Premixed hydrogen-air flame front dynamics in channels with central and peripheral ignition

Experimental and analytical study of burning hydrogen-air mixtures with 12, 13, and 15 vol% hydrogen concentrations in channels with central and peripheral ignition was performed. Flame propagation speeds were determined by shadow and infrared high-speed imaging in the transverse and longitudinal directions, respectively. It was found that the increase in the flame front speed during the peripheral ignition reaches up to 1.7 times compared to the central ignition depending on mixture content. The pressure growth rate was examined in a closed channel. It was estimated that the time to reach a maximum pressure is 1.1 times less in the case or peripheral ignition than the central one. An analytical model was formed to describe the dynamics of the flame front in both cases. The model of a “reversed finger-flame” generated by a peripheral ignition was presented. The obtained results could be used in designing hydrogen-fueled combustible engines with the reduced knock-effect.     

A numerical study on the combustion limits of mesoscale methane jet flames with hydrogen addition

A meso-scale jet flame model was established for the flame ports of domestic gas stoves. The influences of hydrogen addition ratio (β = 0%–25%) on the combustion limits were explored. The results show that with the increase of hydrogen addition ratio, the blow-off limit increases obviously, while the extinction limit decreases slightly, namely, the combustible range expands significantly. Quantitative analysis was carried out in terms of chemical effect and thermal effect. It was found that hydrogen addition will reduce O₂ fraction in the pre-mixture for a constant equivalence ratio. Under near-extinction limit condition, since the flame is located at the nozzle exit, the external O₂ cannot be entrained into or diffuse into the upstream of the flame, which leads to the decrease of reaction rate. However, for the near-blow-off cases, the external O₂ can be entrained and diffuse into the flame, which compensates the difference of O₂ content in the pre-mixture. Therefore, the combustion reaction is enhanced by hydrogen addition because more H radicals can be produced. In addition, as the flame is located closer to the tube with the increase of hydrogen addition ratio, heat transfer between flame and tube wall is augmented and the preheating of fresh mixture is strengthened by the inner tube wall. This heat recirculation effect becomes especially notable in low velocity cases. In conclusion, the extension of extinction limit by hydrogen addition is attributed to the thermal effect, while the increase of blow-off limit is mainly due to the intensification of chemical effect.     

Vinyl-functionalized polyborosiloxane for improving mechanical and flame-retardancy performances of silicone rubber foam composites

In this work, we first synthesized vinyl-terminated polyborosiloxane (pBS) filler, and then incorporated it into silicone rubber foam (SRF) matrix to prepare composite materials through a simple chemical dehydrogenative foaming method under ambient conditions. The pBS filler with reactive groups could form physical and chemical crosslinking networks in SRF, leading to an excellent dispersion level of pBS in the SRF matrix. Moreover, the inserted pBS could remarkably improve the mechanical and flame-retardancy properties of SRF-pBS composites. Intriguingly, the SRF-pBS6 foam containing 6 wt% of pBS possessed a uniform porous structure and balanced mechanical properties (σ_b = 65.4 kPa, ε_b = 56.7%, compression stress 97.1 kPa), thermal conductivity (0.102 W (m K)^?1), limiting oxygen index (29.8%) and UL-94 rating (V-0) among the prepared foams. In addition, the incorporated pBS (6 wt%) could synergistically catalyze the formation of a silicon–boron strengthened ceramic-like protective layer under fire and was capable of suppressing heat and smoke production in the SRF-pBS6 foam. The present work provides a promising way for developing high mechanical and flame-retardant polymeric foam materials with good thermal insulation. © 2021 Society of Industrial Chemistry.     

Effects of acoustic excitation on pinch-off flame structure and NOx emissions in H2/CH4 flame

The flame structure and exhaust emissions of pinch-off flames, in which flames are separated under acoustic excitation conditions, were studied. Flame structure analysis was performed using OH1 chemiluminescence measurements, and exhaust emissions analysis was performed with a gas analyzer. Structure analysis of the pinch-off flame for acoustic excitation was performed basis the OH1 images, and various structures were confirmed according to the forcing frequency and velocity perturbation intensity. To analyze the correlation between the flame structure and NO_x emission, the flame residence time and emission index of NO_x (EINO_x) were analyzed according to the Strouhal number. The flame residence time and EINO_x decreased as the velocity perturbation intensity increased; analyzing the NO_x emission characteristics is limited when based only on the flame residence time. 1/2-power scaling was followed by EINO_x analysis and the Strouhal number was normalized to the flame residence time.     

Immersion corrosion behavior,electrochemical performance and corrosion mechanism of subsonic flame sprayed FeCoCrMoSi amorphous coating in 3.5% NaCl solution

A FeCoCrMoSi amorphous coating (AC) was fabricated on Ti6Al4V alloy (TA) by subsonic flame spraying (SFS) technique, which was used to improve its corrosion resistance. The morphology, element distribution and chemical composition of obtained coating were analyzed using a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X–ray Fluorescence (XRF), respectively, and its amorphous structure was confirmed by X–ray diffraction (XRD). The immersion corrosion behavior and electrochemical performance of FeCoCrMoSi AC immersed in 3.5% NaCl solution for the different days were systematically investigated, and the corrosion mechanism of amorphous structure was also discussed by the model of passive film. The results show that the FeCoCrMoSi AC exhibits the dense amorphous structure, which is beneficial to improving the anti–corrosion performance of TA. The potentiodynamic polarization curve (PPC) and electrochemical impedance spectroscopy (EIS) indicate that the FeCoCrMoSi AC with the lowest i_corr of 1.479 × 10^?6 A·cm^?2 immersed for 60 days has the largest capacitor loop diameter of 7.53 × 10⁵ and charge transfer resistance R_ct of 4.31 × 10⁴ Ω, showing the highest comprehensive corrosion resistance. The mechanism of corrosion resistance is contributed to the Cr–rich passive film, which is further stabilized by the addition of Mo.     

不同煤种在一维火焰燃烧过程中硫污染物排放特性研究

试验研究了不同煤种在一维火焰燃烧过程中硫污染物的排放特性，发现不同煤种在相同工况下燃烧硫污染物排放特性差别很大、燃烧温度、二次风温度、煤粉细度和过量空气系数对硫析出产物形式、浓度有较大影响．对锅炉燃烧调整，控制硫污染物排放，防止水冷壁高温腐蚀有一定的指导意义．     

煤矿用阻燃钢丝绳芯输送带浅谈

介绍了ST型煤矿用阻燃钢丝绳芯输送带的型号规格、性能要求、结构特点、阻燃机理、使用要求及发展趋势，为使用单位相关人员更好地使用与维护提供帮助。     

废弃印刷线路板Pb,Cd和Cr的测定

研究用原子吸收分光光度计测定废弃印刷线路板中重金属元素Pb，Cd和Cr的含量。结果表明，方法灵敏、快速、准确、操作方便，实用性强。Pb，Cd和Cr的回收率在98．9％～103．6％之间，相对标准偏差RSD〈1．45％。     

气相火焰燃烧合成铁掺杂二氧化钛纳米晶及其结构性质研究

采用气相扩散火焰燃烧制备了铁掺杂二氧化钛纳米品,并利用XRD、EPR、ICP-AES和XPS等测试手段对该催化剂晶相组成、晶粒尺寸及表面性质进行了分析.研究表明,铁掺杂改性对制备TiO2的晶相组成及晶粒尺寸都会产生影响.随着掺入量的增加,掺杂相Fe3 逐渐向TiO2体相富集,并促进了TiO2表面氧空位的生成.     

采用火焰焊补技术修补焦炉炭化室炉底破损

以某焦化厂焦炉炭化室为研究对象,分析了炭化室炉底破损的特点。在采用泥浆喷补法修补破损表面效果不佳后,改用火焰焊补方法。探讨了火焰焊补炉底破损表面的准备工作、焊补操作及后续工作,分析了火焰焊补过程中应注意的问题。火焰焊补后经过一段时间的运行,焊补部位平滑光洁,推焦操作电流稳定,出焦正常,推焦杆无明显振动,修补效果良好。