Journal articles: 'Laser-Induced incandescence/fluorescence'

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Vander Wal, Randall L. "Investigation of soot precursor carbonization using laser-induced fluorescence and laser-induced incandescence." Combustion and Flame 110, no. 1-2 (July 1997): 281–84. http://dx.doi.org/10.1016/s0010-2180(97)00072-2.

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Meyer, Terrence R., Sukesh Roy, Vincent M. Belovich, Edwin Corporan, and James R. Gord. "Simultaneous planar laser-induced incandescence, OH planar laser-induced fluorescence, and droplet Mie scattering in swirl-stabilized spray flames." Applied Optics 44, no. 3 (January 20, 2005): 445. http://dx.doi.org/10.1364/ao.44.000445.

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Hayashida, Kazuhiro, Kenji Amagai, Keiji Satoh, and Masataka Arai. "Experimental Analysis of Soot Formation in Sooting Diffusion Flame by Using Laser-Induced Emissions." Journal of Engineering for Gas Turbines and Power 128, no. 2 (February 9, 2005): 241–46. http://dx.doi.org/10.1115/1.2056536.

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Two-dimensional images of OH fluorescence, polycyclic aromatic hydrocarbons (PAHs) fluorescence, and laser-induced incandescence (LII) from soot were measured in a sooting diffusion flame. To obtain an accurate OH fluorescence image, two images were taken with the laser wavelength tuned to (“on”) and away from (“off”) the OH absorption line. An accurate OH fluorescence image was obtained by subtracting the off-resonance image from the on-resonance image. For the PAH fluorescence and LII measurements, temporally resolved measurements were used to obtain the individual images; the LII image was obtained by detecting the LII signal after the PAH fluorescence radiation had stopped and the PAH fluorescence image was obtained by subtracting the LII image from the simultaneous image of PAH fluorescence and LII. Based on the obtained images, the relative location of OH, PAH, and soot in the flame was discussed in detail. To investigate the PAH size distribution in a sooting flame using LIF, an estimation strategy for PAH size is proposed. Emission spectra were measured at several heights in the flame using a spectrograph. Since the emission wavelength of PAH fluorescence shifts toward longer wavelengths with increasing PAH size, the main PAH components in the emission spectra could be estimated. The results suggest that PAH grows and the type of PAH changes as the soot inception region was approached. Near the soot inception region, we estimated that the PAHs, which have over 16 carbon atoms, mainly constituted the emission spectrum.

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He, Xu, Xiao Ma, Fujia Wu, and Jianxin Wang. "MD2-3: Investigation of Soot Formation in the Oxygenated Fuels Flame by Laser Induced Fluorescence and Incandescence(MD: Measurement and Diagnostics,General Session Papers)." Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines 2008.7 (2008): 577–84. http://dx.doi.org/10.1299/jmsesdm.2008.7.577.

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Hayashi, Jun, Nozomu Hashimoto, Noriaki Nakatsuka, Kazuki Tainaka, Hirofumi Tsuji, Kenji Tanno, Hiroaki Watanabe, Hisao Makino, and Fumiteru Akamatsu. "Simultaneous imaging of Mie scattering, PAHs laser induced fluorescence and soot laser induced incandescence to a lab-scale turbulent jet pulverized coal flame." Proceedings of the Combustion Institute 37, no. 3 (2019): 3045–52. http://dx.doi.org/10.1016/j.proci.2018.09.028.

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Kosaka, H., T. Aizawa, and T. Kamimoto. "Two-dimensional imaging of ignition and soot formation processes in a diesel flame." International Journal of Engine Research 6, no. 1 (February 1, 2005): 21–42. http://dx.doi.org/10.1243/146808705x7347.

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The processes of ignition and formation of soot precursor and soot particles in a diesel spray flame achieved in a rapid compression machine (RCM) were imaged two-dimensionally using the laser sheet techniques. For the two-dimensional imaging of time and of location where ignition first occurs in a diesel spray, planar laser-induced fluorescence (PLIF) of formaldehyde was applied to a diesel spray in an RCM. Formaldehyde has been hypothesized to be one of the stable intermediate species marking the start of oxidation reactions in a transient spray under compression ignition conditions. In this study, the laser-induced fluorescence (LIF) images of the formaldehyde formed in a diesel fuel spray during the ignition process have been obtained by exciting formaldehyde with the third harmonic of a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser. The LIF images of formaldehyde in a spray revealed that the time when the first fluorescence is detected is almost identical with the time when the total heat release due to low-temperature oxidation reactions equals the heat absorption by fuel vaporization in the spray. The formaldehyde level rose steadily until the high-temperature reaction phase of diesel spray ignition. At the start of this ‘hot-ignition’ phase, the formaldehyde concentration fell rapidly, thus signalling the end of the low-temperature ignition phase. Increases in the initial ambient gas temperatures advanced the hot-ignition starting time. The first hot ignition occurred in the periphery of spray head at initial ambient gas temperatures between 580 and 660 K. When the ambient gas temperature was increased to 790 K, the position of the first ignition moved to the central region of the spray head. For the investigation of soot formation processes in a diesel spray flame, simultaneous imaging of the soot precursor and soot particles in a transient spray flame in an RCM was conducted by PLIF and by planar laser-induced incandescence (PLII) techniques. The third harmonic (355 nm) and the fundamental (1064 nm) laser pulses from an Nd:YAG laser, between which a delay of 44 ns was imposed by 13.3 m of optical path difference, were used to excite LIF from the soot precursor and laser-induced incandescence (LII) from soot particles in the spray flame. The LIF and the LII were separately imaged by two image-intensified charge-coupled device cameras with identical detection wavelengths of 400 nm and bandwidths of 80 nm. The LIF from the soot precursor was mainly located in the central region of the spray flame between 40 and 55 mm (between 270 and 370 times the nozzle orifice diameter d°) from the nozzle orifice. The LII from soot particles was observed to surround the soot precursor LIF region and to extend downstream. The first appearance of the LIF from the soot precursor in the spray flame preceded the appearance of the LII from soot particles. The intensity of the LIF from the soot precursor reached its maximum immediately after rich premixed combustion. In contrast, the intensity of the LII from soot particles increased gradually and reached its maximum after the end of injection. Measured LIF spectra, of the soot precursor in the spray flame, were very broad with the peak between 430 and 460 nm.

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Chorey, Devashish, Prasad Boggavarapu, Devendra Deshmukh, Ravikrishna Rayavarapu, and Yogeshwar Nath Mishra. "Comparison between Different Optical Configurations of Active-FRAME Setup in Multispectral Imaging of Flames." Photonics 11, no. 2 (February 4, 2024): 144. http://dx.doi.org/10.3390/photonics11020144.

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Snapshot multispectral imaging of chemical species in the flame is essential for improved understanding of the combustion process. In this article, we investigate the different configurations of a structured laser sheet-based multispectral imaging approach called the Frequency Recognition Algorithm for Multiple Exposures (FRAME). Using FRAME, a snapshot of Laser-Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAH) excited by 283.5 nm laser and Laser-Induced Incandescence (LII) of soot particles excited by 532 nm laser are acquired simultaneously on a single FRAME image. A laminar diffusion flame of acetylene produced by a Gülder burner is used for the experiments. The standard FRAME approach is based on creating two spatially modulated laser sheets and arranging them in a cross-patterned configuration (X). However, the effect of using different configurations (angles) of the two laser sheets on the multispectral planar imaging of the flame has not yet been studied. Therefore, we have compared the FRAME approach in four different configurations while keeping the same flame conditions. First, we have compared the relation between laser fluence and LII signals with and without spatial modulation of the 532 nm laser sheet and found that both detections follow the same curve. When comparing the maps of flame species reconstructed from the standard FRAME configuration and other configurations, there are some dissimilarities. These differences are attributed to minor changes in the imaging plane, optical alignment, laser path length, different modulation frequencies of the laser sheet, laser extinction, laser fluence, etc.

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Aizawa, T., and H. Kosaka. "Investigation of the Early Soot Formation Process in a Transient Spray Flame Via Spectral Measurements of Laser-Induced Emissions." International Journal of Engine Research 7, no. 2 (April 1, 2006): 93–101. http://dx.doi.org/10.1243/146808705x60825.

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In order to investigate the early soot formation process in a diesel spray flame, two-dimensional imaging and spectral measurements of laser-induced emission from soot precursors and soot particles in a transient spray flame achieved in a rapid compression machine (2.8 MPa, 710 K) were conducted. The 3rd harmonic (355 nm) and 4th harmonic (266 nm) Nd: YAG (neodymium-doped yttrium aluminium garnet) laser pulses were used as the light source for laser-induced fluorescence (LIF) from soot precursors and laser-induced incandescence (LII) from soot particles in the spray flame. The two-dimensional imaging covered an area between 30 and 55 mm downstream from the nozzle orifice. The results of two-dimensional imaging showed that strong laser-induced emission excited at 266 nm appears only on the laser incident side of the spray flame, in contrast to an entire cross-sectional distribution of the emission excited at 355 nm, indicating that 266 nm-excited emitters are stronger absorbers and more abundant than 355 nm-excited emitters in the spray flame. The spectral measurements were conducted at three different positions, 35, 45, and 55 mm downstream from the nozzle orifice, along the central axis of the spray, where LIF from soot precursors was observed in a previous two-dimensional imaging study. The spectra measured in upstream positions showed that broad emission peaked at around 400–500 nm, which is attributable to LIF from polycyclic aromatic hydrocarbons (PAHs). The spectra measured in downstream positions appeared very much like grey-body emission from soot particles.

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SATOH, Keiji, Kazuhiro HAYASHIDA, Kenji AMAGAI, and Masataka ARAI. "Laser Measurement of Polycyclic Aromatic Hydrocarbons in the Flame (1st Report, Separation of Laser-Induced Fluorescence and Incandescence by Time-Resolved Measurement)." Transactions of the Japan Society of Mechanical Engineers Series B 70, no. 692 (2004): 1051–57. http://dx.doi.org/10.1299/kikaib.70.1051.

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AIZAWA, Tetsuya, Hidenori KOSAKA, and Yukio MATSUI. "2-D Imaging of Soot Formation Process in a Transient Spray Flame by Laser-induced Fluorescence and Incandescence Techniques." Proceedings of the JSME annual meeting 2002.4 (2002): 95–96. http://dx.doi.org/10.1299/jsmemecjo.2002.4.0_95.

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AIZAWA, Tetsuya, Hidenori KOSAKA, and Yukio MATSUI. "2-D Imaging of Soot Formation Process in a Transient Spray Flame by Laser-induced Fluorescence and Incandescence Techniques." Transactions of the Japan Society of Mechanical Engineers Series B 69, no. 680 (2003): 981–87. http://dx.doi.org/10.1299/kikaib.69.981.

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Taketani, Fumikazu, Yugo Kanaya, Takayuki Nakamura, Naoki Takeda, Kazuhiro Koizumi, Noritomo Hirayama, Takuma Miyakawa, Xiaole Pan, Nobuhiro Moteki, and Nobuyuki Takegawa. "Analysis of the mixing state of airborne particles using a tandem combination of laser-induced fluorescence and incandescence techniques." Journal of Aerosol Science 87 (September 2015): 102–10. http://dx.doi.org/10.1016/j.jaerosci.2015.05.002.

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13

Mishra, Yogeshwar Nath, Prasad Boggavarapu, Devashish Chorey, Lars Zigan, Stefan Will, Devendra Deshmukh, and Ravikrishna Rayavarapu. "Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera." Sensors 20, no. 19 (September 27, 2020): 5534. http://dx.doi.org/10.3390/s20195534.

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In this article, the application of the FRAME (Frequency Recognition Algorithm for Multiple Exposures) technique is presented for multi-species measurements in symmetric and asymmetric ethylene/air diffusion flames. Laminar Bunsen-type and swirled diffusion flames are investigated to gain a better understanding of sooting combustion. For this purpose, simultaneous imaging is conducted in terms of Laser-Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAH) and Laser-Induced Incandescence (LII) of soot particles. Subsequently, the approach is utilized for simultaneous imaging of hydroxyl (OH)-LIF and soot-LII. Here, the modulated LIF- and LII-signals are acquired together as a single sub-image—with a single exposure utilizing the full sensor size of a single camera. By employing the frequency-recognition algorithm on the single image, the LIF- and LII-signals are spectrally isolated—generating two individual LIF- and LII-images. The flame luminosity and out-of-focus light such as reflected surrounding laser light are detected as non-modulated signals in the unprocessed image. These unwanted signals are suppressed using the image post-processing, and, therefore, the image contrast of the two resulting images is improved. It is found that PAHs mainly exist in the inner region near the burner and are surrounded by soot. The majority of the OH is distributed on the outer edges of the flame—representing the reaction zone and soot-oxidation region of the flame.

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Geigle, Klaus Peter, William O’Loughlin, Redjem Hadef, and Wolfgang Meier. "Visualization of soot inception in turbulent pressurized flames by simultaneous measurement of laser-induced fluorescence of polycyclic aromatic hydrocarbons and laser-induced incandescence, and correlation to OH distributions." Applied Physics B 119, no. 4 (March 20, 2015): 717–30. http://dx.doi.org/10.1007/s00340-015-6075-3.

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Bejaoui, Salma, Romain Lemaire, and Eric Therssen. "Analysis of Laser-Induced Fluorescence Spectra Obtained in Spray Flames of Diesel and Rapeseed Methyl Ester Using the Multiple-Excitation Wavelength Laser-Induced Incandescence Technique with IR, UV, and Visible Excitations." Combustion Science and Technology 187, no. 6 (January 30, 2015): 906–24. http://dx.doi.org/10.1080/00102202.2014.973949.

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Milea, A. S., A. Perrier, M. Caceres, G. Godard, A. Vandel, G. Cabot, and F. Grisch. "Study Of Soot Aggregate Formation And Oxidation In A Swirled Stratified Premixed Ethylene/Air Flame." Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 20 (July 11, 2022): 1–15. http://dx.doi.org/10.55037/lxlaser.20th.125.

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Soot particles are one of the main causes of today's pollution because of their negative contribution to global warming and human health. Aviation is one of the domains dealing with soot reduction as the new engine concepts are developed to reduce fuel consumption and global emissions. Despite the fact that most combustion devices used for air transportation operate at high pressure (e.g., aircraft gas turbines up to 40 bar), our understanding of soot formation and oxidation in such conditions is not yet at an appropriate level, as there is still a fundamental lack of experimental data and corresponding predictive models in the literature. Thus, the objective of the current study is to evaluate soot formation and oxidation processes in stratified, swirled, premixed ethylene/air flames examined with a variety of laser diagnostics designed to simultaneously measure soot particle and soot precursor 2D-distributions, as well as the flame structure and the aerodynamic field. For that, the SIRIUS burner was selected because of its ability to produce flames with topologies similar to those encountered in aircraft combustors. Soot particle distributions are measured by Planar Laser-induced incandescence (PLII) diagnostic. The flame structure is obtained by detecting the hydroxyl radicals (OH) with Planar laser-induced fluorescence (PLIF). A second PLIF diagnostic is also used to investigate the production of polycyclic aromatic hydrocarbons (PAH) with the detection of two benzene rings molecules which are recognized as good precursors of soot nucleation and growth. Finally, the particle Image Velocimetry (PIV) diagnostic is used for measuring the velocity distributions. These laser diagnostics are coupled together in order to obtain cross-correlations between several scalar parameters playing a determining role in the soot formation/consumption processes. The experimental results collected at atmospheric pressure are reviewed and critically assessed. A scenario describing the link between the soot inception, growth, aggregation and oxidation processes is proposed by analyzing velocity, OH, PAHs and soot distributions. In particular, the data reveal the presence of distinct regions for these processes. Incipient soot production zone is strongly function of specific local conditions of velocity, PAH concentration, and strain rate encountered at the interface of the internal recirculation zone and the fuel/air jet. The central part of the inner recirculation zone in which large structures move at low velocities provides suitable conditions for the aggregation of nascent soot particles while an oxidation region located in the upper zone of the internal recirculation zone favors the consumption of soot.

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Rao, Lingzhe, Yilong Zhang, Sanghoon Kook, Kenneth S. Kim, and Chol-Bum Kweon. "Understanding the soot reduction associated with injection timing variation in a small-bore diesel engine." International Journal of Engine Research, August 6, 2019, 146808741986805. http://dx.doi.org/10.1177/1468087419868058.

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This study shows the in-cylinder soot reduction mechanism associated with injection timing variation in a small-bore optical diesel engine. For the three selected injection timings, three optical-/laser-based imaging diagnostics were performed to show the development of high-temperature reaction and soot within the cylinder, which include OH* chemiluminescence, planar laser–induced fluorescence of hydroxyl and planar laser–induced incandescence. In addition, detailed soot morphology analysis was conducted using thermophoresis-based soot particle sampling from two locations within the piston bowl, and the subsequent analysis of transmission electron microscope (TEM) images of the sampled soot aggregates was also conducted. The results suggest that when fuel injection timing is varied, ambient gas temperature makes a predominant effect on soot formation and oxidation. This is primarily combustion phasing effect as the advanced fuel injection moved the start of combustion closer to the top dead centre, and therefore, soot formation and oxidation occurred at elevated ambient gas temperature. There was an overall development pattern of in-cylinder soot consistently found for three injection timings of this study. The planar laser–induced incandescence images showed that a few small soot pockets first appear around the jet axis, which promptly grow into large soot regions behind the head of the flame marked planar laser–induced fluorescence of hydroxyl. The soot signals disappear due to significant oxidation induced by surrounding OH radicals. When the injection timing is advanced, the soot formation becomes higher as indicated by higher total laser–induced incandescence coverage, increased sampled particle counts and larger and more stretched soot aggregate structures. However, soot oxidation is also enhanced under this elevated ambient temperature environment. At the most advanced injection timing of this study, the enhanced soot oxidation outperformed the increased soot formation with both peak laser–induced incandescence signal coverage and late-cycle coverage showing lower values than those of more retarded injection timings.

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Cau, M., N. Dorval, B. Attal-Trétout, J. L. Cochon, A. Foutel-Richard, A. Loiseau, V. Krüger, M. Tsurikov, and C. D. Scott. "Formation of carbon nanotubes:In situoptical analysis using laser-induced incandescence and laser-induced fluorescence." Physical Review B 81, no. 16 (April 8, 2010). http://dx.doi.org/10.1103/physrevb.81.165416.

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"Optical Analytical Technique for Carbonaceous Particles Using Laser-Induced Electro-Avalanche Fluorescence and Laser-Induced Incandescence." Sensors and Materials, 2013, 57. http://dx.doi.org/10.18494/sam.2013.857.

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Jüngst, N., and S. A. Kaiser. "Visualization of soot formation from evaporating fuel films by laser-induced fluorescence and incandescence." Proceedings of the Combustion Institute, August 2020. http://dx.doi.org/10.1016/j.proci.2020.06.076.

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Chorey, Devashish, Matthias Koegl, Prasad Boggavarapu, Florian J. Bauer, Lars Zigan, Stefan Will, R. V. Ravikrishna, Devendra Deshmukh, and Yogeshwar Nath Mishra. "3D mapping of polycyclic aromatic hydrocarbons, hydroxyl radicals, and soot volume fraction in sooting flames using FRAME technique." Applied Physics B 127, no. 11 (October 11, 2021). http://dx.doi.org/10.1007/s00340-021-07692-9.

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AbstractWe report the three-dimensional (3D) mapping of polycyclic aromatic hydrocarbons (PAHs), soot, and hydroxyl radicals (OH) in ethylene/air diffusion flames. A structured illumination-based frequency recognition algorithm for multiple exposures (FRAME) approach is combined with sample translation to intersect the flame in several two-dimensional planes. The FRAME technique has been used for recording a snapshot of multiple species on a single camera. It relies on extracting the amplitude of spatial modulation of two or more probed species encoded on a single sub-image. Here, the FRAME technique is first applied for simultaneous imaging of PAH by laser-induced fluorescence (PAH-LIF) and soot by laser-induced incandescence (LII). Sequentially, it is employed for simultaneous mapping of OH-LIF and soot-LII. The LII signal is converted to absolute soot volume fraction (fv) maps using a line-of-sight light extinction measurement. Finally, we have demonstrated the approach for layer-wise 2D imaging of soot volume fraction and averaged 3D mapping of multiple species.

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Meng, Hu, Yihua Ren, Florence Cameron, and Heinz Pitsch. "In-situ temperature and major species measurements of sooting flames based on short-gated spontaneous Raman scattering." Applied Physics B 129, no. 2 (January 29, 2023). http://dx.doi.org/10.1007/s00340-023-07972-6.

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AbstractSpontaneous Raman scattering is a conventional in-situ laser-diagnostic method that has been widely used for measurements of temperature and major species. However, utilization of Raman scattering in sooting flames suffers from strong interference including laser-induced fluorescence, laser-induced incandescence, and flame luminosity, which has been a challenge for a long time. This work introduces an easy-to-implement and calibration-free Raman scattering thermometry in sooting flames based on a 355-nm nanosecond-pulsed laser beam. Several strategies were utilized to increase the signal-to-noise ratio and suppress the interference: (1) nanosecond intensified CCD gate width; (2) optimized intensified CCD gate delay; (3) specially designed focused laser beam; (4) ultraviolet polarizer filter. The temperature was obtained by fitting the spectral profile of Stokes-Raman scattering of N2 molecules without any calibrations. Based on the measured temperature, the mole fraction of major species can be evaluated. This method was applied to measure the temperature and major species profiles in a steady ethylene–air counterflow diffusion flame with a spatial resolution of 1.2 mm × 10.8 mm × 0.13 mm. The experimental results agree well with the simulation results in both sooting and non-sooting regions, demonstrating the feasibility of this method for quantitative diagnostics of temperature and major species in multiphase reacting flows.

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Mishra, Yogeshwar Nath, Peng Wang, Florian J. Bauer, Yide Zhang, Dag Hanstorp, Stefan Will, and Lihong V. Wang. "Single-pulse real-time billion-frames-per-second planar imaging of ultrafast nanoparticle-laser dynamics and temperature in flames." Light: Science & Applications 12, no. 1 (February 21, 2023). http://dx.doi.org/10.1038/s41377-023-01095-5.

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AbstractUnburnt hydrocarbon flames produce soot, which is the second biggest contributor to global warming and harmful to human health. The state-of-the-art high-speed imaging techniques, developed to study non-repeatable turbulent flames, are limited to million-frames-per-second imaging rates, falling short in capturing the dynamics of critical species. Unfortunately, these techniques do not provide a complete picture of flame-laser interactions, important for understanding soot formation. Furthermore, thermal effects induced by multiple consecutive pulses modify the optical properties of soot nanoparticles, thus making single-pulse imaging essential. Here, we report single-shot laser-sheet compressed ultrafast photography (LS-CUP) for billion-frames-per-second planar imaging of flame-laser dynamics. We observed laser-induced incandescence, elastic light scattering, and fluorescence of soot precursors - polycyclic aromatic hydrocarbons (PAHs) in real-time using a single nanosecond laser pulse. The spatiotemporal maps of the PAHs emission, soot temperature, primary nanoparticle size, soot aggregate size, and the number of monomers, present strong experimental evidence in support of the theory and modeling of soot inception and growth mechanism in flames. LS-CUP represents a generic and indispensable tool that combines a portfolio of ultrafast combustion diagnostic techniques, covering the entire lifecycle of soot nanoparticles, for probing extremely short-lived (picoseconds to nanoseconds) species in the spatiotemporal domain in non-repeatable turbulent environments. Finally, LS-CUP’s unparalleled capability of ultrafast wide-field temperature imaging in real-time is envisioned to unravel mysteries in modern physics such as hot plasma, sonoluminescence, and nuclear fusion.

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Lachaux, Thierry, Mark P. B. Musculus, Satbir Singh, and Rolf D. Reitz. "Optical Diagnostics of Late-Injection Low-Temperature Combustion in a Heavy-Duty Diesel Engine." Journal of Engineering for Gas Turbines and Power 130, no. 3 (April 2, 2008). http://dx.doi.org/10.1115/1.2830864.

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A late-injection, high exhaust-gas recirculation rate, low-temperature combustion strategy is investigated in a heavy-duty diesel engine using a suite of optical diagnostics: chemiluminescence for visualization of ignition and combustion, laser Mie scattering for liquid-fuel imaging, planar laser-induced fluorescence (PLIF) for both OH and vapor-fuel imagings, and laser-induced incandescence for soot imaging. Fuel is injected at top dead center when the in-cylinder gases are hot and dense. Consequently, the maximum liquid-fuel penetration is 27 mm, which is short enough to avoid wall impingement. The cool flame starts 4.5 crank angle degrees (CAD) after the start of injection (ASI), midway between the injector and bowl rim, and likely helps fuel to vaporize. Within a few CAD, the cool-flame combustion reaches the bowl rim. A large premixed combustion occurs near 9 CAD ASI, close to the bowl rim. Soot is visible shortly afterward, along the walls, typically between two adjacent jets. OH PLIF indicates that premixed combustion first occurs within the jet and then spreads along the bowl rim in a thin layer, surrounding soot pockets at the start of the mixing-controlled combustion phase near 17 CAD ASI. During the mixing-controlled phase, soot is not fully oxidized and is still present near the bowl rim late in the cycle. At the end of combustion near 27 CAD ASI, averaged PLIF images indicate two separate zones. OH PLIF appears near the bowl rim, while broadband PLIF persists late in the cycle near the injector. The most likely source of broadband PLIF is unburned fuel, which indicates that the near-injector region is a potential source of unburned hydrocarbons.

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Maffina, Aurora, Mathieu Roussillo, Philippe Scouflaire, Nasser Darabiha, Denis Veynante, Sebastien Candel, and Benedetta Franzelli. "Role of the Equivalence Ratio On Soot Formation in a Perfectly Premixed Turbulent Swirled Flame: A Combined Experimental and Les Study." Journal of Engineering for Gas Turbines and Power, October 19, 2023, 1–12. http://dx.doi.org/10.1115/1.4063832.

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Abstract The understanding of processes that govern soot production in aero-engines is fundamental for the design of new combustion systems with low environmental impact. Many combustors, more specifically those used in aero-engines, feature rich flame regions typically exploited in the so-called Rich-Quench-Lean technology. Thus, it is important to consider rich turbulent flames operating in the premixed mode. To this purpose, a model scale swirled combustor, called EM2Soot, was designed at the EM2C laboratory to analyze soot production under perfectly premixed rich conditions. In this work, the effect of the equivalence ratio on soot production in this burner is experimentally characterized and numerically simulated. Measurements of Planar Laser Induced Fluorescence of Polycyclic Aromatic Hydrocarbons were performed to examine soot precursors presence, whereas soot volume fraction is measured with Planar Laser Induced Incandescence. Large Eddy Simulations (LES) are carried out using models already established in literature. By considering a range of equivalence ratios, the soot volume fraction from the experiments was found to reach a maximum near 1.8, whereas a lower level of soot volume fraction was measured for lower and for higher equivalence ratios. The large eddy simulations are found to be in qualitative agreement with experimental data in terms of PAHs and soot location. The soot volume fractions fv are notably overestimated with respect to the LII measurements. However, the numerical results correctly retrieve a reduction of soot production for the highest considered equivalence ratio value and can be used to explain the experimental behaviour.

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Algoraini, Safa, Zhiwei Sun, Bassam B. Dally, and Zeyad T. Alwahabi. "Low-pressure ethylene/air laminar premixed flames: characterisations and soot diagnostics." Applied Physics B 129, no. 2 (January 21, 2023). http://dx.doi.org/10.1007/s00340-023-07975-3.

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AbstractIn this work, the structure of laminar premixed ethylene/air flat flames at low pressure are studied experimentally. The aim of the work is to exploit the spatial expansion of laminar 1D flames and advanced laser techniques to better understand the conditions and precursors affecting soot particles inception. Soot volume fraction (fv) profiles were measured using laser-induced incandescence (LII), while spatial distribution of the CH* and C2* radicals was measured using spatially resolved emission spectroscopy. Spatially resolved laser-induced fluorescence has been used to record emission from 2–3 rings, 3–4 rings and > 5 rings. The temperature of soot particles (Ts) was evaluated through fitting the spectrally resolved soot luminosity, while flame gaseous temperature (Tg) was measured using a fine thermocouple. The laminar flow velocity was modeled and used to evaluate the reaction time at each HAB. Taking advantage of the expanded flame structure at low pressure, the profiles of CH*, C2*, soot and temperatures, as a function of the height above the burner, were well resolved. It was found that CH* and C2* chemiluminescence overlap in space. The thickness of CH* layer is larger than that of C2*, and it peaks at slightly different location, CH* appears approximately 1 mm before C2*. The distance between the two peaks decreases linearly with the increase in pressure. The lowest value of the initial soot volume fraction (fv) was 0.19 ppb, measured at pressure 27 kPa. It was found that fv scales with the pressure following a power function of the form fv α Prn, where n is 2.15 ± 0.7. It was observed that, in all the flames investigated, the initial soot particles first appear at a common critical inception temperature, Tinception, of 1465 ± 66 K. It was found that the Tinception is lower than the maximum flame temperature, Tmax, by ~ 45° and appeared ~ 1 mm further than the location of Tmax. Using the Lagrangian quantity dfv/dt and fv, it was possible to reveal the soot growth rate, kSG. At pressure of 27 kPa, the value of kSG was evaluated as 20 s−1.

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Ibrahim N.H., Mohamed, M. Udayakumar, Sivan Suresh, Suvanjan Bhattacharyya, and Mohsen Sharifpur. "Coupling LES with soot model for the study of soot volume fraction in a turbulent diffusion jet flames at various Reynolds number configurations." International Journal of Numerical Methods for Heat & Fluid Flow ahead-of-print, ahead-of-print (December 21, 2020). http://dx.doi.org/10.1108/hff-07-2020-0458.

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Purpose This study aims to investigate the insights of soot formation such as rate of soot coagulation, rate of soot nucleation, rate of soot surface growth and soot surface oxidation in ethylene/hydrogen/nitrogen diffusion jet flame at standard atmospheric conditions, which is very challenging to capture even with highly sophisticated measuring systems such as Laser Induced Incandescence and Planar laser-induced fluorescence. The study also aims to investigate the volume of soot in the flame using soot volume fraction and to understand the global correlation effect in the formation of soot in ethylene/hydrogen/nitrogen diffusion jet flame. Design/methodology/approach A large eddy simulation (LES) was performed using box filtered subgrid-scale tensor. A filtered and residual component of the governing equations such as continuity, momentum, energy and species are resolved and modeled, respectively. All the filtered and residual components are numerically solved using the ILU method by considering PISO pressure–velocity solver. All the hyperbolic flux uses the QUICK algorithm, and an elliptic flux uses SOU to evaluate face values. In all the cases, Courant–Friedrichs–Lewy (CFL) conditions are maintained unity. Findings The findings are as follows: soot volume fraction (SVF) as a function of a flame-normalized length for three different Reynolds number configurations (Re = 15,000, Re = 8,000 and Re = 5,000) using LES; soot gas phase and particulate phase insights such as rate of soot nucleation, rate of soot coagulation, rate of soot surface growth and soot surface oxidation for three different Reynolds number configurations (Re = 15,000, Re = 8,000 and Re = 5,000); and soot global correction using total soot volume in the flame volume as a function of Reynolds number and Froude number. Originality/value The originality of this study includes the following: coupling LES turbulent model with chemical equilibrium diffusion combustion conjunction with semi-empirical Brookes Moss Hall (BMH) soot model by choosing C6H6 as a soot precursor kinetic pathway; insights of soot formations such as rate of soot nucleation, soot coagulation rate, soot surface growth rate and soot oxidation rate for ethylene/hydrogen/nitrogen co-flow flame; and SVF and its insights study for three inlet fuel port configurations having the three different Reynolds number (Re = 15,000, Re = 8,000 and Re = 5,000).

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Giusti, Andrea, Epaminondas Mastorakos, Christoph Hassa, Johannes Heinze, Eggert Magens, and Marco Zedda. "Investigation of Flame Structure and Soot Formation in a Single Sector Model Combustor Using Experiments and Numerical Simulations Based on the Large Eddy Simulation/Conditional Moment Closure Approach." Journal of Engineering for Gas Turbines and Power 140, no. 6 (February 13, 2018). http://dx.doi.org/10.1115/1.4038025.

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In this work, a single sector lean burn model combustor operating in pilot only mode has been investigated using both experiments and computations with the main objective of analyzing the flame structure and soot formation at conditions relevant to aero-engine applications. Numerical simulations were performed using the large eddy simulation (LES) approach and the conditional moment closure (CMC) combustion model with detailed chemistry and a two-equation model for soot. The CMC model is based on the time-resolved solution of the local flame structure and allows to directly take into account the phenomena associated to molecular mixing and turbulent transport, which are of great importance for the prediction of emissions. The rig investigated in this work, called big optical single sector rig, allows to test real scale lean burn injectors. Experiments, performed at elevated pressure and temperature, corresponding to engine conditions at part load, include planar laser-induced fluorescence of OH (OH-PLIF) and phase Doppler anemometry (PDA) and have been complemented with new laser-induced incandescence (LII) measurements for soot location. The wide range of measurements available allows a comprehensive analysis of the primary combustion region and can be exploited to further assess and validate the LES/CMC approach to capture the flame behavior at engine conditions. It is shown that the LES/CMC approach is able to predict the main characteristics of the flame with a good agreement with the experiment in terms of flame shape, spray characteristics and soot location. Finite-rate chemistry effects appear to be very important in the region close to the injection location leading to the lift-off of the flame. Low levels of soot are observed immediately downstream of the injector exit, where a high amount of vaporized fuel is still present. Further downstream, the fuel vapor disappears quite quickly and an extended region characterized by the presence of pyrolysis products and soot precursors is observed. The strong production of soot precursors together with high soot surface growth rates lead to high values of soot volume fraction in locations consistent with the experiment. Soot oxidation is also very important in the downstream region resulting in a decrease of the soot level at the combustor exit. The results show a very promising capability of the LES/CMC approach to capture the main characteristics of the flame, soot formation, and location at engine relevant conditions. More advanced soot models will be considered in future work in order to improve the quantitative prediction of the soot level.

Journal articles on the topic 'Laser-Induced incandescence/fluorescence'

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