开缝钝体对微型燃烧器燃烧性能改善的研究

为了提高微型燃烧器内的燃烧稳定性,将开缝钝体稳燃技术应用于微型燃烧器中,采用详细化学反应机理模拟了不同速度下微型开缝钝体燃烧器与微型常规钝体燃烧器的燃烧情况。结果表明:开缝钝体燃烧器火焰宽度一致性较好,火焰中心温度沿轴向分布更加均匀;开缝钝体燃烧器燃烧效率高于常规钝体燃烧器;当缝隙直径为0.1 mm时,微型开缝钝体燃烧器吹熄极限达到最高,高于微型常规钝体燃烧器。开缝钝体能有效改善微型燃烧器的燃烧状况。     

低热值煤层气部分预混式旋流燃烧器结构优化研究

针对低热值煤层气部分预混式旋流燃烧器,通过加装钝体对其结构进行了优化研究,采用数值分析的方法考察了钝体对燃烧器出口速度、温度及甲烷浓度分布等的影响规律.研究表明:在燃气管外壁上加装钝体可以提高燃烧器的部分预混效果,缩短火焰长度;在支撑管出口加装钝体可以提高燃烧器出口气流的射流刚性,使炉内温度分布趋于均匀,同时提高回流区卷吸高温烟气的能力和范围,在喷口出口形成稳定的高温区.通过加装两部分钝体的方法,对燃烧器进行局部优化改进后,燃烧器在保证射流刚性的同时达到良好的燃烧稳定性;燃烧器出口轴向速度梯度和温度随出口钝体锥度的增大而提高,出口钝体锥度应选择34.21°为宜.     

微尺度甲烷扩散火焰及其熄灭特性

用不同直径微/小尺度圆管对甲烷在空气中的扩散燃烧进行实验研究,分析了微/小尺度火焰的结构,考察了影响火焰高度的相关因素,详细探讨了火焰的熄灭极限特点,并拟合了淬熄速度与喷管出口直径d之间的经验关系式.结果表明,火焰的高度与喷管出口速度呈线性关系,随d减小而减小;H/d(火焰高度/喷口直径)与出口处Re值成正比,与d无关;随尺度d的减少,下限(淬熄速度)增大,火焰的稳燃区间变小,稳定燃烧条件苛刻.     

高炉煤气直流燃烧器的试验研究

对常规直流燃烧器和不同锥形半角的扩口直流燃烧器进行了高炉煤气稳燃试验,分析了高炉煤气的稳定着火原理、淬熄现象及脱火特性.结果表明:小内径直流燃烧器对燃烧具有强烈的淬熄作用;燃烧器类型对高炉煤气的脱火极限有较大影响,扩口直流燃烧器的脱火极限高于常规直流燃烧器.     

变功率下Rijke预混燃烧器的热声不稳定

为探索燃烧过程中热声不稳定的产生机理,对Rijke预混燃烧器热声不稳定进行了试验研究.Rijke预混燃烧器为直径40 mm、管长1 066 mm的不锈钢圆管,下端封闭,上端开口;致密堇青石材质的多孔介质稳燃体位于燃烧器1/4管长处,甲烷与空气的预混气体在稳燃体上方燃烧形成平面火焰作为加热热源.试验发现,Rijke预混燃烧器的燃烧温度和热声不稳定强度都随功率的变化而线性变化,获得的声压级位于132～143 dB.另外,Rijke预混燃烧器内热声不稳定的主峰频率几乎不受功率的影响,但幅值为最大峰值一半时的高频率和低频率之差随着功率的增大而不断减小,说明燃烧功率越大时,热声不稳定的声能就越集中于主峰频率.     

甲烷_空气在微小型Swiss_roll燃烧器内燃烧的实验研究

为了解微小型Swiss-roll燃烧室的工作特点,进行了甲烷/空气预混气的燃烧实验,获得了燃烧器的可燃极限,研究了回热对燃烧器可燃极限的影响.结果表明,当甲烷流量在O.8～2.7mg/s之间时,所设计的微燃烧器能够实现cH4/空气的稳定燃烧,并确保火焰位于燃烧器的中心.存在回热时,燃烧器的富氧极限减小,从没有回热时的0.7减小到O.5.但是可燃极限并不关于ER=1对称,富燃极限大,而富氧极限小.同时,对微燃烧器进行了数值模拟,结果表明,燃烧器中心的回流区使燃烧器能够在较大的可燃极限范围内稳定工作.     

新型钝体稳燃器的空气动力场的试验研究

众所周知,钝体后方的回流区具有燃烧的作用,本文提出了一种新型结构的锯齿钝体,并对其空气动力场进行了详细的试验研究和结果分析,试验结果表明：新型锯齿锲钝体较普通的楔形钝体具有较好的稳燃效果,从而为新型锯齿钝体稳燃器的设计和实际运用提供了依据。     

氢燃料微混燃烧器燃烧特性研究

针对带中心钝体的四喷嘴微混燃烧器,运用ANSYS FLUENT软件,采用热态小火焰生成流形的方法对燃烧器模型进行数值模拟,并与实验研究相结合,研究了甲烷/氢气混合燃料(体积组分40%CH₄-60%H₂)微混燃烧条件下的燃/空掺混,流场、温度场、火焰形态及污染物排放等基础燃烧特性。研究结果表明：微混燃烧器采用空气和燃料径向进气的结构有利于燃/空掺混,在燃烧器出口的掺混均匀性指数达到0.959;燃烧器钝体结构处存在较明显的小型中心回流区,有助于火焰稳定;当量比在0.4～0.8范围内,火焰根部稳定附着在微混喷嘴的出口,火焰彼此相互独立,实验中燃烧器火焰形态与仿真OH^*场分布基本一致;绝热火焰温度在1 500～2 050 K范围内,模型燃烧室出口NO_x排放浓度均低于16×10^-6,CO排放浓度均低于11×10^-6,表明该微混燃烧器的污染物排放水平较低且燃烧效率极高。     

劣质煤高强度燃烧的理论研究

本文从连续介质流的守恒方程组出发,研究了质量交换,热量交换和动量交换强化的方法,指出在燃烧初期局部狭窄区域内若能扩大速度梯度、压力梯度, 浓度梯度和温度梯度的“四大差别”,就有可能实现劣质煤粉的高强度燃烧.文中以大量的冷态和热态试验结果,特别是钝体燃烧器、可控涡燃烧器和稳燃腔燃烧器的最新成果论达了上达理论的正确性.     

多孔介质中预混火焰猝熄及自稳定性研究

分析了多孔介质中预混火焰的猝熄效应,试验测定了一系列工况下泡沫陶瓷的猝熄直径和自稳定范围,为多孔介质燃烧器的开发设计提供了依据。通过分析发现,猝熄直径受到多个参数的影响,包括：混合气体的流速u、预混气体的层流火焰传播速度SL、燃烧室空管Re、预混气体的导温系数a、当量比φ以及多孔介质固体温度Ts。通过对多孔介质中燃烧的自稳定性试验研究,发现了多孔介质燃烧器中火焰稳定极限(吹脱极限和回火极限)与多孔介质平均孔径和气流速度及燃烧当量比的关系。     

Experimental study on the interactions for bluff-body and swirl in stabilized flame process

This paper focuses on investigating the interaction effects for swirl and bluff-body in stabilized flame process. Particle image velocimetry was used to measure velocity fields in three burners. First, the comparison of flames in bluff-body stabilized burners with and without swirl is presented. The results of the experiments present the variations of bluff-body stabilized flame when swirl is added into burner: the maximum reverse flow velocity and the maximum mean average radial velocity decrease; the maximum radial rootmean squared fluctuating (rms) velocity increases; the values of the axial velocity peak on the side of nozzle axis are lower, and the distance between the peak and centerline is bigger; the location of the maximum radial rms velocity moves to the outlet of annular air-flow from central recirculation zone (CRZ). Then, the comparison of flames in swirl burners with and without bluff-body is provided. The results of the experiments show the changes of swirling flame when bluff-body is added into swirl burner: the air vortex in the CRZ moves to the burner; the peak values of axial mean and rms velocity decrease; the distance between centerline and the mean axial and rms velocity peak increase; the peak of mean radial velocity decreases, and the peak of rms raidial velocity increase. The data from this experiment can also be established as benchmarks for the development and validation of combustion numerical simulations.     

Flame stability and emission characteristics of propane-fueled flat-flame miniature combustor for ultra-micro gas turbines

An engineering model of a propane-fueled miniature combustor was developed for ultra-micro gas turbines. The combustion chamber had a diameter of 20 mm, height of 4 mm, and volume of 1.26 cm³. The flat-flame burning method was applied for lean-premixed propane–air combustion. To create the stagnation flow field for a specific flat-flame formation, a flat plate was set over the porous plate in the combustion chamber. A burning experiment was performed to evaluate the combustion characteristics. The flame stability limit was sufficiently wide to include the design operation conditions of an equivalence ratio of 0.55 and air mass flow rate of 0.15 g/s, and the dominant factors affecting the limit were clarified as the heat loss and velocity balance between the burning velocity and the premixture flow velocity at the porous plate. CO, total hydrocarbons (THC), and NO_x emission characteristics were established based on the burned gas temperatures in the combustion chamber and the temperature distribution in the combustor. At an air mass flow rate of less than 0.10 g/s, CO and THC emissions were more than 1000 ppm due to large heat loss. As the air mass flow rate increased, the heat loss decreased, but CO emissions remained large due to the short residence time in the combustion chamber. NO_x emission depended mainly on the burned gas temperature in the combustion chamber as well as on the residence time. To reduce emissions despite the short residence time, a platinum mesh was placed after the combustion chamber, which drastically decreased the CO emissions. The combustor performance was compared with that of other miniature combustors, and the results verified that the present combustor has suitable combustion characteristics for a UMGT, although the overall combustor size and heat loss need to be reduced.     

Experimental study on premixed CH4/air mixture combustion in micro Swiss-roll combustors

Excess enthalpy combustion is a promising approach to stabilize flame in micro-combustors. Using a Swiss-roll combustor configuration, excess enthalpy combustion can be conveniently achieved. In this work, three types of Swiss-roll combustors with double spiral-shaped channels were designed and fabricated. The combustors were tested using methane/air mixtures of various equivalence ratios. Both temperature distributions and extinction limits were determined for each combustor configuration at different methane mass flow rates. Results indicate that the Swiss-roll combustors developed in the current study greatly enhance combustion stability in center regions of the combustors. At the same time, excess enthalpy combustors of the Swiss-roll configuration significantly extend the extinction limits of methane/air mixtures. In addition, the effects of combustor configurations and thermal insulation arrangements on temperature distributions and extinction limits were evaluated. With heat losses to the environment being significant, the use of thermal insulations further enhances the flame stability in center regions of the Swiss-roll combustors and extends flammable ranges.     

A new principle of ignition and flame stability for low-volatile pulverized coal with slitted bluff-body burner

On the basis of analysing the lean flammability limits of pulverized coal combustion and the mechanism of flame stabilization of low-volatile pulverized coal by the bluff-body burner, a new principle is presented that improves ignition and flame stability of low-volatile pulverized coal. For example, some methods separate the low-volatile pulverized coals from primary air just after they enter the combustion chamber and concentrate them around the boundary and inside of the recirculation region where favourable conditions are created for the volatile contents to be released and matched with the ambient air. According to this principle a new kind of burner, called a slitted bluff-body, is invented, with which it is easier to ignite low-volatile pulverized coal and to stabilize and intensify the flame.     

Fabrication and performance test of catalytic micro-combustors as a heat source of methanol steam reformer

Two different types of H₂ catalytic micro-combustors were fabricated and evaluated as a heat source of methanol steam reformer through MEMS fabrication technology with photosensitive glass wafers. In a packed-bed micro-combustor design, ceramic foam coated with Pt was the catalyst bed. In the thin-film-coated combustor, Al₂O₃ was used as catalyst supports and coated on the combustion chamber wall. Pt was coated on the Al₂O₃ thin-film, which was constructed on the wall. The preparation of Al₂O₃ coating solution and coating process was set up based on sol–gel method. Both combustors had a combustion chamber whose height was 1 mm and the external volume of combustors was 1.8 cm³. Catalytic combustion of H₂ was stable with both combustors. H₂ conversions were over 90% for packed-bed micro-combustor and over 99% for Pt/Al₂O₃ coated micro-combustor. Both combustors burned 80 ml/min of H₂. The catalytic micro-combustors fabricated were applicable to the methanol steam reforming system for 20 W level PEMFC.     

Experimental Study of Twin Pulse Jet Engines

IntroductionDue to a liInited capacity of natural petrol resourcesand a necessity to protCct the atmosphere against NO.pollutions, a development of advanced combustors fOrpower plants or jet engines should become an essentialrole in recent researches. A simPle method of pulsedcombustion to enhance the efficiency (constant volumecombustion, higher kinetic energy of the gas), wasproposed at the end of the last century in France bywtl'], MareOnnet and Esnault-Pelteriel'], who opeIatedin l906 …     

Experimental Study of Twin Pulse Jet Engines for Power Plant Application

The total efficiency of power plants depends on the energy conversion in a combustor and a turbine. Considerably higher energy transfer rates can be obtained from a pulsed combustion, but unsteady flow of a single jet combustor reduces the turbine efficiency. Therefore, two pulse combustors were set in parallel and connected to a settling chamber that supplies a flow with constant pressure to the turbine. The aim of investigations presented here is a demonstration of technical feasibility for industrial applications and to show the benefits obtained from the pulse combustors.     

Experimental study of humid air reverse diffusion combustion in a turbulent flow field

Experiments were performed to investigate the differences between the propane/air turbulent diffusion reactive flows past bluff-body and the propane/humid air turbulent diffusion reactive flows in the same conditions. The velocity distributions of the non-humid reactive flow fields and the humid reactive flow fields were measured by particle image velocimetry (PIV) techniques. The temperature fields were measured by high temperature thermocouples, and NO_x distributions were obtained by using gas detection instruments. The results show that although humid air reactive flow fields are similar to non-humid flow fields in general, there are some differences in the humid air combustion flow field comparing with the non-humid combustion flow field: the center of the reversed-flow region goes forward; the dimension of the reversed-flow region is smaller; the peak temperature and NO_x formation are reduced. It is suggested that humid air combustion is helpful to shorten the axial length of combustors, and reduce the formation of pollutants. __________ Translated from Journal of Shanghai Jiaotong University, 2006, 40(8): 1 287–1 292 [译自: 上海交通大学学报]     

Pulse combustion: The mechanisms of NOx production

A study has been performed to elucidate the fundamental mechanisms controlling the production of NO in a Helmholtz-type pulse combustor. Cycle-resolved measurements of velocity and temperature in the combustion chamber were made. These measurements were combined with the Zeldovich NO formation mechanism to explain the mechanism responsible for the low NO formation found in pulse combustors.

The mechanism responsible for low NO formation found in pulsating flow as compared to nonpulsating flow was found to be a short residence time at high temperature. Three different possible mechanisms for this short residence time were investigated: (1) hot products from combustion are cooled by mixing with the cooler exhaust gases entering the combustion chamber from the tail pipe, thus quenching the NO formation reaction (“Automatic Exhaust Gas Recirculation”), (2) hot combustion products are quickly cooled by mixing with the incoming cold reactants, and (3) residual products with a lower overall temperature (due to an increased rate of heat transfer in the combustion chamber) readily mix with hot products producing a short residence time at high temperature. It is shown that the mechanism responsible for the low NO emission in pulse combustors is a result of item 3. A short residence time at high temperature is caused by rapid mixing with cooler residual gases that are lower in temperature due to increased rates of heat transfer in the combustion chamber.     

Effect of micro-pin-fin arrays on the heat transfer and combustion characteristics in the micro-combustor

Micro-combustor is an important component elements of the micro-thermophotovoltaic (MTPV) conversion device. The combustion stability is critical to improve its thermal performance, and thus three kinds of combustors are compared by computational fluid dynamics (CFD), which includes single – channel combustor, alternate permutation combustor and in-line combustor. The influences of micro-pin-fin arrays on the performance of the micro-combustor are discussed. Results indicate that the maximum surface temperature of combustor with fins is about 100 K higher than that without fins and the mean temperature and heat flux of in-line combustor are always higher in magnitude than those of the alternate permutation combustor. Analysis in this paper reveals that comparing with single-channel combustor, the micro-combustor with fins greatly enhances the heat transfer process through the wall. There are low velocity zones in the tail of fins, which can gather the reactants and prolong the residence time which make the combustion more sufficient and improve the effect of stable combustion. Meanwhile, under calculated conditions, the influence of micro-pin-fin arrays on the combustion reaction is stronger as the flow rate increase. The fin array in micro-combustor does not only improve the wall temperature but also minimize the wall temperature difference along the axial direction. Moreover, when the inlet velocity is larger than 4 m/s, the hydrogen conversion ratios of micro-combustors with fins was not strengthened obviously with the further increase of inlet velocity.