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41.
This work describes new type of combustion instability for which the 3-way coupling between mixing, flame heat release, and acoustics is modified by local buoyancy effects. Measurements of fuel mixture fraction are made for a non-premixed jet flame in a combustion chamber to assess the dynamics of mixing under imposed acoustic oscillations (22-55 Hz). Infrared laser absorption and phase resolved acetone-planar laser induced fluorescence are used to measure the fuel mixture fraction and then the degree of fuel/air mixing is calculated by determining the unmixedness. Results show acoustic excitation causes oscillations in the degree of fuel/air mixing at the driving frequency, which results in oscillatory flame behavior. This oscillatory flame behavior couples to the buoyancy and this in turn affects the mixing. Results also show that the mixing becomes less effective when the excitation frequency is increased or when the flame is present, compared to the non-reacting case. This work describes a key coupling mechanism that occurs when buoyancy is a significant factor in the flow field. 相似文献
42.
《Ceramics International》2016,42(9):11217-11223
Reaction ignition and chemical mechanisms in volume combustion synthesis of TiB2 via TiO2–B2O3–Mg precursors were studied using in-situ differential thermal analysis, X-ray diffraction, scanning electron microscopy and thermochemical modeling. Mg–TiO2 samples ignited at 607 °C through a sudden single step solid-solid reaction while Mg–B2O3 samples ignited at 810 °C after melting of magnesium. X-ray diffraction analysis revealed that reduction of TiO2 occurs in multiple steps and forms intermediate compounds. Results showed that heat released from the first reaction between TiO2 and Mg ignites the reactions between Mg, Ti and B2O3 resulting in the formation of TiB2. Samples with larger TiO2 particle size or a higher sample surface to volume ratio showed a two-step reaction behavior and the released heat in the first solid state reaction was insufficient for the propagation of the reaction throughout the sample. In addition, Mg3B2O6 undesired by-product was formed as a result of this two-step reaction. 相似文献
43.
《Ceramics International》2020,46(11):19228-19231
As a promising high-temperature ceramic, aluminum silicon carbide (Al4SiC4) has attracted much attention. Al4SiC4 is usually synthesized at high temperatures with a long reaction time in an electric furnace. Self-propagating high-temperature synthesis (SHS) is a promising technique for rapid synthesis. In this study, Al4SiC4 was prepared by the SHS method from a mixture of silicon, aluminum and carbon black with the addition of poly(tetrafluoroethylene) (PTFE) as an exothermic promoter. The experimental results showed that the use of a high-pressure Ar atmosphere could retain the gaseous materials in the pellet mixture, and the PTFE additive promoted the formation of silicon carbide. In addition, the oxide layer present on the surface of silicon particles inhibited the reaction between silicon and carbon. As a result, high-purity Al4SiC4 could be synthesized from aluminum, silicon, and carbon black with 15 wt% PTFE under 1.0 MPa Ar atmosphere in several seconds by the SHS method. 相似文献
44.
进排气系统压力波模拟计算的发展 总被引:2,自引:0,他引:2
综述了内燃机进排气系统压力波模拟计算的发展。简要介绍了容积法和特征线法,着重介绍了在一维解法中的最新技术:具有流正迁移(FCT)的二步Lax=Wendroff法,认为它是继特征线法之后的又以一个标准算法。该算法具有高精度,高速度等优良特性,将逐步特征线法。最后介绍多维模型及解法的最新发展。 相似文献
45.
A rapid and simple way of producing bulk graded Al2O3/YAG/YSZ ternary eutectics was investigated. The combustion reaction between Al/Fe2O3/Y2O3/ZrO2 led to the formation of molten mixtures consisting of Al2O3/YAG/YSZ, and the subsequent separation of the ceramic melt from the iron melt was realized under ultra-high-gravity field, followed by the solidification of the ceramic melt. The as-solidified ceramic ingot sank into the iron melt, where an instantaneous isostatic pressure about 2 MPa was exerted on the around of the ceramic ingot resulting in an enhanced degree of densification. Microstructure analysis demonstrated that densified ceramic was composed of Al2O3/YAG/YSZ ternary eutectics. The phase composition, morphologies, hardness and fracture toughness of the eutectic product changed gradually along the direction of high gravity field. The maximum density of the eutectic ceramic was 97.32%, correspondingly, the maximum value of the Vickers hardness and fracture toughness reached 17.82 GPa and 5.51 MPa m1/2, respectively. 相似文献
46.
Laser-extinction diagnostics can provide spatially and temporally resolved measurements of attenuation from combustion-generated soot within the path of the beam. When laser-extinction techniques are utilized in high-pressure combustion environments, however, a number of complications may be encountered that are not present in low-pressure environments. Several of these experimental difficulties were investigated in diesel engine environments, and solutions that facilitated acquisition of reliable laser-extinction data were demonstrated. Beam steering due to refractive index gradients within the combusting gases was observed, and a full-angle beam divergence of over 100 mrad was measured. A spatial-filtering scheme was employed to reduce the collection of forward-scattered light and background combustion luminosity while ensuring full collection of the steered beam. To further reject combustion luminosity, a narrow-bandpass laser-line filter was employed, after diffusing the transmitted light sufficiently to avoid the effects of significant spatial non-uniformities of the filter. As the windows were subjected to thermal and mechanical stresses, dynamic etaloning effects due to the photoelastic properties of synthetic fused silica were observed. Dynamic changes in the polarization of the exit beam were also observed, as stress-induced birefringence in the windows caused dynamic phase retardation of the transmitted beam. Although these photoelastic effects could not be eliminated, they were mitigated by introducing curvature to the wavefronts in the laser-extinction beam and using polarization-insensitive elements in the detection optics. Soot deposits on window surfaces were removed ablatively using a coaxial, high-energy, pulsed Nd:YAG laser beam. 相似文献
47.
介绍了研究发动机燃烧过程的模拟实验装置(定容燃烧弹和多功能燃烧弹)及单缸试验机,着重分析它们的工作原理、结构及特点。为研究内燃机的燃烧过程从而改善其燃烧特性所需的各式各样的实验装置的设计提供了有力的依据和信息参考。 相似文献
48.
Jian Liu Zhen Zhao Chunming Xu Aijun Duan Ling Zhu Xuezhong Wang 《Catalysis Today》2006,118(3-4):315-322
Vanadium oxides supported on γ-Al2O3, SiO2, TiO2, and ZrO2 were studied on their molecular structures and reactive performances for soot combustion. To investigate the effect of different alkali metals on the structures and reactivities of supported-vanadium oxide catalysts, they were doped into the V4/TiO2 catalyst which had the best intrinsic activity for soot combustion in the selected supported vanadium oxide catalysts. The experimental results demonstrated that the catalytic properties of these catalysts depended on the vanadium loading amount, support nature, and the presence or the absence of alkali metals. The spectroscopic analysis (FT-IR and UV–vis) and H2-TPR results revealed that the higher activity of alkali-promoted vanadium oxide catalysts could be related to the ability of alkali metal promoting the redox cycle of the active vanadyl species. TG results showed that adding alkali to Vm/TiO2 catalyst was beneficial to lowering their melting points. Low melting points could ensure the good surface atom migration ability, which would improve the contact between the catalyst and soot. Due to the alkali metal components promoting the redox ability and the mobility of the catalysts, alkali-modified vanadium oxide catalysts could remarkably improve their catalytic activities for soot combustion. The catalytic activity order for soot combustion followed Li > Na > K > Rb > Cs in the catalyst system of alkali-V4/TiO2, and the reason why it followed this sequence was discussed. 相似文献
49.
直喷式柴油机瞬态工况燃烧噪声控制研究 总被引:1,自引:0,他引:1
开展多缸柴油机瞬态工况燃烧噪声的控制研究。分别在四缸自然吸气发动机、增压发动机、引入EGR发动机和高压共轨发动机上开展了不同负荷工况下的瞬态与稳态工况的燃烧噪声测试分析,开展了增压、EGR和喷射策略对燃烧噪声控制研究。增压对瞬态工况的燃烧噪声有一定的抑制作用,增压对恒转速增转矩瞬态工况燃烧噪声的控制效果要好于对恒转矩增转速工况。瞬态工况引入适当的EGR有助于燃烧噪声的降低,EGR控制瞬态工况燃烧噪声的关键是能够实时对EGR率进行调节。相对于稳态工况,瞬态工况下应取较大的预喷量和与主预喷间隔,并得到试验的验证。 相似文献
50.