ABSTRACT
A detailed chemical kinetic mechanism has been developed to describe the oxidation of small hydrocarbon and oxygenated hydrocarbon species. The reactivity of these small fuels and ...intermediates is of critical importance in understanding and accurately describing the combustion characteristics, such as ignition delay time, flame speed, and emissions of practical fuels. The chosen rate expressions have been assembled through critical evaluation of the literature, with minimum optimization performed. The mechanism has been validated over a wide range of initial conditions and experimental devices, including flow reactor, shock tube, jet‐stirred reactor, and flame studies. The current mechanism contains accurate kinetic descriptions for saturated and unsaturated hydrocarbons, namely methane, ethane, ethylene, and acetylene, and oxygenated species; formaldehyde, methanol, acetaldehyde, and ethanol.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
The oxidation of syngas mixtures was investigated experimentally and simulated with an updated chemical kinetic model. Ignition delay times for H2/CO/O2/N2/Ar mixtures have been measured using two ...rapid compression machines and shock tubes at pressures from 1 to 70bar, over a temperature range of 914–2220K and at equivalence ratios from 0.1 to 4.0. Results show a strong dependence of ignition times on temperature and pressure at the end of the compression; ignition delays decrease with increasing temperature, pressure, and equivalence ratio. The reactivity of the syngas mixtures was found to be governed by hydrogen chemistry for CO concentrations lower than 50% in the fuel mixture. For higher CO concentrations, an inhibiting effect of CO was observed. Flame speeds were measured in helium for syngas mixtures with a high CO content and at elevated pressures of 5 and 10atm using the spherically expanding flame method. A detailed chemical kinetic mechanism for hydrogen and H2/CO (syngas) mixtures has been updated, rate constants have been adjusted to reflect new experimental information obtained at high pressures and new rate constant values recently published in the literature. Experimental results for ignition delay times and flame speeds have been compared with predictions using our newly revised chemical kinetic mechanism, and good agreement was observed. In the mechanism validation, particular emphasis is placed on predicting experimental data at high pressures (up to 70bar) and intermediate- to high-temperature conditions, particularly important for applications in internal combustion engines and gas turbines. The reaction sequence H2+HO˙2↔H˙+H2O2 followed by H2O2(+M)↔O˙H+O˙H(+M) was found to play a key role in hydrogen ignition under high-pressure and intermediate-temperature conditions. The rate constant for H2+HO˙2 showed strong sensitivity to high-pressure ignition times and has considerable uncertainty, based on literature values. A rate constant for this reaction is recommended based on available literature values and on our mechanism validation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Alcohols, such as butanol, are a class of molecules that have been proposed as a bio-derived alternative or blending agent for conventional petroleum derived fuels. The structural isomer in ...traditional “bio-butanol” fuel is 1-butanol, but newer conversion technologies produce iso-butanol and 2-butanol as fuels. Biological pathways to higher molecular weight alcohols have also been identified. In order to better understand the combustion chemistry of linear and branched alcohols, this study presents a comprehensive chemical kinetic model for all the four isomers of butanol (e.g., 1-, 2-, iso- and tert-butanol). The proposed model includes detailed high-temperature and low-temperature reaction pathways with reaction rates assigned to describe the unique oxidation features of linear and branched alcohols. Experimental validation targets for the model include low pressure premixed flat flame species profiles obtained using molecular beam mass spectrometry (MBMS), premixed laminar flame velocity, rapid compression machine and shock tube ignition delay, and jet-stirred reactor species profiles. The agreement with these various data sets spanning a wide range of temperatures and pressures is reasonably good. The validated chemical kinetic model is used to elucidate the dominant reaction pathways at the various pressures and temperatures studied. At low-temperature conditions, the reaction of 1-hydroxybutyl with O2 was important in controlling the reactivity of the system, and for correctly predicting C4 aldehyde profiles in low pressure premixed flames and jet-stirred reactors. Enol–keto isomerization reactions assisted by radicals and formic acid were also found to be important in converting enols to aldehydes and ketones under certain conditions. Structural features of the four different butanol isomers leading to differences in the combustion properties of each isomer are thoroughly discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A detailed chemical kinetic model containing 329 species and 1888 reversible reactions has been developed to describe the oxidation of toluene and its intermediates. The model has been validated over ...a wide range of experimental conditions, including flow reactor, shock tube, jet-stirred reactor, and flame studies, and for toluene, phenol, benzene, and cyclopentadiene as initial reactants. Good agreement is obtained between predictions and experimental results for all venues and initial reactants. The model is of utility not only for predictions of toluene and benzene chemistry but also for providing a needed submodel to describe higher molecular-weight alkyl aromatics more typical of those found in higher molecular-weight fuels.
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IJS, KILJ, NUK, PNG, UL, UM
Ethanol is a renewable source of energy and significant attention has been directed to the development of a validated chemical kinetic mechanism for this fuel. The experimental data for the ...autoignition of ethanol in the low temperature range at elevated pressures are meager. In order to provide experimental data sets for mechanism validation at such conditions, the autoignition of homogeneous ethanol/oxidizer mixtures has been investigated in a rapid compression machine. Experiments cover a range of pressures (10–50bar), temperatures (825–985K) and equivalence ratios of 0.3–1.0. Ignition delay data are deduced from the experimental pressure traces. Under current experimental conditions of elevated pressures and low temperatures, chemistry pertaining to hydroperoxyl radicals assumes importance. A chemical kinetic mechanism that can accurately predict the autoignition characteristics of ethanol at low temperatures and elevated pressures has been developed and this mechanism is compared with other models available in the literature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract Objective Prophylactic salpingo-oophorectomy is recommended to women who carry a BRCA1 or BRCA2 mutation to reduce the risks of breast, ovarian and fallopian tube cancer. We measured the ...impact of prophylactic salpingo-oophorectomy on menopausal symptoms and sexual functioning in women with a BRCA mutation. Methods Women who underwent prophylactic salpingo-oophorectomy between October 1, 2002 and June 26, 2008 for a known BRCA1 or BRCA2 mutation were invited to participate. Participants completed questionnaires before prophylactic surgery and again one year after surgery. Measures of sexual functioning and menopausal symptoms before and after surgery were compared. Satisfaction with the decision to undergo prophylactic salpingo-oophorectomy was evaluated. Results 114 women who underwent prophylactic surgery completed questionnaires before and one year after surgery. Subjects who were premenopausal at the time of surgery ( n = 75) experienced a significant worsening of vasomotor symptoms (hot flashes, night sweats and sweating) and a decline in sexual functioning (desire, pleasure, discomfort and habit). The increase in vasomotor symptoms and the decline in sexual functioning were mitigated by HRT, but symptoms did not return to pre-surgical levels. HRT decreased vaginal dryness and dyspareunia; however, the decrease in sexual pleasure was not alleviated by HRT. Satisfaction with the decision to undergo prophylactic salpingo-oophorectomy remained high regardless of increased vasomotor symptoms and decreased sexual function. Conclusions Women who undergo prophylactic salpingo-oophorectomy prior to menopause experience an increase in vasomotor symptoms and a decrease in sexual functioning. These symptoms are improved by HRT, but not to pre-surgical levels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This study presents new ignition delay data measured in a rapid compression machine over a wide range temperature, pressure and fuel/air ratio. This data is an extension of that measured previously ...(D. Darcy, C.J. Tobin, K. Yasunaga, J.M. Simmie, J. Würmel, T. Niass, O. Mathieu, S.S. Ahmed, C.K. Westbrook, H.J. Curran, Combust. Flame, 159 (2012) 2219–2232.) for the oxidation of n-propylbenzene in a high-pressure shock tube. The data was obtained for equivalence ratios of 0.29, 0.48, 0.96, and 1.92, at compressed gas pressures of 10, 30 and 50atm, and over the temperature range of 650–1000K. Experimental data was also obtained at 50atm for all equivalence ratios in our new heated high-pressure shock tube and this is also presented here. Comparisons between the data obtained in both the rapid compression machine and the shock tube facilities showed excellent agreement. A previously published chemical kinetic mechanism has been improved and a low-temperature reaction mechanism has been added to simulate ignition delay times at the lower temperature conditions of this study by adding the appropriate species and reactions including alkyl-peroxyl and hydroperoxy-alkyl radical chemistry. Special attention was given to RȮ2 isomerizations and HȮ2 elimination reactions involving the secondary benzylic site on n-propylbenzene to obtain good agreement with the present experimental results. In general, good agreement was obtained between the model and experiments and consistent trends were observed and these are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Ab Initio Study of the Decomposition of 2,5-Dimethylfuran Simmie, John M; Metcalfe, Wayne K
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
08/2011, Volume:
115, Issue:
32
Journal Article
Peer reviewed
The initial steps in the thermal decomposition of 2,5-dimethylfuran are identified as scission of the C–H bond in the methyl side chain and formation of β- and α-carbenes via 3,2-H and 2,3-methyl ...shifts, respectively. A variety of channels are explored which prise the aromatic ring open and lead to a number of intermediates whose basic properties are essentially unknown. Once the furan ring is opened demethylation to yield highly unsaturated species such as allenylketenes appears to be a feature of this chemistry. The energetics of H abstraction by the hydroxyl radical (and other abstracting species) from a number of mono- and disubstituted methyl furans has been studied. H-atom addition to 2,5-dimethylfuran followed by methyl elimination is shown to be the most important route to formation of the less reactive 2-methylfuran. Identification of 2-ethenylfuran as an C6H6O intermediate in 2,5-dimethylfuran flames is probably not correct and is more likely the isomeric 2,5-dimethylene-2,5-dihydrofuran for which credible formation channels exist.
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IJS, KILJ, NUK, PNG, UL, UM
The pyrolytic and oxidative behaviour of the biofuel 2,5-dimethylfuran (25DMF) has been studied in a range of experimental facilities in order to investigate the relatively unexplored combustion ...chemistry of the title species and to provide combustor relevant experimental data. The pyrolysis of 25DMF has been re-investigated in a shock tube using the single-pulse method for mixtures of 3% 25DMF in argon, at temperatures from 1200 to 1350K, pressures from 2 to 2.5atm and residence times of approximately 2ms.
Ignition delay times for mixtures of 0.75% 25DMF in argon have been measured at atmospheric pressure, temperatures of 1350–1800K at equivalence ratios (ϕ) of 0.5, 1.0 and 2.0 along with auto-ignition measurements for stoichiometric fuel in air mixtures of 25DMF at 20 and 80bar, from 820 to 1210K.
This is supplemented with an oxidative speciation study of 25DMF in a jet-stirred reactor (JSR) from 770 to 1220K, at 10.0atm, residence times of 0.7s and at ϕ=0.5, 1.0 and 2.0.
Laminar burning velocities for 25DMF-air mixtures have been measured using the heat-flux method at unburnt gas temperatures of 298 and 358K, at atmospheric pressure from ϕ=0.6–1.6. These laminar burning velocity measurements highlight inconsistencies in the current literature data and provide a validation target for kinetic mechanisms.
A detailed chemical kinetic mechanism containing 2768 reactions and 545 species has been simultaneously developed to describe the combustion of 25DMF under the experimental conditions described above. Numerical modelling results based on the mechanism can accurately reproduce the majority of the experimental data. At high temperatures, a hydrogen atom transfer reaction is found to be the dominant unimolecular decomposition pathway of 25DMF. The reactions of hydrogen atom with the fuel are also found to be important in predicting pyrolysis and ignition delay time experiments.
Numerous proposals are made on the mechanism and kinetics of the previously unexplored intermediate temperature combustion pathways of 25DMF. Hydroxyl radical addition to the furan ring is highlighted as an important fuel consuming reaction, leading to the formation of methyl vinyl ketone and acetyl radical. The chemically activated recombination of HȮ2 or CH3Ȯ2 with the 5-methyl-2-furanylmethyl radical, forming a 5-methyl-2-furylmethanoxy radical and ȮH or CH3Ȯ radical is also found to exhibit significant control over ignition delay times, as well as being important reactions in the prediction of species profiles in a JSR. Kinetics for the abstraction of a hydrogen atom from the alkyl side-chain of the fuel by molecular oxygen andHȮ2 radical are found to be sensitive in the estimation of ignition delay times for fuel–air mixtures from temperatures of 820 to 1200K.
At intermediate temperatures, the resonantly stabilised 5-methyl-2-furanylmethyl radical is found to predominantly undergo bimolecular reactions, and as a result sub-mechanisms for 5-methyl-2-formylfuran and 5-methyl-2-ethylfuran, and their derivatives, have also been developed with consumption pathways proposed. This study is the first to attempt to simulate the combustion of these species in any detail, although future refinements are likely necessary.
The current study illustrates both quantitatively and qualitatively the complex chemical behaviour of what is a high potential biofuel. Whilst the current work is the most comprehensive study on the oxidation of 25DMF in the literature to date, the mechanism cannot accurately reproduce laminar burning velocity measurements over a suitable range of unburnt gas temperatures, pressures and equivalence ratios, although discrepancies in the experimental literature data are highlighted. Resolving this issue should remain a focus of future work.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The objective of this study was to estimate the risk of contralateral breast cancer in BRCA1 and BRCA2 carriers; and measure the extent to which host, family history, and cancer treatment-related ...factors modify the risk.
Patients were 810 women, with stage I or II breast cancer, for whom a BRCA1 or BRCA2 mutation had been identified in the family. Patients were followed from the initial diagnosis of cancer until contralateral mastectomy, contralateral breast cancer, death, or last follow-up.
Overall, 149 subjects (18.4%) developed a contralateral breast cancer. The 15-year actuarial risk of contralateral breast cancer was 36.1% for women with a BRCA1 mutation and was 28.5% for women with a BRCA2 mutation. Women younger than 50 years of age at the time of breast cancer diagnosis were significantly more likely to develop a contralateral breast cancer at 15 years, compared with those older than 50 years (37.6 vs 16.8%; P=0.003). Women aged <50 years with two or more first-degree relatives with early-onset breast cancer were at high risk of contralateral breast cancer, compared with women with fewer, or no first-degree relatives with breast cancer (50 vs 36%; P=0.005). The risk of contralateral breast cancer was reduced with oophorectomy (RR 0.47; 95% CI 0.30-0.76; P=0.002).
The risk of contralateral breast cancer risk in BRCA mutation carriers declines with the age of diagnosis and increases with the number of first-degree relatives affected with breast cancer. Oophorectomy reduces the risk of contralateral breast cancer in young women with a BRCA mutation.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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