新一代航空发动机燃烧室

针对新一代高油气比(0.051及以上)航空发动机燃烧室,本文提出头部采用化学恰当比直接混合燃烧设计方案。对于新一代高压比(70及以上)低排放民用航空发动机燃烧室,由于其自着火延迟时间极短,因此采用贫油直接混合燃烧,而不能采用预混合预蒸发燃烧。本文提出了一种贫油直接混合低排放燃烧室方案,其燃油空气模由简单的压力雾化喷嘴和轴向旋流器组成,结合燃油分级技术降低污染物排放,该燃烧室具有较好的燃烧稳定性。这两类燃烧室的燃烧空气分数非常大,因此存在慢车贫油熄火问题。文中针对两类燃烧室分别提出了相应的解决方案,同时介绍了火焰筒外壁面及内壁面的冷却设计方案。本文研究成果可为下一代航空发动机燃烧室的发展提供指导作用。     

改进加力室V型火焰稳定器性能的试验研究

本文描述加力燃烧室开缝V型火焰稳定器.模型试验得出,总压恢复系数增加,贫油熄火边界扩大,燃烧效率提高;台架试验时可降低单位油耗约1％其结果是令人鼓舞的. 一、试验设备 试验设备为低压燃烧试验系统,总空气流量为1.4kg/s。供油分两处:前排用喷油杆,距稳定器约3米,油量古总油量的70％,这股油可完全蒸发;后排用单个离心喷嘴,占     

预混多喷嘴火焰自激振荡燃烧的实验研究

针对甲烷/空气预混多喷嘴火焰的自激振荡燃烧进行了激光可视化实验研究。采用动态压力传感器记录压力脉动,利用激光诱导荧光技术对多喷嘴火焰结构进行相同步测量。实验结果表明,多喷嘴燃烧室的压力脉动频率为41 Hz,幅值为1370 Pa。火焰沿着轴向发生周期性跳动,在0°~60°相位时,喷嘴发生回火。中心火焰的推举高度比外侧火焰高,但燃烧反应强度低于外侧火焰。在相邻火焰干涉区发生局部熄火与重新点燃,相邻火焰干涉区和火焰根部区的不稳定热释放和压力脉动的耦合是引起预混多喷嘴火焰自激振荡燃烧的主要原因。     

基于FGM的旋流预混燃烧室超大涡模拟

针对航空发动机燃烧室等复杂工程中的预混燃烧问题发展高精度、高效的数值预测方法,本研究发展了火焰面生成流型(FGM)详细化学反应建表方法结合超大涡模拟方法(VLES),对工程中的GE LM6000预混旋流燃烧室燃烧开展了高精度数值研究,并与实验结果进行了比较。计算结果表明,VLES-FGM方法可以较准确地预测出旋流预混燃烧室内的流场及温度场分布。为了进一步模拟航空发动机真实的燃烧工况,对原始单头部燃烧室使用周期性边界条件来类比全环燃烧室。计算结果表明,VLES-FGM方法计算得到的周期性燃烧室流场回流区相比较固壁边界燃烧室较小,并且固壁边界燃烧室温度场具有明显的颈部结构,燃烧室下游的高温区分布更为均匀。本文计算结果表明基于FGM燃烧模型的自适应湍流模拟方法VLES对于模拟复杂航空发动机相关的旋流预混燃烧具有很大的应用潜力。     

燃气轮机燃烧室燃烧天然气和燃烧中低热值煤气的比较

本文使用商业软件FLUENT,对某燃气轮机燃烧室燃烧大然气和燃烧中低热值煤气进行了比较。原本燃烧天然气的燃烧室直接改为燃烧中低热值煤气,会产生燃料射流速度太快的问题,使阻燃孔失效,火焰太长,高温燃气直接冲击下简壁出口。仅仅增大燃料喷嘴口径可以在一定程度上改善燃烧室内流动结构,使掺混孔起一定的作用,气膜冷却射流也将高温区抬离了下简壁。     

低气压下多通道纳秒脉冲等离子体点火特性研究

高空低温、低压的极端条件导致航空发动机二次启动困难,纳秒脉冲放电过程中产生化学效应、热力学效应和气体动力学效应,逐步应用于点火技术。针对低压环境,研究了纳秒脉冲放电特性以及放电对火核发展的影响。对比分析了三种放电方式在常压、低压环境的点火概率、火核发展以及压力延迟、上升时间。结果表明:高频纳秒脉冲放电上升沿陡、脉宽窄,能够提高放电效率,在静止燃气中引起湍流现象,使火核具有类细胞结构层,加速扩展。在低压、贫油条件下,纳秒脉冲式放电点火效率更高,新型点火激励器增大初始火核,大幅提高点火效率。纳秒脉冲放电能够减少压力延迟时间,新型点火激励器能将压力延迟时间缩短24%(初始压力0.1 MPa,当量比1.0)。     

直喷柴油机火焰浮起长度的数值模拟研究

采用三维CFD模型模拟了直喷柴油机缸内喷雾燃烧过程,模拟缸压曲线得到了实验的验证.通过高温区与喷嘴之间的稳定距离来确定柴油机火焰浮起长度,研究在不同进气条件下火焰浮起长度的变化情况.该模型成功地预测了火焰浮起长度随着初始进气压力的增大而减少,随着进气温度的升高出现先增大后减少的趋势.同时模拟了在不同EGR率下柴油机缸内燃烧情况,发现火焰浮起长度和燃料着火延迟时间都随EGR率的增加而增大.     

拉伸流扩散火焰面结构及熄火的研究

对拉伸层流扩散火焰面进行了数值模拟,考察了在以往湍流燃烧的火焰面模型中,假定Lewis数等于1的可靠性,研究了不同分子扩散和火焰辐射对火焰面结构、氮氧化物排放和熄火临界的影响.计算结果表明,Lewis数等于1的假定在火焰面结构的计算中存在很大的近似性,火焰辐射可以引起低拉伸条件下的熄火临界.     

湍流燃烧自适应求解技术在低排放燃烧室计算中的应用

基于各向异性非结构网格生成技术, 开发了面向复杂几何和复杂湍流燃烧问题的自适应求解算法, 并进行了程序代码的可靠性验证工作, 展示了各向异性网格自适应算法在降低问题求解规模、提高火焰面和流场计算精度等方面的优势.应用该自适应求解技术准确捕捉到了一维预混层流火焰、二维对冲火焰和三维本生灯湍流火焰的流场信息, 火焰面附近的温度、速度、组分等物理量与实验值吻合很好.对一款富油-快速混合-贫油(rich-burn, quick-mix, lean-burn, RQL)低排放发动机燃烧室进行了计算分析, 发现了燃烧室内的热声不稳定现象.      

IET短周期涡轮实验台模拟高空涡轮性能试验研究

本文介绍了中国科学院工程热物理研究所(IET)短周期涡轮实验台的结构、特点和试验过程,参照高空台对航空发动机模拟高空试验的要求,对短周期涡轮试验台和长周期高空台发动机模拟试验进行了比较,探讨了利用短周期实验台进行模拟高空涡轮性能试验的可行性.通过一个低压模型涡轮的试验,验证了本实验台在进行涡轮模拟高空性能试验方面的功能和可信性,从而拓展了本实验台的使用领域.试验获得的模型涡轮的设计点性能以及变工况特性,为研究低雷诺数条件下涡轮内部流动机理和设计提供了丰富的实验数据.     

Concept and combustion characteristics of ultra-micro combustors with premixed flame

Under micro-scale combustion influenced by quenching distance, high heat loss, shortened diffusion characteristic time, and flow laminarization, we clarified the most important issues for the combustor of ultra-micro gas turbines (UMGT), such as high space heating rate, low pressure loss, and premixed combustion. The stability behavior of single flames stabilized on top of micro tubes was examined using premixtures of air with hydrogen, methane, and propane to understand the basic combustion behavior of micro premixed flames. When micro tube inner diameters were smaller than 0.4 mm, all of the fuels exhibited critical equivalence ratios in fuel-rich regions, below which no flame formed, and above which the two stability limits of blow-off and extinction appeared at a certain equivalence ratio. The extinction limit for very fuel-rich premixtures was due to heat loss to the surrounding air and the tube. The extinction limit for more diluted fuel-rich premixtures was due to leakage of unburned fuel under the flame base. This clarification and the results of micro flame analysis led to a flat-flame burning method. For hydrogen, a prototype of a flat-flame ultra-micro combustor with a volume of 0.067 cm³ was made and tested. The flame stability region satisfied the optimum operation region of the UMGT with a 16 W output. The temperatures in the combustion chamber were sufficiently high, and the combustion efficiency achieved was more than 99.2%. For methane, the effects on flame stability of an upper wall in the combustion chamber were examined. The results can be explained by the heat loss and flame stretch.     

Flow characterization and dilution effects of N_2 and CO_2 on premixed CH_4/air flames in a swirl-stabilized combustor

Numerically-aided experimental studies are conducted on a swirl-stabilized combustor to investigate the dilution effects on flame stability, flame structure, and pollutant emissions of premixed CH4/air flames. Our goal is to provide a systematic assessment on combustion characteristics in diluted regimes for its application to environmentally-friendly approaches such as biogas combustion and exhanst-gas recirculation technology. Two main diluting species, N2 and CO2, are tested at various dilution rates. The results obtained by means of optical diagnostics show that five main flame regimes can be observed for Nz-diluted flames by changing excess air and dilution rate. CO2-diluted flames follow the same pattern evolution except that all the domains are shifted to lower excess air. Both N2 and CO2 dilution affect the lean blow- out （LBO） limits negatively. This behavior can be counter-balanced by reactant preheating which is able to broaden the flammability domain of the diluted flames. Flame reactivity is degraded by increasing dilution rate. Meanwhile, flames are thickened in the presence of both diluting species. NOx emissions are significantly reduced with dilution and proved to be relevant to flame stability diagrams： slight augmentation in NOx emission profiles is related to transitional flame states where instability occurs. Although dilution results in increase in CO emissions at certain levels, optimal dilution rates can still be proposed to achieve an ideal compromise.     

Towards the development of an efficient low-NOx ammonia combustor for a micro gas turbine

Recent studies have demonstrated stable generation of power from pure ammonia combustion in a micro gas turbine (MGT) with a high combustion efficiency, thus overcoming some of the challenges that discouraged such applications of ammonia in the past. However, achievement of low NOx emission from ammonia combustors remains an important challenge. In this study, combustion techniques and combustor design for efficient combustion and low NOx emission from an ammonia MGT swirl combustor are proposed. The effects of fuel injection angle, combustor inlet temperature, equivalence ratio, and ambient pressure on flame stabilization and emissions were investigated in a laboratory high pressure combustion chamber. An FTIR gas analyser was employed in analysing the exhaust gases. Numerical modeling using OpenFOAM was done to better understand the dependence of NO emissions on the equivalence ratio. The result show that inclined fuel injection as opposed to vertical injection along the combustor central axis resulted to improved flame stability, and lower NH₃ and NOx emissions. Numerical and experimental results showed that a control of the equivalence ratio upstream of the combustor is critical for low NOx emission in a rich-lean ammonia combustor. NO emission had a minimum value at an upstream equivalence ratio of 1.10 in the experiments. Furthermore, NO emission was found to decrease with ambient pressure, especially for premixed combustion. For the rich-lean combustion strategy employed in this study, lower NOx emission was recorded in premixed combustion than in non-premixed combustion indicating the importance of mixture uniformity for low NOx emission from ammonia combustion. A prototype liner developed to enhance the control and uniformity of the equivalence ratio upstream of the combustor further improved ammonia combustion. With the proposed liner design, NOx emission of 42?ppmv and ammonia combustion efficiency of 99.5% were achieved at 0.3?MPa for fuel input power of 31.44?kW.     

机载光学整流罩与扫描反射镜尺寸及渐晕的设计分析

为满足机载光电系统的成像作用距离要求,对机载光学整流罩以及扫描反射镜的设计尺寸进行了理论仿真分析计算,并对研制的样机进行了试验研究。以实例形式给出了整流罩设计的作用距离与相关参量的计算结果,讨论了整流罩扫描系统的渐晕大小。装备该整流罩系统的样机,在近万米高空对音速某战机的红外长波扫描搜索距离可达到86 km,红外中波跟踪达到180 km,激光测距达到47 km。结果表明:根据探测作用距离理论模型分析计算,研制的机载光学整流罩及扫描反射镜光学系统达到了设计要求。     

Neutrons for probing the ice nucleation on atmospheric soot particles

Soot resulting from combustion of kerosene in aircraft engines can act as condensation nuclei for water/ice in the atmosphere and promote the formation of contrails that turn into artificial cirrus clouds and affect the climate. The mechanisms of nucleation of water/ice particles are not well identified. Studies ??in situ?? are difficult to realize, so we try to determine by neutron diffraction the nucleation of water/ice adsorbed on soot collected at the outlet of an aircraft engine combustor within the conditions of the upper troposphere. The results are compared with those obtained on model laboratory soot. The comparison highlights the role of chemical impurities and structural defects of original aircraft engine soot on the nucleation of water/ice in atmospheric conditions.     

基于CARS技术的超燃冲压发动机点火过程温度测量

相干anti-Stokes Raman散射（coherent anti-Stokes Raman scattering，CARS）技术作为一种非接触测量手段，已广泛应用于多种发动机模型燃烧室温度测量及地面试验.然而，目前的工作主要集中在稳态燃烧场温度的测量，缺乏用高分辨率的单脉冲来测量瞬变的燃烧火焰温度及组分浓度的研究.基于CARS理论，结合多参数拟合算法，开发了基于MATLAB的CARS光谱计算和拟合程序CARSCF；利用McKenna平面火焰炉在不同工况下进行了温度测量，并与DLR测量结果进行对比，结果显示开发的CARSCF具有较高的测量重复性和准确性；最后将CARS技术应用于测量超燃冲压发动机点火过程中的温度测量，获取了点火过程中的温度.结果显示，在来流Mach数为3的条件下，H₂/air点火过程中温度呈现急剧上升然后缓慢下降，而CARS信号则呈现急剧上升然后急剧下降随后又缓慢上升的趋势，并且在点火过程中最高温度为1 511 K.      

Modelling compression ignition engines by incorporation of the flamelet generated manifolds combustion closure

Tabulated chemistry models allow to include detailed chemistry effects at low cost in numerical simulations of reactive flows. Characteristics of the reactive fluid flows are described by a reduced set of parameters that are representative of the flame structure at small scales so-called flamelets. For a specific turbulent combustion configuration, flamelet combustion closure, with proper formulation of the flame structure can be applied. In this study, flamelet generated manifolds (FGM) combustion closure with progress variable approach were incorporated with OpenFOAM® source code to model combustion within compression ignition engines. For IC engine applications, multi-dimensional flamelet look-up tables for counter flow diffusive flame configuration were generated. Source terms of non-premixed combustion configuration in flamelet domain were tabulated based on pressure, temperature of unburned mixture, mixture fraction, and progress variable. A new frozen flamelet method was introduced to link one dimensional reaction diffusion space to multi-dimensional Computational Fluid Dynamics (CFD) physical space to fulfill correct modelling of thermal state of the engine at expansion stroke when charge composition was changed after combustion and reaction rates were subsided. Predictability of the developed numerical framework were evaluated for Sandia Spray A (constant volume vessel), Spray B (light duty optical Diesel engine), and a heavy duty Diesel engine experiments under Reynolds averaged Navier Stokes turbulence formulation. Results showed that application of multi-dimensional FGM combustion closure can comprehensively predict key parameters such as: ignition delay, in-cylinder pressure, apparent heat release rate, flame lift-off , and flame structure in Diesel engines.