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过量空气系数对工业锅炉的稳定安全运行、节能减排方面具有重要影响。以小火焰伴流燃烧器为对象,基于FLUENT软件,采用了24步甲烷燃烧简化CHEMKIN化学反应动力学机理。对在常规空气氛围、不同过量空气系数条件下的甲烷燃烧进行了数值模拟。分析了燃烧温度、燃烧速率、主要污染物生成情况。得出了过量空气系数对各参数的影响规律以及作用机理。总结了适合工业应用的最佳过量空气系数。 相似文献
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以工业炉的高温空气燃烧技术应用为背景,对一个新型轴向旋流式单烧嘴燃烧室内天然气的高温空气燃烧特性进行了数值研究。采用数值模拟的方法研究了同心式轴向旋流燃烧器(HCASbumer)中螺旋肋片的旋转角度对燃烧特性的影响,其中湍流采用Reynolds应力模型,气相燃烧模拟采用β函数形式的PDF燃烧模型,采用离散坐标法模拟辐射换热过程,NOx模型为热力型与快速型。计算结果表明,对预热空气采用旋转射流时,能明显降低NOx生成量。对于HCAS型燃烧器,随着空气射流旋转角度的增大,燃烧室内的回流区域增大增强,降低了局部的氧体积分数分布,燃烧室中平均温度和最高温度都有所增加,且燃烬程度大幅度提高,而局部高温区缩小,只在靠近入口处出现。总的NOx排放量随着空气射流旋转角度的增大先减小,后增大。因此,适当调整肋片的旋转角度可以降低NOx生成量。 相似文献
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过量空气系数对HCCI汽油机燃烧特性的影响 总被引:3,自引:0,他引:3
在一台Ricardo Hydra单缸四气门汽油机上,利用气门重叠负角方法实现了均质充量压缩着火(HCCI)燃烧,并通过试验研究了过量空气系数对HCCI汽油机燃烧特性的影响.研究结果表明,在相同的转速和气门相位角下,随着过量空气系数的增加,平均指示压力减小,缸内残余废气率也减小,但燃油消耗率的变化趋势与转速有关.在大多数工况下,过量空气系数为1.05时,HCCI发动机的着火时刻最早,燃烧持续期最短.过量空气系数对循环波动的影响与转速和气门相位角有关.随着转速的增加,循环波动增大. 相似文献
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《节能》2020,(1):118-121
由于青海地处高原,工业燃气锅炉在低气压、低含氧量、气候寒冷的特殊环境中工作时,传热、燃烧等方面都受到不同程度影响,锅炉的实际热效率低于同纬度的平原地区。在现有规程中过量空气系数计算公式的基础上,获得高原某地区相关信息(海拔、压力、空气含量),用一个固定的推导过程修正过量空气系数计算公式,得到高海拔地区锅炉运行中过量空气系数新计算模型。该模型通过了德令哈地区、西宁地区的4台燃气热水锅炉的正、反平衡实际测试,验证了计算模型的可靠。并得出同纬度、不同海拔地区,利用尾气中含氧量来计算过量空气系数时,必须考虑高海拔、低氧量对其的影响,海拔越高新计算模型对锅炉效率值的影响就越大的结论。 相似文献
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为研究甲烷-空气非预混燃烧下空气旋流数对流动特性、温度分布及其对污染物NOx生成的影响,利用CFD软件,采用标准的k-ε湍流模型、P-1辐射模型和涡流耗散模型进行数值模拟。结果表明:空气旋流数从0提高到0.8的过程中,形成的中心内回流区会强化燃料和空气混合,中心火焰向燃烧室两侧逐渐扩散,火焰长度变短,且高温区移动到燃烧室的前端,局部高温的产生得到了抑制,燃烧室内的温度场更加均匀,进而导致NOx生成量的下降。同时研究燃烧器几何尺寸对气体停留时间及NOx排放浓度的影响,发现缩小空气入口孔隙半径r和燃空径向隔板间距L会导致气流速度增大,促进反应更快地弥散到整个空间,能够进一步抑制NOx的产生。 相似文献
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为了探究主流旋流和湍流对转静盘腔燃气入侵规律及机理的影响,在封严冷气量固定的条件下,针对主流旋流角、湍流强度以及二者共同作用对燃气入侵规律的影响开展数值模拟研究。研究结果揭示:当仅存在旋流时,腔内Batchelor流动核心的分布位置和规模直接受主流旋流角的影响,同时,该核心的流动特性引起了封严效率的显著变化;此外,旋流角通过影响封严出口上游的压力分布,进一步影响了下游的燃气入侵程度。当无旋流角、改变主流湍流强度时,在极端湍流强度I=20%的工况下,静盘侧Batchelor核心几乎完全消失,盘腔受到严重燃气入侵。当主流湍流强度I固定为20%,旋流角与其共同作用时,入侵状况相较于无旋流角时有所改善,但旋流角SA=15°的工况封严效率反而略低于SA=30°的工况,这主要是因为封严出口上游压力分布在湍流和旋流耦合作用下呈现出不同的波动特征。 相似文献
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Wang Xibin Chen Wansheng Gao Jian Jiang Deming Huang Zuohua 《Frontiers of Energy and Power Engineering in China》2007,1(1):105-112
The spray characteristics of methanol and ethanol with high-pressure swirl injector were explored experimentally and numerically.
experimental results show that the spray characteristics of methanol and ethanol had displayed the same trends as that of
gasoline. Under the low back-pressure ambient conditions, the spray behavior exhibited a hollow cone with wide spray angle
and initial spray slug at the tip, while the spray presented a solid cone in the case of high back-pressure. Vortexes in the
opposite direction existed in the rear part of the spray under low back-pressure ambient conditions while the vortexes formed
in the middle part under high back-pressure ambient conditions. Experiments also showed that methanol had the largest cone
angle, while ethanol and gasoline presented almost the same cone angle. Simulation results indicated that methanol and ethanol
had a slightly larger Sauter mean diameter (SMD) than that of gasoline with swirl injector. The SMD profile of methanol coincided
well with that of ethanol under low back-pressure ambient conditions, but displayed a slightly larger value under high back-pressure
due to fuel evaporation Numerical simulation could successfully demonstrate the spray characteristics of high-pressure swirl
injector for methanol and ethanol fuels.
Translated from Transactions of CSICE, 2006, 24(1): 1–8 [译自: 内燃机学报] 相似文献
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The increasing use of gas turbines in combined cycle power plants together with the high amount of kinetic energy in modern gas turbine exhaust flows focuses attention on the design of gas turbine diffusers as the connecting part between the Brayton/Joule and the Rankine parts of the combined cycle. A scale model of a typical gas turbine exhaust diffuser is investigated experimentally. The test rig consists of a radial type, variable swirl generator which provides the exhaust flow corresponding to different gas turbine operating conditions. Static pressure measurements are carried out along the outer diffuser walls and along the hub of the annular part and along the centerline of the conical diffuser. Velocity distributions at several axial positions in the annular and conical diffuser have been measured using a Laser Doppler Velocimeter (LDV). Pressure recovery coefficients and velocity profiles are depicted as a function of diffuser length for several combinations of swirl strength, tip flow and strut geometries. The diffuser without struts achieved a higher pressure recovery than the diffuser with struts at all swirl angle settings. The diffuser with cylindrical struts achieved a higher pressure recovery than the diffuser with profiled struts at all swirl angle settings. Inlet flows with swirl angles over 18?affected the pressure recovery negatively for all strut configurations. 相似文献
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In a gas/particle two-phase test facility, a three-component particle-dynamics anemometer was used to measure the characteristics of gas/particle two-phase flows in a 29 megawatt (MW) pulverized coal industrial boiler equipped with a new type of swirling pulverized coal burner. The distributions of three-dimensional gas/particle velocity, particle volume flux, and particle size distribution were measured under different working conditions. The mean axial velocity and the particle volume flux in the central region of the burner outlet were found to be negative. This indicated that a central recirculation zone was formed in the center of the burner. In the central recirculation zone, the absolute value of the mean axial velocity and the particle volume flux increased when the external secondary air volume increased. The size of the central reflux zone remained stable when the air volume ratio changed. Along the direction of the jet, the peak value formed by the tertiary air gradually moved toward the center of the burner. This tertiary air was mixed with the peak value formed by the air in the adiabatic combustion chamber after the cross-section of x/d = 0.7. Large particles were concentrated near the wall area, and the particle size in the recirculation zone was small. 相似文献
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采用非预混稳态小火焰模型(Steady Flamelet Model,SFM)耦合110步甲烷燃烧简化机理和Realizable k-ε模型对反扩散-旋流低氮燃烧器进行模拟,对比分析了不同旋流角度(30°,45°和60°)及过量空气系数(1.05,110,115和1.20)下燃烧时燃烧室内各截面轴向速度分布、中心截面温度及NOx质量浓度分布。详细研究了燃烧室内天然气与空气的燃烧特性及NOx的排放规律。模拟结果表明:随着旋流叶片角度逐渐增大,燃烧室内回流作用逐渐增强,导致火焰长度变短、燃烧室内最高温度及出口NO质量浓度逐渐降低;在旋流叶片角度为60°时,出口NO质量浓度仅为114 mg/m3;随着过量空气系数逐渐增大,火焰末端温度逐渐提高,导致燃烧室出口NO排放量逐渐增大;在过量空气系数为1.2时,出口NO质量浓度达到294 mg/m3,相比于过量空气系数为1.05时,其NO排放量增加153%。 相似文献
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燃气轮机燃烧室内NOx生成影响因素的数值研究 总被引:2,自引:0,他引:2
低NOx燃气轮机燃烧室的燃烧特性受到旋流的强烈影响,旋流特性的分析对燃烧室的设计和优化具有非常重要的作用。本文对燃气轮机燃烧室的旋流燃烧流动,应用商用程序FLUENT进行了数值模拟,并分析了旋流数、压强、湍流度对燃烧室内燃烧特性和NOx生成特性的影响。模拟结果表明,随着压强的增加,NOx排放逐渐增加,随着燃料入口湍流度的增加,NOx排放将减少,而随着旋流数的增加,NOx排放先是增加而后减小,同时,NOx随压强变化呈指数规律变化,但不同的燃烧组织形式对指数值有较大的影响。 相似文献
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通过数值模拟的方法研究了过量空气系数、配风方式、空气预热温度和炉排转速等运行参数对床层燃烧和氮氧化物排放特性的影响。研究结果表明:过量空气系数增大可加快床层整体反应速率,缩短反应区长度,增大床层表面氮氧化物质量浓度;合理推迟配风有利于扩展反应区整体长度,充分利用整个炉排;适当降低炉排转速有利于提高煤着火及前期反应速率,稍缩短总体反应区间;提高空气预热温度有利于煤着火和前期反应速率的提高,且有利于煤的燃尽。 相似文献