| 1. |
- He, Yong, et al.
(författare)
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In-situ Measurement of Sodium and Potassium Release during Oxy-Fuel Combustion of Lignite using Laser-Induced Breakdown Spectroscopy: Effects of O-2 and CO2 Concentration
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:2, s. 1123-1130
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced breakdown spectroscopy (LIBS) was used in this study to measure quantitatively the sodium (Na) and potassium (K) release from burning coal particles under oxy-fuel combustion environments. A specially designed laminar premixed burner was employed to provide a postflame environment with different O-2 and CO2 concentrations, in which the effects of O-2 and CO2 on the release of Na and K during coal oxy-fuel combustion were studied systematically. For the devolatilization stage, neither O-2 nor CO2 had significant influence on the Na and K release. The release of Na and K during the char stage, however, changed significantly at different O-2 and CO2 concentrations. Under these experimental conditions, when the O-2 concentration increased from 3.9% to 10.6%, the peak concentration of Na at the char stage increased from 15.2 mg/m(3) to 33.7 mg/m(3), and the maximum concentration of K increased from 6.2 mg/m(3) to 11.7 mg/m(3). When the CO2 concentration increased from 35.8% to 69.4%, the release of Na and K was inhibited during the char stage, with the peak concentration decreasing from 8.9 mg/m(3) to 6.9 mg/m(3) for Na and from 3.7 mg/m(3) to 2.4 mg/m(3) for K. During the ash stage, the release of Na and K decreased with the O-2 concentration, whereas it increased with the CO2 concentration.
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| 2. |
- He, Yong, et al.
(författare)
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Investigation of laminar flame speeds of typical syngas using laser based Bunsen method and kinetic simulation
- 2012
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 95:1, s. 206-213
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Tidskriftsartikel (refereegranskat)abstract
- Synthetic gas (syngas) fuels are promising energy sources in the future. In the current work, laminar flame speeds of typical syngas with different H-2 contents were studied using both experimental measurements and kinetic simulations. Measurements were carried out using the Bunsen method with the flame area derived from the OH planar laser-induced fluorescence (OH-PLIF) images; while kinetic simulations were made using CHEMKIN with two mechanisms: GRI-Mech 3.0 and USC-Mech II. The OH-PLIF based Bunsen method was validated with previous results. Both the experimental and simulated results indicated that the flame speed of syngas increased with H-2 concentration, which, based on the simulation, is attributed to the rapid production of highly reactive radicals and the acceleration of chain-branching reactions by these radicals. In general, predictions with both mechanisms agreed well with measurements, especially for fuel-lean conditions; simulations with USC-Mech II gave better agreement with experimental results at Phi = 0.8 and 0.9 (discrepancy <5%). (C) 2011 Elsevier Ltd. All rights reserved.
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| 3. |
- Huang, Jianqing, et al.
(författare)
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A detailed study on the micro-explosion of burning iron particles in hot oxidizing environments
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- As a promising carbon-free fuel, iron powder can directly combust with air and has great potential to provide clean and high-grad heat for various applications. The combustion characteristics of iron particles are of great significance for developing iron combustion model, designing efficient combustor, and optimizing combustion technologies. In this work, the micro-explosion behavior of burning iron particles was experimentally investigated based on optical diagnostics. With two high-speed cameras operating at 10,000 frames per second, the three-dimensional (3D) motion and mean surface temperature of burning iron particles during the micro-explosion process were measured using the stereo imaging technique and two-color pyrometry, respectively. The probability of micro-explosions in different oxidizing environments were statistically studied. Three distinct micro-explosion modes have been observed. The results showed that the micro-explosion of burning iron particles heavily depended on oxygen concentration. The micro-explosion would slightly reduce the particle surface temperature by 30–70 K within 0.5 ms, since a lot of smaller fragments were produced. In addition, the 3D velocity of most fragments would sharply increase to 2–6 times within 0.2 ms after the micro-explosion occurred. Regarding the mechanism of the micro-explosion, three types of potential gas sources inside the particle were discussed. The sharp gradients of gas temperature and oxygen concentration may facilitate the rapid increase of the internal pressure in the particle, which eventually causes the micro-explosion.
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| 4. |
- Huang, Jianqing, et al.
(författare)
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Clustering-based particle detection method for digital holography to detect the three-dimensional location and in-plane size of particles
- 2021
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Ingår i: Measurement Science and Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 32:5
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Tidskriftsartikel (refereegranskat)abstract
- Digital holography (DH) has been extensively applied in particle field measurements due to its promising ability to simultaneously provide the three-dimensional location and in-plane size of particles. Particle detection methods are crucial in hologram data processing to determine particle size and particle in-focus depth, which directly affect the measurement accuracy and robustness of DH. In this work, inspired by clustering algorithms, a new clustering-based particle detection (CBPD) method was proposed for DH. To the best of our knowledge this is the first time that clustering algorithms have been applied in processing holograms for particle detection. The results of both simulations and experiments confirmed the feasibility of our proposed method. This data-driven method features automatic recognition of particles, particle edges and background, and accurate separation of overlapping particles. Compared with seven conventional particle detection methods, the CBPD method has improved accuracy in measuring particle positions and displacements.
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| 5. |
- Huang, Jianqing, et al.
(författare)
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Quantification of the size, 3D location and velocity of burning iron particles in premixed methane flames using high-speed digital in-line holography
- 2021
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- Due to its low emission and high energy density, iron powder has been proposed as a promising recyclable metal fuel for a future low-carbon society. The comprehensive understanding of combustion behavior of iron particles is crucial for studying fundamental mechanisms, developing suitable combustion technologies, and designing efficient iron powder combustor. In this work, iron particles are combusted in a modified Bunsen burner with a stable metal powder supplying system. As a versatile three-dimensional (3D) imaging technique, high-speed digital in-line holography (DIH) is employed to reconstruct the 3D particle field and simultaneously quantify the size, 3D location and velocity of burning iron particles. The statistical results of three cases with oxygen volume fraction varying from 24% to 40% are obtained and compared at different heights above the burner. Along the height, some typical features of the burning iron particles were observed. The violent combustion of iron particles accelerates the ejection of the particles radially outward from the central region of the flame, resulting in non-uniform spatial distribution of the particles and reducing the particle number density in the measurement volume. Such trend is enhanced with increased oxygen concentration. Besides, the observed particle size enlarged as the height increases, which validates the swelling phenomenon of iron particle oxidation. The results demonstrate that DIH is a powerful tool for in-situ, quantitative characterization of particle dynamics in flames.
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| 6. |
- Li, Bo, et al.
(författare)
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Measurements of NO concentration in NH3-doped CH4 + air flames using saturated laser-induced fluorescence and probe sampling
- 2013
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 160:1, s. 40-46
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of methane + air flames doped with ammonia (4370 ppm of the fuel) has been performed. The goal of this work was to analyze formation of NOx from fuel-N under well-controlled conditions. The Heat Flux method was used for stabilization of non-stretched adiabatic flames on a perforated plate burner at atmospheric pressure. Laser-saturated fluorescence (LSF) and probe sampling were adopted to measure NO concentrations in the post-flame zone. LSF experiments include two series of measurements: in methane + air flames doped with NO and then in flames doped with NH3. In the lean flames seeded with NO, LSF measurements clearly deviates from the model predictions at higher concentrations of NO seeded, that strongly corroborates existence of the lean NO reburning. The modeling accurately predicts [NO] in the neat flame and shows no consumption of NO up to 170 ppm seeded. In (CH4 + NH3) + air mixtures the NO concentrations measured by LSF are in good agreement with the probe sampling results in the whole range of equivalence ratios 0.65
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| 7. |
- Li, Shen, et al.
(författare)
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Ignition and combustion behavior of single micron-sized iron particle in hot gas flow
- 2022
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 241
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Tidskriftsartikel (refereegranskat)abstract
- This work investigated the ignition and combustion process of single micron-sized iron particles in the hot gas flow of burned methane-oxygen-nitrogen mixture. The particle emission intensity was recorded by a high-speed camera in different flame conditions. Particle temperature was derived through two-color pyrometry method employing an ICCD camera equipped with a stereoscope. Based on scanning electron microscopy (SEM) image, the microstructure change of iron particles was investigated. Results showed that the temperature of burning particle rose rapidly and was much higher than the ambient temperature. The fresh iron particles mainly went through several stages in hot gas flow: heating, melting, rapid combustion and cooling. Some of them became bright again after cooling. According to the above combustion process, combustion parameters including ignition delay time, accelerated burning time, total burning time and second stage of combustion time were defined. All the above defined parameters were almost linearly increasing with the increase of particle size under the same oxygen concentration. For iron particles with roughly the same size, the ignition delay time, accelerated burning time and total burning time decreased as the effective oxygen concentration increased especially for particle size larger than 40 µm. The second stage of combustion time for particles with similar size were almost the same under different oxygen concentrations. After combustion, most of the particles change from irregular shape to spherical or ellipsoidal shape, and some of them showed hollow shell structure. A phenomenon of nano-sized particles releasing during the iron particles combustion had been identified. The frequently observed luminous tail was attributed to coming from the thermal radiation of the formed nanoparticles, which was supported by the SEM sampling analysis of the combustion products.
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| 8. |
- Yang, Li, et al.
(författare)
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Investigation of dilution effect on CH4/air premixed turbulent flame using OH and CH2O planar laser-induced fluorescence
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 13:2
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Tidskriftsartikel (refereegranskat)abstract
- Diluting the combustion mixtures is one of the advanced approaches to reduce the NOx emission of methane/air premixed turbulent flame, especially with high diluents to create a distributed reaction zone and mild combustion, which can lower the temperature of reaction zone and reduce the formation of NOx. The effect of N2/CO2 dilution on the combustion characteristics of methane/air premixed turbulent flame with different dilution ratio and different exit Reynolds number was conducted by OH-PLIF and CH2O-PLIF. Results show that the increase of dilution ratio can sharply reduce the concentration of OH and CH2O, and postpone the burning of fuel. Compared with the ultra-lean combustion, the dilution weakens the combustion more obviously. For different dilution gases, the concentration of OH in the combustion zone varies greatly, while the concentration of CH2O in the unburned zone is less affected by different dilution gas. The CO2 dilution has a more significant effect on OH concentration than N2 with the given dilution ratio, but a similar effect on the concentration of CH2O in the preheat zone of flame. However, dilution does not have much influence on the flame structure with the given turbulent intensity.
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| 9. |
- Yang, Li, et al.
(författare)
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Investigation of hydrogen content and dilution effect on syngas/air premixed turbulent flame using OH planar laser-induced fluorescence
- 2021
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Ingår i: Processes. - : MDPI AG. - 2227-9717. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Syngas produced by gasification, which contains a high hydrogen content, has significant potential. The variation in the hydrogen content and dilution combustion are effective means to improve the steady combustion of syngas and reduce NOx emissions. OH planar laser-induced fluorescence technology (OH-PLIF) was applied in the present investigation of the turbulence of a premixed flame of syngas with varied compositions of H2/CO. The flame front structure and turbulent flame velocities of syngas with varied compositions and turbulent intensities were analyzed and calculated. Results showed that the trend in the turbulent flame speed with different hydrogen proportions and dilutions was similar to that of the laminar flame speed of the corresponding syngas. A higher hydrogen proportion induced a higher turbulent flame speed, higher OH concentration, and a smaller flame. Dilution had the opposite effect. Increasing the Reynolds number also increased the turbulent flame speed and OH concentration. In addition, the effect of the turbulence on the combustion of syngas was independent of the composition of syngas after the analysis of the ratio between the turbulent flame speed and the corresponding laminar flame speed, for the turbulent flames under low turbulent intensity. These research results provide a theoretical basis for the practical application of syngas with a complex composition in gas turbine power generation.
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| 10. |
- Zhou, Bo, et al.
(författare)
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Visualization of multi-regime turbulent combustion in swirl-stabilized lean premixed flames
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:7, s. 2954-2958
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous two-species imaging using single-shot planar laser-induced fluorescence have been performed to record high quality image pairs of CH/OH, CH/CH2O and OH/CH2O to visualize the flame front structures in swirl-stabilized lean premixed methane/air flames. The results show that the investigated flames exhibit various flame front structures distinctly in space, which covers: (1) the corrugated flamelet at the leading front; (2) the thin reaction-zone layer with distorted preheat zone in the shear-layer downstream; and (3) quenching, re-ignition and distributed reactions further downstream. The large variation of the flame characteristics in space stems from the entrainment of ambient cold air to the flame that results in flame quenching at the trailing edge of the flame. Thereafter, the unburned fuel/air mixture in the downstream region mixes with the entrained air and the hot combustion products from the upstream leading flame front, leading to reignition with distributed reactions. The current results provide a direct experimental evidence that distributed reactions can be a common combustion mode along with the results (Ref. [1], Zhou et al., 2015) recently reported in the highly turbulent premixed jet flames.
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