共查询到18条相似文献,搜索用时 234 毫秒
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针对采用偏心旋流二次风燃烧技术的300 MWe旋流燃烧器W火焰炉,借助1/10冷模试验台,通过三维激光颗粒动态分析仪测量研究了不同燃尽风率下其主燃区内气固流动特性。随着燃尽风率减小,拱下回流区内回流速度不断增加,且回流区尺寸不断增大。随着燃尽风率由25%减小到10%,在分级分区域,颗粒的最大竖直速度由2 m/s增大到4 m/s.燃尽风率由20.3%减小到10%,拱下回流区内气固两相竖直脉动速度明显增大,气固两相湍流强度将不断增大.在乏气和分级风区域,燃尽风率15%下最大颗粒体积流率是燃尽风率20.3%的2至2.7倍,拱上气流下冲深度明显增加.随着燃尽风率减小,下冲颗粒开始折转向上的位置被推迟,下炉膛空间利用率将不断增加. 相似文献
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采用叶轮型旋流燃烧器,研究了旋流数、叶片数以及流量等因素对氨气预混旋流燃烧火焰稳定性和燃烧极限的影响.实验结果表明,在一定当量比下,氨气预混旋流燃烧火焰会失稳发生回火或振荡抬举;随着旋流数的增大或叶片数的增加,火焰更易失稳发生回火;石英玻璃高度越高,内部流场结构越完整,火焰高度越高。氨气预混旋流火焰贫燃极限在φ=0.64~0.76之间,富燃极限在φ=1.47~1.74之间。随着总流量的增大,贫燃极限逐渐增大,富燃极限波动较大,总体燃烧极限范围变大;随着旋流数的增大、叶片数的增加或石英玻璃高度的升高,燃烧极限范围变窄。 相似文献
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Effect of swirl on combustion dynamics in a lean-premixed swirl-stabilized combustor 总被引:4,自引:0,他引:4
The effect of inlet swirl on the flow development and combustion dynamics in a lean-premixed swirl-stabilized combustor has been numerically investigated using a large-eddy-simulation (LES) technique along with a level-set flamelet library approach. Results indicate that when the inlet swirl number exceeds a critical value, a vortex-breakdown-induced central toroidal recirculation zone is established in the downstream region. As the swirl number increases further, the recirculation zone moves upstream and merges with the wake recirculation zone behind the centerbody. Excessive swirl may cause the central recirculating flow to penetrate into the inlet annulus and lead to the occurrence of flame flashback. A higher swirl number tends to increase the turbulence intensity, and consequently the flame speed. As a result, the flame surface area is reduced. The net heat release, however, remains almost unchanged because of the enhanced flame speed. Transverse acoustic oscillations often prevail under the effects of strong swirling flows, whereas longitudinal modes dominate the wave motions in cases with weak swirl. The ensuing effect on the flow/flame interactions in the chamber is substantial. 相似文献
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1引言预燃室燃烧技术是近十多年来开发研究的一种高燃烧效率低NO。的燃烧技术门.它是一种分级燃烧技术。燃料在预燃室内只是部分地燃烧,在贫氧的一次火焰区内脱挥发分,从而减少了NO。的形成。自1982年以来,我国开发研究了很多种类的预燃室,如旋流、大速差l‘]、偏置射流预燃室等。工程热物理研究所研究开发了逆向复式射流预燃室燃烧器l‘,‘]。经实验室和工业实验证明,该预燃室有极优良的火焰稳定性能和煤种适应性,能够实现较低的NOx排放。本文针对逆向射流预燃室内这一独特的流场结构,利用数值模拟来预报煤粉颗粒在其内的运… 相似文献
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A. Degeneve R. Vicquelin C. Mirat J. Caudal T. Schuller 《Proceedings of the Combustion Institute》2021,38(4):5501-5508
Controlling the flame shape and its liftoff height is one of the main issues for oxy-flames to limit heat transfer to the solid components of the injector. An extensive experimental study is carried out to analyze the effects of co- and counter-swirl on the flow and flame patterns of non-premixed oxy-flames stabilized above a coaxial injector when both the inner fuel and the annular oxidizer streams are swirled. A swirl level greater than 0.6 in the annular oxidizer stream is shown to yield compact oxy-flames with a strong central recirculation zone that are attached to the rim of central fuel tube in absence of inner swirl. It is shown that counter-swirl in the fuel tube weakens this recirculation zone leading to more elongated flames, while co-swirl enhances it with more compact flames. These results obtained for high annular swirl levels contrast with previous observations made on gas turbine injectors operated at lower annular swirl levels in which central recirculation of the flow is mainly achieved with counter-rotating swirlers. Imparting a high inner swirl to the central fuel stream leads to lifted flames due to the partial blockage of the flow at the injector outlet by the central recirculation zone that causes high strain rates in the wake of the injector rim. This partial flow blockage is more influenced by the level of the inner swirl than its rotation direction. A global swirl number is then introduced to analyze the structure of the flow far from the burner outlet where swirl dissipation takes place when the jets mix. A model is derived for the global swirl number which well reproduces the evolution of the mass flow rate of recirculating gases measured in non-reacting conditions and the flame liftoff height when the inner and outer swirl levels and the momentum flux ratio between the two streams are varied. 相似文献
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K. K.J. Ranga Dinesh K. W. Jenkins M. P. Kirkpatrick W. Malalasekera 《Combustion Theory and Modelling》2013,17(6):947-971
Large eddy simulations (LES) of turbulent non-premixed swirling flames based on the Sydney swirl burner experiments under different flame characteristics are used to uncover the underlying instability modes responsible for the centre jet precession and large scale recirculation zone. The selected flame series known as SMH flames have a fuel mixture of methane-hydrogen (50:50 by volume). The LES solves the governing equations on a structured Cartesian grid using a finite volume method, with turbulence and combustion modelling based on the localised dynamic Smagorinsky model and the steady laminar flamelet model respectively. The LES results are validated against experimental measurements and overall the LES yields good qualitative and quantitative agreement with the experimental observations. Analysis showed that the LES predicted two types of instability modes near fuel jet region and bluff body stabilised recirculation zone region. The mode I instability defined as cyclic precession of a centre jet is identified using the time periodicity of the centre jet in flames SMH1 and SMH2 and the mode II instability defined as cyclic expansion and collapse of the recirculation zone is identified using the time periodicity of the recirculation zone in flame SMH3. Finally frequency spectra obtained from the LES are found to be in good agreement with the experimentally observed precession frequencies. 相似文献
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Characteristics and structure of inverse flames of natural gas 总被引:2,自引:0,他引:2
Characteristics and structure of nominally non-premixed flames of natural gas are investigated using a burner that employs simultaneously two distinct features: fuel and oxidiser direct injection, and inverse fuel and oxidiser delivery. At low exit velocities, the result is an inverse diffusion flame that has been noted in the past for its low NOx emissions, soot luminosity, and narrow stability limits. The present study aimed at extending the burner operating range, and it demonstrated that the inverse flame exhibits a varying degree of partial premixing dependent on the discharge nozzle conditions and the ratio of inner air jet and outer fuel jet velocities. These two variables affect the flame length, temperature distributions, and stability limits. Temperature measurements and Schlieren visualisation show areas of enhanced turbulent mixing in the shear region and the presence of a well-mixed reaction zone on the flame centreline. This reaction zone is enveloped by an outer diffusion flame, yielding a unique double-flame structure. As the fuel–air equivalence ratio is decreasing with an increase in the inner jet velocity, the well-mixed reaction zone extends considerably. These findings suggest a method for establishing a flame of uniform high temperature by optimising the coaxial nozzle geometry and flow conditions. The normalised flame length is decreasing exponentially with the air/fuel velocity ratio. Measurements demonstrate that the inverse flame stability limits change qualitatively with varying degree of partial premixing. At the low premixing level, the flame blow-out is a function of the inner and outer jet velocities and the nozzle conditions. The flame blow-out at high degree of partial premixing occurs abruptly at a single value of the inner air jet velocity, regardless of the fuel jet velocity and almost independent of the discharge nozzle conditions. 相似文献
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A method and analysis was developed to quantify the amplitude of deterministic spray unsteadiness based on Phase Doppler Anemometry (PDA), which sampled time‐dependent droplet velocity and size measurements, in order to determine the fluctuations of droplet data rate and number density, which are quantities relevant to fluctuations of droplet concentration. The data processing method of the PDA measurements was assessed in a pulsed spray at a frequency of 20 Hz injected in a swirl‐stabilised burner. Comparisons between quantities relevant to droplet concentration fluctuations, measured by PDA and a light scattering technique, quantified the deterministic spray unsteadiness and agreed to within 15%. The developed PDA approach was applied in the swirl‐stabilised burner to measure the amplitude of deterministic spray unsteadiness of an otherwise steady spray, which was caused by the instability of the atomisation process. The intensity of deterministic fluctuations of droplet data rate and number density, occurring at a frequency range around 600 Hz due to the atomisation process, was quantified to 15% of the corresponding mean value and this spray unsteadiness generated fluctuations on the air and droplet velocity fields. The deterministic spray unsteadiness could survive up to the end of the recirculation zone of the air flow at the burner exit and, therefore, could influence flame stability. 相似文献
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Photography and chemieluminescence from CH radicals have been used to identify the reaction zones and quantify the areas and shapes of kerosene-fuelled flames with swirl numbers of 0.7 and 0.8 and an overall equivalence ratio of 0.25. The air flow was oscillated at a frequency of 350 Hz and the results suggest that the oscillations caused a sequence of vortex rings at the burner exit and that these distorted the reaction zone and increased its area in the near burner region leading to an overall shorter flame. For the swirl number of 0.7, the flame was lifted and the oscillations led to an increase in the average lift off length whereas the higher swirl number caused an attached flame with and without oscillations. The stretch rate, evaluated from the variation of the flame area in time, was higher for the lifted flame suggesting that lift off was caused by local extinction. 相似文献
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《Combustion Theory and Modelling》2013,17(4):731-766
A simple, yet representative, burner geometry is used for the investigation of highly swirling turbulent unconfined, non-premixed, flames of natural gas. The burner configuration comprises a ceramic faced bluff-body with a central fuel jet. The bluff-body is surrounded by an annulus that delivers a swirling primary flow of air. The entire burner assembly is housed in a wind tunnel providing a secondary co-flowing stream of air. This hybrid bluff-body/swirl burner configuration stabilizes complex turbulent flames not unlike those found in practical combustors, yet is amenable to modelling because of its well-defined boundary conditions. Full stability characteristics including blow-off limits and comprehensive maps of flame shapes are presented for swirling flames of three different fuel mixtures: compressed natural gas (CNG), CNG–air (1:2 by volume) and CNG–H2 (1:1 by volume). It is found that with increased fuel flow, flame blow-off mode may change with swirl number, Sg. At low swirl, the flame remains stable at the base but blows off in the neck region further downstream. At higher swirl numbers, the flames peel off completely from the burner's base. Swirling CNG–air flames are distinct in that they only undergo base blow-off. In the low range of swirl number, increasing Sg causes limited improvement in the blow-off limits of the flames investigated and (for a few cases) can even lead to some deterioration over a small intermediate range of Sg. It is only above a certain threshold of swirl that significant improvements in blow-off limits appear. Six flames are selected for further detailed flowfield and composition measurements and these differ in the combination of swirl number, primary axial velocity through the annulus, Us, and bulk fuel jet velocity, Uj. Only velocity field measurements are presented in this paper. A number of flow features are resolved in these flames, which resemble those already associated with non-reacting swirling flows of equivalent swirl obtained with the present burner configuration. Additionally, asymmetric flowfields inherent to some flames are revealed where the fluidic centreline of the flow (defined in the two-dimensional (U–W velocity pair) velocity field by the ?ω? = 0 tangential velocity contour), meanders strongly on either side of the geometric centreline downstream by about one bluff-body diameter. Flow structures revealed by the velocity data are correlated to flame shapes to yield a better understanding of how the velocity field influences the flames physical characteristics. 相似文献