Ignition and Lean Blowout Characteristics of a Reverse-Flow Combustor for an Ultra-Compact Gas Turbine Engine

The flame stability limit and propagation characteristics of a reverse-flow combustor without any flame-stabilized device were experimentally investigated under room temperature and pressure.The results indicate that it is feasible to stabilize the flame in the recirculation zones constructed by the impact jet flow from the primary holes and dilution holes.The flame projected area is mainly distributed in the recirculation zone upstream of the primary holes,whose presence and absence mark the ignition and extinction.During the ignition process,the growth rate and value of the flame projected area first increase and then decrease with the inlet velocity increasing from 9.4 m/s to 42.1 m/s.A rapid reduction followed by a slow reduction of ignition and lean blowout equivalence ratios is achieved by the increased inlet velocity.Then the non-reacting fluid structure in three sections was measured,and detailed velocity profiles were analyzed to improve the understanding of the flame stabilization mechanism.The results are conducive to the design of an ultra-compact combustor.

An LSTM-based approach to detect transition to lean blowout in swirl-stabilized dump combustion systems

Lean combustion is environment friendly with low NO_(x)emissions providing better fuel efficiency in a combustion system.However,approaching towards lean combustion can make engines more susceptible to an undesirable phenomenon called lean blowout(LBO)that can cause flame extinction leading to sudden loss of power.During the design stage,it is quite challenging for the scientists to accurately determine the optimal operating limits to avoid sudden LBO occurrences.Therefore,it is crucial to develop accurate and computationally tractable frameworks for online LBO prediction in low NO_(x)emission engines.To the best of our knowledge,for the first time,we propose a deep learning approach to detect the transition to LBO in combustion systems.In this work,we utilize a laboratory-scale swirl-stabilized combustor to collect acoustic data for different protocols.For each protocol,starting far from LBO,we gradually move towards the LBO regime,capturing a quasi-static time series dataset at different conditions.Using one of the protocols in our dataset as the reference protocol,we find a transition state metric for our trained deep learning model to detect the imminent LBO in other test protocols.We find that our proposed approach is more precise and computationally faster than other baseline models to detect the transition to LBO.Therefore,we endorse this technique for monitoring the operation of lean combustion engines in real time.

An FV-EE model to predict lean blowout limits for gas turbine combustors with different structures and sprays

The occurrence of Lean Blowout(LBO)is a disadvantage that endangers a stable operation of gas turbines.A determination of LBO limits is essential in the design of gas turbine combustors.A semiempirical model is one of the most widely used methods to predict LBO limits.Among the existing semiempirical models for predicting LBO limits,Lefebvre’s LBO model and the Flame Volume(FV)model are particularly suitable for gas turbine combustors.On the basis of Lefebvre’s and FV models,the concept of effective evaporation efficiency is introduced in this paper,and a Flame Volume-Evaporation Efficiency(FV-EE)model is derived and validated.LBO experiments are carried out in a model combustor with 23 different structures and 10 different sprays.The prediction uncertainty of the FV-EE model is less than±13%for all of these 33 structures and sprays,compared with±50%for the FV model and±60%for Lefebvre’s model.Furthermore,the prediction uncertainty of the FV-EE model is also less than±13%for other combustors from available literature.

Analysis on Lean Blowout of Swirl Cup Combustor at Atmospheric Pressure Condition

The experimental data of lean blowout fuel/air ratio of a rectangular swirl cup combustor with different inlet temperatures was obtained at atmospheric pressure condition.Numerical simulations both burning and non-burning were performed corresponding to the experimental data at lean blowout.Results indicated that the size of the recirculation region in the primary zone was obviously smaller when burning than non-burning,but the locations of the cores of their recirculation regions were almost the same.The increase of inlet air temperature didn't mean the rise of the temperature of recirculation region core.The location of the maximum temperature in the primary zone was not the same as that one of the core temperature of the recirculation region.Further more,the reasons were analyzed how the lean blowout fuel/air ratio changed with the inlet temperature increasing under the actions of factors both positive and negative to combustion,and this would be helpful to deepen the understanding of the lean blowout process of swirl cup combustor.

Hybrid method based on flame volume concept for lean blowout limits prediction of aero engine combustors

The Lean Blowout(LBO)limit is crucial for the aircraft engines.The semi-empirical(such as Lefebvre’s LBO model and Flame Volume(FV)model),numerical and hybrid methods are widely utilized for the LBO limit quick prediction.An innovative hybrid method based on the FV concept is proposed.This method can be classified as a semi-empirical/physical based hybrid prediction method.In this hybrid method,it is assumed that the flame volume varies nearly linearly with the fuel/air ratio near the LBO.The flame volume is obtained directly by the numerical simulation using the threshold value of the visible flame boundary as 900 K.Then the final LBO limits is determined by the FV model.On the premise of keeping the good generality of prediction,the hybrid method based on the FV concept can further improve the prediction accuracy.The comparison with the prediction of the existing available methods on fifteen combustors shows that the hybrid method based on the FV concept achieves better prediction accuracy.The prediction uncertainties between the experimental results and the predicted values by the hybrid method based on the FV concept are within about±10%.

A Study on Lean Blowout of Multi-vortexes-dome Model Combustor

The lean blowout experiments of the combustion stability device A (multi-vortexes-dome model combustor) have been carried out at atmospheric pressure. Compared with the device B (single-vortex-dome model combustor), the experimental results show that the device A has a superior lean blowout performance when the combustor reference velocity is within the range from 3.50m/s to 5.59m/s ( while the liner reference velocity is between 3.84 and 6.13m/s), and this superiority will remain stable after the inlet air flow rate reaches a certain value. In order to analyze the phenomena and experimental results, the numerical simulation method is used, and the strain rate and the cold reflux impact are employed to further explain the reason that causes the difference between the two devices' lean blowout characteristics.

Study on the Effects of Dome Fuel Distribution Ratio on Lean Blowout of a Model Combustor

The experimental studies and numerical simulation were conducted on the effects of the dome fuel distribution ratio on the lean blowout of a model combustor.The experimental results indicate that as the key parameter,the dome fuel distribution ratio,increases from 2.06%to 16.67%,the lean blowout equivalence ratio declines obviously at the beginning,and then the decrease slows down,in addition,the amplitude of the pressure fluctuation in the combustor reduces significantly while the dominant frequency keeps basically constant.In order to analyze the experimental results,the numerical simulation is adopted.The temperature and local equivalence ratio distributions are employed to explain the reason why the lean blowout performance improves with the increase of the dome fuel distribution ratio.

A data-driven approach using machine learning for early detection of the lean blowout

A data-driven approach using machine learning is presented for the identification of the critical flame location for the early detection of an incipient lean blowout(LBO)in a realistic gas turbine engine combustor under engine-relevant conditions.This method is demonstrated by utilizing the temperature(T)and the hydroxyl radical mass fraction(YOH)data from high fidelity large eddy simulations(LES)of Jet-A combustion.The fuel flow rate is progressively reduced in numerical simulations with a fixed airflow rate to mimic experimental studies of LBO in the gas turbine combustor.These simulations are the first of their kind for a fully resolved realistic combustor geometry with adaptive mesh refinement and have accurately captured the dynamics of the LBO process and global lean blowout equivalence ratio.Time-series of T and YOH are extracted in the primary zone of the combustor,from stable flame condition to LBO condition,to train the machine learning model.A Support Vector Machine(SVM)model with radial basis function is successfully developed to identify the critical flame location for early detection of incipient LBO condition in a practical combustor for the first time.The performance of the SVM model is quantified using the F-score,and the critical flame location corresponds to the maximum value of the F-score.The critical flame location is found to be in the flame root region and is effective in the early detection of incipient LBO.The conventional statistical measures are compared with the results of the trained machine learning model to assess the feasibility of the latter for online flame health monitoring.The machine learning model successfully prognosticated the LBO approximately 20 ms before the event,and this study has shown significant promise for the use of the SVM model in engine prognostics and health management.

基于Damköhler数的支板稳定器贫油熄火分析方法研究

稳定器的贫油熄火边界预测对于燃烧室的设计具有重要意义。本文开展了支板稳定器的贫油熄火试验,得到了来流温度473~623 K,空气流速在60~130 m/s下的贫油熄火边界。通过数值模拟得到燃烧室的反应场和流场分布,分析了近熄火和稳定燃烧工况时Damköhler数的分布特性。结果表明,流动时间尺度在不同燃油流量下变化不大,化学时间尺度随燃油流量的降低而增大,在近熄火时,Damköhler数大于1的区域为两条明显的带状分布,仅在剪切层保持较高水平,回流区难以加热剪切层的新鲜混气,导致最终熄火;基于CO质量分数确定的关键反应区与实际火焰具有较好的一致性。不同熄火工况下反应区内的平均Damköhler数在1左右波动,最大误差22%,证明基于Damköhler数的贫油熄火分析方法能够揭示贫熄特征,为解决实际熄火预测提供基础。

等离子体拓展氨/空气预混旋流火焰贫燃极限

为探究等离子体对氨-空气预混旋流火焰贫燃极限及燃烧效率的影响规律,将等离子体等效为热源,结合计算流体力学(CFD)燃烧模拟手段分析不同当量比及等离子体放电位置下氨的燃烧特性.结果发现,布置等离子体等效热源后,氨-空气贫燃极限从0.82降至0.78以下,但同时伴随燃烧效率的下降.其原因主要在于等离子体放电输入热量可维持局部高温来防止火焰吹熄并提高局部火焰传播速度.然而,随当量比下降等离子体作用范围减小,导致部分氨逃逸进而引起燃烧不充分及燃烧效率下降.

火焰筒头部结构对燃烧特性影响研究

火焰筒头部结构是影响预混燃烧的关键参数,试验研究了扩张角55°(渐扩)、90°(突扩)火焰筒分别匹配旋流数0.45、0.65旋流器对燃烧性能的影响。结果表明:突扩火焰筒较渐扩具有更低的贫油熄火极限,且无论突扩还是渐扩火焰筒,均匹配较大旋流数(S_(N)=0.65)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0.1313~0.1392;渐扩火焰筒对旋流器适应性差,匹配较小旋流数(S_(N)=0.45)温度场均匀性更好,出口温度分布系数为0.1335;突扩火焰筒在NOx排放上具有优势,且匹配小旋流数更佳;渐扩火焰筒在CO、UHC排放上具有优势,且匹配大旋流数更佳。

燃油周向分级对贫油熄火油气比的影响

为降低贫油熄火油气比,对双头部燃烧室进行了燃油周向分级贫油熄火模拟实验研究。实验考虑了进气速度、进气温度对贫油熄火油气比的影响。采用了三种不同长度的隔板来研究减少两个头部之间相互影响。试验结果表明:与不分级燃烧相比,燃油周向分级燃烧能够显著降低贫油熄火油气比。当燃烧室进气温度低于400K,贫油熄火油气比随燃烧室进气空气流速的上升而明显下降,当进气温度大于400K,贫油熄火油气比对燃烧室进气温度和速度不敏感;采取加在头部之间插入隔板的措施来降低燃烧室贫油熄火比,效果并不显著。

旋流杯燃烧室头部流场与喷雾对贫油熄火的影响

对两种不同的燃烧室头部(三旋流杯头部为A型、双旋流杯头部为B型)进行了研究。对有两种头部的燃烧室进行了冷态流场的数值模拟,用粒子动态分析仪(PDA)测量了两种头部的速度场和喷雾场,结合慢车工况的贫油熄火试验结果进行了分析。结果表明:A型头部喷雾的索太尔平均直径(SMD)和均匀度能满足燃烧室的性能要求,比B型头部的要好,但其贫熄特性不理想。而B型头部的贫熄特性好于A型;A型头部的内旋流器气流流通量应减小一些,以利于喷嘴端部低压区的形成,这样有可能进一步降低贫油熄火油气比。

气量分配对双轴向旋流器燃烧室贫熄性能影响

针对采用双轴向旋流杯结构的某单头部矩形燃烧室,实验研究了头部进气面积及主燃孔布局对燃烧室贫熄特性的影响.实验结果表明:一、二级旋流器进气面积的变化对燃烧室贫油熄火性能有很大影响.一级进气面积增加20%可拓宽贫熄边界11.8%;二级进气面积增加20%可拓宽贫熄边界16.6%.相反,减小一、二级旋流器进气面积都使燃烧室的贫熄性能变差.此外,主燃孔布局的变化对燃烧室贫熄边界几乎没有影响.

采用离心喷嘴的单凹腔驻涡燃烧室点火与贫熄特性

为了研究单凹腔驻涡燃烧室的点火和贫油熄火特性，设计了一个带扩压器和内外机匣的单凹腔驻涡燃烧室矩形试验件，采用试验研究和半经验分析相结合的方法对其点火和贫油熄火进行了研究。试验在常压状态下进行，采用RP3航空煤油作为燃料，所用供油喷嘴为空心锥离心喷嘴，试验中的进口空气温度在287-487K变化，进口空气流量在0.2109-0.4219kg/s变化，对应进口马赫数从0.15变化到0.31。结果表明：单凹腔驻涡燃烧室的点火和贫油熄火油气比均随着燃烧室进口温度和进口流量的增加而减小，单凹腔驻涡燃烧室的点火油气比比贫油熄火油气比约大50%。经过半经验分析，得到了影响单凹腔点火和熄火的综合参数A，该参数能够较好地解释和评价各种因素对贫油熄火的影响。

航空发动机主燃烧室稳定工作范围研究

应用火焰传播理论、二维两相紊流燃烧的k-ε模型、EBU-Arrhen ius模型、颗粒群轨道模型和AD INA软件,计算出了某型在研航空发动机在不同飞行状态下的主燃烧室贫油熄火时的流场、温度场和压力场;计算值与试验结果比较吻合,证实了数值模拟的合理性和可行性。

旋流数对不含氢气的低热值燃气预混熄火特性的影响

设计了具有不同旋流数（0.6-1.2）的多个旋流器,针对以CO为主要成分且不含H2的低热值燃气（4.89-11.33,MJ/m3）进行实验,研究旋流对其预混燃烧熄火特性的影响.在实验参数范围内发现,热值越低的燃料,熄火时对应的旋流数越小;随着旋流数变化,熄火时火焰形状差异显著;N2对低热值燃料预混燃烧稳定性的负面作用比CO2更明显;通过实验得到能以预混燃烧方式稳燃低热值燃气（热值为4.89-5.28,MJ/m3且以CO为主要可燃成分）的旋流器结构和相关参数.

自稳火双旋流杯在非受限空间内的燃烧特性

采用试验方法研究了一种适用于切向驻涡燃烧室的自稳火双旋流杯在非受限空间内的燃烧特性.自稳火双旋流杯的方案特点是采用两级径向旋流器,燃油从中心离心喷嘴喷出,根据旋流器旋流强度和气量分配形成不同布局形式.在常温常压条件下,以RP-3航空煤油为燃料,测量了三种结构的自稳火双旋流杯火焰特性以及贫油熄火油气比,结果表明:随着内旋流器气量减少和旋流数增加,火焰稳定性将有所增强,但火焰长度及总体形状没有变化.

亚燃冲压模型燃烧室高空负压试验

为了验证亚燃冲压燃烧室在高空负压条件下稳定工作的能力,设计了带蒸发式值班火焰稳定器与直射式喷油装置的亚燃冲压模型燃烧室,对该模型燃烧室进行了冷态流阻试验、贫油熄火边界试验以及不同截面燃烧效率试验研究。研究结果表明,试验件的冷态流阻系数略大于1,冷态总压恢复系数0.98以上;蒸发式火焰稳定器贫油熄火边界较宽;两截面燃烧效率最低相差6%,最高相差19%,在高空负压条件下,增加燃烧段长度能显著提高燃烧效率。

基于特征参数准则的舰船燃机燃烧室贫熄预测

贫油熄火极限是衡量舰船燃气轮机燃烧室性能的重要参数之一,针对贫油熄火极限的数值预测,提出并详细阐述了特征参数准则的核心原理和预测流程,并使用计算流体力学(CFD)软件FLUENT数值模拟分析了某环形燃烧室和某环管型燃烧室的贫油熄火过程,得到了主燃孔及旋流器流量分配和油滴平均直径对燃气轮机贫油熄火极限的影响规律,并与实验值进行了对比。结果表明:使用特征参数准则所得计算值与实验数据误差较小,适用于指导工程实践。