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951.
利用废气余热或其他热源预热燃料和/或助燃空气可称为预热燃烧技术。事实上,该技术已广泛应用于火焰炉,并在节约燃料和其他方面均取得了明显的效果。本文借助于热平衡分析和无量纲分析方法,对火焰炉预热燃烧节约燃料效果问题给出一种理论研究结果,内容包括一系列具有实用价值的方程和较为详尽的分析讨论,并同时用若干实例进行分析检验。 相似文献
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采用小尺度箱体及液化石油气模拟室内燃气泄漏的条件,通过电火花点火,实验研究了在燃气泄漏过程中的着火与火焰蔓延的现象与规律.实验结果表明,火焰首先在燃料燃烧的浓限和稀限之间的可燃区域传播,并且在化学恰当比附近区域的传播速度最大,因此燃气的动态浓度场决定了火焰蔓延的形状.并表明可燃区域是一个逐渐发展的区域,最终其高度与窗沿高度相当,在此区域内点火最容易成功,因此是气体燃料泄漏后发生火灾的最危险的区域.实验结果还揭示了在火焰蔓延过程中,存在着由火焰面推进传播向空间整体燃烧过渡的现象. 相似文献
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Artur GUTKOWSKI 《热科学学报(英文版)》2006,(2)
Following the quantitative determination of dust cloud parameters, this study investigated the flame propagation through cornstarch dust clouds in a vertical duct of 780 mm height and 160×160 mm square cross section, and gave particular attention to the effect of turbulence on flame characteristics. The turbulence induced by dust dispersion process was measured using a particle image velocimetry (PIV) system. Upward propagating dust flames were visualized with direct light and shadow photography. The results show that a critical value of the turbulence intensity can be specified below which laminar flame propagation would be established. This transition condition is about 10 cm/s. The measured propagation speed of laminar flames appears to be in the range of 0.45-0.56 m/s, consistent with the measurements reported in the literature. For the present experimental conditions, the flame speed is little sensitive to the variations in dust concentration. Some information on the flame structure was revealed from the shadow records, showing the typical heterogeneous feature of dust combustion process. 相似文献
958.
Giuliano Amantini Jonathan H. Frank Beth Anne V. Bennett Mitchell D. Smooke Alessandro Gomez 《Combustion and Flame》2007,150(4):292-319
The structure of a time-dependent methane/enriched-air flame established in an axisymmetric, laminar counterflow configuration is investigated, as the flame interacts with two counterpropagating toroidal vortices. Computationally, the time-dependent equations are written using a modified vorticity–velocity formulation, with detailed chemistry and transport, and are solved implicitly on a nonstaggered, nonuniform grid. Boundary conditions are chosen to create local extinction and reignition in the vicinity of the axis of symmetry. Experimentally, CO planar laser-induced fluorescence (PLIF), OH PLIF, and an observable proportional to the forward reaction rate (RR) of the reaction CO+OH→CO2+H are measured. Particle image velocimetry (PIV) is used to characterize the velocity field of the vortical structures and to provide detailed boundary conditions for the simulations. Excellent agreement is found between model and experiments to the minutest morphological details throughout the interaction. The validated model is then used to probe the dynamics of the two-dimensional extinction process with high temporal resolution. During the initial phase of the interaction, the flame is locally extinguished by the two vortices. The resulting edge flame propagates outward as an extinction front, with a structure that does not depart significantly from that of a diffusion flame. The front recedes from the axis of symmetry with a negative propagation speed that reaches a value as large as six times that of the freely propagating laminar flame with the same reactant concentrations found at the stoichiometric surface. As the front propagates outward, it transitions to an ignition front, and it reaches a positive propagation speed comparable to that of the freely propagating laminar flame. During this transition, it develops a characteristic premixed “hook,” with a lean premixed branch, a stoichiometric segment that evolves into the remnant of the original primary diffusion flame, and a much weaker secondary diffusion flame resulting from a secondary peak in heat release in the original unperturbed diffusion flame. No evidence of a distinct rich premixed flame is found. The edge flame stabilizes at a radial location where the local gaseous speed equals the propagation speed of the front. When the local perturbation has decayed below the flame propagation speed, the flame edge starts reigniting the mixing layer as an ignition wave that propagates with an essentially frozen structure along the stoichiometric surface until the original diffusion flame structure is fully recovered. Implications for flamelet modeling of turbulent flames with local extinction are discussed. 相似文献
959.
Parametric and statistical investigation of the behavior of a lifted flame over a turbulent free-jet structure 总被引:1,自引:0,他引:1
Partially premixed combustion is involved in many practical applications, due to partial premixing of combustible and oxidant gases before ignition, or due to local extinctions, which lead to mixing of reactants and burned gases. To investigate some features of flames in stratified flows, the stabilization processes of lifted turbulent jet flames are studied. This work offers a large database of liftoff locations of flames stabilized on turbulence-free jets for different fuels and nozzle diameters studied over their flame stability domains. Methane, propane, and ethylene flames are investigated for nozzle diameters of 2, 3, 4, and 5 mm. Blowout velocities are measured and compared with an approach based on large-scale structures of the jet. The axial and radial locations of the flame base are measured by planar laser-induced fluorescence (PLIF) of the OH radical through high sampling (at least 5000 points). From this large database the average locations of the flame base are analyzed for the fuels investigated. The pdfs exhibit an evolution of their shapes according to the region of the turbulent jet where the flame stabilizes (potential core, transition to turbulence, or fully developed turbulence regions). This dependence is probably due to the interaction of the flame with the jet structures. This is confirmed by the comparison between the amplitude of the height fluctuations and the local size of the large-scale structures deduced from particle image velocimetry measurements and self-similarity laws for velocity. The results show the flame can be carried over a distance equal to the local diameter of the jet within the region of fully developed turbulence for propane and ethylene, and over a slightly larger distance for methane. 相似文献
960.
预混合气在多孔介质中往复流动下的超绝热燃烧技术(简称RSCP)被称为划时代的燃烧技术,文章探讨了RSCP燃烧器的工作原理,全面阐述了多孔介质和换向装置在其中的作用;从能量守恒定理出发,通过数学分析给出了超绝热火焰产生的理论依据,提出超绝热现象是多孔介质中积累的热量的热传播波与混合气燃烧时的燃烧波叠加的结果。 相似文献