共查询到19条相似文献,搜索用时 93 毫秒
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脉动供燃料燃烧技术及火焰频率特征 总被引:1,自引:0,他引:1
介绍了一种天然气的新型脉动供燃料燃烧技术,该技术能有效降低NOx,提高传热效率,节约能源,且改造简易,运行经济;阐述了其技术原理,综述了其发展状况,指出对我国燃烧技术改进的重要意义.利用直接摄像技术,对一个采用该燃烧方式的射流火焰在不同流量脉动频率下的火焰类型和结构特征进行了研究.结果发现,随脉动频率变化出现了丰富的火焰类型.燃气脉动与系统共振特性相耦合影响火焰脉动特性,在系统共振和谐振频率附近,火焰根部出现崩溃混合,且火焰湍动升起,火焰长度变短.在某些频率下火焰直长,具有清晰的贫富燃交替结构. 相似文献
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针对基于燃烧的微小型动力装置存在燃烧效率低、火焰传播速度慢的问题,设计了一个可视化的、特征间距仅为0.45 mm的微尺度定容燃烧室,实验比较了0~1的掺氢比例下,丙烷/氢气/空气预混火焰在该燃烧室内的传播以及加速过程.实验发现没有掺氢时,丙烷/空气预混火焰需要在0.25 MPa初始压力下才能够传播;当掺氢比例为0.2时,火焰在传播过程中会发生从缓燃到爆燃的转变,这种燃烧模态的转变可以大幅缩短燃烧室内火焰传播时间,极大提升火焰传播速度.实验还发现掺氢比例以及初始压力的提升均能使得微尺度火焰传播速度提升. 相似文献
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基于燃料燃烧的微型能源动力装置具有高能量密度特性,可提供瓦到百瓦级的能量输出,因此在过去的20年间受到广泛关注。国内外学者研制了微型的燃气轮机、内燃机、推进装置、燃烧器、热电转换装置及热光电转换系统等不同类型的能源动力装置。然而,由于微尺度条件下燃烧环境和常规尺度存在差异,材料、密封及润滑等方面的技术瓶颈,目前大部分微型能源动力装置的性能未能到达预期的目标。由于微尺度燃烧基础理论有别于传统的常规尺度燃烧理论,随着其重要性的凸显,国内外学者对其进行了广泛深入的研究,更加清晰地揭示了微尺度火焰及燃烧的基本特性。本文首先介绍了国内外微型能源动力装置及系统的研究进展,然后对微尺度条件下预混及非预混火焰的研究现状进行了总结,在本文的最后部分提出了微燃烧相关亟待解决的科学及工程问题。 相似文献
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为研究不同配比下生物柴油混合燃料燃烧特性,设计了一套生物质液体燃料雾化蒸发燃烧系统,该系统可产生生物柴油及其混合燃料层流预混火焰,结合OH-PLIF平面激光诱导荧光技术测定并分析燃烧火焰的高度和锋面面积以及层流预混火焰的传播速度和OH-PLIF总信号强度等燃烧特性.结果表明随着正丁醇或乙醇添加比例的增大,两种混合燃料燃烧火焰高度、火焰锋面面积呈下降趋势;火焰传播速度呈上升趋势.在混合燃料中,正丁醇的体积分数越大,燃烧火焰OH-PLIF总信号强度越大,而乙醇的体积分数越大,混合燃料燃烧火焰OH-PLIF总信号强度越小. 相似文献
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Experimental investigation of burning rates of pure ethanol and ethanol blended fuels 总被引:1,自引:0,他引:1
Shintre Parag 《Combustion and Flame》2009,156(5):997-1005
A fundamental experimental study to determine the burning rates of ethanol and ethanol-blended fossil fuels is presented. Pure liquid ethanol or its blends with liquid fossil fuels such as gasoline or diesel, has been transpired to the surface a porous sphere using an infusion pump. Burning of the fuel takes place on the surface of the porous sphere, which is placed in an air stream blowing upwards with a uniform velocity at atmospheric pressure and temperature under normal gravity conditions. At low air velocities, when ignited, a flame envelopes the sphere. For each sphere size, air stream velocity and fuel type, the fuel feed rate will vary and the same is recorded as the burning rate for that configuration. The flame stand-off distances from the sphere surface are measured by post-processing the digital image of the flame photograph using suitable imaging software. The transition velocity at which the flame moves and establishes itself at the wake region of the sphere has been determined for different diameters and fuel types. Correlations of these parameters are also presented. 相似文献
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Smaller scale and higher energy density power sources have received increasing interest in last few years. A photographic method was adopted to study the characteristics of ethanol evaporation and its diffusion flame under the effect of a DC field in present study. A transparent quartz glass tube with an inner diameter of 1.8 mm and an outer diameter of 3 mm was used as a burner. A laminar diffusion flame was established on top of the vertical burner, and a DC field was imposed on the flame along the jet direction. Test conditions involved fuel mass flow rates of 1.0 to 2.2 ml/h, and electric field voltages of 0 to 10 kV. The extremely small ethanol flow rates were accurately controlled by a syringe pump. The flame shapes and the dynamic ethanol vapor–liquid interface were visually observed using a high speed CCD camera. It was found from the experiments that the extent of ethanol evaporation and the diffusion flame shape both change with the mass flow rates of ethanol. The direction and intensity of the DC field have a great impact on the extent of evaporation, flame structure, and soot emission. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20283 相似文献
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缸内喷射少量二甲醚(DME)形成微火源引燃汽油复合燃烧,可以拓展汽油稀释燃烧的界限,进一步提高发动机的经济性.基于三维计算流体动力学(CFD)结合化学反应动力学模拟,分析了不同微引燃燃料缸内分布作用下初始自燃点的产生机制,为集聚型和离散型微火源的类型判定提供辨识依据.结果表明:微火源的形成受到局部温度和DME浓度的共同作用,离散型微火源主要受到局部温度的影响,而集聚型微火源主要受到DME局部浓度的影响.离散型微火源可以提高缸内整体活性,促进火焰传播与多点自燃;集聚型微火源可以引燃高稀释混合气.甲醛的净生成速率变化特征可用于定量识别不同类型的微火源,判别依据为:在过渡阶段缸内甲醛质量变化不超过最大质量的10%,且甲醛净生成速率的导数存在多个0点,表明高浓度甲醛分布区域快速消耗与低温区域甲醛生成过程共同进行. 相似文献
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In view of the potential of bio-ethanol as an alternative fuel and the particulate matter (PM) issues during gasoline combustion, the soot distribution characteristics of ethanol-gasoline blends in laminar diffusion flames were studied on a Gülder liquid burner using the two-color laser induced incandescence (TC-LII) technique. During the experiments, the ethanol ratio in the blends was varied from 20% to 80% by volume in order to investigate quantitatively the soot reduction potential of ethanol. In order to study the effect of reduction in carbon content due to ethanol addition on soot formation, the experiments were performed under a fixed fuel mass flow rate and a fixed carbon mass flow rate. It was found that both peak and average soot volume fraction in the flame reduced significantly with increasing ethanol content under both fuel supplying modes, however, this effect was progressively less pronounced as ethanol content increased. By comparing the two fueling modes, it was found that the reduction in carbon content due to ethanol addition has little impact on soot reduction. For a given ethanol blending ratio, the soot reduction under the same carbon mass flow rate was only slightly smaller than that under the same fuel mass flow rate. In terms of flame characteristics, the initial height of soot formation increases with increasing ethanol content under both fuel supply modes mainly due to the increased fuel outlet velocity. Radially, the peak soot location moves from the outside towards the center gradually as height increases. However, along the center line of the flame, the initial height of soot formation decreases with increasing ethanol content under the same fuel flow rate, whereas the trend remained similar to that in the whole flame under the same carbon flow rate. 相似文献
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J.B. Greenberg 《Combustion and Flame》2007,148(4):187-197
An evolution equation for a laminar flame front propagating into an air and liquid fuel mist cloud is derived for the first time, accounting for both the finite-rate evaporation of the fuel droplets and the slip velocity between them and their host environment. The asymptotic analysis employed in developing the equation exploits the usual inverse large activation energy parameter associated with chemical reaction in the flame and a small drag parameter. It is demonstrated that, in the no-slip velocity case, increasing the vaporization Damköhler number can produce flame extinction, presumably due to the more intense heat loss incurred due to droplet heat absorption necessary for vaporization. Droplet drag can also induce extinction due to the longer residence time of the droplets in any locale (than if there was no slip), leading to more vaporization with greater attendant heat loss. The predicted results for droplet velocity are compared to independent experimental data from the literature with good qualitative agreement. 相似文献
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As an alternative or supplement to small batteries, the much-anticipated micro-direct methanol fuel cell (μDMFC) faces several key technical issues such as methanol crossover, reactant delivery, and byproduct release. This paper addresses two of the issues, removal of CO2 bubbles and delivery of methanol fuel, in a non-prohibitive way for system miniaturization. A recently reported bubble-driven pumping mechanism is applied to develop active μDMFCs free of an ancillary pump or a gas separator. The intrinsically generated CO2 bubbles in the anodic microchannels are used to pump and circulate the liquid fuel before being promptly removed as a part of the pumping mechanism. Without a discrete liquid pump or gas separator, the widely known packaging penalty incurred within many micro-fuel-cell systems can be alleviated so that the system's power/energy density does not decrease dramatically as a result of miniaturization. Since the power required for pumping is provided by the byproduct of the fuel cell reaction, the parasitic power loss due to an external pump is also eliminated. The fuel circulation is visually confirmed, and the effectiveness for fuel cell applications is verified during continuous operation of a μDMFC for over 70 min with 1.2 mL of 2 M methanol. The same device was shown to operate for only 5 min if the pumping mechanism is disabled by blocking the gas venting membrane. Methanol consumption while utilizing the reported self-circulation mechanism is estimated to be 46%. Different from common pump-free fuel delivery approaches, the reported mechanism delivers the fuel actively and is independent of gravity. 相似文献
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Liangliang Sun Yong Hao Chunming Zhang Ran Ran Zongping Shao 《International Journal of Hydrogen Energy》2010
This paper presents a systematic study of a direct-flame solid oxide fuel cell (DF-SOFC) operating on methanol and ethanol flames by SEM, EIS, I-V polarization and mass spectrometer (MS) characterizations and numerical simulation. The experimental study demonstrated that, by adopting a conventional Ni + Sm0.2Ce0.8O1.9 (SDC) anode, irreversible carbon deposition and a drop of cell performance was observed when running the cell on an ethanol flame, while no carbon was deposited by operating on a methanol flame. Fuel cell stability tests indicated significant degradation in performance after 3 h of operation on an ethanol flame, while no degradation was observed after 30 h of operation on a methanol flame. A simple qualitative explanation of the difference observed in the electrochemical performance for the fuel cell operating on a methanol flame and an ethanol flame is presented based on numerical simulation. 相似文献