| 1. |
- Alekseev, Vladimir A., et al.
(författare)
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Nitric oxide formation in flames of NH3/DME binary mixtures : Laser-induced fluorescence measurements and detailed kinetic analysis
- 2024
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Ingår i: Fuel. - 0016-2361. ; 371
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Tidskriftsartikel (refereegranskat)abstract
- Binary mixture of ammonia (NH3) and dimethyl ether (DME) has been considered in literature as a potential fuel for practical use. Nitric oxide (NO) is a major product of combustion of NH3-containing fuels, and its formation routes have to be comprehensively studied. In this work, concentration profiles of NO were experimentally measured in laminar axisymmetric flames using planar laser-induced fluorescence. The molar percentage of NH3 in the NH3/DME fuel mixture varied from 10% to 60%. Emission levels of NO have reached as much as around 1% for mixtures with around 50% NH3. NO formation was analyzed with numerical simulations of 1D laminar flames and several detailed kinetic mechanisms. Modeling was performed in Chemkin with the steady-state burner-stabilized and free-propagating planar laminar flame reactor models. It was observed that the most recent versions of the contemporary NH3/DME models are able to reproduce the experiments, and their predictions agree with each other due to similarities in the NH3 submechanisms. Kinetic analysis has revealed some disagreement was observed in terms of how much direct chemical coupling between carbon- and nitrogen-containing species affects NO formation.
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| 2. |
- Amdani, Rima Zuriah, et al.
(författare)
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Raman spectroscopy for characterizing porous carbon
- 2020
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Ingår i: Laser Applications to Chemical, Security and Environmental Analysis, LACSEA 2020. - 9781557528209
-
Konferensbidrag (refereegranskat)abstract
- Raman spectroscopy is performed to disclose structural properties of porous carbon samples including lignocellulosic biomass. Analysis of spectral signatures of carbon, around 1350 cm-1 and 1580 cm-1, indicates higher porosity for the biomass sample.
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| 3. |
- Brackmann, Christian, et al.
(författare)
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Experimental and modeling study of nitric oxide formation in premixed methanol + air flames
- 2020
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 213, s. 322-330
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Tidskriftsartikel (refereegranskat)abstract
- Validation and further development of models for alcohol combustion requires accurate experimental data obtained under well-controlled conditions. To this end, measurements of nitric oxide, NO, mole fractions in premixed laminar methanol + air flames have been performed using saturated laser-induced fluorescence, LIF. The methanol flames have been stabilized at atmospheric pressure and initial gas temperature of 318 K at equivalence ratios ɸ = 0.7–1.5 using the heat flux method that allows for simultaneous determination of their laminar burning velocity. The LIF signal is converted into NO mole fraction via calibration measurements, which have been performed in flames of methane, methanol and syngas seeded with known amounts of NO. The experimental approach is verified by the measurements of NO mole fractions in the post flame zone of methane flames, investigated in previous studies at similar conditions. Data on the NO formation together with burning velocities for methanol and methane obtained under adiabatic flame conditions provide highly valuable input for model validation. They have been compared with predictions of six different chemical kinetic mechanisms. Summarizing the behavior of all models tested with respect to burning velocities and NO formation in flames of methane and methanol, the mechanism of Glarborg et al. (2018) and the San Diego mechanism (2019) demonstrate uniformly satisfactory performance.
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| 4. |
- Ding, Pengji, et al.
(författare)
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Femtosecond laser-induced quantum-beat superfluorescence of atomic oxygen in a flame
- 2021
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Ingår i: Physical Review A. - 2469-9926. ; 104:3
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Tidskriftsartikel (refereegranskat)abstract
- Among different approaches to generate mirrorless lasing, resonant multiphoton pumping of gas constituents by deep-UV laser pulses exhibits so far the highest efficiency and produces measurable lasing energies, but the underlying mechanism was not yet fully settled. Here, we report lasing generation from atomic oxygen in a methane-air flame via femtosecond two-photon excitation. Temporal profiles of the lasing pulses were measured for varying concentrations of atomic oxygen, which shows that the peak intensity and time delay of the lasing pulse approximately scales as N and 1/N, respectively, where N represents the concentration. These scaling laws match well with the prediction of oscillatory superfluorescence (SF), indicating that the lasing we observed is essentially SF rather than amplified spontaneous emission. In addition, the quantum-beating effect was also observed in the time-resolved lasing pulse. A theoretical simulation based on nonadiabatic Maxwell-Bloch equations well reproduces the experimental observations of the temporal dynamics of the lasing pulses. These results on fundamentals should be beneficial for the better design and applications of lasing-based techniques.
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| 5. |
- Fan, Qingshuang, et al.
(författare)
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Flame structure and burning velocity of ammonia/air turbulent premixed flames at high Karlovitz number conditions
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 238
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents experimental studies of the structures and burning velocities of premixed ammonia/air jet flames at high Karlovitz (Ka) number conditions. Simultaneous planar laser-induced fluorescence (PLIF) imaging of imidogen (NH) and hydroxyl (OH) radicals was performed to investigate the local flame structure and Laser Doppler Anemometry (LDA) measurements were employed for extracting complement relevant turbulent quantities from the flow field. All the selected cases are located in the regime of distributed reaction zones (DRZ) in the Borghi-Peters diagram, with a maximum Karlovitz (Ka) number and turbulent intensity (u′/SL) up to 1008 and 240, respectively. The OH- and NH-PLIF data were used to determine the flame surface density, flame-surface area ratio, and turbulent burning velocity (ST). The main findings include: (a) The NH layer remains thin and continuous over the investigated range of turbulent intensity and Karlovitz number, and the thickness keeps constant statistically without any significant broadening by turbulent eddies; (b) Spatial correlations of the NH and OH radicals show that overlap of NH and OH layers always exists in a thin region where OH has a weaker signal intensity; (c) The ratio of turbulent to laminar burning velocity (ST/SL) shows a nearly linear increase with turbulent intensity, while the ratio of wrinkled flame surface area to that of ensemble-averaged flame surface area increases only slightly with turbulent intensities. The slower increase of wrinkled flame surface area with turbulent intensity can be attributed to under-resolution in the current state-of-the-art PLIF experiments, the neglection of 3D flame wrinkles in 2D experiments, and the increase in flame stretch factor at high turbulent intensities.
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| 6. |
- Fan, Qingshuang, et al.
(författare)
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Structure and scalar correlation of ammonia/air turbulent premixed flames in the distributed reaction zone regime
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 241
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Tidskriftsartikel (refereegranskat)abstract
- Instantaneous structures of turbulent premixed ammonia/air flames on a piloted jet burner were investigated using simultaneous planar laser-induced fluorescence (PLIF) and Rayleigh thermometry measurements. Two-dimensional spatial distributions of temperature were simultaneously measured with those of the NH radical and the NO pollutant, respectively. Experiments were conducted for stoichiometric flames under five jet velocities. All flames are located in the distributed reaction zone regime of the Borghi-Peters diagram with the Karlovitz (Ka) number ranging from 274 to 4720. The NH PLIF images are used to characterize the fuel consumption layer of the reaction zones since the formation of NH is associated with the consumption of ammonia. The NH PLIF results show that under all flame conditions investigated, the NH layer remains thin in the proximity of the burner while it becomes progressively thickened and distorted by turbulence with increasing turbulent intensity and axial distance. For flames with Ka of 274, the NH layer essentially remains thin, while at Ka of 590 or higher, significant broadening of the NH layer is observed. Probability density functions (PDFs) of the NH layer thickness show that the NH layer can be broadened by 3 – 4 times as the flames are developed downstream. The broadening of the NH layer is considered to indicate that the flames are in the distributed reaction zone regime. The boundary between the thin-reaction zone regime and the distributed reaction zone regime occurs at a much larger Ka than that in methane/air flames. The broadening of the NH layer is due to the penetration of the turbulent eddies and the merging of flame branches. The latter occurs mainly near the flame tips. NO is shown to exist in a wide region in space, across the preheat zone, reaction zone, and postflame zone. NO formation occurs mainly in the reaction zone, however, it is transported by turbulence eddies to the preheat zone and by convection to the postflame zone. The temperature measurements indicate that the preheat zone is broadened in all flames investigated. The broadening of the preheat zone is moderately sensitive to the Ka number while it is more sensitive to the integral length scale of the flames.
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| 7. |
- Fooladgar, Ehsan, et al.
(författare)
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CFD modeling of pyrolysis oil combustion using finite rate chemistry
- 2021
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 299
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports the first Computational Fluid Dynamics (CFD) model developed for biomass pyrolysis oil spray combustion using Finite-Rate Chemistry (FRC) approach. To make the CFD calculations feasible, a reduced mechanism for modeling the combustion of biomass Fast Pyrolysis Oil (FPO) based on the POLIMI 1412 mechanism and a model for eugenol oxidation was developed. The reduced mechanism consisted of 200 reactions and 71 species. This level of complexity was found to be a good tradeoff between predictive power and computational cost such that the reduced model could be used in CFD modeling. The predictive power of the reduced mechanism was demonstrated via 0D (adiabatic, premixed, constant pressure reactor), 1D (laminar counterflow flame) and 3D (CFD of a methane-air flat-flame piloted FPO spray flame) calculations. Results from CFD were compared against experimental data from non-intrusive optical diagnostics. The reduced model was successfully used in CFD calculations—the computational cost was approximately 2 orders of magnitude higher than that of a simplified model. Using the reduced mechanism, the concentration of pollutants, minor combustion products, and flame radicals could be predicted—this is added capability compared to already existing models. The CFD model using the reduced mechanism showed quantitative predictive power for major combustion products, flame temperature, some pollutants and temperature, and qualitative predictive power for flame radicals and soot.
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| 8. |
- Gong, Miaoxin, et al.
(författare)
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Fiber-based stray light suppression in spectroscopy using periodic shadowing
- 2021
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Ingår i: Optics Express. - 1094-4087. ; 29:5, s. 7232-7246
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Tidskriftsartikel (refereegranskat)abstract
- Stray light is a known strong interference in spectroscopic measurements. Photons from high-intensity signals that are scattered inside the spectrometer, or photons that enter the detector through unintended ways, will be added to the spectrum as an interference signal. A general experimental solution to this problem is presented here by introducing a customized fiber for signal collection. The fiber-mount to the spectrometer consists of a periodically arranged fiber array that, combined with lock-in analysis of the data, is capable of suppressing stray light for improved spectroscopy. The method, which is referred to as fiber-based periodic shadowing, was applied to Raman spectroscopy in combustion. The fiber-based stray-light suppression method is implemented in an experimental setup with a high-power high-repetition-rate laser system used for Raman measurements in different room-temperature gas mixtures and a premixed flame. It is shown that the stray-light level is reduced by up to a factor of 80. Weak spectral lines can be distinguished, and therefore better molecular species identification, as well as concentration and temperature evaluation, were performed. The results show that the method is feasible and efficient in practical use and that it can be employed as a general tool for improving spectroscopic accuracy.
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| 9. |
- Han, Xinlu, et al.
(författare)
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Experimental and kinetic modeling study of NO formation in premixed CH4+O2+N2 flames
- 2021
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 223, s. 349-360
-
Tidskriftsartikel (refereegranskat)abstract
- The nitric oxide (NO) formation in methane (CH4) flames has been widely investigated, with quite a few kinetic mechanisms available in the literature. However, studies have shown that there are often discrepancies between the simulations using various mechanisms and the experimental results. To elucidate reactions leading to these discrepancies, experiments were designed to measure the NO formation in the post flame zone of CH4+O2+N2 flames with the oxygen ratio, xO2 = O2/(O2+N2), varying from 0.2 to 0.27. The experiments were carried out on a heat flux burner at atmospheric pressure and 298 K using saturated Laser-induced fluorescence. The equivalence ratio, ϕ, was changed from 0.7 to 1.6. The corresponding laminar burning velocity, SL, for each condition was also measured using the heat flux method. A comparison was made for the present experimental data and simulation results using the Konnov, Glarborg, NOMecha 2.0, and San Diego mechanisms, and none of them well reproduced the new NO experimental data for all investigated conditions. Numerical analyses show that the increment of NO mole fraction in stoichiometric and fuel-lean flames when the xO2increases is mostly defined by the thermal-NO production, which is found to be over-predicted, especially by the Konnov and San Diego mechanisms. The rate constant of reaction NO+N = N2+O was derived as [Formula presented]cm3 / mol s over 225–2400 K temperature range. The rate constants of four reactions controlling CH mole fraction profiles and prompt-NO formation were updated based on the analysis of the literature data that yields an improved performance of the Konnov mechanism.
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| 10. |
- Kim, Haisol, et al.
(författare)
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Signal-enhanced Raman spectroscopy with a multi-pass cavity for quantitative measurements of formaldehyde, major species and temperature in a one-dimensional laminar DME-air flame
- 2022
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 244
-
Tidskriftsartikel (refereegranskat)abstract
- While Raman spectroscopy provides opportunities for simultaneous detection and quantitative analysis of multiple species, it also suffers from certain limitations, such as low signal strength, which often makes it unsuitable for the study of minor species. The present work employs a high-repetition-rate and high-power laser and re-introduces an amplification technique to improve the detection limit, providing an up to 45-time signal enhancement. The amplification is achieved by employing a multi-pass cavity, and different modes were tested and optimized for the measurements. This multi-pass setup has enabled the detection of formaldehyde (CH2O), which is present in stoichiometric dimethyl ether (DME)-air flames on a sub-percent level, and, therefore, known to be challenging to study with Raman spectroscopy. Furthermore, Raman cross-sections of CH2O and DME, which have not been reported in the literature to the authors’ knowledge, are obtained ab initio using Raman scattering activities in the literature. The cross-sections are 6.63 and 22.43, respectively, for CH2O and DME, normalized by the Raman cross-section of nitrogen. The CH2O detection limit in flame with was estimated to 40 ppm with the present experimental settings. Mole fractions of CH2O, nitrogen (N2), water (H2O), carbon dioxide (CO2), oxygen (O2), DME (CH3OCH3), carbon monoxide (CO), and hydrogen (H2) measured in the flame show good agreement when compared with modeling results obtained using two chemical kinetic mechanisms. Flame temperatures were evaluated from the N2 Raman signals, and the steep temperature gradient is successfully resolved experimentally with the multi-pass setup and well predicted by the models.
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| 11. |
- Kim, Haisol, et al.
(författare)
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Suppression of unpolarized background interferences for Raman spectroscopy under continuous operation
- 2021
-
Ingår i: Optics Express. - 1094-4087. ; 29:2, s. 1048-1063
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Tidskriftsartikel (refereegranskat)abstract
- A time-resolving filtering technique developed to improve background suppression in Raman spectroscopy is presented and characterized. The technique enables separation of signal contributions via their polarization dependency by the addition of a waveplate to a normal measurement system and data post-processing. As a result, background interferences of broadband laser-induced fluorescence and incandescence, as well as flame luminosity and blackbody radiation, were effectively suppressed from Raman spectra. Experimental setting parameters of the method were investigated under well-controlled conditions to assess their impact on the background-filtering ability, and the overall trend was understood. The fluorescence background was effectively suppressed for all investigated settings of modulation period, number of accumulations, and recording duration, with the spectrum quality preserved after the filtering. For practical application, the method was tested for measurements in a sooting flame accompanied by a strong luminosity and interfering laser-induced background signals. The technique resulted in a 200-fold decrease of the background and allowed for quantitative analyses of concentrations and temperatures from the filtered data. Thus, the method shows strong potential to extend the applicability of Raman spectroscopy, in particular for in situ diagnostics under challenging experimental conditions.
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| 12. |
- Kim, Haisol, et al.
(författare)
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Time-resolved polarization lock-in filtering for background suppression in Raman spectroscopy of biomass pyrolysis
- 2020
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 224, s. 219-224
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Tidskriftsartikel (refereegranskat)abstract
- Laser-based Raman spectroscopy is a powerful technique for non-intrusive measurements of chemical composition in gas, liquid, and solids. However, weak signals make it challenging to employ the technique for diagnostics under harsh conditions with various background interferences. To overcome such limitations, we have devised a method, polarization lock-in filtering (PLF) based on temporal modulation of the excitation laser polarization, to filter out polarization-independent signals from acquired data. The PLF method applied for continuous Raman spectroscopy measurements of a biomass pyrolysis process showed promising filtering abilities for unwanted background fluorescence signals. A broadband fluorescence background interference was suppressed by up to a factor of 50. Therefore, released species during the biomass pyrolysis process were readily identified with their Raman spectrum signatures and their amounts quantified. In addition, the PLF method provided Raman spectra of low background, from which a gradual change in hydrocarbons released at different stages during the pyrolysis could be observed. Altogether, the efficient background suppression method increases the general applicability of Raman spectroscopy under conditions where interfering signals present a challenge and a limiting factor.
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| 13. |
- Lavadera, Marco Lubrano, et al.
(författare)
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Experimental and modeling study of laminar burning velocities and nitric oxide formation in premixed ethylene/air flames
- 2021
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:1, s. 395-404
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Tidskriftsartikel (refereegranskat)abstract
- Adiabatic laminar burning velocities and post-flame NO concentrations for flat, non-stretched, premixed C2 H 4 /air flames were experimentally determined with a heat flux burner of improved design, over equivalence ratios ranging from 0.7 to 2, at atmospheric pressure and initial temperature of 298 K. Recognizing that C2 H 4 is a main intermediate in high-temperature oxidation pathways of heavy hydrocarbons, these data are essential for the development, validation and optimization of kinetic models for any fuel. The present measurements were then compared with the data available in the literature obtained with different techniques under the same experimental conditions. Regarding burning velocity measurements, the comparison showed considerable scatter among existing stretch-corrected data, which corroborate the necessity for the present adiabatic, non-stretched results. Regarding NO concentrations, an excellent agreement was observed between the present in situ, non-intrusive laser-induced fluorescence measurements and the only dataset available in the literature, determined by the phenol disulfonic acid method. A comparison of experimental and computational results using two contemporary comprehensive, detailed chemical kinetic mechanisms, along with one from the authors presented in this work, was also conducted and discussed. Discrepancies between experiments and model predictions and among models themselves were observed under rich conditions. Notwithstanding, the present updated model showed overall good performances in reproducing both laminar burning velocities and nitric oxide concentrations. Further numerical analyses were performed to identify the main causes of the observed differences. The results showed that the description of the relative importance of reactions involving vinyl and hydrogen cyanide consumption pathways, due to remaining uncertainties, lead to the different model behaviors.
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| 14. |
- Li, Bo, et al.
(författare)
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Temperature measurements in heated gases and flames using carbon monoxide femtosecond two-photon laser-induced fluorescence
- 2023
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Ingår i: Sensors and Actuators A: Physical. - : Elsevier BV. - 0924-4247. ; 353
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Tidskriftsartikel (refereegranskat)abstract
- Nonintrusive temperature measurement is crucial in combustion research. Here, we propose a thermometric technique based on femtosecond two-photon laser-induced fluorescence of carbon monoxide (CO-fs-TPLIF). A femtosecond laser with a wavelength of 230 nm was used as an excitation source. Owing to its intrinsic broad bandwidth, dual vibrational bands of the B1Σ+ ← X1Σ+ transition of CO can be simultaneously excited. As a result, the fluorescence from the conventional bands (0,n) and the hot vibrational bands (1,n) of the B1Σ+ → A1Πu transition of CO can be simultaneously detected. Hence, the temperature-dependent Boltzmann distribution can be assessed from the relative fluorescence intensity related to different ro-vibrational states, and the temperature can be extracted from the analysis of the recorded fluorescence spectra. Two temperature calibration methods were developed, for the low-temperature range (298–1173 K), the rotational-state-associated bandwidths of the spectra were used; for the flame temperature range, the spectral intensity ratios between the hot vibrational bands (1-n) and the conventional bands (0-n) were used. The CO-fs-TPLIF thermometric technique features the advantages of a simple optical setup and the ability of one-dimensional measurements with high spatial resolution.
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| 15. |
- Li, Zhongshan, et al.
(författare)
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Laser diagnostics in combustion and beyond dedicated to Prof. Marcus Aldén on his 70th birthday
- 2024
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Ingår i: Combustion and Flame. - 0010-2180. ; 263
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Forskningsöversikt (refereegranskat)abstract
- Laser diagnostics has been one of the most powerful tools in advancing state-of-the-art combustion research over the last five decades. Prof. Marcus Aldén, one of the most well-known pioneers in this field, has contributed many influential original publications over more than 40 years of his research career. In this paper, we will review some selected contributions, with emphasis on optical techniques developed and applied by Marcus and the group in Lund under his leadership, which are expected to play important roles in facing the challenge of the transition to a carbon-neutral energy system. A brief biography of Marcus is presented in the introduction section, including a summary of his academic services and achievements. The following sections are organized into chapters on different well-recognized techniques, i.e., laser-induced fluorescence, Raman and Rayleigh scattering, thermographic phosphors, coherent anti-Stokes Raman spectroscopy, resonant four-wave mixing, and additional novel technical developments and approaches. The description often follows different categories, including technique development, activities using relatively mature techniques for studies of combustion phenomena, and applications of the most mature techniques in practical devices. The last part of the paper includes a short interview with Marcus for his comments, suggestions, and thoughts on the future challenges and opportunities in this field. This article, on the one hand, is an acknowledgment of the outstanding contribution of Marcus to the field of combustion research and, on the other hand, intends to provide a valuable review of laser diagnostics in combustion research.
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| 16. |
- Lubrano Lavadera, Marco, et al.
(författare)
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Experimental and modeling study of NO formation in ethyl formate + air flames
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 245
-
Tidskriftsartikel (refereegranskat)abstract
- Premixed ethyl formate + air flames have been investigated at atmospheric pressure and initial temperatures from 298 to 348 K. The burning velocities were determined using the heat flux method for equivalence ratios from 0.6 to 1.5 and were compared with limited data available in the literature and with measurements for the C3H6O2 isomer, methyl acetate, obtained under the same conditions. In ethyl formate flames with the initial temperature of 298 K, the concentrations of nitric oxide were measured using laser-induced fluorescence downstream the flame front at heights above the burner of 5 and 10 mm and compared with similar experiments for methyl acetate obtained using the same equipment. It was demonstrated that the burning velocities, as well as NO concentrations in ethyl formate flames, are higher than those in methyl acetate at otherwise identical conditions. The NO mole fraction downstream the flame front of both fuels peaks in stoichiometric mixtures and decreases both in lean and rich flames. The detailed kinetic model developed for the C3H6O2 isomers using rate constants selected from the literature accurately reproduces all the new experimental results reported in the present work.
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| 17. |
- Lubrano Lavadera, Marco, et al.
(författare)
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Experimental and modeling study of NO formation in methyl acetate + air flames
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 242
-
Tidskriftsartikel (refereegranskat)abstract
- Premixed laminar flat non-stretched flames of methyl acetate + air have been studied at atmospheric pressure. The heat flux method was employed to stabilize the flames over equivalence ratios ɸ = 0.7–1.5 at initial gas temperatures from 298 to 348 K. The laminar burning velocities of methyl acetate + air mixtures have been measured at these conditions and compared with the literature data. Laser-induced fluorescence was used to measure NO concentrations in the post-combustion region of the flames at 298 K. The detailed kinetic mechanism of the authors was extended by the reactions of methyl acetate, mostly relying on the model developed by Ahmed et al. (2019). The mechanism was tested against selected literature data from measurements in a shock tube and jet-stirred reactor. Moreover, it was compared with new measurements of the laminar burning velocity and NO concentrations in methyl acetate flames. In all cases, good agreement between the experimental and modeling results was observed. A comparison with LIF measurements obtained for methane + air flames at the same conditions shows that NO concentrations in methyl acetate flames are lower than those in methane + air flames both in stoichiometric and rich mixtures. These differences were interpreted using sensitivity and rate-of-production analyses of NO formation via different routes.
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| 18. |
- Lubrano Lavadera, Marco, et al.
(författare)
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Laminar burning velocities and nitric oxide formation in premixed dimethyl ether/air flames : Experiments and kinetic modeling
- 2022
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 246
-
Tidskriftsartikel (refereegranskat)abstract
- Adiabatic laminar burning velocities and post-flame NO mole fractions for flat, non-stretched, premixed dimethyl ether/air flames were experimentally determined with a heat flux burner combined with laser-induced fluorescence diagnostics, over equivalence ratios ranging from 0.7 to 1.6, at atmospheric pressure and initial temperatures from 298 to 338 K. The present burning velocity measurements were then compared with selected data available in the literature obtained with different techniques. The comparison showed reasonably good agreement with recent datasets obtained at different temperatures, as well as possible outliers not suitable for the validation of kinetic models. The detailed kinetic mechanism of the authors was extended by the reactions of dimethyl ether. A comparison of experimental and computational results using two contemporary detailed chemical kinetic mechanisms, along with the one from the authors presented in this work, was also conducted and discussed. Discrepancies between experiments and model predictions and among models themselves were observed, especially under rich conditions. Further numerical analyzes were performed to identify the main causes of the observed differences. Notwithstanding, the present model showed overall good performances in reproducing both laminar burning velocities and nitric oxide mole fractions. Kinetic modeling was also performed to enhance the understanding of the intrinsic NOx emission characteristics of dimethyl ether by comparing the present measurements with those obtained for ethanol/air flames under identical conditions.
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| 19. |
- Lubrano Lavadera, Marco, et al.
(författare)
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Measurements of the laminar burning velocities and NO concentrations in neat and blended ethanol and n-heptane flames
- 2021
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 288
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Tidskriftsartikel (refereegranskat)abstract
- Adiabatic laminar burning velocities and post-flame NO mole fractions for neat and blended ethanol and n-heptane premixed flames were experimentally determined using a heat flux burner and laser-induced fluorescence. The flames were stabilized at atmospheric pressure and at an initial temperature of 338 K, over equivalence ratios ranging from 0.6 to 1.5. These experiments are essential for the development, validation and optimization of chemical kinetic models, e.g. for the combustion of gasoline-ethanol fuel mixtures. It was observed that the addition of ethanol to n-heptane leads to an increase in laminar burning velocity that is not proportional to the ethanol content and to a decrease of NO formation. Such a NO reduction is due to the slightly lower flame temperatures of ethanol, which decrease the production of thermal-NO at 0.6 < Φ < 1.2, while under fuel-rich conditions this behavior is due to the lower concentrations of CH radicals, which decrease the production of prompt-NO. At Φ > 1.3, the lower NO formation through the prompt mechanism in the ethanol flames is partially offset by a lower rate of NO consumption through the reburning mechanism. New experimental results were compared with predictions of the POLIMI detailed chemical kinetic mechanism. An excellent agreement between measurements and simulated results was observed for the laminar burning velocities over the equivalence ratio range investigated; however, discrepancies were found for the NO mole fractions, especially under rich conditions. Further numerical analyses were performed to identify the main causes of the observed differences. Differences found at close-to stoichiometric conditions were attributed to an uncertainty in the thermal-NO mechanism. In addition, disagreement under rich conditions could be explained by the relative importance of reactions in hydrogen cyanide consumption pathways.
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| 20. |
- Månefjord, Hampus, et al.
(författare)
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A biophotonic platform for quantitative analysis in the spatial, spectral, polarimetric, and goniometric domains
- 2022
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 93:11
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Tidskriftsartikel (refereegranskat)abstract
- Advanced instrumentation and versatile setups are needed for understanding light interaction with biological targets. Such instruments include (1) microscopes and 3D scanners for detailed spatial analysis, (2) spectral instruments for deducing molecular composition, (3) polarimeters for assessing structural properties, and (4) goniometers probing the scattering phase function of, e.g., tissue slabs. While a large selection of commercial biophotonic instruments and laboratory equipment are available, they are often bulky and expensive. Therefore, they remain inaccessible for secondary education, hobbyists, and research groups in low-income countries. This lack of equipment impedes hands-on proficiency with basic biophotonic principles and the ability to solve local problems with applied physics. We have designed, prototyped, and evaluated the low-cost Biophotonics, Imaging, Optical, Spectral, Polarimetric, Angular, and Compact Equipment (BIOSPACE) for high-quality quantitative analysis. BIOSPACE uses multiplexed light-emitting diodes with emission wavelengths from ultraviolet to near-infrared, captured by a synchronized camera. The angles of the light source, the target, and the polarization filters are automated by low-cost mechanics and a microcomputer. This enables multi-dimensional scatter analysis of centimeter-sized biological targets. We present the construction, calibration, and evaluation of BIOSPACE. The diverse functions of BIOSPACE include small animal spectral imaging, measuring the nanometer thickness of a bark-beetle wing, acquiring the scattering phase function of a blood smear and estimating the anisotropic scattering and the extinction coefficients, and contrasting muscle fibers using polarization. We provide blueprints, component list, and software for replication by enthusiasts and educators to simplify the hands-on investigation of fundamental optical properties in biological samples.
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| 21. |
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| 22. |
- Nilsson, Elna JK, et al.
(författare)
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Evaluation of combustion properties of vent gases from Li-ion batteries
- 2023
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Ingår i: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 585
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Tidskriftsartikel (refereegranskat)abstract
- Fire incidents involving Li-ion batteries is an increasing concern as the use of battery electric vehicles is increasing. Abuse conditions such as heating can result in ejection of flammable and toxic gases, presenting a health risk and risk of explosion or fire. The purpose of the present work is to increase the understanding of combustion of gas mixtures vented from Li-ion batteries. The investigation uses a new merged kinetic mechanism including hydrocarbons, hydrogen, carbon oxides, carbonates and fluorinated compounds. Seven typical Li-ion vent gas mixtures were selected based on published studies, and ignition and laminar flames were simulated. Modeling reveal a large variation in laminar burning velocity, flame temperature and heat release. Determining factors for laminar flames are the relative content of the carbonates and hydrogen gas, and the inert carbon dioxide. Gases from highly charged battery cells have the shortest ignition time at high temperatures and the fastest laminar burning velocity. The results can be used as input in computational fluid dynamics or safety engineering modeling. In addition, the versatile kinetic model can be used for fundamental studies of the combustion process and for generation of combustion characteristics such as laminar burning velocities for other vent gas mixtures.
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| 23. |
- Pushp, Mohit, et al.
(författare)
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Infrared Spectroscopy for Online Measurement of Tars, Water, and Permanent Gases in Biomass Gasification
- 2021
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 75:6, s. 690-697
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Tidskriftsartikel (refereegranskat)abstract
- Online measurements of the raw gas composition, including tars and water, during biomass gasification provide valuable information in fundamental investigations and for process control. Mainly consisting of hydrocarbons, tars can, in principle, be measured using Fourier transform infrared (FT-IR) spectroscopy. However, an instrument subjected to raw gas runs the risk of condensation of tars on optical components and subsequent malfunction. Therefore, an external cell, heated to at least 400 ℃, has been designed to ensure that tars remain in the gas phase during FT-IR measurements. The cell was used for on-line FT-IR measurements of permanent gases (CO, CO2, CH4), water, and tars during the operation of a lab-scale downdraft gasifier using wood pellets, bark pellets, and char chips. Based on calibration, the measurement error of permanent gases was estimated to be 0.2%. Concentrations evaluated from spectral signatures of hydrocarbons in tar are in good agreement with results from solid-phase adsorption measurements and correlated well with operational changes in the gasifier. © The Author(s) 2021.
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| 24. |
- Rocha, Rodolfo C., et al.
(författare)
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Structure and laminar flame speed of an ammonia/methane/air premixed flame under varying pressure and equivalence ratio
- 2021
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Ingår i: Energy and Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 35:9, s. 7179-7192
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a joint experimental and numerical study on premixed laminar ammonia/methane/air flames, aiming to characterize the flame structures and NO formation and determine the laminar flame speed under different pressure, equivalence ratio, and ammonia fraction in the fuel. The experiments were carried out in a lab-scale pressurized vessel with a Bunsen burner installed with a concentric co-flow of air. Measurements of NH and NO distributions in the flames were made using planar laser-induced fluorescence. A novel method was presented for determination of the laminar flame speed from Bunsen-burner flame measurements, which takes into account the non-uniform flow in the unburned mixture and local flame stretch. NH profiles were chosen as flame front markers. Direct numerical simulation of the flames and one-dimensional chemical kinetic modeling were performed to enhance the understanding of flame structures and evaluate three chemical kinetic mechanisms recently reported in the literature. The stoichiometric and fuel-rich flames exhibit a dual-flame structure, with an inner premixed flame and an outer diffusion flame. The two flames interact, which affects the NO emissions. The impact of the diffusion flame on the laminar flame speed of the inner premixed flame is however minor. At elevated pressures or higher ammonia/methane ratios, the emission of NO is suppressed as a result of the reduced radical mass fraction and promoted NO reduction reactions. It is found that the laminar flame speed measured in the present experiments can be captured by the investigated mechanisms, but quantitative predictions of the NO distribution require further model development.
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| 25. |
- Ruchkina, Maria, et al.
(författare)
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Simultaneous single-shot imaging of H and O atoms in premixed turbulent flames using femtosecond two-photon laser-induced fluorescence
- 2023
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Ingår i: Optics Express. - 1094-4087. ; 31:8, s. 12932-12943
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Tidskriftsartikel (refereegranskat)abstract
- A method based on femtosecond two-photon excitation has been developed for simultaneous visualization of interference-free fluorescence of H and O atoms in turbulent flames. This work shows pioneering results on single-shot simultaneous imaging of these radicals under non-stationary flame conditions. The fluorescence signal, showing the distribution of H and O radicals in premixed CH4/O2 flames was investigated for equivalence ratios ranging from ϕ = 0.8 to ϕ = 1.3. The images have been quantified through calibration measurements and indicate single-shot detection limits on the order of a few percent. Experimental profiles have also been compared with profiles from flame simulations, showing similar trends.
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