Kinetic modeling study of ethanol and dimethyl ether addition to premixed low-pressure propene–oxygen–argon flames

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 laser-induced 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 C₁- to C₆-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.     

利用同步辐射研究乙醇和二甲醚低压预混火焰成分

在低压预混层流火焰条件下,利用同步辐射光电离技术,结合分子束质谱法,对当量比为1的二甲醚和乙醇火焰进行了研究.通过扫描火焰中光子的能量,描绘出PIE曲线,探测到了这两种燃料燃烧过程中包含的同分异构中间产物;同时,通过扫描燃烧炉不同位置的光子能量谱,获得了火焰中重要物质的摩尔分数.比较两者的火焰结构,结果表明,这一对同分异构的燃料燃烧时,由于分子结构不同,它们的中间产物和相同中间产物的摩尔分数有很大差异,含氧的中间产物摩尔分数有较大差异.另外,在二甲醚火焰中还发现了甲乙醚,拓宽了对含氧碳氢化合物燃烧的认识.     

The influence of ethanol addition on a rich premixed benzene flame at low pressure

The aim of the study is to analyze the effect of ethanol in rich benzene flame, to observe the influence of this oxygenated species and to understand the kinetics of ethanol in the benzene combustion. Two premixed rich benzene/oxygen/argon (11.5% C₆H₆, 43.2% O₂, 45.3% Ar) and benzene/ethanol/oxygen/argon (10.7% C₆H₆, 2.1% C₂H₅OH, 43.2% O₂, 44.0% Ar) flat flames are stabilized at low pressure (45 mbar) on a burner with the same equivalence ratio of 2.0. Identification and monitoring of signal intensity profiles of species within the flames are carried out using molecular beam mass spectrometry (M.B.M.S.). The substitution of some C₆H₆ by C₂H₅OH is responsible for a reduction of the maximum concentrations of main intermediate species such as C₂H₂, C₄H₂, C₄H₄ and C₅H₆. The UCL mechanism is extended to heavier hydrocarbons, tested against these flames to check its validity and used to underline the effect of ethanol on soot precursors formation. It contains 1028 elementary reactions and 184 chemical species.     

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.     

An experimental and kinetic modeling study of 2-methyltetrahydrofuran flames

Clean combustion processes are of paramount importance in the transition of the energy system towards increased sustainability. In an attempt to partially replace conventional fossil fuels, bio-derived oxygenates attract rising attention as alternative transportation fuels. Among this class of fuels, cyclic structures that can be derived from cellulosic biomass are particularly interesting. Here we present a study of premixed, laminar low-pressure flames of 2-methyltetrahydrofuran (2-MTHF) with an equivalence ratio of ? = 1.7 at 40 mbar. Time-of-flight molecular-beam mass spectrometry (MBMS) with electron ionization (EI) was used to analyze and quantify mole fraction profiles of reactants, products, and most intermediate species including radicals involved in the combustion process. As a valuable complement, MBMS using single-photon ionization (PI) by vacuum ultraviolet radiation permitted isomer identification as well as independent concentration information under similar flame conditions. A detailed combustion model for 2-MTHF was developed, and the flame structure and species information were examined in conjunction with these experiments.     

Identification of combustion intermediates in isomeric fuel-rich premixed butanol-oxygen flames at low pressure

Laminar premixed low-pressure flames fueled by either one of the four isomers of butanol were investigated by a molecular-beam photoionization mass spectrometer using vacuum ultraviolet (VUV) synchrotron radiation as the ionization source. The photoionization efficiency (PIE) spectra of most flame intermediates were measured between 7.75 and 11.00 eV. By comparing the resulting PIE spectra to known ionization energies (IEs) or known PIE spectra of pure substances, most hydrocarbon and oxygenated combustion intermediates, including some radicals, in the mass range from m/z=15 to 106 were assigned and identified in the four butanol flames. The results show that the higher-mass oxygenated species in butanol flames are strongly affected by the fuel structure, while many hydrocarbon isomers appear almost independent of the fuel structure. The respective dissociation mechanisms of the fuels, including complex fission, simple fission, and H-atom abstraction, are in good agreement with previous results from nonpremixed butanol flames.     

An experimental and kinetic investigation of premixed furan/oxygen/argon flames

The detailed chemical structures of three low-pressure (35 Torr) premixed laminar furan/oxygen/argon flames with equivalence ratios of 1.4, 1.8 and 2.2 have been investigated by using tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry. About 40 combustion species including hydrocarbons and oxygenated intermediates have been identified by measurements of photoionization efficiency spectra. Mole fraction profiles of the flame species including reactants, intermediates and products have been determined by scanning burner position with some selected photon energies near ionization thresholds. Flame temperatures have been measured by a Pt–6%Rh/Pt–30%Rh thermocouple. A new mechanism involving 206 species and 1368 reactions has been proposed whose predictions are in reasonable agreement with measured species profiles for the three investigated flames. Rate-of-production and sensitivity analyses have been performed to track the key reaction paths governing furan consumption for different equivalence ratios. Both experimental and modeling results indicate that few aromatics could be formed in these flames. Furthermore, the current model has been validated against previous pyrolysis results of the literature obtained behind shock waves and the agreement is reasonable as well.     

Combustion of butanol isomers – A detailed molecular beam mass spectrometry investigation of their flame chemistry

The combustion chemistry of the four butanol isomers, 1-, 2-, iso- and tert-butanol was studied in flat, premixed, laminar low-pressure (40 mbar) flames of the respective alcohols. Fuel-rich (? = 1.7) butanol–oxygen–(25%)argon flames were investigated using different molecular beam mass spectrometry (MBMS) techniques. Quantitative mole fraction profiles are reported as a function of burner distance. In total, 57 chemical compounds, including radical and isomeric species, have been unambiguously assigned and detected quantitatively in each flame using a combination of vacuum ultraviolet (VUV) photoionization (PI) and electron ionization (EI) MBMS.Synchrotron-based PI-MBMS allowed to separate isomeric combustion intermediates according to their different ionization thresholds. Complementary measurements in the same flames with a high mass-resolution EI-MBMS system provided the exact elementary composition of the involved species. Resulting mole fraction profiles from both instruments are generally in good quantitative agreement.In these flames of the four butanol isomers, temperature, measured by laser-induced fluorescence (LIF) of seeded nitric oxide, and major species profiles are strikingly similar, indicating seemingly analog global combustion behavior. However, significant variations in the intermediate species pool are observed between the fuels and discussed with respect to fuel-specific destruction pathways. As a consequence, different, fuel-specific pollutant emissions may be expected, by both their chemical nature and concentrations.The results reported here are the first of their kind from premixed isomeric butanol flames and are thought to be valuable for improving existing kinetic combustion models.     

Investigation of critical equivalence ratio and chemical speciation in flames of ethylbenzene–ethanol blends

This work investigates five different one-dimensional, laminar, atmospheric pressure, premixed ethanol/ethylbenzene flames (0%, 25%, 50%, 75% and 90% ethanol by weight) at their soot onset threshold (?_critical). Liquid ethanol/ethylbenzene mixtures were pre-vaporized in nitrogen, blended with an oxygen–nitrogen mixture and, upon ignition, burned in premixed one-dimensional flames at atmospheric pressure. The flames were controlled so that each was at its visual soot onset threshold, and all had similar temperature profiles (determined by thermocouples). Fixed gases, light volatile hydrocarbons, polycyclic aromatic hydrocarbons (PAH), and oxygenated aromatic hydrocarbons were directly sampled at three locations in each flame. The experimental results were compared with a detailed kinetic model, and the modeling results were used to perform a reaction flux analysis of key species. The critical equivalence ratio was observed to increase in a parabolic fashion as ethanol concentration increased in the fuel mixture. The experimental results showed increasing trends of methane, ethane, and ethylene with increasing concentrations of ethanol in the flames. Carbon monoxide was also seen to increase significantly with the increase of ethanol in the flame, which removes carbon from the PAH and soot formation pathways. The PAH and oxygenated aromatic hydrocarbon values were very similar in the 0%, 25% and 50% ethanol flames, but significantly lower in the 75% and 90% ethanol flames. These results were in general agreement with the model and were reflected by the model soot predictions. The model predicted similar soot profiles for the 0%, 25% and 50% ethanol flames, however it predicted significantly lower values in the 75% and 90% ethanol flames. The reaction flux analysis revealed benzyl to be a major contributor to single and double ring aromatics (i.e., benzene and naphthalene), which was identified in a similar role in nearly sooting or highly sooting ethylbenzene flames. The presence of this radical was significantly reduced as ethanol concentration was increased in the flames, and this effect in combination with the lower carbon to oxygen ratios and the enhanced formation of carbon monoxide, are likely what allowed higher equivalence ratios to be reached without forming soot.     

The predictive capability of an automatically generated combustion chemistry mechanism: Chemical structures of premixed iso-butanol flames

The chemical compositions of four low-pressure premixed flames of iso-butanol are investigated with an emphasis on assessing the predictive capabilities of an automatically generated combustion chemistry model. This kinetic model had been extensively tested against earlier experimental data [S.S. Merchant, E.F. Zanoelo, R.L. Speth, M.R. Harper, K.M. Van Geem, W.H. Green, Combust. Flame (2013), http://dx.doi.org/10.1016/j.combustflame.2013.04.023.] and also shows impressive capabilities for predicting the new flame data presented here. The new set of data consists of isomer-resolved mole fraction profiles for more than 40 species in each of the four flames and provides a comprehensive benchmark for testing of any combustion chemistry model for iso-butanol. Isomer-specificity is achieved by analyzing flames, which are burner-stabilized at equivalence ratios of ? = 1.0–1.5 and at pressures between 15 and 30 Torr, with molecular-beam mass spectrometry and single-photon ionization by tunable vacuum-ultraviolet synchrotron radiation. Predictions of the C₂H₄O, C₃H₆O, and C₄H₈O enol–aldehyde–ketone isomers are improved compared to the earlier work by Hansen et al. [N. Hansen, M. R. Harper, W. H. Green, Phys. Chem. Chem. Phys. 13 (2011) 20262-20274] on similar n-butanol flames. A reaction path analysis identifies prominent fuel-consumption and oxidation sequences. Almost all of the species mole fraction data reported here are predicted within the measurement uncertainties of a factor of two to three. Some significant differences with previous published models are highlighted.     

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.     

Experimental and kinetic modeling study of methyl butanoate and methyl butanoate/methanol flames at different equivalence ratios and C/O ratios

Premixed laminar methyl butanoate/oxygen/argon and methyl butanoate/methanol/oxygen/argon flames were studied with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry at 30 torr (4.0 kPa). Three flames were investigated in the experiment: MB (methyl butanoate) flame F1.54 (? = 1.54, C/O = 0.479), MB flame F1.67 (? = 1.67, C/O = 0.511) and MB/methanol flame F1.67M (? = 1.67, C/O = 0.479). By measuring the signal intensities at different distances from the burner surface, the mole fraction profiles of intermediates are derived. Experimental results show that the flame front shifts downstream and peak mole fractions of intermediates increase remarkably with the increase of equivalence ratio for pure MB fuel. When methanol is added, the peak mole fractions of most intermediates including those of soot precursors decrease remarkably at the same equivalence ratio, while peaks of soot precursors vary little (only slightly decreasing) at same C/O ratio. It is concluded that the formation of soot precursors is more sensitive to C/O ratio than to equivalence ratio. Besides, more CO₂ is produced near the burner surface in MB flame than that in MB/methanol flame, and this validates an early production of CO₂ in methyl ester oxidation. In addition, a modified MB detailed mechanism is used to model flame structure, and improved agreements between the experimental and predicted results are realized. Based on the simulation results, reaction flux and sensitivity are analyzed for CO₂ and C₃H₃, respectively.     

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part III: 2,5-Dimethylfuran

This work is the third part of a study focusing on the combustion chemistry and flame structure of furan and selected alkylated derivatives, i.e. furan in Part I, 2-methylfuran (MF) in Part II, and 2,5-dimethylfuran (DMF) in the present work. Two premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of DMF were studied with electron–ionization molecular-beam mass spectrometry (EI-MBMS) and gas chromatography (GC) under two equivalence ratios (? = 1.0 and 1.7). Mole fractions of reactants, products, and stable and radical intermediates were measured as a function of the distance to the burner. Kinetic modeling was performed using a reaction mechanism that was further developed in the present series, including Part I and Part II. A reasonable agreement between the present experimental results and the simulation is observed. The main reaction pathways of DMF consumption were derived from a reaction flow analysis. Also, a comparison of the key features for the three flames is presented, as well as a comparison between these flames of furanic compounds and those of other fuels. An a priori surprising ability of DMF to form soot precursors (e.g. 1,3-cyclopentadiene or benzene) compared to less substituted furans and to other fuels has been experimentally observed and is well explained in the model.     

Experimental and modeling study of formaldehyde combustion in flames

The increased use of alcohols in internal combustion engines has driven the attention to formaldehyde emissions. Yet the experimental database on formaldehyde flames is limited. The experimental structures of two formaldehyde flames have been investigated at low pressure (30 mbar) using a molecular beam sampling coupled with a mass spectrometer. The initial compositions are for the lean flame (? = 0.22): 18% CH₂O and 82% O₂, and for the stoichiometric one (? = 1.09): 17.7% CH₂O, 16.3% O₂ and 66.0% Ar. A kinetic model, previously elaborated, has been improved by building a complete submechanism taking into account the formation and consumption of species involved in the formaldehyde combustion. The improved mechanism contains 107 chemical species and 568 reactions in order to simulate these two formaldehyde flames accurately. The reliability of this kinetic model has also been tested in ethanol and acetaldehyde flames. This allows the extension of its validity range.     

Flame temperature, fuel structure, and fuel concentration effects on soot formation in inverse diffusion flames

Insights into soot formation processes are gained from chemical sampling and thermocouple probing of co-flowing inverse diffusion flames (IDFs), with the oxidizer in the center. The transition from near-to slightly sooting flames and the effects of flame temperature, fuel concentration, and fuel structure (using methane, ethene, propene and 1-butene) are investigated. The aromatic content of IDFS scales with the fuel's sooting tendency, and suggests that the formation of the aromatic ring is a controlling step in soot formation. In addition to the relatively well-established reactions involving C4 and C2 species, benzene may form directly from two C3 species for fuels that readily produce C3 species during pyrolysis and/or oxidative pyrolysis. The total concentration of growth species increases almost linearly with fuel concentration, but depends more weakly on flame temperature than would be expected if pure pyrolysis governed the intermediate hydrocarbon behavior.     

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.     

Measurements and modeling study of intermediates in ethanol and dimethy ether low-pressure premixed flames using synchrotron photoionization

A molecular-beam flame-sampling photoionization mass spectrometer, employing synchrotron radiation, was applied to detect new intermediates and to measure mole fractions in the low-pressure laminar premixed stoichiometric ratio dimethyl ether (DME)/O₂/Ar and ethanol/O₂/Ar flames respectively. With the help of the means mentioned above, flame species of the two fuels, including isomeric intermediates, were unambiguously identified and the temperature profiles and mole fraction profiles of intermediates were also compared and analyzed. Additionally, five detailed oxidation mechanisms were applied to the modeling study to verify current mechanism for the two fuels. Based on the comparative experimental and modeling study of the two flames at low pressure, the oxidation mechanism for DME and ethanol was revised and a new one was suggested in the present work. The results calculated by the revised mechanism showed that the modeling prediction agreed with those experimental results measured in DME and ethanol flames as well as with the ones in five flames from the experiments done by the other people. In the measurement all species with mole fraction higher than 10⁻⁴ were considered, including those which have not been included in the present five mechanisms. Meanwhile, the mole fractions of the species which had not been considered by current mechanism such as ethenol, acetone and ethyl methyl ether (EME) were also included in the modeling study. Besides, the reaction paths and species conversion ratio analysis were also conducted to show the difference before and after the mechanism revised.     

Demonstration of a burner for the investigation of partially premixed low-temperature flames

A burner, which stabilizes near-one-dimensional low-temperature flames at atmospheric pressure, was designed to access the combustion regime near 1500 K for quantitative species diagnostics. Combustion temperatures between 1300 and 1800 K in argon-diluted methane-oxygen flames were achieved by preheating the burner and adapting the inert gas flow. Mass spectrometry with electron ionization was used to determine mole fractions profiles of reactants, products, and intermediates. Combustion parameters were varied including stoichiometry, diluent mole fraction and preheat temperature. Mole fraction profiles resemble those taken in regular premixed flat flames. A number of C₁- and C₂-intermediates as well as some oxygenated species were identified. Higher-mass species (m/z > 42) were not detected in the low-temperature methane-oxygen flames which contain 90% argon in the cold gases.     

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part II: 2-Methylfuran

This is Part II of a series of three papers which jointly address the combustion chemistry of furan and its alkylated derivatives 2-methylfuran (MF) and 2,5-dimethylfuran (DMF) under premixed low-pressure flame conditions. Some of them are considered to be promising biofuels. With furan as a common basis studied in Part I of this series, the present paper addresses two laminar premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of MF which were studied with electron–ionization molecular-beam mass spectrometry (EI-MBMS) and gas chromatography (GC) for equivalence ratios ? = 1.0 and 1.7, identical conditions to those for the previously reported furan flames. Mole fractions of reactants, products as well as stable and reactive intermediates were measured as a function of the distance above the burner. Kinetic modeling was performed using a comprehensive reaction mechanism for all three fuels given in Part I and described in the three parts of this series. A comparison of the experimental results and the simulation shows reasonable agreement, as also seen for the furan flames in Part I before. This set of experiments is thus considered to be a valuable additional basis for the validation of the model. The main reaction pathways of MF consumption have been derived from reaction flow analyses, and differences to furan combustion chemistry under the same conditions are discussed.     

Combustion chemistry of the propanol isomers — investigated by electron ionization and VUV-photoionization molecular-beam mass spectrometry

The combustion of 1-propanol and 2-propanol was studied in low-pressure, premixed flat flames using two independent molecular-beam mass spectrometry (MBMS) techniques. For each alcohol, a set of three flames with different stoichiometries was measured, providing an extensive data base with in total twelve conditions. Profiles of stable and intermediate species, including several radicals, were measured as a function of height above the burner. The major-species mole fraction profiles in the 1-propanol flames and the 2-propanol flames of corresponding stoichiometry are nearly identical, and only small quantitative variations in the intermediate species pool could be detected. Differences between flames of the isomeric fuels are most pronounced for oxygenated intermediates that can be formed directly from the fuel during the oxidation process. The analysis of the species pool in the set of flames was greatly facilitated by using two complementary MBMS techniques. One apparatus employs electron ionization (EI) and the other uses VUV light for single-photon ionization (VUV-PI). The photoionization technique offers a much higher energy resolution than electron ionization and as a consequence, near-threshold photoionization-efficiency measurements provide selective detection of individual isomers. The EI data are recorded with a higher mass resolution than the PI spectra, thus enabling separation of mass overlaps of species with similar ionization energies that may be difficult to distinguish in the photoionization data. The quantitative agreement between the EI- and PI-datasets is good. In addition, the information in the EI- and PI-datasets is complementary, aiding in the assessment of the quality of individual burner profiles. The species profiles are supplemented by flame temperature profiles. The considerable experimental efforts to unambiguously assign intermediate species and to provide reliable quantitative concentrations are thought to be valuable for improving the mechanisms for higher alcohol combustion.