| 1. |
- Heimdal Nilsson, Elna, et al.
(författare)
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Re-evaluation of the reaction rate coefficient of CH3Br + OH with implications for the atmospheric budget of methyl bromide
- 2013
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 80, s. 70-74
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Tidskriftsartikel (refereegranskat)abstract
- The reaction rate coefficient k(CH3Br + OH) has been determined in the temperature range 298-373 K, using pulse radiolysis/UV kinetic spectroscopy, and at 298 K using a relative rate method. The Arrhenius expression obtained from a fit to the experimental results is (2.9 +/- 0.9) x 10(-12) exp(-(1230 +/- 125)/T) cm(3) molecule(-1) s(-1), which is greater than the expression currently recommended. The relative rate experiments give k(298 K) = (4.13 +/- 0.63) x 10(-14) cm(3) molecule(-1) s(-1). The results of the absolute and relative rate experiments indicate that the source budget of atmospheric CH3Br should be reinvestigated, as was recently done for CH3Cl. (C) 2013 Elsevier Ltd. All rights reserved.
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| 2. |
- Heimdal Nilsson, Elna, et al.
(författare)
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Tropospheric Photolysis Rates of the Acetaldehyde Isotopologues CD3CHO and CD3CDO Relative to CH3CHO Measured at the European Photoreactor Facility.
- 2015
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Ingår i: The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory. - : American Chemical Society (ACS). - 1520-5215. ; 119:11, s. 2562-2567
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Tidskriftsartikel (refereegranskat)abstract
- Acetaldehyde is a hazardous pollutant found in indoor and ambient air. Acetaldehyde photolysis is pressure- and wavelength-dependent with three distinct product channels. In this study, the photolysis rates of CH3CHO, CD3CDO, and CD3CHO are studied in natural tropospheric conditions using long path FTIR spectroscopy, at the European Photoreactor Facility (EUPHORE) in Valencia, Spain. The average relative photolysis rate as an average of four experiments for the fully deuterated isotopologue is jCH3CHO/jCD3CDO = 1.75 ± 0.04, and as a result of a single experiment jCH3CHO/jCD3CHO = 1.10 ± 0.10. These results, combined with our previous determination of jCH3CHO/jCH3CDO = 1.26 ± 0.03, provide mechanistic insight into the photodissociation dynamics of the photoexcited species. Despite the extensive isotopic scrambling in photoexcited acetaldehyde that has recently been reported, the position of the substitution has a clear effect on the relative photolysis rates.
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| 3. |
- Alekseev, Vladimir, et al.
(författare)
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Experimental Uncertainties of the Heat Flux Method for Measuring Burning Velocities
- 2016
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 1563-521X .- 0010-2202. ; 188:6, s. 853-894
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Tidskriftsartikel (refereegranskat)abstract
- The laminar burning velocity is a fundamental property of combustiblemixtures important for kinetic model validation as well as for practicalapplications. Many efforts are directed towards its accurate determination.The heat flux method is one of the commonly recognized methodsfor measuring laminar burning velocity, however, the information on theaccuracy of the method is scattered in the literature. In the present work,an attempt wasmade to summarize and extend the available informationon the different factors contributing to the experimental uncertainty ofthe heat flux method. Experimental setup of the Lund University group,typical for the heat flux community, and the procedures used to determinethe burning velocity are described. Furthermore, the influence ofdifferent uncertainty factors, originating from each part of the setup, isanalyzed. Asymmetric heat fluxes and the method for determining flamesurface area were found to give an important contribution to the totalerror. As a result of this, some of the previously published data have beenre-evaluated. Finally, recommendations are presented on how to controlor reduce the uncertainties in the heat flux measurements, and possibledirections for future research, aimed at improvement of the accuracy andunderstanding of the method, are outlined.
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| 4. |
- Alekseev, Vladimir, et al.
(författare)
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Laminar premixed flat non-stretched lean flames of hydrogen in air
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:10, s. 4063-4074
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocity of lean hydrogen + air flames at standard conditions is still a debated topic in combustion. The existing burning velocity measurements possess a large spread due to the use of different measurement techniques and data processing approaches. The biggest uncertainty factor in these measurements comes from the necessity to perform extrapolation to the flat flame conditions, since all of the previously obtained data were recorded in stretched flames. In the present study, laminar burning velocity of lean hydrogen + air flames and its temperature dependence were for the first time studied in stretch-free flat flames on a heat flux burner. The equivalence ratio was varied from 0.375 to 0.5 and the range of the unburned gas temperatures was 278-358 K. The flat flames tended to form cells at adiabatic conditions, therefore special attention was paid to the issue of their appearance. The shape of the flames was monitored by taking OH* images with an EM-CCD camera. In most cases, the burning velocity had to be extrapolated from flat subadiabatic conditions, and the impact of this procedure was quantified by performing measurements in H-2 + air mixtures diluted by N-2. The effect of extrapolation was estimated to be of negligible importance for the flames at standard conditions. The measured burning velocities at 298 K showed an important difference to the previously obtained literature values. The temperature dependence of the burning velocity was extracted from the measured results. It was found to be in agreement with the trends predicted by the detailed kinetic modeling, as opposed to a vast majority of the available literature data. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 5. |
- Bardin, Maxim E., et al.
(författare)
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Laminar Burning Velocities of Dimethyl Carbonate with Air
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:9, s. 5513-5517
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities of dimethyl carbonate (DMC) + air flames at initial gas mixture temperatures of 298, 318, 338, and 358 K are reported. Nonstretched flames were stabilized on a perforated plate burner at atmospheric pressure, and the laminar burning velocities were determined using the heat flux method. The overall accuracy of the burning velocities was evaluated to be typically better than +/- 1 cm/s. The effects of unburned mixture temperature on the laminar burning velocity of DMC were analyzed using the correlation S-L = S (T-u/T-u0)(alpha). The present experimental results indicated that the power exponent a reaches a minimum in slightly rich mixtures corresponding to the maximum burning velocity. Modeling of these results has been attempted using the mechanism developed by Glaude et al. It was found that this model significantly overpredicts laminar burning velocities of methanol, ethanol, and DMC; however, it accurately reproduces the temperature power exponent alpha for dimethyl carbonate flames.
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| 6. |
- Burke, Sinead M., et al.
(författare)
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An experimental and modeling study of propene oxidation. Part 2: Ignition delay time and flame speed measurements
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:2, s. 296-314
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data obtained in this study (Part II) complement the speciation data presented in Part I, but also offer a basis for extensive facility cross-comparisons for both experimental ignition delay time (IDT) and laminar flame speed (LFS) observables. To improve our understanding of the ignition characteristics of propene, a series of IDT experiments were performed in six different shock tubes and two rapid compression machines (RCMs) under conditions not previously studied. This work is the first of its kind to directly compare ignition in several different shock tubes over a wide range of conditions. For common nominal reaction conditions among these facilities, cross-comparison of shock tube IDTs suggests 20-30% reproducibility (2 sigma) for the IDT observable. The combination of shock tube and RCM data greatly expands the data available for validation of propene oxidation models to higher pressures (2-40 atm) and lower temperatures (750-1750 K). Propene flames were studied at pressures from 1 to 20 atm and unburned gas temperatures of 295-398 K for a range of equivalence ratios and dilutions in different facilities. The present propene-air LFS results at 1 atm were also compared to LFS measurements from the literature. With respect to initial reaction conditions, the present experimental LFS cross-comparison is not as comprehensive as the IDT comparison; however, it still suggests reproducibility limits for the LFS observable. For the LFS results, there was agreement between certain data sets and for certain equivalence ratios (mostly in the lean region), but the remaining discrepancies highlight the need to reduce uncertainties in laminar flame speed experiments amongst different groups and different methods. Moreover, this is the first study to investigate the burning rate characteristics of propene at elevated pressures (>5 atm). IDT and LFS measurements are compared to predictions of the chemical kinetic mechanism presented in Part I and good agreement is observed. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 7. |
- Christensen, Moah, et al.
(författare)
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Kinetics of premixed acetaldehyde plus air flames
- 2015
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 35, s. 499-506
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Tidskriftsartikel (refereegranskat)abstract
- Non-stretched laminar burning velocities, SL, of acetaldehyde + air mixtures at initial gas mixture temperatures, T, of 298, 318, 338, 348 and 358 K are reported for the first time. The flames were stabilized on a perforated plate burner at 1 atm using the heat flux method at conditions where the net heat loss from the flame to the burner is zero. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the burning velocities was estimated to be typically better than + 1 cm/s. Experimental results were compared with predictions of several kinetic models from the literature. Recent model of Leplat et al. (2011) [30] developed for acetaldehyde and ethanol oxidation showed the closest agreement with the measurements as compared to the Konnov and San Diego models. The effects of initial temperature on the adiabatic laminar burning velocities of acetaldehyde were interpreted using the correlation S-L = S-L0 (T/T-0)(alpha). Particular attention was paid to the variation of the power exponent alpha with equivalence ratio. The existence of a minimum in alpha in the slightly rich mixtures is demonstrated experimentally and confirmed computationally. The model of Leplat et al. was further analyzed using sensitivity analysis and it was concluded that the deviation of the modelled results when comparing with experiments is not a result of the fuel specific reactions but rather the sub-mechanisms of C1 and H-2/O-2. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 8. |
- Christensen, Moah, et al.
(författare)
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The temperature dependence of the laminar burning velocities of methyl formate plus air flames
- 2015
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 157, s. 162-170
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities, S-L, of methyl formate and air flames were determined at atmospheric pressure and initial gas temperatures, T, of 298, 318, 338 and 348 K. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner at adiabatic conditions, generated using the heat flux method. These new experimental data shed light on discrepancies seen in previously published results, and the temperature dependence of the laminar burning velocity of methyl formate was analysed using expression S-L = S-L0(T/T-0)(alpha). It was found that the power exponent, alpha, has a minimum close to equivalence ratio, phi, of 1.0. Both the laminar burning velocities and alpha coefficient were compared with predictions of the mechanisms of Glaude et al. (2005), Dooley et al. (2010) and Dievart et al. (2013). While the two latter mechanisms are in generally good agreement in lean mixtures, the Glaude mechanism over predicts the experimental burning velocities over the entire range of equivalence ratios. The temperature dependences predicted by the Glaude and Dievart mechanisms, however, are rather close and agree well with the measurements. To elucidate these differences and similarities in the performance of two mechanisms, the sensitivity analysis of the power exponent alpha was performed for the first time. It was demonstrated that examination of the temperature dependence of the burning velocity provides an independent approach for analysis of experimental data consistency. (c) 2015 Elsevier Ltd. All rights reserved.
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| 9. |
- Heimdal Nilsson, Elna, et al.
(författare)
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Laminar burning velocities of acetone in air at room and elevated temperatures
- 2013
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 105, s. 496-502
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities of acetone + air mixtures at initial gas mixture temperatures of 298, 318, 338 and 358 K are reported. Non-stretched flames were stabilized on a perforated plate burner at 1 atm, and laminar burning velocities were determined using the heat flux method, at conditions where the net heat loss from the flame to the burner is zero. The overall accuracy of the burning velocities was estimated to be better than +/- 1.0 cm s (1). Very good reproducibility of the results and excellent agreement with modeling using a recently updated chemical kinetic model brings confidence in the validity of the reported results. Previous determinations of laminar burning velocities for acetone have provided inconsistent results. In the present work it is suggested that this can in part be attributed to the chemically aggressive nature of acetone. (C) 2012 Elsevier Ltd. All rights reserved.
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| 10. |
- Heimdal Nilsson, Elna, et al.
(författare)
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Pressure dependent isotopic fractionation in the photolysis of formaldehyde-d(2)
- 2014
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 14:2, s. 551-558
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Tidskriftsartikel (refereegranskat)abstract
- The isotope effects in formaldehyde photolysis are the key link between the delta D of methane emissions and the delta D of atmospheric in situ hydrogen production. A few recent studies have suggested that a pressure dependence in the isotopic fractionation can partly explain enrichment of deuterium with altitude in the atmosphere. The mechanism and the extent of this pressure dependency is, however, not adequately described. In the present work D2CO and H2CO were photolyzed in a static reaction chamber at bath gas pressures of 50, 200, 400, 600 and 1000 mbar; these experiments compliment and extend our earlier work with HDCO vs. H2CO. The UV lamps used for photolysis emit light at wavelengths that primarily dissociate formaldehyde into molecular products, CO and H-2 or D-2. The isotope effect k(H2CO)/k(D2CO) = 3.16 +/- 0.03 at 1000 mbar is in good agreement with results from previous studies. Similarly to what was previously shown for k(H2CO)/k(HDCO), the isotope effect decreased as pressure decreased. In addition, a model was constructed using RRKM theory to calculate the lifetime of excited formaldehyde on the S-0 surface, to investigate its role in the observed pressure dependent photolytic fractionation of deuterium. The model shows that part of the fractionation is a result of competition between the isotopologue dependent rates of unimolecular dissociation and collisional relaxation. We suggest that the remaining fractionation is due to isotope effects in the rate of the non-radiative transition from S-1 to S-0, which are not considered in the present model.
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