SwePub - search: WFRF:(Li Zhongshan)

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1.	Li, Xiaofeng, et al. (author) 双色光束增强飞秒激光氮气标记示踪测速技术的研究 2022 In: Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics. - 0253-231X. ; 43:10, s. 2826-2830 Journal article (peer-reviewed)abstract In this work, the fluorescence of FLEET (femtosecond laser electron excited tagging) was enhanced by two color femtosecond laser. the intensity of FLEET was increased about 20% with two laser pulses that were 400 μJ/pulse at 266 nm and 3 mJ/pulse at 800 nm, and the results indicated that there was nearly no influence on lifetime and wavelength of fluorescence from FLEET. This result provides many information for the following studies.
2.	Gao, Qiang, et al. (author) Femtosecond-laser electronic-excitation tagging velocimetry using a 267 nm laser 2019 In: Sensors and Actuators, A: Physical. - : Elsevier BV. - 0924-4247. ; 287, s. 138-142 Journal article (peer-reviewed)abstract Femtosecond (fs)-laser electronic-excitation tagging velocimetry (FLEET) in a nitrogen flow field using a 267 nm laser was performed under the condition of fs-laser filamentation. The filamentous properties and their effects on velocity measurements were investigated and were compared with those of an 800 nm fs-laser. The results show that the required energy of the 267 nm laser pulse is as low as hundreds of μJ, and this is beneficial for reducing the potential perturbations to the flow flied. The filaments induced by the 267 nm laser are longer and thinner than are those induced by the 800 nm laser, which enlarges the velocity measurements region, and a precision of 1.3% was achieved.
3.	Han, Lei, et al. (author) Simultaneous measurements of velocity and concentration of gas flow using femtosecond laser-induced chemiluminescence 2022 In: Optics and Lasers in Engineering. - : Elsevier BV. - 0143-8166. ; 155 Journal article (peer-reviewed)abstract The mixing process in a gas flow plays a crucial role in chemical reactions, and simultaneous measurements of both velocity and mixture fraction are desired to fathom the process. Here, we report a scheme for simultaneously measuring both velocity and concentration by femtosecond laser-induced chemiluminescence. The femtosecond laser would induce chemical reactions that generate CN radicals in the B state. The transition of CN (X-B) would emit fluorescence with both strong intensity and long duration, and the decay of the fluorescence versus time showed prominent benefits for the simultaneous measurement. This measurement was accomplished by an ICCD camera worked in the on-chip multi-exposure mode, i.e., the camera had two exposures in succession to capture two luminescent lines on one image. The first line was used to measure the methane concentration and hence, the mixture fraction through a calibration procedure. The second line was the first line displaced by the flow in a known time interval and we demonstrate an algorithm to derive the one dimensional-two components velocity fields from the line shapes of the luminescent lines. The detection limit of the concentration is estimated to be 152 ppm and the minimum measurable velocity is estimated to be 5 m/s.
4.	Hsu, Li-Jen, et al. (author) Sodium and Potassium Released from Burning Particles of Brown Coal and Pine Wood in a Laminar Premixed Methane Flame Using Quantitative Laser-Induced Breakdown Spectroscopy 2011 In: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 65:6, s. 684-691 Journal article (peer-reviewed)abstract A quantitative point measurement of total sodium ([Na](total)) and potassium ([K](total)) in the plume of a burning particle of Australian Loy Yang brown coal (23 +/- 3 mg) and of pine wood pellets (63 +/- 3 mg) was performed using laser-induced breakdown spectroscopy (LIBS) in a laminar premixed methane flame at equivalence ratios (Phi) of 1.149 and 1.336. Calibration was performed using atomic sodium or potassium generated by evaporation of droplets of sodium sulfite (Na2SO3) or potassium sulfate (K2SO4) solutions seeded into the flame. The calibration compensated for the absorption by atomic alkalis in the seeded flame, which is significant at high concentrations of solution. This allowed quantitative measurements of sodium (Na) and potassium (K) released into the flame during the three phases of combustion, namely devolatilization, char, and ash cooking. The [Na](total) in the plume released from the combustion of pine wood pellets during the devolatilization was found to reach up to 13 ppm. The maximum concentration of total sodium ([Na](total)(max)) and potassium ([K](total)(max)) released during the char phase of burning coal particles for Phi = 1.149 was found to be 9.27 and 5.90 ppm, respectively. The [Na](total)(max) and [K](total)(max) released during the char phase of burning wood particles for Phi = 1.149 was found to be 15.1 and 45.3 ppm, respectively. For the case of Phi = 1.336, the [Na](total)(max) and [K](total)(max) were found to be 13.9 and 6.67 ppm during the char phase from burning coal particles, respectively, and 21.1 and 39.7 ppm, respectively, from burning wood particles. The concentration of alkali species was higher during the ash phase. The limit of detection (LOD) of sodium and potassium with LIBS in the present arrangement was estimated to be 29 and 72 ppb, respectively.
5.	Li, Bo, et al. (author) Comprehensive CO detection in flames using femtosecond two-photon laser-induced fluorescence 2017 In: Optics Express. - 1094-4087. ; 25:21, s. 25809-25818 Journal article (peer-reviewed)abstract We demonstrate a femtosecond two-photon laser-induced fluorescence (fs-TPLIF) technique for sensitive CO detection, using a 230 nm pulse of 9 µJ and 45 fs. The advantages of fs-TPLIF in excitation of molecular species were analyzed. Spectra of CO fs-TPLIF were recorded in stable laminar flames spatially resolved across the flame front. A hot band (1, n) together with the conventional band (0, n) of the B→A transitions were observed in the burned zone and attributed to the broadband nature of the fs excitation. The CO fs-TPLIF signal recorded across the focal point of the excitation beam shows a relatively flat intensity distribution despite of the steep laser intensity variation, which is beneficial for CO imaging in contrast to nanosecond and picosecond TPLIF. This phenomenon can be explained by photoionization, which over the short pulse duration dominates the population depletion of the excited B state due to the high peak power, but only contributes in total a negligible X state depletion due to the low pulse energy. Single-shot CO fs-TPLIF images in methane/air flames were recorded by imaging the broadband fluorescence. The results indicate that fs-TPLIF is a promising tool for CO imaging in flames.
6.	Li, Bo, et al. (author) Femtosecond laser-induced cyano chemiluminescence in methane-seeded nitrogen gas flows for near-wall velocimetry 2018 In: Journal of Physics D: Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 51:29 Journal article (peer-reviewed)abstract We demonstrate a velocimetric technique based on femtosecond laser-induced cyano (CN) chemiluminescence (FLICC). High intensity emission originated from CN(B-X) fluorescence was observed in filaments generated by focusing a femtosecond laser in methane-seeded nitrogen gas flows. The emission is strong and can last for hundreds of microseconds with a proper methane concentration. FLICC was adopted for velocity measurements, and promising results were obtained for near-wall measurements.
7.	Li, Bo, et al. (author) Filamentary anemometry using femtosecond laser-extended electric discharge - FALED 2018 In: Optics Express. - 1094-4087. ; 26:16, s. 21132-21140 Journal article (peer-reviewed)abstract We demonstrate a non-contact spatiotemporally resolved comprehensive method for gas flow velocity field measurement: Filamentary Anemometry using femtosecond Laser-extended Electric Discharge (FALED). A faint thin plasma channel was generated in ambient air by focusing an 800-nm laser beam of 45 fs, which was used to ignite a pulsed electric discharge between two electrodes separated over 10 mm. The power supplier provided a maximum voltage up to 5 kV and was operated at a burst mode with a current duration of less than 20 ns and a pulse-to-pulse separation of 40 μs. The laser-guided thin filamentary discharge plasma column was blowing up perpendicularly by an air jet placed beneath in-between the two electrodes. Although the discharge pulse was short, the conductivity of the plasma channel was observed to sustain much longer, so that a sequence of discharge filaments was generated as the plasma channel being blown up by the jet flow. The sequential bright thin discharge filaments can be photographed using a household camera to calculate the flow velocity distribution of the jet flow. For a direct comparison, a flow field measurement using FLEET [Michael, Appl. Opt. 50, 5158 (2011)] was also performed. The results indicate that the FALED technique can provide instantaneous nonintrusive flow field velocity measurement with good accuracy.
8.	Li, Bo, et al. (author) Methyl Radical Imaging in Methane-Air Flames Using Laser Photofragmentation-Induced Fluorescence 2015 In: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 69:10, s. 1152-1156 Journal article (peer-reviewed)abstract Imaging detection of methyl radicals has been performed in laminar premixed methane-air flames at atmospheric pressure. A nanosecond Q-switched neodymium-doped yttrium aluminum garnet (Nd : YAG) laser was employed to provide the fifth-harmonic-generated 212.8 nm laser beam. The intense ultraviolet (UV) laser pulse was sent through the flame front to photodissociate The methyl (CH3) radicals in the reaction zone of the flames stabilized on a piloted jet flame burner. The emission spectra from the photodissociated fragments were collected using an imaging spectrometer with the flame-front structure spatially resolved. Combining the spatial and spectral information, we recognized that the emission from the (A-X) methine (CH) transitions located at 431 nm was generated from the CH3 photolysis and could be used to visualize the distribution of CH3 radicals. With proper filtering, the high-power UV laser (around 15 mJ/pulse) provided by the compact Nd : YAG laser makes it possible to visualize CH3 distribution naturally generated in the reaction zone of laminar methane-air premixed flames.
9.	Li, Bo, et al. (author) Strategy of interference-free atomic hydrogen detection in flames using femtosecond multi-photon laser-induced fluorescence 2017 In: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 42:6, s. 3876-3880 Journal article (peer-reviewed)abstract Hydrogen atoms are key species in combustion of hydrogen/hydrocarbon fuels. Interference-free detection of hydrogen atoms natively generated in flames using femtosecond laser-induced fluorescence (LIF) was investigated employing two colors, i.e., 243 nm and 486 nm, as excitation source: two-photon excitation followed by a relay one-photon excitation. This strategy was compared with another commonly adopted two-photon LIF strategy using 205 nm for excitation. The potential interferences were investigated, and a direct verification method was proposed to prove this strategy be interference-free, and imaging of hydrogen atoms natively generated in methane/air flames was achieved.
10.	Li, Xiaofeng, et al. (author) Enhancement of femtosecond laser-induced plasma fluorescence using a nanosecond laser 2019 In: Optics Express. - 1094-4087. ; 27:4, s. 5755-5763 Journal article (peer-reviewed)abstract We demonstrate the enhancement of femtosecond (fs) laser-induced filaments in air and nitrogen flow fields using a nanosecond (ns) laser. With the ns laser being imposed on the filaments, the length and the emission intensity of the filaments were largely increased. Temporally resolved spectra of the enhanced filaments were obtained. The results show that the ns laser enhanced the short-lifetime fluorescence of nitrogen, which comes from the transition processes of N 2 + (B 2 Σ u + - X 2 Σ g + ), N 2 (B 3 Π g - A 3 Σ u + ) and N 2 (C 3 Π u - B 3 Π g ). However, it had little effect on the long-lifetime chemiluminescence, which mainly comes from reactions such as N 2 (A 3 Σ u + ) + N 2 (A 3 Σ u + ) → N 2 (X 1 Σ g + , v = 0) + N 2 (B 3 Π g ). A possible explanation of this phenomenon is given, and this phenomenon might have potential applications in instantaneous one-dimensional measurements of various species in gas flow fields.
11.	Li, Yu, et al. (author) In situ analysis of Na and K in a laminar premixed flame by laser-induced breakdown spectroscopy 2013 In: Chemical Research in Chinese Universities. - : Springer Science and Business Media LLC. - 1005-9040 .- 2210-3171. ; 29:6, s. 1149-1152 Journal article (peer-reviewed)abstract Laser-induced breakdown spectroscopy(LIBS) was used to in situ monitor the concentration of alkali elements in combustion environments. Particular efforts were made to optimize the temporally resolved spectra of Na and K elements. Calibration curves were constructed by relating the intensities of the specific lines to the corresponding elemental concentrations. The detection limits of Na and K elements were found to be temperature-dependent. The results indicate that LIBS can be a powerful tool for in situ monitoring Na and K concentrations in combustion environments.
12.	Zhu, Zhifeng, et al. (author) One-dimensional equivalence ratio measurements by femtosecond laser filament-triggered discharge plasma spectroscopy 2023 In: Optics and Lasers in Engineering. - : Elsevier BV. - 0143-8166. ; 160 Journal article (peer-reviewed)abstract Equivalence ratio measurements are of great importance for combustion systems. In this paper, femtosecond laser filament-triggered discharge plasma spectroscopy is proposed for one-dimensional equivalence ratio measurements of combustion flow fields. The optical emission spectra of femtosecond laser filament-triggered discharge plasma in methane-air premixed laminar flames were measured. The spectral intensity ratios of different species show a linear correlation with the equivalence ratio. It can be demonstrated that femtosecond laser filament-triggered discharge plasma spectroscopy can be used for equivalence ratio measurements. We investigated the effect of the temperature of the methane-air mixture on the equivalence ratio measurements. We further analyzed the one-dimensional spatial intensity distributions of the plasma spectral lines. The results demonstrated the capability of femtosecond laser filament-triggered discharge plasma spectroscopy for one-dimensional equivalence ratio measurements. Finally, femtosecond laser filament-triggered discharge plasma spectroscopy was applied to a methane diffusion flame and measured the one-dimensional equivalence ratios of the diffusion flame at different heights. Femtosecond laser filament-triggered discharge plasma spectroscopy offers a new method for one-dimensional equivalence ratio measurements of combustion flow fields.
13.	Baudoin, Eric, et al. (author) Effect of partial premixing on stabilization and local extinction of turbulent methane/air flames 2013 In: Flow, Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1573-1987 .- 1386-6184. ; 90:2, s. 269-284 Journal article (peer-reviewed)abstract Abstract in UndeterminedThe stabilization characteristics and local extinction structures of partially premixed methane/air flames were studied using simultaneous OH-PLIF/PIV techniques, and large eddy simulations employing a two-scalar flamelet model. Partial premixing was made in a mixing chamber comprised of two concentric tubes, where the degree of partial premixing of fuel and air was controlled by varying the mixing length of the chamber. At the exit of the mixing chamber a cone was mounted to stabilize the flames at high turbulence intensities. The stability regime of flames was determined for different degree of partial premixing and Reynolds numbers. It was found that in general partially premixed flames at low Reynolds numbers become more stable when the level of partial premixing of air to the fuel stream decreases. At high Reynolds numbers, for the presently studied burner configuration there is an optimal partial premixing level of air to the fuel stream at which the flame is most stable. OH-PLIF images revealed that for the stable flames not very close to the blowout regime, significant local extinction holes appear already. By increasing premixing air to fuel stream successively, local extinction holes grow in size leading to eventual flame blowout. Local flame extinction was found to frequently attain to locations where locally high velocity flows impinging to the flame. The local flame extinction poses a future challenge for model simulations and the present flames provide a possible test case for such study.
14.	Coskun, Gökhan, et al. (author) Analysis of in-cylinder H2O2 and HO2 distributions in an HCCI engine - Comparison of laser-diagnostic results with CFD and SRM simulations 2015 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:9, s. 3131-3139 Journal article (peer-reviewed)abstract By applying a novel approach to evaluate photofragmentation laser-induced fluorescence (PFLIF) imaging, experimental quantitative information on the temporal in-cylinder distribution of hydrogen peroxide (H2O2) in a homogeneous charge compression ignition (HCCI) engine was extracted. The results from PFLIF were then compared to those obtained from chemical kinetics simulations using computational fluid dynamics (CFD) and a stochastic reactor model (SRM). For the CFD simulations, a sector mesh was applied using Reynolds-averaged Navier-Stokes (RANS) equations together with a reduced chemical kinetic model. These simulations provided detailed information on the spatial distribution of H2O2, HO2 as well as other important species and temperature. The SRM, which offers substantially reduced simulation times but no spatial information, was used with the same reduced kinetic model. Two-dimensional images from PFLIF and CFD show a fair temporal agreement, while details of the spatial distributions disagree. The CFD images show that the combustion chemistry is affected by the interaction with the cylinder walls with, for instance, a local delay of the formation and consumption of H2O2. By using probability density functions (PDFs) of H2O2 and HO2 mass fractions, comparisons could be made between experimental data and both the CFD and SRM simulations. In general the range of mass fractions show good agreement but the experimental distributions are wider. Possible reasons for this discrepancy are actual heterogeneities in the H2O2/HO2 concentration distributions not predicted by the model, spatial temperature variations, which will influence the strength of the PFLIF signal, spatial variations in the laser profiles, not accounted for in the data processing, and photon noise. The good agreement between the CFD and SRM shows the relevance of fast PDF based simulation tools. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
15.	Duwig, Christophe, et al. (author) High resolution imaging of flameless and distributed turbulent combustion 2012 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 159:1, s. 306-316 Journal article (peer-reviewed)abstract Planar laser-induced fluorescence (PLIF) and Rayleigh scattering measurements were used for the study of turbulence/combustion interactions in distributed reaction regimes including flameless or MILD combustion. A novel laboratory scale burner (Distributed and Flameless Combustion Burner - DFCB) was used to reach uniquely high Karlovitz numbers, presently reported up to 14,400. It consists of a highly turbulent piloted high speed jet burner with a vitiated coflow. Six cases are reported whereas two of them (leaner cases) led to an invisible reacting zone, though still emitting light in the UV and near infrared range. Simultaneous OH/CH(2)O PLIF image with 50 mu m spatial resolution were achieved to capture the variation of intermediate species in the reaction layer. When complemented with temperature images obtained by Rayleigh scattering measurement, it provided insights of the reaction front structures as well as measures of the flame brush thicknesses. In particular, variations in the jet velocity highlighted the influence of turbulent mixing (hence turbulence/chemistry interaction) on the flame structures as depicted by the formation of relatively large pools of CH(2)O. Further, variations in the jet stoichiometry impacted on the reaction zone visibility but only marginally on the intensity and moderately on the overall shape of the OH and CH(2)O signals. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
16.	Gao, Jinlong, et al. (author) Planar laser-induced imaging of CH3 for high resolution single-shot reaction-zone visualization in premixed methane/air flames over broad stoichiometric ratios 2022 In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 243 Journal article (peer-reviewed)abstract We report a novel approach for single-shot planar imaging of CH3 radicals in premixed methane and air flames. A 213 nm beam from the 5th harmonic of an Nd:YAG laser was resonantly absorbed by the CH3 radicals, which were excited to the highly pre-dissociative upper level and dissociated to H2 and CH (X), as the main dissociation channel. The CH radicals were consequently excited by a 388 nm beam from an alexandrite laser, and the fluorescence from the excited CH radicals was collected off-resonant at 431 nm. Using this Photo-Fragmentation Planar Laser-Induced Fluorescence (PF-PLIF) technique, instantaneous flame front structures, represented by CH3 radicals, can be visualized with high spatial resolution over a broad range of stoichiometric ratios. Signal-to-noise ratios up to 50 were observed for premixed methane/air flame with stoichiometric ratio as low as 0.26. The CH radicals naturally presented in flame front are more than 400 times lower in concentration than the CH3 radicals in premixed methane/air flames even at the conditions close to stoichiometric or slightly fuel rich cases where the highest CH concentrations exist, and the CH3/CH concentration ratios increase dramatically moving towards fuel lean conditions. By adopting a structured illumination of the 213 nm pump beam, the naturally presented CH radicals were visualized simultaneously with CH3 at slightly fuel rich laminar flames, where the CH signal intensity was 5 times lower than that from CH3. The results indicate that the CH3 PF-PLIF technique can provide much stronger signal than the CH PLIF and presented a much promising potential for applications in fuel-lean flames. Finally, the CH3 PF-PLIF was performed in premixed turbulent flames to demonstrate the feasibility of this technique for flame front visualization in turbulent premixed flames.
17.	Gao, Qiang, et al. (author) Gas Temperature Measurement Using Differential Optical Absorption Spectroscopy (DOAS) 2018 In: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 72:7, s. 1014-1020 Journal article (peer-reviewed)abstract A nonintrusive method for flow gas temperature measurement using differential optical absorption spectroscopy (DOAS) was demonstrated. A temperature-dependent spectra (TDS) originated from the DOAS spectra of sulfur dioxide (SO2) in the wavelength range of 276–310 nm was introduced, and the relationship between the TDS and the temperature was built through experimental calibration process. This relationship is found to be independent of SO2 concentration and can be used for temperature measurements. The experimental results indicated that the precision of the TDS method is < ± 0.3% for SO2 concentrations higher than 150 ppm with the optical path length of 170 mm. For lower concentrations, the precision is estimated to be ± 0.4% at 1 ppm. The relative deviation between the temperature measured by the TDS method and that measured by a thermocouple is within 3% in the temperature range of 298–750 K, and the TDS method has a quicker response to the fast-changing temperature than the thermocouple.
18.	Gao, Qiang, et al. (author) Spatiotemporally resolved spectra of gaseous discharge between electrodes triggered by femtosecond laser filamentation 2022 In: Applied Physics B: Lasers and Optics. - : Springer Science and Business Media LLC. - 0946-2171. ; 128:10 Journal article (peer-reviewed)abstract Atmospheric pressure discharge plasma is widely utilized in industry and science. However, due to the spatiotemporal uncertainty of the natural discharge, it is difficult to measure the discharge plasma spectra with a high spatiotemporal resolution. This prevents the accurate investigation of discharge plasma evolution and limits further applications. Here, we harnessed a femtosecond laser filament to trigger and guide a high-voltage discharge, i.e., the discharge plasma channel is rigorously controlled by the filament in both space and time. Therefore, the spectra of the plasma channel with a high spatiotemporal resolution could be measured using an imaging spectrometer. The spectra of the whole process of femtosecond laser filament-triggered discharge plasma are thoroughly studied. According to the spectral emission features, the whole process is divided into three stages: femtosecond laser filamentation, streamer propagation, and discharge. The spectral emissions at different stages can be utilized as required according to the spectral emission features. Based on the spatiotemporally resolved spectra of the streamer, the streamer propagation velocity is calculated to be about 3 × 105 m/s. In addition, atomic emissions from a discharge plasma triggered by femtosecond laser filament can be used for one-dimensional component measurements of flow fields.
19.	Han, Lei, et al. (author) Cryogenic to high temperature measurements in gas flows by femtosecond laser-induced CN luminescence 2024 In: Measurement: Journal of the International Measurement Confederation. - 0263-2241. ; 229 Journal article (peer-reviewed)abstract Temperature is a crucial parameter of gas flow fields. Here, we present a novel thermometry technique for gas flow based on femtosecond laser-induced cyano (CN) luminescence. Specifically, a femtosecond laser with a central wavelength of 267 nm is used to induce CN violet emissions in a nitrogen flow seeded with a trace amount of methane. The spectral peak of CN B2Σ+- X2Σ+ (0,0) transitions shift to longer wavelengths with increasing temperatures, and the concentration of methane does not influence this spectral shift. The calibration curve of the spectral peak position and the temperature ranging from 93 to 1028 K is obtained through the experiment, and the curve exhibits a nearly linear trend in the low-temperature regime, and an uncertainty of 3.6 % at 173 K is obtained. The technique's wide temperature measurement capability makes it suitable for gas flow temperature measurements, particularly in environments with significant temperature variations, such as wind tunnels.
20.	Han, Lei, et al. (author) Deep Neural Network-Based Generation of Planar CH Distribution through Flame Chemiluminescence in Premixed Turbulent Flame 2023 In: Energy and AI. - : Elsevier BV. - 2666-5468. ; 12 Journal article (peer-reviewed)abstract Flame front structure is one of the most fundamental characteristics and, hence, vital for understanding combustion processes. Measuring flame front structure in turbulent flames usually needs laser-based diagnostic techniques, mostly planar laser-induced fluorescence (PLIF). The equipment of PLIF, burdened with lasers, is often too sophisticated to be configured in harsh environments. Here, to shed the burden, we propose a deep neural network-based method to generate the structures of flame fronts using line-of-sight CH* chemiluminescence that can be obtained without the use of lasers. A conditional generative adversarial network (C-GAN) was trained by simultaneously recording CH-PLIF and chemiluminescence images of turbulent premixed methane/air flames. Two distinct generators of the C-GAN, namely Resnet and U-net, were evaluated. The former net performs better in this study in terms of both generating snap-shot images and statistics over multiple images. For chemiluminescence imaging, the selection of the camera's gate width produces a trade-off between the signal-to-noise (SNR) ratio and the temporal resolution. The trained C-GAN model can generate CH-PLIF images from the chemiluminescence images with an accuracy of over 91% at a Reynolds number of 5000, and the flame surface density at a higher Reynolds number of 10,000 can also be effectively estimated by the model. This new method has the potential to achieve the flame characteristics without the use of laser and significantly simplify the diagnosing system, also with the potential for high-speed flame diagnostics.
21.	Han, Lei, et al. (author) Flame front visualization in highly turbulent jet flames using CH3 photofragmentation laser-induced fluorescence 2023 In: Optics and Laser Technology. - : Elsevier BV. - 0030-3992. ; 159 Journal article (peer-reviewed)abstract Flame front visualization using methyl photofragmentation laser-induced fluorescence (CH3-PF-LIF) was demonstrated in turbulent premixed methane/air flames. A pump–probe method was used to detect CH3, where CH3 was first photolyzed to CH (X2П) fragments using a pump laser (212.8 nm), and the fragments were subsequently excited to CH in the C2Σ+ state by a probe laser at 314.4 nm. By detecting fluorescence from CH (C-X), instantaneous two-dimensional flame front imaging with a high signal-to-noise (SNR) ratio was achieved in fuel-lean and turbulent flames. A laser excitation scan was conducted to ensure that the detection of CH3 did not interfere with the other emissions. Visualization using CH3-PF-LIF was compared with visualization with conventional CH planar laser-induced fluorescence (CH-PLIF). The SNR of CH3-PF-LIF imaging is almost ten times higher than those of CH-PLIF, and flame front visualization using CH3-PF-LIF shows more topological structures than CH-PLIF in fuel-lean and highly turbulent flames.
22.	Han, Lei, et al. (author) Pump-probe strategy for instantaneous 2D detection of CH3in flames using a single laser 2022 In: Applied Optics. - 1559-128X. ; 61:25, s. 7361-7365 Journal article (peer-reviewed)abstract Visualization of the reaction zone of flames using CH radicals as markers is restricted by the low concentration of CH in fuel-lean conditions. To address this, methyl radicals (CH3) are employed as a substitution of CH in premixed methane/air flames. A pump-probe method was adopted with the pump laser photolyzing CH3 and the probe laser detecting the photolyzed CH(X25) fragments. Laser excitation scanswere performed to ensure that the fluorescence detected was from CH only. Visualization of the reaction zone of flames was accomplished by a CH3 photofragmentation laser-induced fluorescence technique in fuel-lean conditions (the equivalence ratio of 0.4), where CH planar laser-induced fluorescence did not work in both laminar and turbulent jet flames. The proposed pump-probe method of CH3 can be used to visualize the reaction zone of hydrocarbon combustion under both fuel-lean and fuel-rich conditions with a superior signal-to-noise ratio.
23.	He, Yong, et al. (author) 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 In: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:2, s. 1123-1130 Journal article (peer-reviewed)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.
24.	He, Yong, et al. (author) Investigation of laminar flame speeds of typical syngas using laser based Bunsen method and kinetic simulation 2012 In: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 95:1, s. 206-213 Journal article (peer-reviewed)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.
25.	Hu, CH, et al. (author) Visible-to-ultraviolet upconversion in Pr3+: Y2SiO5 crystals 2006 In: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 325:2, s. 563-566 Journal article (peer-reviewed)abstract The visible-to-ultraviolet upconversion in Pr3+:Y2SiO5 crystals have been investigated at room temperature for three different Pr3+ ion concentrations. The upconverted luminescence bands at the UV region from 270 to 350 nm were obtained with visible laser excitation. The upconversion mechanism was studied by observing the absorption and excitation spectra, the dependence of upconverted luminescence on pump power, and the decay profiles of the upconverted luminescence. It was found that the upconverted luminescence was produced by excited-state-absorption process using the P-3(J) and I-1(6) as intermediate states. (c) 2006 Elsevier B.V. All rights reserved.

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