5 research outputs found
Quantities of Interest in Jet Stirred Reactor Oxidation of a High-Octane Gasoline
This work examines
the oxidation of a well-characterized, high-octane-number
FACE (fuel for advanced combustion engines) F gasoline. Oxidation
experiments were performed in a jet-stirred reactor (JSR) for FACE
F gasoline under the following conditions: pressure, 10 bar; temperature,
530â1250 K; residence time, 0.7s; equivalence ratios, 0.5,
1.0, and 2.0. Detailed species profiles were achieved by identification
and quantification from gas chromatography with mass spectrometry
(GC-MS) and Fourier transform infrared spectrometry (FTIR). Four surrogates,
with physical and chemical properties that mimic the real fuel properties,
were used for simulations, with a detailed gasoline surrogate kinetic
model. Fuel and species profiles were well-captured and -predicted
by comparisons between experimental results and surrogate simulations.
Further analysis was performed using a quantities of interest (QoI)
approach to show the differences between experimental and simulation
results and to evaluate the gasoline surrogate kinetic model. Analysis
of the multicomponent surrogate kinetic model indicated that iso-octane
and alkyl aromatic oxidation reactions had impact on species profiles
in the high-temperature region; however, the main production and consumption
channels were related to smaller molecule reactions. The results presented
here offer new insights into the oxidation chemistry of complex gasoline
fuels and provide suggestions for the future development of surrogate
kinetic models
Effect of the Methyl Substitution on the Combustion of Two Methylheptane Isomers: Flame Chemistry Using Vacuum-Ultraviolet (VUV) Photoionization Mass Spectrometry
Alkanes with one or more methyl substitutions
are commonly found
in liquid transportation fuels, so a fundamental investigation of
their combustion chemistry is warranted. In the present work, stoichiometric
low-pressure (20 Torr) burner-stabilized flat flames of 2-methylheptane
and 3-methylheptane were investigated. Flame species were measured
via time-of-flight molecular-beam mass spectrometry, with vacuum-ultraviolet
(VUV) synchrotron radiation as the ionization source. Mole fractions
of major end-products and intermediate species (e.g., alkanes, alkenes,
alkynes, aldehydes, and dienes) were quantified axially above the
burner surface. Mole fractions of several free radicals were also
measured (e.g., CH<sub>3</sub>, HCO, C<sub>2</sub>H<sub>3</sub>, C<sub>3</sub>H<sub>3</sub>, and C<sub>3</sub>H<sub>5</sub>). Isomers of
different species were identified within the reaction pool by an energy
scan between 8 and 12 eV at a distance of 2.5 mm away from the burner
surface. The role of methyl substitution location on the alkane chain
was determined via comparisons of similar species trends obtained
from both flames. The results revealed that the change in CH<sub>3</sub> position imposed major differences on the combustion of both fuels.
Comparison with numerical simulations was performed for kinetic model
testing. The results provide a comprehensive set of data about the
combustion of both flames, which can enhance the erudition of both
fuels combustion chemistry and also improve their chemical kinetic
reaction mechanisms
Effect of the Methyl Substitution on the Combustion of Two Methylheptane Isomers: Flame Chemistry Using Vacuum-Ultraviolet (VUV) Photoionization Mass Spectrometry
Alkanes with one or more methyl substitutions
are commonly found
in liquid transportation fuels, so a fundamental investigation of
their combustion chemistry is warranted. In the present work, stoichiometric
low-pressure (20 Torr) burner-stabilized flat flames of 2-methylheptane
and 3-methylheptane were investigated. Flame species were measured
via time-of-flight molecular-beam mass spectrometry, with vacuum-ultraviolet
(VUV) synchrotron radiation as the ionization source. Mole fractions
of major end-products and intermediate species (e.g., alkanes, alkenes,
alkynes, aldehydes, and dienes) were quantified axially above the
burner surface. Mole fractions of several free radicals were also
measured (e.g., CH<sub>3</sub>, HCO, C<sub>2</sub>H<sub>3</sub>, C<sub>3</sub>H<sub>3</sub>, and C<sub>3</sub>H<sub>5</sub>). Isomers of
different species were identified within the reaction pool by an energy
scan between 8 and 12 eV at a distance of 2.5 mm away from the burner
surface. The role of methyl substitution location on the alkane chain
was determined via comparisons of similar species trends obtained
from both flames. The results revealed that the change in CH<sub>3</sub> position imposed major differences on the combustion of both fuels.
Comparison with numerical simulations was performed for kinetic model
testing. The results provide a comprehensive set of data about the
combustion of both flames, which can enhance the erudition of both
fuels combustion chemistry and also improve their chemical kinetic
reaction mechanisms
Measurements of Positively Charged Ions in Premixed Methane-Oxygen Atmospheric Flames
<p>Cations and anions are formed as a result of chemi-ionization processes in combustion systems. Electric fields can be applied to reduce emissions and improve combustion efficiency by active control of the combustion process. Detailed flame ion chemistry models are needed to understand and predict the effect of external electric fields on combustion plasmas. In this work, a molecular beam mass spectrometer (MBMS) is utilized to measure ion concentration profiles in premixed methaneâoxygen argon burner-stabilized atmospheric flames. Lean and stoichiometric flames are considered to assess the dependence of ion chemistry on flame stoichiometry. Relative ion concentration profiles are compared with numerical simulations using various temperature profiles, and good qualitative agreement was observed for the stoichiometric flame. However, for the lean flame, numerical simulations misrepresent the spatial distribution of selected ions greatly. Three modifications are suggested to enhance the ion mechanism and improve the agreement between experiments and simulations. The first two modifications comprise the addition of anion detachment reactions to increase anion recombination at low temperatures. The third modification involves restoring a detachment reaction to its original irreversible form. To our knowledge, this work presents the first detailed measurements of cations and flame temperature in canonical methaneâoxygen-argon atmospheric flat flames. The positive ion profiles reported here may be useful to validate and improve ion chemistry models for methane-oxygen flames.</p
Detection and Identification of the Keto-Hydroperoxide (HOOCH<sub>2</sub>OCHO) and Other Intermediates during Low-Temperature Oxidation of Dimethyl Ether
In
this paper we report the detection and identification of the
keto-hydroperoxide (hydroperoxymethyl formate, HPMF, HOOCH<sub>2</sub>OCHO) and other partially oxidized intermediate species arising from
the low-temperature (540 K) oxidation of dimethyl ether (DME). These
observations were made possible by coupling a jet-stirred reactor
with molecular-beam sampling capabilities, operated near atmospheric
pressure, to a reflectron time-of-flight mass spectrometer that employs
single-photon ionization via tunable synchrotron-generated vacuum-ultraviolet
radiation. On the basis of experimentally observed ionization thresholds
and fragmentation appearance energies, interpreted with the aid of <i>ab initio</i> calculations, we have identified HPMF and its
conceivable decomposition products HCÂ(O)ÂOÂ(O)ÂCH (formic acid anhydride),
HCÂ(O)ÂOOH (performic acid), and HOCÂ(O)ÂOH (carbonic acid). Other intermediates
that were detected and identified include HCÂ(O)ÂOCH<sub>3</sub> (methyl
formate), <i>cycl</i>-CH<sub>2</sub>âOâCH<sub>2</sub>âOâ (1,3-dioxetane), CH<sub>3</sub>OOH (methyl
hydroperoxide), HCÂ(O)ÂOH (formic acid), and H<sub>2</sub>O<sub>2</sub> (hydrogen peroxide). We show that the theoretical characterization
of multiple conformeric structures of some intermediates is required
when interpreting the experimentally observed ionization thresholds,
and a simple method is presented for estimating the importance of
multiple conformers at the estimated temperature (âŒ100 K) of
the present molecular beam. We also discuss possible formation pathways
of the detected species: for example, supported by potential energy
surface calculations, we show that performic acid may be a minor channel
of the O<sub>2</sub> + CÌH<sub>2</sub>OCH<sub>2</sub>OOH reaction,
resulting from the decomposition of the HOOCH<sub>2</sub>OCÌHOOH
intermediate, which predominantly leads to the HPMF