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Study on the oxidation and release of gases in spontaneous coal combustion using a dual-species sensor employing laser absorption spectroscopy
摘要： Coal spontaneous combustion (CSC) is a common hazard in coal mines and a significant reason for the loss of coal in stockpiles and mines. To investigate the oxidation and release of gas due to of CSC, a miniature purpose-built laser-based sensor system capable of precise gas measurement and data processing was configured. A distributed feedback (DFB) diode laser with a central wavelength of 2.33 μm, in conjunction with a Herriot-type cell and wavelength modulation spectroscopy (WMS), was used for the simultaneous detection of methane (CH4) and carbon monoxide (CO) during coal combustion. The second-harmonic of WMS was applied to ensure sensor robustness and sensitivity with long-term performance for the system being evaluated by calculating the Allan-Werle deviations for the concentrations of CH4 and CO. The limits of detection (LoDs) for CH4 and CO were 0.05 ppm based on integration times of 120 s and 70 s, respectively. The dual-species sensor was employed for real-time and in situ investigations of coal samples for temperatures ranging from 85 °C to 200 °C and was considered suitable for integration into field monitoring equipment, especially for online early warning forecasting applications in CSC.
关键词： Wavelength modulation spectroscopy,Spontaneous coal combustion,Chemical inhibitor,Laser-based dual-species sensor,Self-heating oxidation
更新于2025-09-12 10:27:22
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Lean combustion analysis using a corona discharge igniter in an optical engine fueled with methane and a hydrogen-methane blend
摘要： The robustness of combustion initiation is one of the main issues of actual spark-ignition engines, especially for highly-diluted or lean mixtures. In this work, the effects on combustion stabilization obtained by the usage of a radio-frequency corona igniter were evaluated on a single-cylinder optical engine. The comparison with a conventional spark igniter was carried out using pure methane fuel and a blend of hydrogen and methane. For each combination of fuel and igniter, the combustion stability was explored at different air–fuel ratios, from stoichiometric conditions to the lean stable limit (up to λ = 2.0 with the corona igniter and the hydrogen-methane mixture). The combustion analysis was carried out by using the synchronized indicating and imaging data. The latter is essential to estimate the contribution of the corona igniter, which was found to be considerable only before the 5% of mass fraction burned. The corona effect igniter, with respect to a conventional spark igniter, was able to extend the lean stable limit of about 0.15 λ units with methane fuel, and about 0.10 λ units with the hydrogen-methane blend in the tested engine point. Early flame analysis confirmed the capability of corona igniter to improve combustion onset speed and to obtain a more stable and repeatable flame kernel. The findings of this study can help for a better implementation of corona ignition with gaseous low-carbon fuels, and in particular to achieve a higher lean limit extension without the drawback of a performance decay given by a substantial hydrogen enrichment.
关键词： Hydrogen,Lean combustion,Corona ignition,Methane,Optical engine
更新于2025-09-12 10:27:22
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OH planar laser-induced fluorescence measurement for H<sub>2</sub>/O<sub>2</sub> jet diffusion flames in rocket combustion condition up to 7.0 MPa
摘要： This study focuses on the application of OH planar laser-induced fluorescence (OH-PLIF) in high-pressure rocket combustion conditions, up to 7.0 MPa. The signal to noise ratio of PLIF degrades in high-pressure combustion owing to effects such as line broadening and interference from intense chemiluminescence. The OH(2,0) band excitation method was applied to obtain the OH(2,1) fluorescence emitted near 290 nm and filter out the intense OH(0,0) band chemiluminescence emitted near 308 nm. The gaseous H2/O2 (GH2/GO2) jet diffusion flame was formed using a recessed coaxial shear injector. The GH2/GO2 injection Reynolds number, Re (ReH2/ReO2 ≈ 2320/22800–4660/45600), was varied to examine the variation of the flame structure and reaction zone thickness under each pressure condition Pc, and Re injection condition. In addition, the variation of the experimentally derived full width at half maximum (FWHM) of the radial OH distribution, ?OH, with the Damk?ehler number, Da, was compared with that of the simulated FWHM of the OH mole fraction, ?OH-SIM. The OH distribution was clearly observed in the instantaneous PLIF image while eliminating the intense OH chemiluminescence even in the highest pressure condition of 7.0 MPa, which is a pressure higher than any of the previous OH-PLIF studies conducted on rocket combustion. The flame structure showed the typical characteristics of a turbulent jet diffusion flame and depended on Re rather than on the chamber pressure Pc. The variation of ?OH with Da corresponded qualitatively with ?OH-SIM and showed the characteristics of flame stretch in the vicinity of the injector.
关键词： Jet diffusion flame,High-pressure combustion,Laser-induced fluorescence,Chemiluminescence,OH(2,0) band excitation
更新于2025-09-11 14:15:04
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A comprehensive experimental characterisation of a novel porous media combustion-based thermophotovoltaic system with controlled emission
摘要： The high temperatures of combustion systems make them suitable for coupling with thermophotovoltaic systems. In practice, it is quite challenging to reduce heat losses and the spectral mismatch between the emission of the combustion source and the spectral response of photovoltaic (PV) cells. In an effort to pull these disparate energy-focussed research fields together, this paper explores the use of a low-cost erbia (Er2O3) coating on a novel porous media combustion-based thermophotovoltaic (PMC-TPV) reactor for continuous combined heat and power generation. In this work, three different configurations were analysed, including a non-coated porous foam, a coated porous foam, and a coated quartz container. As such, this study provides the first in-depth analysis and characterisation of all salient components of a PMC-TPV system. It includes a detailed characterisation of a 24-cell gallium antimonide (GaSb) array, which was attached to a heat sink and used to harvest the radiant emission from a hot (> 1200 °C), yttria-stabilised zirconia/alumina composite (YZA) ceramic foam. Since the ceramic foam does not have an ideal emissivity curve for these cells, the ability of the erbia coating to control the spectral emission was measured. The results show that by applying the erbia coating to the outer surface of the YZA foam (e.g. using a simple 2-step process of dip coating followed by curing/calcination), it is possible to increase performance, achieving a maximum in-band emission fraction of 25.4% at a firing rate of 1300 kW/m2 (i.e. around 10% of increase than that for non-coated configuration), which provides a temperature of 1285 °C. Additionally, a maximum power output of 1 W was achieved by using erbia coating on YZA foam. For the third configuration, the use of the erbia coating on the quartz tube (instead of the YZA foam) leads to an increase in the maximum core temperature of the reactor up to 1443 °C; however, this also leads to a decrease in electrical performance due to a lower in-band fraction. These findings show that applying an erbia coating on an industrial radiant emitter could enable a combined heat and power processes to gain around 30% increase of electrical output. Finally, since the PV fill factor was lower than expected, and electroluminescence measurements indicated cell damage, these findings also reveal the importance of continuously monitoring PV parameters in PMC-TPV systems.
关键词： Thermophotovoltaic systems,Direct energy conversion,Porous media combustion
更新于2025-09-11 14:15:04
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Performances of a Research CFR Octane Rating Unit Engine and Dacia Single Cylinder SI Engine Ignited by a LASER System
摘要： At this time, the severe legislation regarding the level limits of the waste and exhaust gases released by thermal engines and also the necessity of engines efficiency improvement boost the engine research domain to bring in front the use of new technologies that can be used to control the in-cylinder combustion process. Now, the new technologies is represented by LASER spark plug systems which can be successfully used at petrol engines. LASER spark plug technology can have many advantages for engine operation control, an ignition system that could provide improved combustion is the one using plasma generation and a Q-switched LASER that results in pulses with high MW power. The LASER spark plug device used in the current research was a LASER medium Nd:YAG/Cr4+:YAG ceramic structure made up of a 8.0-mm long, 1.0-at.% Nd:YAG ceramic, optically-bonded to a Cr4+:YAG c. It was developed and constructed similar to classical spark plug and could be assembled on a CFR Octane Rating Unit Engine as well as on a Dacia Single Cylinder SI Engine which led to several results among which: influences on in-cylinder pressure, combustion and pollutant emissions.
关键词： pollutant emissions,combustion,LASER spark plug,pressures,new technologies
更新于2025-09-11 14:15:04
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Understanding and Interpreting Laser Diagnostics in Flames: A Review of Experimental Measurement Techniques
摘要： There is a wealth of existing experimental data of flames collected using laser diagnostics. The primary objective of this review is to provide context and guidance in interpreting these laser diagnostic data. This educational piece is intended to benefit those new to laser diagnostics or with specialization in other facets of combustion science, such as computational modeling. This review focuses on laser-diagnostics in the context of the commonly used canonical jet-in-hot-coflow (JHC) burner, although the content is applicable to a wide variety of configurations including, but not restricted to, simple jet, bluff body, swirling and stratified flames. The JHC burner configuration has been used for fundamental studies of moderate or intense low oxygen dilution (MILD) combustion, autoignition and flame stabilization in hot environments. These environments emulate sequential combustion or exhaust gas recirculation. The JHC configuration has been applied in several burners for parametric studies of MILD combustion, flame reaction zone structure, behavior of fuels covering a significant range of chemical complexity, and the collection of data for numerical model validation. Studies of unconfined JHC burners using gaseous fuels have employed point-based Rayleigh-Raman or two-dimensional Rayleigh scattering measurements for the temperature field. While the former also provides simultaneous measurements of major species concentrations, the latter has often been used in conjunction with planar laser-induced fluorescence (PLIF) to simultaneously provide quantitative or qualitative measurements of radical and intermediary species. These established scattering-based thermography techniques are not, however, effective in droplet or particle laden flows, or in confined burners with significant background scattering. Techniques including coherent anti-Stokes Raman scattering (CARS) and non-linear excitation regime two-line atomic fluorescence (NTLAF) have, however, been successfully demonstrated in both sooting and spray flames. This review gives an overview of diagnostics techniques undertaken in canonical burners, with the intention of providing an introduction to laser-based measurements in combustion. The efficacy, applicability and accuracy of the experimental techniques are also discussed, with examples from studies of flames in JHC burners. Finally, current and future directions for studies of flames using the JHC configuration including spray flames and studies and elevated pressures are summarized.
关键词： moderate or intense low oxygen dilution (MILD) combustion,autoignition,vitiated coflow burner (VCB),laser-induced fluorescence (LIF),thermography,jet in hot coflow (JHC),planar laser diagnostics
更新于2025-09-11 14:15:04
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Experimental investigation on premixed hydrogen/air combustion in varied size combustors inserted with porous medium for thermophotovoltaic system applications
摘要： Micro combustion stabilization is challenged by the large heat loss ratio, and the operating conditions are narrow because of the small combustor size. In this work, experimental tests combined with numerical simulations are carried out to investigate the premixed H2-air combustion with and without porous medium. The results indicate that the flame stabilization is greatly enhanced in the combustor with porous medium, and the wall temperature with porous medium is 188 K higher than that of the free flame in the tube with a length 22 mm, an outer diameter 7 mm and the wall thickness 0.5 mm. The appropriate porosity of porous medium is selected for each combustor to achieve a better thermal performance and high radiation temperature. With the increase of combustor diameter, the limitations in terms of inlet velocity and flame blowout are expanded and the radiation surface area is also increased for a higher energy output. The radiation temperature and surface area play important roles in the application of micro thermo-photovoltaic system. The combustor with a length 27 mm and an outer diameter 7 mm is able to achieve an optimal balance between the contingent negative variation of radiation surface area and radiation temperature, delivering an electrical power of 1.41 W with an efficiency 1.39% for the micro-TPV system with InGaAsSb PV cells when the H2 flow rate is 3.03 g/h and equivalence ratio Φ = 0.85.
关键词： Micro combustion,Porous medium,Porosity,Electrical power
更新于2025-09-11 14:15:04
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AIP Conference Proceedings [AIP Publishing PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ICAM 2019 - Kerala, India (12–14 June 2019)] PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ICAM 2019 - Photoluminescence study of (Sm0.95 Ce0.05)2O3 nanoparticles for LED applications
摘要： Nanophosphors are a blazing area which has gained momentum in the present day research due to the fabulous unique properties of nanoparticles from their respective bulk. The rare earth doped sesquioxides have received considerable attention due to its unique properties like high chemical and thermal stabilities, intense UV absorption and also its use in solid state lightings, LASERS and so on. Here, we have synthesized (Sm0.95 Ce0.05)2O3 nanocrystalline powder using combustion method. Powder X-ray diffraction was used to study the structural characterization of the synthesized sample and the result confirmed that the synthesized nanoparticles had a nanocrystalline structure with a cubic phase and ? space group. The crystal structure and the shape of the particles have a tremendous effect on the photoluminescent properties. The surface morphology and the size of the particles were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM micrographs showed that the synthesized particles appear to be spherical. The TEM results confirmed that the particles formed were spherical and in nano regime. Phosphors with spherical morphology will surely enhance the photoluminescent properties of the materials. Hence the synthesized sample will have good luminescent characteristics. The optical properties of the sample were studied using ultraviolet –visible (UV-Vis) data analysis and photoluminescence (PL) studies. The absorption peaks obtained are at 364nm, 376, 405, 464 nm and 476nm which correspond to 6H5/2 → 4D3/2, 6H5/2 → 4D1/2, 6H5/2 → 6F7/2, 6H5/2 → 4I13/2 and 6H5/2 → 4I11/2 transitions respectively. On excitation, these particles showed a strong emission at 605 nm which corresponds to 4G5/2 →6H7/2 transition and other emissions at 563 nm and 647nm correspond to 4G5/2 →6H5/2 and 4G5/2 →6H5/2 transitions revealing that it is an orange-red emissive phosphor. This novel nanophosphor can offer new possibilities for the development of white light-emitting diodes (WLEDs) which can be excited by the near-UV chips and also in solid state lightings.
关键词： combustion method,LED applications,photoluminescence,Nanophosphors,(Sm0.95 Ce0.05)2O3
更新于2025-09-11 14:15:04
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Towards Customized Spatial Resolution in TDLAS Tomography and Hugh McCann
摘要： Tunable diode laser absorption spectroscopy (TDLAS) tomography has been widely employed to spatially and temporally resolve gas parameters in combustion processes. The requirements placed on the spatial resolution of a tomographic image vary in industrial applications, depending on the size of the target field and the necessity to detect small features. Based on an optimized beam arrangement, this work proposes a scheme to customize the spatial resolution in the design of TDLAS tomography systems. To the best of our knowledge, the proposed scheme, for the first time, quantifies the impact on the spatial resolution of varying the number of samples of the imaging space, in both angular and linear dimensions. More importantly, the proposed scheme can be used to determine the most effective optical layout that would achieve a desired spatial resolution. The reduction in the system complexity will enable the sensor to be installed in practical combustors while maintaining reliability. Finally, we apply the proposed scheme in a case study based on experimental data previously acquired from an automotive engine.
关键词： tunable diode laser absorption spectroscopy (TDLAS),spatial resolution,combustion diagnosis,tomography,beam arrangement
更新于2025-09-11 14:15:04
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Fabrication of La2O3 Uniformly Doped Mo Nanopowders by Solution Combustion Synthesis Followed by Reduction under Hydrogen
摘要： This work reports the preparation of La2O3 uniformly doped Mo nanopowders with the particle sizes of 40–70 nm by solution combustion synthesis and subsequent hydrogen reduction (SCSHR). To reach this aim, the foam-like MoO2 precursors (20–40 nm in size) with different amounts of La2O3 were first synthesized by a solution combustion synthesis method. Next, these precursors were used to prepare La2O3 doped Mo nanopowders through hydrogen reduction. Thus, the content of La2O3 used for doping can be accurately controlled via the SCSHR route to obtain the desired loading degree. The successful doping of La2O3 into Mo nanopowders with uniform distribution were proved by X-ray photon spectroscopy and transmission electron microscopy. The preservation of the original morphology and size of the MoO2 precursor by the La2O3 doped Mo nanopowders was attributed to the pseudomorphic transport mechanism occurring at 600 ?C. As shown by X-ray diffraction, the formation of Mo2C impurity, which usually occurs in the direct H2 reduction process, can be avoided by using the Ar calcination-H2 reduction process, when residual carbon is removed by the carbothermal reaction during Ar calcination at 500 ?C.
关键词： hydrogen reduction,La2O3,Mo nanopowder,doping,solution combustion synthesis
更新于2025-09-10 09:29:36