反应压力对微小空间氢氧燃烧过程影响的数值分析

基于氢氧19步基元反应化学动力学机理,对微燃烧器氢氧燃烧过程进行数值分析.研究表明:受反应机理控制,反应压力对微小空间燃烧过程的影响呈现复杂的非线性特性;较高的反应压力有利于提高微燃烧器氢氧燃烧效率,减少表面传热损失对微小空间燃烧稳定性和充分性的不利影响;但高压下链终止基元反应的主导作用导致微小空间燃烧着火滞后时间增加,使DamkOhler数降低,从而不可能无限制地提高反应压力来强化微燃烧器的燃烧负荷率.     

油田组合式旋流燃烧器燃烧分析

在油田生产和勘探过程中，燃油锅炉是新疆、哈萨克斯坦、俄罗斯等冬季高寒区域施工现场最重要的加热设备。燃烧器是锅炉的核心部件，为加强锅炉设备的节能性、可靠性和维护保养便捷性，对燃烧器的燃烧效率、安装空间、设备复杂性等均具有较高的要求。因此，本文根据现场使用情况，提出一种组合式旋流燃烧器结构，在传统燃烧器基础上从进气方式以及燃烧器结构两方面进行改进，同时可以将油气田井口的伴生气或可燃废气进行利用，提升经济性。通过数值技术模拟了燃烧过程，对炉内温度场、速度场、组分分布进行了可视化研究。结果表明，本文提出的燃烧器结构燃烧充分，燃烧效率高，整体结构小，可以有效节约空间与制造成本，在油气田生产现场具有推广价值。     

微空间下氢氧催化燃烧特性的数值分析

以CHEMKIN-IV中高速柱塞流反应器(PFR)作为燃烧室模型进行仿真分析.基于氢氧十九步基元反应化学动力学机理,分析了反应压力、当量比、进气流速对微空间下氢氧燃烧的影响.获得了燃烧室轴向温度场随当量比系数的变化规律,发现其最高温度出现在当量比约为1时,分析了较高的反应压力有利于提高微燃烧器氢氧燃烧效率,但过高的反应压力将导致微小空间燃烧着火滞后时间增加,使Damk(O)hler数降低.这些特性分析为Power MEMS的设计提供科学依据.     

微燃烧器外墙壁热损失对微尺度燃烧特性的影响分析

以美国麻省理工学院(MIT)研制的硅基六晶片微燃烧器为研究对象,研究其外墙壁热损失状况对该燃烧器燃烧特性的影响程度。采用考虑了基元反应动力学机理燃烧程序的二维CFD数值分析方法,研究在微燃烧器入口处氢气/空气当量比、流量不变的情况下,其外墙壁热损失状况对燃烧器燃烧特性的影响程度。整个计算过程包括混合气体的流动路径、燃烧器的内部区域以及其墙壁面;同时在计算过程中也考虑了混合气体的流体动力学特性、传热学特性和详细的基元反应机理。计算结果表明,燃烧器外墙壁的热传递状况不但影响燃烧器的燃烧性能,还对整个燃烧器的结构寿命影响较大。随着外墙壁热传递状况的改善,如从150 W/(m2·K)增大到250 W/(m2·K),燃烧器排出气体的温度、燃烧性能均出现降低或下降的趋势,但外墙壁的热传递系数过小,如50 W/(m2·K)时,燃烧器的微细通道内将发生回燃。结果表明,利用二维CFD数值模拟的方法研究微尺度燃烧器燃烧特性可行,与国外实际测量结果较为相近,为今后微型燃气轮机燃烧器的研制及改进提供了一定的参考依据。     

车用甲醇重整制氢反应器设计及催化换热性能的研究

甲醇燃料汽车是利用发动机尾气余热提供能量催化甲醇重整制氢,将反应后的产物作为燃料通入气缸内燃烧,为发动机提供动力,可以实现汽车节能,降低排放污染。甲醇重整反应器对汽车动力性能影响至关重要,为了使反应气体达到催化反应温度,设计适当的反应器并模拟其催化换热过程尤为关键。通过热力计算设计了螺旋管式和直管式两种甲醇反应器,建立反应器模型,以化学反应宏观动力学模型为基础,基于Fluent软件对反应器的换热及化学反应过程进行数值模拟。通过对反应器的温度场、流场及各组分浓度分布等模拟结果进行分析,比较了螺旋管与直管反应器换热性能的差异。同时改变边界条件,分别探讨了水醇比、冷流流量、热流流速对反应器催化换热性能、甲醇转化率及氢气产出量的影响。     

催化气体传感器的恒温检测方法及其在瓦斯检测中的应用

可然性气体催化燃烧放热导致催化气体传感器的敏感元件温度升高,由于热耗散和化学反应速度(即催化燃烧的放热速率)与温度的非线性,使得传感器的输出与被测气体浓度(特别是在较高的检测浓度下)呈非线性.采用恒温检测方法,即采用输出反馈调节传感器工作电流以保持传感器温度恒定的检测方法可解决该问题,且可扩大检测浓度范围.对甲烷气体的实验结果表明:其线性浓度范围达到10%.     

燃气燃烧器的CFX仿真

利用Ansys Workbench,给出了燃气燃烧器的网格划分情况.同时,在CFX下建立了燃气燃烧器的燃烧材料模型和燃烧反应模型.并运用其仿真技术,模拟了燃烧器燃烧过程的温度场、NO质量分数、辐射特性等参数.     

微热光电系统燃烧的若干影响因素的试验研究

微热光电(MPTV)系统是一种新型微动力机电系统。通过试验研究,分析阐述了不同氢氧混合气流量、氢氧混合比等因素对MTPV燃烧器内的燃烧状况、管壁以及出口端面的温度分布的影响。试验证明,氢氧混合气在微型燃烧器内易实现稳定燃烧。当流量为2.167×10-5m3/s、混合比为2:1时,微型燃烧器的壁面温度可以达到1 300K左右。     

挥发雾化式燃油加热器CO气体排放的影响因素研究

燃烧器是影响燃油加热器CO、 NOx、 UHC等污染物排放指标的关键部件。工程上需要在满足功率、效率等基本性能的基础上,尽量降低尾气的排放。本文依据燃烧物理学理论,划分了蒸发式燃烧器燃烧过程的不同功能区域,依据化学动力学理论对各区域分别描述了CO产生的影响机制,并基于此改进燃烧器进气射流结构,对进气射流静压场进行了数值仿真,并通过试验验证了该改进对改善CO排放的积极影响,对低排放蒸发式燃烧器的设计研究提供一定的参考价值。     

一种船用液体燃料蜗壳旋流器的数值研究与性能验证

为实现船用液体燃料蜗壳旋流器的可靠性点火,提高其燃烧的稳定性和燃烧效率,采用RNG k-ε双方程湍流模型,设计出一种满足船用特殊需要的蜗壳旋流器,列举了7组不同戊烷和空气进口流量,对该具体尺寸的蜗壳旋流器的液雾燃烧过程进行了数值模拟和试验验证,得到了蜗壳旋流器内部流场以及出口处的烟气温度场和燃烧产物的组分浓度分布。分析对比这7组进口流量对该蜗壳旋流器的出口温度和出口气体组分的影响,找到了满足船用需要的该具体尺寸蜗壳旋流器对应的最佳燃料进口流量。该模拟和试验结果为蜗壳旋流器的结构设计提供了理论依据。     

同步辐射真空紫外光电离质谱在燃烧和催化研究中的应用进展

燃烧是当今世界的主要能源来源,在交通运输、工业生产和航空航天等领域发挥着重要的作用.燃烧过程伴随着污染物的产生,带来严重的环境问题.为了提高燃烧效率、降低污染物排放,我们需要理解并认识燃烧,最终可以控制燃烧.中间产物是燃烧反应网络的链载体,对关键中间产物定性和定量测量是认识燃烧的重要环节,也是发展和验证燃烧反应动力学模...     

空气分级炉膛煤粉燃烬模型及实炉试验对比

传统的炉膛分区段传热设计模型忽略了煤粉燃烬计算,适用于非空气分级燃烧。随着空气分级低NOx燃烧技术的普遍应用,在炉膛分区段传热计算中引入煤粉燃烧模型以确定沿炉膛高度燃烬分布,对于提高炉膛上部屏式或辐射受热面蒸汽温度设计准确性有较为重要的意义。建立了改进型分区段传热计算和煤粉燃烧相耦合的空气分级炉膛燃烬和传热模型,对一台空气分级低NOx燃烧锅炉进行了全负荷工况试验,采用该模型对试验工况进行燃烬和传热模拟,得到空气分级锅炉炉膛煤粉燃烧过程的物理图景以及煤粉沿炉膛高度燃尽分布,并研究了燃烧模式和表面反应动力学参数等对燃烬度分布的影响。结果表明,炉膛出口煤粉颗粒燃烬度数值解与大部分测试数据吻合较好,煤粉颗粒燃烧后期灰分引起热退火抑制效应以及炉内局部烟气含氧量分布不均匀是引起模型误差的主要因素,所建立的燃烧和传热耦合模型与传统的炉膛分区段传热模型计算量相当,适合工程应用。     

Catalytic combustion behaviors of methane and propane over the PD-based catalyst in the BOP for MCFC power generation systems

Catalytic combustion is generally accepted as an environmentally preferred alternative for generation of heat and power from fossil fuels, as it has stable combustion under very lean conditions with such low emissions as NOx, CO and UHC typically at temperatures lower than in the conventional flame combustion. Yet, the commercial application of catalytic combustion has been delayed due to the difficulty in handling complicated reaction processes occurring over the catalysts. In this work, numerical studies on the catalytic combustion behavior over Pd-based catalysts for the BOP (balance of plant) of MCFC power generation systems have been conducted. After introducing the governing equations, numerical investigations on the catalyst performance with the gaseous CH₄ and C₃H₈ fuels are conducted by changing such parameters as excess air ratio, space velocity, inlet temperature, and H₂ addition over the catalytic combustion systems adopted in the BOP of 5 kW MCFC power generation systems. Catalytic combustion is found to be more active in case of lower excess air ratio, lower space velocity, higher inlet temperature, and higher supply rates of additional H₂ fuel. Also, it can be found that the reaction rate is faster and the outlet temperature is higher when C₃H₈ is used rather than CH₄.     

A numerical study on the flow characteristics in the mixing region of the catalytic combustor

Catalytic combustion is usually accomplished by a chemical reaction at the catalyst surface. Therefore, it is important that the fuel and air stream be well mixed and supplied uniformly. In this study, a perforated plate is used to enhance the mixing and flow uniformity for stable catalytic combustion. Also, a numerical simulation is performed to investigate the variation of flow characteristics according to various parameters. The results show that the uniformity of mixing and flow can be effectively improved for most of the cases by using a well-designed perforated plate.     

催化燃烧与旋转回热耦合的燃气轮机性能分析

低热值燃气总量巨大,种类繁多,很大一部分由于热值过低无法点火燃烧,常直接排入大气,造成能源浪费,加剧环境污染。为了利用这部分低热值燃气,提出一种催化燃烧与旋转回热耦合的新型燃气轮机系统,把催化燃烧室和高温换热器两个部件融合于一个部件中。相比传统燃气轮机,该燃机具有独特的优势:以低热值燃气为主燃料,采用催化燃烧;旋转回热保证了催化燃烧反应持续发生;结构布局更加紧凑。分析这种新型燃气轮机系统的热力循环特点,计算100 k W级新型燃机的热力性能,研究旋转周期等参数对性能的影响。结果表明:在使用甲烷浓度为2%的低浓度燃气时,透平入口温度保证在1 030~1 200 K,燃机能正常工作,从理论上证明了该新型系统是可行的;不同旋转周期之间系统运行的热力参数变化在3%以内,呈现准周期性;旋转周期之内系统运行的热力参数呈现波动变化;旋转周期减小,燃机输出功率和热效率降低,其波动性也降低。     

磁场辅助燃烧合成法制备La2Mg17- Ni复合储氢材料

磁场辅助燃烧合成法(MACS)制备的La2 Mg17 - Ni复合材料具有多相结构,强磁场促进添加相Ni在LLa-Mg合金表面形成Mg2NiH4相.其PGT曲线出现两个平台,最大吸氢量为4.162Wt.％,Mg2 NiH4相起到储氢相和催化相的双重作用.Ni能使材料初始放氢温度从625 K降低到520 K.     

Numerical analysis of the combustion process in a four-stroke compressed natural gas engine with direct injection system

In this paper, a numerical study to simulate and analyze the combustion process occurred in a compressed natural gas direct injection (CNG-DI) engine by using a multi-dimensional computational fluid dynamics (CFD) code was presented. The investigation was performed on a single cylinder of the 1.6-liter engine running at wide open throttle at a fixed speed of 2000 rpm. The mesh generation was established via an embedded algorithm for moving meshes and boundaries for providing a more accurate transient condition of the operating engine. The combustion process was characterized with the eddy-break-up model of Magnussen for unpremixed or diffusion reaction. The modeling of gaseous fuel injection was described to define the start and end of injection timing. The utilized ignition strategy into the computational mesh was also explained to obtain the real spark ignition timing. The natural gas employed is considered to be 100% methane (CH₄) with three global step reaction scheme. The CFD simulation was started from the intake valves opening until the time before exhaust valves opening. The results of CFD simulation were then compared with the data obtained from the single-cylinder engine experiment and showed a close agreement. For verification purpose, comparison between numerical and experimental work are in the form of average in-cylinder pressure, engine power as well as emission level of CO and NO. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

Reduced Quasi-Dimensional Combustion Model of the Direct Injection Diesel Engine for Performance and Emissions Predictions

A new concept of reduced quasi-dimensional combustion model for a direct injection diesel engine is developed based on the previously developed quasi-dimensional multi-zone model to improve the computational efficiency. In the reduced model, spray penetration and air entrainment are calculated for a number of zones within the spray while three zones with aggregated spray zone concept are used for the calculation of spray combustion and emission formation processes. It is also assumed that liquid phase fuel appears only near the nozzle exit during the breakup period and that spray vaporization is immediate in order to reduce the computational time. Validation of the reduced model with experimental data demonstrated that the new model can predict engine performance and NO and soot emissions reasonably well compared to the original model. With the new concept of reduced model, computational efficiency is significantly improved as much as 200 times compared to the original model.     

The relationship between firing modes and nitric oxide emission in highly preheated air combustion

The influence of combustion air at temperatures on nitric oxide emission was studied. The nitric oxide emission generally increases with a rise in the temperature of the combustion air. However, if combustion products for dilution of fuel or combustion air are used before the combustion reaction, then the nitric oxide emission can be reduced even when highly preheated air for combustion air is used. Combustion in low oxygen concentrations flattens the firing mode, resulting in a uniform reaction, and, thus, low nitric oxide emission can be achieved.     

3-D Simulation of the combustion process for di-methyl ether-fueled diesel engine

The characteristics of spray, auto-ignition, and the combustion process of di-methyl ether(DME) were investigated using a 3-D simulation of a combustion vessel under various engine conditions, including high temperature and pressure. Spray impingement and nonpremixed combustion models were incorporated into the computational fluid dynamics code, called STAR-CD. A Peng-Robinson equation of state was introduced to calculate the evaporation rate of DME droplets that were exposed to high-pressure conditions. A Laminar flamelet concept was used to simulate non-premixed combustion. A skeletal chemical kinetics mechanism consisting of 28 species and 45 reactions was used as the chemical mechanism for DME. Compared with the experimental data, the flamelet concept combustion model predicted the essential features of the combustion process and auto-ignition characteristics of the DME spray reasonably well for various initial conditions. The combustion process of a direct injection engine fueled by DME was also simulated and verified through experimental data.