major products (>86%). Increases of O₂:ethanol ratio promote CO formation at the expense of C₂ hydrocarbons. H₂ selectivity and H₂ + CO selectivity are maximized at O₂:ethanol ratios of 0.3 and 0.5, respectively. Increases of feed flow rate accompanied by current increases allow the reactor to operate with high throughput. The LHV energy efficiency is increased with increasing feed flow rate, reaching 85% at high ethanol flow rates, conditions that also increase throughput. In contrast to catalytic and homogenous reactions, not all O₂ is consumed at high O₂:ethanol ratio for the low temperature plasma reaction. A radical reaction pathway of H abstraction from –OH and the α-H in ethanol to form CH₃CHO followed by C–C scission is proposed. The produced hydrogen rich gas can be potentially used in fuel cells and engines.