旋流杯结构对火焰筒头部流场影响的试验研究

为深人研究旋流杯安装角、两级流量比、二级流通面积和套筒扩张角对火焰筒头部冷态流场的影响， 采用2D-3C粒子图像测速仪在常温常压下开展了相关试验研究。结果显示:适当增加叶片安装角可增大气 流的径向与切向速度分量，这一效果有助于提高油气掺混质量；内外两级流量比的增加将导致高速脉动区域 向内部移动，有利于燃油雾化，但回流区较窄、轴向速度较大，不利于稳定火焰和合理温度场的形成；随着二 级旋流面积的增大，回流区直径增大，射流速度降低，有利于稳定火焰;套筒扩张段在一定程度上对旋转射流 起引导作用，增大套筒扩张角将导致气流径向扩散能力加强。     

旋流器结构参数对TAPS燃烧室性能的影响

利用数值模拟手段探究旋流器叶片角度对双环预混旋流(TAPS)燃烧室性能的影响。针对本文研究的特定结构及工况,结论如下:一级、二级叶片角增大时,参考线上切向速度仅在特定位置变化较明显,燃烧效率与压力损失均呈上升趋势。三级叶片角增加,火焰筒中心区域气流切向速度变化较大,回流区体积明显增大,燃烧效率与压力损失也逐渐升高。预测所得压力损失y与燃烧效率z随三级叶片角x的变化关系式分别为:y=0.063 17×x+3.313 96和z=0.026 11×x+97.821 39。结果可为燃气轮机TAPS燃烧室的旋流器设计提供参考。     

火焰筒扩张角与旋流匹配对燃烧特性的影响

为研究旋流器流量分配对干式低排放(Dry Low Emission,DLE)燃烧室燃烧特性的影响规律,针对单头部中心分级旋流燃烧室,以天然气作为燃料,在保持旋流数不变的前提下开展两级旋流器不同空气分配比例下的试验测试和数值模拟,获得不同结构参数条件下燃烧室的综合燃烧性能以及污染物排放等变化规律。研究表明：随主燃级/预燃级旋流器流量比增大,燃烧室中心回流区变小、回流区长度变短;预燃级局部当量比的增大造成燃烧室出口CO排放增加,主燃区燃烧加剧,热力型NOx排放也增加;同时,燃烧室中心高温区域向燃烧室出口方向扩张,出口温度分布均匀性变差。     

一体化加力燃烧室燃烧性能数值研究

针对某两级中心分级分区单头部燃烧室结构参数对头部下游流场结构的影响,采用数值模拟结合正交设计的方法研究了头部结构参数（一/二级旋流数、值班级套筒张角、隔离段高度比）的变化对燃烧室流动特性的影响规律和程度。结果表明：中心回流区最大宽度随着二级旋流数、隔离段高度比、一级旋流数、值班级套筒张角4个结构参数的增大而增大,并且影响程度依次降低;中心回流区长度随着一/二级旋流数的增大而增大,套筒张角和隔离段高度比则对中心回流区长度的影响程度较小;值班级和主燃级旋流器的旋流数偏大以及值班级套筒张角偏大都会导致台阶回流区消失     

降低冒烟数燃烧室火焰筒头部改进设计研究

为了解决某型航空发动机燃烧室冒烟数较大的问题,通过分析航空煤油的燃烧化学反应过程和燃烧室内油气掺混燃烧过程,确认了炭烟的产生主要发生在初级反应阶段火焰筒的头部区域。因此提出改进措施,将火焰筒头部的单级旋流器更换为旋流杯,并对旋流杯的结构参数进行调整。采用数值模拟及扇形试验对改进前后的火焰筒性能进行对比分析。研究表明：相对于单级旋流器,旋流杯使燃烧室头部流场由单涡结构变为双涡结构,燃油分布更加均匀,在头部高温的环境中降低了局部富油程度,从而减少了头部炭烟的生成;改进后,燃烧室冒烟数大幅降低,总压恢复系数变化不大,贫油熄火油气比达到了0.004 6,能够满足发动机使用要求。     

旋流强度对F级燃气轮机燃烧稳定性影响分析

旋流器是目前燃烧室中常用的稳定火焰的结构,主要通过气体经过旋流器后在下游形成的回流区来稳定火焰。一般采用旋流数表征旋流器的旋流强度。旋流数一方面会影响空气和燃料的掺混,另一方面会影响回流区的尺寸,从而对火焰的长度和稳定性产生影响。针对某重型燃气轮机的燃烧器,采用数值模拟的方法分析了旋流数变化对热态温度场的影响,同时采用三维有限元方法分析了旋流数对燃烧稳定性的影响。结果表明:旋流数增加,会使得火焰更加紧凑,长度缩短,同时使得燃烧室二阶周向模态稳定性恶化,不稳定的风险增加;降低旋流数会使得火焰长度增加,轴向模态稳定性恶化。该研究结果可为类似机组的相关设计研究提供参考和借鉴。     

天然气低排放旋流燃烧室头部结构性能研究

本文设计了一种旋流燃烧室的旋流器及预混段结构。通过冷态数值模拟的方法评估了掺混段出口的总压损失及掺混不均匀度。计算结果显示同向双级旋流器能够在相对较低的总压损失下获得较好的掺混效果。之后通过相同的方法确定影响该型旋流器性能的四个几何参数:内层旋流数、外层旋流数、喷嘴直径和内外层流道面积比。研究结果得出了旋流器设计的具体尺寸。配合该旋流器设计,又通过燃烧数值模拟设计了三种掺混区布局。结果表明,较短的中心钝体结构会引起火焰锋面位置向燃烧室下游偏移,造成平面型火焰面,另外还会在掺混区中产生不稳定的回流区。最后通过改变预混段外径、中心体长度和直径得到了综合性能良好的燃烧室结构。     

双径向反向旋流器燃烧室冷态流场数值研究

文章采用数值模拟的方法对一种新设计的双径向旋流器燃烧室的冷态流场进行了研究,并对旋流器的重要设计参数进行了计算和验证.研究表明:双径向反向旋流器能在燃烧区形成有效的回流区,同时反向旋转加强了燃料空气混合,有利于污染控制.从旋流数来看,燃烧区旋流数均大于0.6,旋流强度足以形成有效的回流区用于稳燃.最后文章研究了此结构下两级旋流器的流量系数并与初始设计用值进行了比较.     

旋流器和射流孔流通面积对燃烧室流场及温度场影响的数值研究

针对微型燃气轮机机组中燃烧室总压损失较高的问题,利用ANSYS Fluent软件对火焰筒内部的流场和温度场进行了数值模拟研究,分析了增大火焰筒旋流器及射流孔的流通面积前后,火焰筒内轴向速度、切向速度、回流区、壁面温度和出口温度分布等的变化规律。结果表明:同时增大旋流器、主燃孔和掺混孔的流通面积,分别增大21%、40%和44%,总压损失由6. 34%降至3. 97%,但会引起火焰筒内回流区范围减小,掺混效果降低和燃烧不稳定等问题。     

旋流杯矩阵下游冷态流场特征分析

基于分级贫油直射燃烧概念的多点喷雾燃烧室在降低航空发动机氮氧化物排放方面显示出极大的潜力,在传统航空发动机燃烧室模型的基础上构建了相邻旋流杯旋转方向相同(顺转)和相反(逆转)两种3×3旋流杯矩阵,数值计算采用可实现k-ε湍流模型,对比分析了旋流杯矩阵下游流场特性。结果表明,对于逆转旋流杯矩阵,部分旋流杯下游回流区相互靠近,而且回流区的长度与回流速度均大于顺转旋流杯矩阵情况。有利于维持火焰稳定,但燃烧情况下气流在高温环境中滞留时间增加,不利于降低氮氧化物排量。对于顺转和逆转两种旋流杯矩阵,下游回流区边缘处湍流动能最大值与湍流动能分布相似。     

Large eddy simulation and preliminary modeling of the flow downstream a variable geometry swirler for gas turbine combustors

This work presents a novel swirler with variable blade configuration for gas turbine combustors and industrial burners. The flow dynamics downstream the swirler was explored using Large Eddy Simulation (LES). The resolved turbulence kinetic energy in the region where the flow exhibits the main flow phenomena was well above 80% of the total turbulent kinetic energy of the flow. It was evidently shown that the new swirler produces a central recirculation zone and a Rankine vortex structure which are necessary for swirl flame stabilization. Two Reynolds-averaged NavierStokes (RANS) simulation cases utilizing the standard and realizable k-ε turbulence models were also conducted for two objectives. The first is to demonstrate the validity of RANS/eddy-viscosity models in predicting the main characteristics of swirling flows with comparison to the LES results. The second objective is to comparatively investigate the flow features downstream the new swirler in both co-rotating and counter-rotating blade configurations. The results show that the counter-rotating configuration produces higher turbulence kinetic energy and more compact recirculation zone compared to the co-rotating configuration.     

富氧燃烧对投运混煤锅炉低负荷稳燃性的影响

火焰筒头部结构对预混燃烧性能有重要影响,为了探讨旋流器与火焰筒扩张角相互作用关系,试验研究了扩张角为35°（渐扩）、90°（突扩）的火焰筒分别匹配旋流数为0.55,0.75旋流器对燃烧性能的影响。试验结果表明：渐扩火焰筒总压损失较突扩火焰筒减小约3.4%~4.4%,且匹配较小旋流数具有更高的总压恢复系数;突扩火焰筒较渐扩火焰筒具有更低的贫油熄火极限,且无论突扩火焰筒还是渐扩火焰筒,匹配较大旋流数旋流器后均具有更低的熄火极限;突扩型火焰筒温度场对旋流器适应性好,各旋流数下均获得较均匀温度场,出口温度分布系数为0.134 1~0.141 6;渐扩火焰筒温度场对旋流器适应性差,匹配较小旋流数旋流器后温度场均匀性更好,出口温度分布系数为0.135 7;突扩火焰筒NOx排放量更低,且匹配小旋流数旋流器更佳;渐扩火焰筒CO和碳氢化合物（UHC）排放更低,且匹配大旋流数旋流器更佳。     

Development of high intensity CDC combustor for gas turbine engines

Colorless distributed combustion (CDC) has been demonstrated to provide ultra-low emission of NOx and CO, improved pattern factor and reduced combustion noise in high intensity gas turbine combustors. The key feature to achieve CDC is the controlled flow distribution, reduce ignition delay, and high speed injection of air and fuel jets and their controlled mixing to promote distributed reaction zone in the entire combustion volume without any flame stabilizer. Large gas recirculation and high turbulent mixing rates are desirable to achieve distributed reactions thus avoiding hot spot zones in the flame. The high temperature air combustion (HiTAC) technology has been successfully demonstrated in industrial furnaces which inherently possess low heat release intensity. However, gas turbine combustors operate at high heat release intensity and this result in many challenges for combustor design, which include lower residence time, high flow velocity and difficulty to contain the flame within a given volume. The focus here is on colorless distributed combustion for stationary gas turbine applications. In the first part of investigation effect of fuel injection diameter and air injection diameter is investigated in detail to elucidate the effect fuel/air mixing and gas recirculation on characteristics of CDC at relatively lower heat release intensity of 5 MW/m³ atm. Based on favorable conditions at lower heat release intensity the effect of confinement size (reduction in combustor volume at same heat load) is investigated to examine heat release intensity up to 40 MW/m³ atm. Three confinement sizes with same length and different diameters resulting in heat release intensity of 20 MW/m³ atm, 30 MW/m³ atm and 40 MW/m³ atm have been investigated. Both non-premixed and premixed modes were examined for the range of heat release intensities. The heat load for the combustor was 25 kW with methane fuel. The air and fuel injection temperature was at normal 300 K. The combustor was operated at 1 atm pressure. The results were evaluated for flow field, fuel/air mixing and gas recirculation from numerical simulations and global flame images, and emissions of NO, CO from experiments. It was observed that the larger air injection diameter resulted in significantly higher levels of NO and CO whereas increase in fuel injection diameter had minimal effect on the NO and resulted in small increase of CO emissions. Increase in heat release intensity had minimal effect on NO emissions, however it resulted in significantly higher CO emissions. The premixed combustion mode resulted in ultra-low NO levels (<1 ppm) and NO emission as low as 5 ppm was obtained with the non-premixed flame mode.     

Optimization of flame stabilization methods in the premixed microcombustion of hydrogen–air mixture

The premixed combustion of a lean hydrogen–air mixture is analyzed in this study to examine various properties and flame stabilization. A two-dimensional (2D) analysis of a microscale combustor is performed with various shapes of bluff bodies (e.g., circular and triangular). Nine bluff bodies are placed at the entrance of the microscale combustor and solved with 2D governing equations. The analysis is performed with the three velocities of 10, 20, and 30 m/s, but the equivalence ratio is fixed in all cases. The various characteristics of the microscale combustor are studied such as the temperature of the wall, difference in peak temperature, the mean velocity at the outlet, and temperature of the exhaust gases. Flame stabilization depends on various factors such as bluff body shape and size, and the velocity of the fuel–air mixture at the inlet and recirculation zone. In comparison to all bluff body cases, we observe that the wall blade bluff body is the most efficient (low exhaust gas temperature, large recirculation zone, low mean velocity at the outlet of the microcombustor, and high wall temperature) compared with all eight other bluff body cases. Combustion efficiency is directly proportional to the wall temperature, meaning that the microcombustor with wall blade bluff bodies is more efficient with a stabilized flame. The simulation results are compared with published data on an L/D ratio of 15.     

Study on nonpremixed methane/air combustion from flame structure and NOX emission aspect for different burner head structures

In the present study, the air turbulator, which is a part of a nonpremixed burner, is investigated numerically in terms of its effects on the diffusion methane flame structure and NO_X emissions. A computational fluid dynamics (CFD) code was used for the numerical analysis. At first, four experiments were conducted using natural gas fuel. In the experimental studies, the excess air ratio was taken constant as 1.2, while the fuel consumption rate was changed between 22 and 51 Nm³/h. After the experimental studies, the CFD studies were carried out. Pure methane was taken as fuel for the simulations. The nonpremixed combustion model with the steady laminar flamelet model (SFM) approach was used in the combustion analyses. Methane‐air extinction mechanism with 17 species and 58 reactions was used for the simulations. The results obtained from the CFD studies were confronted with the measurements of the flue gas emissions in the experimental studies. Then, a modified burner head was analysed numerically for the different air turbulator blade numbers and angles. The CFD results show that increasing the air turbulator blade number and angle causes the thermal NO emissions to be reduced in the flue gas by making the flame in the combustion chamber more uniform than the original case. This new flame structure provides better mixing of the fuel and combustion air. Thus, the diffusion flame structure in the combustion chamber takes the form of the partially premixed flame structure. The maximum reduction in the thermal NO emissions in the flue gas is achieved at 38% according to the original case.     

Burning rates and temperatures of flames in excess-enthalpy burners: A numerical study of flame propagation in small heat-recirculating tubes

This study investigates flame propagation in small thermally-participating tubes where the wall acts as a heat-recirculating medium. This fundamental configuration allows heat in the combustion products to be recirculated into the reactants, resulting in excess enthalpy and enhanced burning rates. Preheating of the reactants by heat recirculation has traditionally been considered to be the dominant mechanism leading to large burning rates observed in such systems. This is mainly supported by results from physical models based on a one-dimensional (1-D) representation of the system, where the radial diffusion of heat from wall surface to channel centerline is not accurately captured. In this study, a 2-D formulation with conjugate heat transfer, which accurately resolves the transport of heat inside the gas-wall system, is used to model the excess-enthalpy phenomenon. Steadily-propagating stoichiometric methane–air flames are simulated inside an adiabatic tube of finite wall-thickness, over a wide range of inlet flow velocities and small tube diameters. Burning-rate enhancement is found to be caused not only by preheating, associated with heat recirculation, but also by an increase in flame-front area. Flame elongation is more pronounced with increasing tube diameter and inlet velocity, up to a point where the change in flame-front area becomes dominant in enhancing burning rate. In that case, heat recirculation is a necessary condition for flames to couple to the thermal wave in the wall and elongate, but does not provide a significant increase in enthalpy or temperature that would otherwise be needed for high burning rates to be observed. As the diameter is reduced, the effect of preheating becomes increasingly important for burning-rate enhancement compared to flame area increase. At very small diameters, smaller than the flame thickness, the increase in burning rate is seen to be predominantly attributable to preheating. However, preheating is seen to become limited as inflow velocity is increased, due to 2-D effects inside the fluid that interfere with heat recirculation. These findings demonstrate that 2-D effects inside the fluid can have a prohibitive influence on the burning-rate enhancement attributed to preheating, but that they also give rise to an additional mechanism, associated with the change in flame surface area, responsible for burning-rate enhancement in heat-recirculating burners.     

Combustion characteristics of a slotted swirl combustor: An experimental test and numerical validation

Combustion performance of a non-premixed combustor with a slotted swirler was experimentally and numerically investigated. The velocity and temperature profiles in the downstream of the swirler were measured in both cold-flow and combustion experiments. Concentration of CO₂ emission was measured by utilizing a flue gas analyzer and the combustion efficiency was accordingly determined. The same experiments with a non-slotted swirler were repeated for comparison. The results show that, compared to the non-slotted swirler, the slotted swirler results in a larger recirculation zone, in which the flow velocity is smaller and the temperature is higher, implying the enhanced combustion performance. The combustion efficiency of the slotted swirler based on the measured CO₂ emission is 75%, which is higher than 60% of the non-slotted swirler. These results suggest that the slotted swirler holds potential to enhance the combustion performance of gas turbine combustor and merits further, comprehensive studies.     

Study on main flow and fuel injector configurations for Scramjet applications

A parametric study of combustor inlet configuration for supersonic combustion ramjet (Scramjet) engine has been conducted by solving two-dimensional full Navier–Stokes equations. The main stream is air of Mach 5 entering through the configured inlet of the combustor and gaseous hydrogen is injected from the configured jet on the side wall. The parameters included are air stream angle and injection angle. On the effect of air stream angle, strong interaction between main and injecting flows can be observed for smaller angle causing sharp increase in mixing efficiency on the top of injector. Also high momentum of air stream towards the side wall causes no recirculation at the upstream of injector and the system becomes unable for flame holding. For the variation of injection angle, results show that in upstream of injector the mixing is dominated by recirculation and in downstream the mixing is dominated by mass concentration of hydrogen. Upstream recirculation is dominant for injecting angle 60° and 90°. Incorporating the various effects, perpendicular injection shows the maximum mixing efficiency and its large upstream recirculation region has a good flame holding capability.