波瓣形混合器加力燃烧室冷态流场特性分析

以某波瓣形混合器加力燃烧室三维模型为研究对象,采用CFD方法对模型进行数值分析,建模时重点对波瓣形混合器和环形火焰稳定器进行网格加密。以飞行试验工况点获取的低压涡轮后总温、总压结合Gasturb软件计算出加力燃烧室出口的总温、总压作为整体流场CFD计算的边界条件进行计算。计算结果表明：经过波瓣形混合器后,内、外涵气流能够在较短轴向距离充分混合,总压恢复系数最大为0.984;在接近出口处热混合效率达到0.516;气流经过环形火焰稳定器后,形成明显的低压回流区,且在出口处截面静压分布均匀,因此该加力燃烧室模型具有非加力状态流阻小的特点。通过对该型加力燃烧室流场特性分析,为加力燃烧室加力接通前内部参数获取提供技术支撑。     

微型燃气轮机燃油燃烧室燃烧特性的模化试验研究

基于模化试验方法,对设计的100kW级微型燃气轮机燃油燃烧室在额定工况下的性能以及在保持微型燃气轮机燃烧室出口排气温度不变的情况下,改变进口空气温度对燃烧室燃烧特性的影响进行了研究。结果表明,燃烧室燃烧效率达到99%以上,总压恢复系数达到94.5%,出口温度最大不均匀度低于20%,NOx排放指标低于9g/kg,火焰筒壁面温度分布均匀。此外,随着燃烧室进口温度的升高,燃烧效率增大,出口温度最大不均匀度减少,CO和UHC的排放指标明显降低,但总压恢复系数有所降低,NOx排放指标有所升高。     

进气畸变对回流燃烧室性能的影响研究

针对燃气轮机实际运行过程中不同火焰筒之间的空气流量畸变问题,以回流燃烧室为研究对象,开展三维数值模拟,分析进气流量改变对燃烧室多物理场分布特征和燃烧室性能的影响。结果表明：进气流量偏离理想设计对燃烧室回流区结构、温度场、总压恢复系数和燃烧效率等参数产生不利影响,而对燃烧室空气流量分配比例、主燃孔和掺混孔射流深度等参数的影响不明显;随着进气流量的减小,燃烧火焰拉长,燃烧室出口温度均匀性变差,燃烧效率急剧降低。     

天然气塔式同轴分级燃烧室掺氢燃烧特性 数值模拟研究

为了解天然气掺氢对贫预混燃气轮机性能的影响,采用Chemkm-pro研究了燃料的化学反应动力学 特性,对比了不同当量比、掺氢比下的绝热火焰温度、层流火焰传播速度及点火延迟时间,结果表明掺氢能缩 短燃料点火延迟时间,增加绝热火焰温度及提高火焰传播速度。进一步以天然气塔式同轴分级燃烧室为研 究对象,研究了掺氢比对燃烧室燃烧场分布及燃烧效率、总压损失系数、温度分布不均匀度、一氧化碳及氮氧 化物排放量等性能参数的影响。结果表明,随着掺氢比的增加,燃烧效率上升,总压损失系数增加,温度分布 不均匀度下降,一氧化碳排放量下降,氮氧化物排放量增加。掺氢比在35%时燃烧室发生回火。在30% ~ 35%掺氢比范围内,燃烧室性能参数变化较大。其中,总压损失系数增幅为24. 74%,温度分布不均匀度降幅 为31.11%,氮氧化物排放量增幅为416.12%。     

气膜孔位置对气冷凹腔支板冷却效果影响分析

为了解决一体化加力燃烧室中凹腔支板壁面温度过高的问题,提出了一种新的冷却结构方案,同时采用三维数值模拟方法针对不同气膜孔位置的结构模型进行计算,研究了气膜孔位置对额定工况下一体化加力燃烧室内气动热力性能的影响,重点研究了气膜孔位置对燃烧室内凹腔支板的引气率、壁面最高温度、后缘支板冷却效果等气动热力性能指标的影响。结果表明：引气率随着气膜孔位置靠后而线性增大且增长梯度逐渐减小,最大值相对于最小值增加了124.3%;后缘支板冷却效果随着气膜孔中心与来流方向所成角度α的增大不断上升,增大幅度为89.3%,冷却效果最终保持在0.35左右;随着气膜孔位置的不断后移,最高壁温不断降低且降幅不断放缓,最终最高温度保持在1 075 K左右;气膜孔不断后移的过程中,总压恢复系数不断降低。     

喷嘴布局对加力燃烧室燃烧性能的影响

为研究喷嘴布局对加力燃烧室燃烧过程及主要燃烧性能参数的影响,选择了某典型加力燃烧室,设计了两种喷嘴布局及在两个典型状态点的供油策略。方案1的喷杆数量少,喷嘴布置得更集中,内区喷杆在状态点1不工作;方案2的喷杆数量多,喷嘴布置得更分散,所有喷杆在不同状态点均工作。此外,两种方案喷嘴对应的喷射区域存在明显差别。应用FLUENT模拟不同喷油条件下,加力燃烧室在两个状态点的燃烧情况。数值模拟结果表明：方案2使加力燃烧室内燃油分布得更均匀,改善了燃烧过程,提高了不同状态点的总温。相较于方案1,方案2使加力燃烧室在状态点1的总温升增加了49 K、燃烧效率提高了0.033,在状态点2的总温升增加了64 K、燃烧效率提高了0.041。然而,方案1在两个状态点的热态总压恢复系数较方案2分别高0.004和0.003。     

当量比对涡轮叶间燃烧性能影响的数值模拟

为探究涡轮叶间燃烧性能,设计了4种不同当量比的工况,利用 FLUENT 软件的 Realizable k-ε湍流模型、PDF 燃烧模型、DO 辐射模型和离散相模型对燃烧室的流动及燃烧进行数值模拟.结果表明:燃烧室能在广泛的当量比(2.59~0.81)下保持性能稳定,燃烧效率保持在96%以上、总压损失低于2.4%,气体温度提高650,K 左右;降低当量比,能够提高燃烧效率,降低 CO、UHC、NOx 等污染物排放,改善温度分布,但会造成更大的总压损失;最优当量比等于1.00,此时燃烧效率在99.95%以上,总压损失相对低(1.5%),出口径向温度呈抛物线型分布,最适合燃烧室设计.与文献对比发现,选取的工况合理,其结果对涡轮叶间燃烧室设计具有参考价值     

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。     

微型燃气轮机富氧燃烧室数值及试验研究

研究了一种采用烟气循环富氧燃烧的微型燃气轮机燃烧室.由燃烧稳定、总压恢复系数、出口温度场等几个方面确定燃烧室基本的几何尺寸,在空气以及氧气体积分数30%的O2/CO2工况下,利用CFD软件和试验对设计燃烧室的热态流场、燃烧效率、压力损失等性能进行了对比研究.结果表明,在富氧燃烧条件下,设计的燃烧室流场合理,燃烧稳定、效率高,压力损失小,基本上达到了设计要求;在空气工况下,会出现燃烧效率低、出口温度过高、不均匀系数过高等问题.     

逆流式旋流一体化双燃料喷嘴性能研究

以某型100 kW微型燃气轮机燃烧室为研究对象,采用化学回热循环方式,选择一种可以同时燃用重整气和柴油的逆流式旋流一体化双燃料喷嘴,通过调整喷嘴结构参数对其重整气喷射部分进行分析。结果表明:喷嘴吹扫孔角度增加至60°,孔径增加至3 mm时喷嘴附近温度约降低为650 K;增加重整气通道和重整气喷射孔面积,可有效降低重整气的喷射速度;燃烧室出口温度场特性良好,总压恢复系数为98.1%,燃烧效率为99.1%。     

半封闭狭窄通道内甲烷/空气预混火焰传播不稳定性实验研究

针对贫油预混预蒸发燃烧室主燃级中横喷液雾现象进行研究,综合考虑RP-3航空煤油横喷液雾的雾化、蒸发和自燃过程构建自燃预测模型,基于CH基团随时间的变化规律对自燃延迟时间进行预测。结合试验测试结果对模型进行校验,并进一步分析温度、压力、流速、射流动量比等变量对自燃延迟时间的影响规律。结果表明：对于直射式喷嘴形成的横喷液雾,其下游的油气分布主要受射流动量比和流动速度的影响,射流动量比决定了液雾的总体油气比,流动速度则主要影响液滴的粒径及其蒸发时间;随着压力、射流动量比及气流速度的增加,自燃延迟时间均会缩短,相比于预混燃料液雾的自燃延迟时间受负温度效应的影响较弱。     

Gas entrainment in an evaporating spray jet

Gas entrainment induced by a spray jet can be significantly affected by the spray evaporation rate. In this study, we have directly measured the air entrainment induced by a liquid nitrogen spray jet into an unbounded and stagnant room air. It is realized that the air entrainment is proportional to the axial gradient of oxygen mass flow in a pure nitrogen spray jet. Hence, the air entrainment can be determined by a combined measurement of local cross-sectional distributions of oxygen concentration, gas temperature and gas velocity along the jet path. These measurements are directly obtained using an in situ oxygen concentration analyzer, a thermocouple system, and a Laser Doppler Velocimeter. In order to evaluate the effect of evaporation rate, direct measurements and numerical simulations of the air entrainment by a cold gaseous jet of nitrogen (at a temperature slightly above that of liquid nitrogen) into room air are also performed. Measurements of the entrainment rate and flow similarity of the gaseous jets without droplets compared very well against those from the single-phase jet theories and numerical simulation, which validates our experimental approach and analysis method. Our experimental results indicate rough flow similarities exist in evaporating spray jets with round nozzles. Although the air entrainment by the liquid nitrogen spray is found significantly increased, as compared to that by the cold gaseous jet of nitrogen from the same nozzle and at the same jetting velocity, the increased ratio is far less than the equivalent momentum ratio of the liquid nitrogen spray to the gas nitrogen jet. This experimental finding suggests that the evaporation of spray markedly weakens the gas entrainment. In this study, a parametric model is also developed to provide a theoretical basis of the data analysis for the cross-section averaged spray evaporation rate within the spray jet region.     

合成气自点火延迟特性分析

合成气的自点火延迟时间是预混器设计的关键参数之一,合成气富含大量的H2,因此自点火延迟时间要比常规燃料短很多,预混段过长将会导致自点火的危险。目前燃气轮机条件下的合成气自点火延迟的实验数据仍然很少,且尚未出现一种可以准确预测低温高压下合成气自点火延迟时间的化学反应机理。主要分析了温度、压力、当量比、氧含量、氢含量五大因素对自点火延迟时间的影响,并且修正了GRI3．0、Song等机理来模拟低温反应中的扰动因素影响,得到了较好的结果,同时还在Walton经验公式的基础上做了一定修改,使之与目前存在的数据更为接近。     

Autoignited laminar lifted flames of methane, ethylene, ethane, and n-butane jets in coflow air with elevated temperature

The autoignition characteristics of laminar lifted flames of methane, ethylene, ethane, and n-butane fuels have been investigated experimentally in coflow air with elevated temperature over 800 K. The lifted flames were categorized into three regimes depending on the initial temperature and fuel mole fraction: (1) non-autoignited lifted flame, (2) autoignited lifted flame with tribrachial (or triple) edge, and (3) autoignited lifted flame with mild combustion.For the non-autoignited lifted flames at relatively low temperature, the existence of lifted flame depended on the Schmidt number of fuel, such that only the fuels with Sc > 1 exhibited stationary lifted flames. The balance mechanism between the propagation speed of tribrachial flame and local flow velocity stabilized the lifted flames. At relatively high initial temperatures, either autoignited lifted flames having tribrachial edge or autoignited lifted flames with mild combustion existed regardless of the Schmidt number of fuel. The adiabatic ignition delay time played a crucial role for the stabilization of autoignited flames. Especially, heat loss during the ignition process should be accounted for, such that the characteristic convection time, defined by the autoignition height divided by jet velocity was correlated well with the square of the adiabatic ignition delay time for the critical autoignition conditions. The liftoff height was also correlated well with the square of the adiabatic ignition delay time.     

Design consideration for cross jet air mixing in municipal solid waste incinerators

In mass-burning municipal solid waste incinerators, overfire air injection plays a key role in the improvement of mixing and reaction between oxygen and incomplete combustion products and/or pollutants. However, the design parameters of overfire air nozzles are not well understood and sometimes confusing. In this paper, major design parameters concerning cross jet air nozzles are discussed along with flow simulation results for simplified furnace geometry. The overall performance of jet air mixing and the effects of design parameters are quantitatively evaluated. The flow simulation results are interpreted in terms of the penetration depth of the jet into the main flow, the size of the recirculation zone and the ratio of the unmixed portion of the gas flow. The momentum flux ratio J of the jet to the cross flow strongly affects the penetration depth of the jet and the mixing of two flow streams. As the inter-nozzle distance S (in non-dimensional form) decreases, the penetration depth decreases but the size of the recirculation zone increases and the resultant mixing deteriorates. The degree of mixing of the jet with the cross gas stream is evaluated in terms of the mass-averaged probability distribution of the relative concentration. Fresh air disperses more efficiently into the gas stream as J and S increase. The momentum flux ratio and the inter-nozzle distance are considered as important design parameters, and optimum values of these variables can be chosen for the given furnace conditions. This numerical evaluation also provides a basis for similarity considerations in cold flow model tests and the validity of the two-dimensional idealization. © 1997 by John Wiley & Sons, Ltd.     

Autoignited laminar lifted flames of methane/hydrogen mixtures in heated coflow air

Autoignited lifted flame behavior in laminar jets of methane/hydrogen mixture fuels has been investigated experimentally in heated coflow air. Three regimes of autoignited lifted flames were identified depending on initial temperature and hydrogen to methane ratio. At relatively high initial temperature, addition of a small amount of hydrogen to methane improved ignition appreciably such that the liftoff height decreased significantly. In this hydrogen-assisted autoignition regime, the liftoff height increased with jet velocity, and the characteristic flow time – defined as the ratio of liftoff height to jet velocity – correlated well with the square of the adiabatic ignition delay time. At lower temperature, the autoignited lifted flame demonstrated a unique feature in that the liftoff height decreased with increasing jet velocity. Such behavior has never been observed in lifted laminar and turbulent jet flames. A transition regime existed between these two regimes at intermediate temperature.     

Numerical analysis of the influence of two-phase flow mass and heat transfer on n-heptane autoignition

This paper investigates the influence of liquid fuel presence on the autoignition of n-heptane/air mixtures over a wide range of conditions encountered in internal combustion engines. To this end, evaporating droplet physics and skeletal chemistry mechanisms are simultaneously solved considering a homogeneous constant-pressure reactor. A skeletal mechanism is introduced to account for specific kinetics behavior in the Negative Temperature Coefficient (NTC) region. The impact of mass and heat source terms during evaporation is emphasized by comparing a two-phase flow scenario with a purely gaseous case. The competition between fuel vapor availability and the evaporation-induced gas temperature decrease is specific to two-phase flow autoignition. On the one hand, droplet evaporation delay restricts the gaseous local fuel/air equivalence ratio and consequently the kinetics runaway. On the other hand, temperature reduction due to evaporation may either reduce or enhance chemical reactivity, depending on the local thermodynamic conditions lying either inside or outside the NTC region. By simultaneously accounting for evaporation source terms and skeletal chemistry, we can reproduce the already experimentally observed transformation of the NTC region into a Zero Temperature Coefficient (ZTC) region depending on thermodynamic conditions and droplet size. The ZTC phenomenon appears when combustion heat-release starts before complete droplet evaporation. Since the ZTC behavior can be captured using the point source approach, in which droplets are considered only as zero-dimensional source terms of mass and energy, the present results pave the way for future exploration of NTC chemistry in sprays with a direct numerical simulation of discrete particles considering detailed chemistry and turbulent flows.     

Autoignited laminar lifted flames of propane in coflow jets with tribrachial edge and mild combustion

Characteristics of laminar lifted flames have been investigated experimentally by varying the initial temperature of coflow air over 800 K in the non-premixed jets of propane diluted with nitrogen. The result showed that the lifted flame with the initial temperature below 860 K maintained the typical tribrachial structure at the leading edge, which was stabilized by the balance mechanism between the propagation speed of tribrachial flame and the local flow velocity. For the temperature above 860 K, the flame was autoignited without having any external ignition source. The autoignited lifted flames were categorized in two regimes. In the case with tribrachial edge structure, the liftoff height increased nonlinearly with jet velocity. Especially, for the critical condition near blowout, the lifted flame showed a repetitive behavior of extinction and reignition. In such a case, the autoignition was controlled by the non-adiabatic ignition delay time considering heat loss such that the autoignition height was correlated with the square of the adiabatic ignition delay time. In the case with mild combustion regime at excessively diluted conditions, the liftoff height increased linearly with jet velocity and was correlated well with the square of the adiabatic ignition delay time.     

Effects of turbulence and carrier fluid on simple, turbulent spray jet flames

This paper presents simultaneous LIF images of OH and the two-phase acetone fuel concentration as well as detailed single-point phase-Doppler measurements of velocity and droplet flux in three turbulent spray flames of acetone. This work forms part of a larger program to study spray jets and flames in a simple, well-defined geometry, aimed at providing a platform for developing and validating predictive tools for such flows. Spray flames that use nitrogen or air as droplet carrier are investigated and issues of flow field, droplet dispersion, size distribution, and evaporation are addressed. The joint OH/acetone concentration images reveal a substantial similarity to premixed flame behavior when the carrier stream is air. When the carrier is nitrogen, the reaction zone has a diffusion flame structure. There is no indication of individual droplet burning. The results show that evaporation occurs close to the jet centerline rather than in the outer shear layer. Turbulence does not have a significant impact on the evaporation rates. A small fraction of the droplets escapes the reaction zone unburned along the centerline and persists far downstream of the flame tip. The proportion of this droplet residue increases with shorter residence times as observed for the higher velocity flame.     

Investigation of reverse flow distributed combustion for gas turbine application

In this paper reverse flow modes of colorless distributed combustion (CDC) have been investigated for application to gas turbine combustors. Rapid mixing between the injected fuel and hot oxidizer has been carefully explored for spontaneous ignition of the mixture to achieve distributed combustion reactions. Distributed reactions can be achieved in premixed, partially premixed or non-premixed modes of combustor operation with sufficient entrainment of burned gases and faster turbulent mixing between the reactants. In the present investigation reverse flow modes consisting of three configurations at thermal intensity of 28 MW/m³-atm and five configurations at thermal intensity of 57 MW/m³-atm have been investigated and these high thermal loadings represent characteristic gas turbine combustion conditions. In all the configurations the air injection port is positioned at the combustor exit end, whereas the location of fuel injection ports is changed to give different configurations. The results are presented on the exhaust emissions and radical emissions using experiments, and evaluation of flowfield using numerical simulations. Ultra-low NO_x emissions were found for both the premixed and non-premixed combustion modes investigated here. Cross-flow configuration, wherein the fuel is injected at high velocity cross stream to the air jet resulted in characteristics closest to premixed combustion mode. Change in fuel injection location resulted in changing the combustion characteristics from closer to diffusion mode to distributed regime. This feature is beneficial for part load operation where higher stability limit is desirable.