Electron ionization, photoionization and photoelectron/photoion coincidence spectroscopy in mass-spectrometric investigations of a low-pressure ethylene/oxygen flame

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This paper is concerned with the investigation of the chemical structure of a low-pressure, fuel-rich (ɸ=1.8) premixed laminar flame fueled with 2-methyl-2-butene employing flame-sampling molecular-beam mass spectrometry with vacuum-ultraviolet single-photon ionization. Partially isomer-resolved mole fraction profiles can be explained by a decomposition scheme based on hydrogen abstraction and addition reactions. The presence of 9 allylic C-H bonds compared to only one vinylic C-H bond is the key feature that governs the fuel consumption and subsequent hydrocarbon growth reactions. Compared to other alkenes, including e.g., 1-butene, 2-butene, and iso-butene [Schenk et al., Combust. Flame. 160 (2013) 487-503], 2-methyl-2-butene shows a remarkable tendency to form soot precursor molecules such as toluene. In particular, experimental evidence is provided here that toluene, o-xylene, and styrene can be a starting point for PAH formation, thus serving as first aromatic rings besides benzene. The formation of toluene, o-xylene, and styrene can be traced back to the reactions of the resonantly stabilized C 4 H 5 [•CH 2-C≡C-CH 3 and CH 2 =CH-•C=CH 2 ] radicals and the C 5 H 7 [CH 2 =C(CH 3)-•C=CH 2 ] radicals that are readily formed

Section: Discussionmentioning

confidence: 99%

Consumption and hydrocarbon growth processes in a 2-methyl-2-butene flame

Ruwe

Moshammer

Hansen

et al. 2017

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“…Further experimental studies on DMC combustion kinetics need to be conducted in the future. For example, recognizing that fuel radicals can be detected using photoelectron photoion coincidence spectroscopy (PEPICO) [62], PEPICO investigation on DMC flames can further improve the mechanism especially for the initial decomposition steps.…”

Section: Discussionmentioning

confidence: 99%

An experimental and kinetic modeling study on dimethyl carbonate (DMC) pyrolysis and combustion

Sun

Yang

Hansen

et al. 2016

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Dimethyl carbonate (DMC) is a promising oxygenated additive or substitute for hydrocarbon fuels, because of the absence of C-C bonds and the large oxygen content in its molecular structure. To better understand its chemical oxidation and combustion kinetics, flow reactor pyrolysis at different pressures (40, 200 and 1040 mbar) and low-pressure laminar premixed flames with different equivalence ratios (1.0 and 1.5) were investigated. Mole fraction profiles of many reaction intermediates and products were obtained within estimated experimental uncertainties. From theoretical calculations and estimations, a detailed kinetic model for DMC pyrolysis and high-temperature combustion consisting of 257 species and 1563 reactions was developed. The performance of the kinetic model was then analyzed using detailed chemical composition information, primarily from the present measurements. In addition, it was examined against the chemical structure of an opposed-flow diffusion flame, relying on global combustion properties such as the ignition delay times and laminar burning velocities. These extended comparisons yielded overall satisfactory agreement, demonstrating the applicability of the present model over a wide range of high-temperature conditions. . Introduction Oxygenated hydrocarbon fuels derived from biomass are attracting considerable attention either as replacements of, or additives to, conventional hydrocarbon fuels in internal combustion engines. They offer potential benefits as renewable fuels, with a long-term zero CO 2 debt, and the tendency to reduce soot formation [1][2][3]. Dimethyl carbonate [CH 3 OC(=O)OCH 3 , DMC], being non-toxic and highly miscible with diesel fuels, is one of such promising clean fuels. Carbon-carbon bonds are absent in the DMC molecular structure which contains three oxygen atoms. In a diesel engine study, Miyamoto et al. [2] found that the extent of soot reduction mainly depended on the amount of oxygen present in the fuel. Furthermore, when the oxygen content of the fuel was above 25% by mass, soot emission fell beyond detection. Although the fuel's structure and the particular combustion conditions are of non-negligible influence on the emissions, it is worthwhile to consider the high oxygen content (53% by mass) of DMC: it suggests that DMC addition in small amounts could achieve significant soot reduction. From laboratory experiments [4,5] to practical engine operations [6-9], extensive studies have been conducted on the effects of adding DMC to hydrocarbon fuels. Specifically, Rubino and Thomson [4] used a counter-flow propane/air diffusion flame to study the inhibition of soot precursor formation by adding oxygenated compounds including DMC. They observed a remarkable reduction of soot precursors such as acetylene (C 2 H 2 ) and benzene (C 6 H 6 ), as well as a linear relationship between the C 2 H 2 concentration and the additive's oxygen and C-C bond content. Furthermore, Chen et al. [5] found that concentrations of most C 1 -C 5 hydrocarbon intermediates decreased in low-p...

“…Recent reports on innovative experiments like the iPEPICO approach [23,24] in combustion environments have proven to be promising tools for investigating complex chemical reaction networks. Also, the kinetic modeling of such complex fuel systems is highly demanding and takes traditional methods to their limits.…”

Section: Introductionmentioning

confidence: 99%

1-, 2- and 3-Pentanol combustion in laminar hydrogen flames – A comparative experimental and modeling study

Köhler

Kathrotia

Oßwald

et al. 2015

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a b s t r a c tOxidation pathways of three different pentanol isomers 1-, 2-and 3-pentanol are investigated using the electron-ionization molecular-beam mass spectrometry (EI-MBMS) technique. New experimental speciation data was obtained from laminar, flat, low-pressure H 2 /O 2 /Ar base flames seeded with equal amounts of pre-vaporized 1-, 2-or 3-pentanol. The experimental investigation is supported by kinetic modeling. Here, one single detailed reaction mechanism for the three linear pentanol isomers has been constructed and compared against new and existing experimental data. The model itself was obtained by an open-source reaction model generation software (RMG) and tested against existing ignition delay times, flame speeds and new quantitative experimental results for mole fraction profiles of major and intermediate species.The overall discussion of individual species profiles is guided by the model-based reaction flow analysis focusing on the initial steps of the fuel destruction paths for the three pentanols down to C3-hydrocarbon species. Therefore, the reaction pathways for the initial fuel destruction steps are shown and analyzed using combined experimental and predicted results. Analysis is performed by means of secondary decay products for each of the three pentanols. The kinetic reaction model was successfully tested against available ignition delay time and laminar flame speed data. Comparisons against 23 new quantitative species profiles are presented for each of the pentanol doped flames. In general, a good predictive capability of the detailed model can be noted for all three investigated straight-chain pentanols regarding the mole fraction profiles of major and intermediate species.