自激振荡预混燃烧的实验

通过动态压力测量、化学自发荧光相同步测量的方法对自激振荡燃烧动力学过程进行了实验研究,分析了不同空气流量、化学当量比和边界条件对振荡燃烧过程的影响.实验结果显示,燃烧热负荷的提高会导致燃烧段压力脉动幅值的提高,使燃烧更加不稳定.化学当量比越接近熄火极限,压力脉动的频率越高.同时燃烧室进出口边界条件的改变也会对振荡频率产生影响.     

响应函数虚部对振荡燃烧的影响

本文用一实例简洁、通俗地分析了推进剂响应函数的虚部对火箭发动机振荡燃烧频率的影响.这种影响是计算频率与实际测得频率有偏差的主要因素.     

热声耦合振荡燃烧的实验研究与分析

热声耦合振荡是在推进系统工作中经常遇到的危害系统工作及安全的现象。它是由非稳定燃烧放热和压力脉动互相耦合产生的系统振荡过程。通过对天然气预混燃烧过程中的热声耦合振荡现象进行了实验研究,分析了不同当量比、热负荷和进出口边界条件下天然气燃烧的动态过程,分析其稳定范围及振荡模态随影响因素的变化规律。结果显示振荡频率随着当量比的减小有所增加,但是没有发生模态变化。在常压条件、接近贫燃熄火极限时,热声耦合振荡现象消失,压力脉动频率跃升至500 Hz或1000 Hz附近的高频。燃烧室出口越接近阻塞条件,燃烧过程的稳定范围越小。同时入口边界位置越接近燃烧段,压力脉动频率越高。热功率变化也会对脉动频率和声压级数值产生影响。另外还采用线性扰动分析方法对天然气燃烧动态过程进行理论分析,进一步研究了不同条件下旋流预混燃烧的热声耦合振荡模态。     

射频感性耦合等离子体中的受迫振荡研究

实验研究了匹配状态、放电气压对氩气射频感性耦合等离子体中受迫振荡的影响.结果表明:受迫振荡总是出现在放电的正反馈区;在高气压下(>30Pa)受迫振荡的频率较低.对于使用射频感性耦合等离子体进行薄膜沉积的参数选择给予了理论指导.     

Culick的线性声振荡燃烧理论研究

本文对F·E·C·Culick的线性声振荡燃烧理论进行了概括。对其特点和理论价值进行了评述,井提出了自己的看法。     

低频振荡燃烧研究综述

总结了影响涡扇发动机加力燃烧室和冲压发动机燃烧室的结构及运转因素，综述了有关振荡燃烧机理研究的一些结果以及几项很有意义的主动控制技术。结论是，目前国内外所进行的低频振荡燃烧的机理、预测及控制工作，尚处于探索阶段。     

基于全连接神经网络的分层旋流火焰燃烧振荡预报

为了指导主动控制系统抑制燃烧振荡,有必要针对不同的燃烧振荡预报手段开展研究和验证.以甲烷预混同心分层旋流火焰的时均图像为基础,采用降低图像分辨率和提取火焰结构特征参数这两种不同的方式对火焰图像信息进行简化处理,并使用全连接神经网络对燃烧振荡进行预报研究.结果发现,两种方式都可以较为准确地预报燃烧振荡,精度均达到90％以...     

隔离段内正激波串受迫振荡特性研究

为了解隔离段在真实燃烧室反压作用下的工作特性,通过数值方法模拟燃烧室振荡燃烧引起的脉动反压,在来流Mai=2条件下,探讨了脉动反压引起的激波串受迫振荡特性。结果表明,在反压脉动条件下,激波串前缘位置周期振荡,其振荡频率与反压脉动频率一致,振幅与反压脉动频率负相关,反压脉动频率600Hz时,振幅仅为管道长2.97%;就抗反压能力而言,在反压脉动条件下,隔离段能承受比定常状态更大的反压峰值,且脉动频率越大,可承受瞬态反压峰值越大。激波串的受迫振荡包含两种形式:激波串整体位置的前后运动和激波节之间的相对运动。在一定程度内,反压脉动频率较低时(50Hz,100Hz),激波串整体位置的前后运动是主要的受迫振荡形式,激波节之间的相对运动很弱;随反压脉动频率升高(300Hz,600Hz),激波节之间的相对运动加剧,逐渐成为激波串受迫振荡的主要形式。另外,在激波串振荡过程中,激波串往上下游运动经过同一位置时,激波串形态会出现迟滞,这是导致总压恢复系数迟滞的原因。     

不同直径圆球诱导燃烧的振荡机制与频率特性

为了分析不同直径圆球诱导振荡燃烧的规律,并揭示圆球大小在振荡燃烧现象中所发挥的深层次作用,采用二维轴对称Euler方程和基元反应模型,对不同直径的圆球在H2/air预混气体中诱导振荡燃烧的现象开展数值模拟研究.研究发现,振荡频率并不是简单地随直径增大而逐渐从高频向低频连续过渡,而是存在两次突变,形成了超高频、高频以及低...     

过渡型凹腔超声速燃烧流动振荡抑制方法

针对长深比为10.0的过渡型凹腔在隔离段入口马赫数为3.0条件下存在的冷流自激振荡现象,提出了一种凹腔内增加肋条抑制振荡的方案。通过试验和数值计算,对该方案抑制振荡的效果进行了检验,并分析了肋条增加前后燃烧室流场结构和燃烧性能的差别。研究发现：通过在凹腔内增加肋条能够消除过渡型凹腔冷流工况下存在的175.8 Hz的自激振荡,燃烧流场也更加稳定;增加肋条后凹腔的稳焰能力有所降低,部分在凹腔未完全燃烧的煤油进入扩张段后继续发生反应,从而使燃烧区向下游延伸、增大,发动机的燃烧效率和净推力分别降低5.4%和8.9%,但推力更加平稳;燃烧室一维平均热流密度峰值由2.9 MW/m²降低至1.8 MW/m²,燃烧室的热环境大幅改善。     

挂滴燃烧中的微汽泡行为和液滴跳动

利用高速显微摄像技术,观察研究了RP-3微尺度挂滴燃烧过程中,微汽泡的核化、生长、聚并和溢出的行为过程及液滴跳动现象.结果得出:①液滴中微汽泡产生的位置;②在蒸发初期时由微汽泡引起液滴体积的膨胀;③在燃烧中由汽泡行为导致液滴的跳动;④液滴燃烧的稳定(不爆裂)现象.分析了表面张力在挂滴燃烧过程中的作用,确定了挂滴稳定燃烧的临界条件下的临界特征体积在2.5~5.0μL.      

Experimental study of rotating gliding arc discharge plasma-assisted combustion in an aero-engine combustion chamber

The combustion chamber is the core component of an aero-engine, and affects its reliability and security operation, even the performance of the aircraft. In this work, a Plasma-Assisted Combustion(PAC) test platform was developed to validate the feasibility of using PAC actuators to enhance annular combustor performance. Two plans of PAC(rotating gliding arc discharge plasma) were designed, Assisted Combustion from Primary Holes(ACPH) and Assisted Combustion from Dilution Holes(ACDH). Comparative experiments and analysis between conventional combustion and PAC were conducted to study the effects of ACPH and ACDH on the performances including average outlet temperature, combustion efficiency, pattern factor under four different excessive air coefficients(0.8, 1, 2, and 4), and lean blowout performance at different inlet airflow velocities. Experimental results show that the combustion efficiency is improved after PAC compared with that in normal conditions, and the combustion efficiency of ACPH increases2.45%, 1.49%, 1.04%, and 0.47%, while it increases 2.75%, 1.67%, 1.36%, and 0.36% under ACDH conditions. The uniformity of the outlet temperature field and the lean blowout performance are improved after PAC. Especially for ACPH, the widening of the lean blowout limit is8.3%, 12.4%, 12.8%, and 25% respectively when the inlet velocity ranges from 60 m/s to120 m/s. These results offer new perspectives for using PAC devices to enhance aero-engine combustors' performances.     

带圆筒头部火焰筒两相燃烧流场及性能计算

在三维任意曲线坐标系下采用代数雷诺应力紊流模型模拟紊流粘性,Arrhen inus-EBU紊流模型模拟燃烧室内化学反应速率,采用随机轨道模型模拟气液两相之间的相互作用,数值分析不同进口气流参数对带双圆筒头部环形燃烧室两相紊流燃烧流场的影响,同时采用多维经验分析法预估燃烧室性能。通过两种工况计算表明:在最大工况下所得的燃烧流场和燃烧室性能均优于慢车工况。计算结果与试验数据符合较好,表明燃烧过程的数值模拟以及多维经验分析法可为燃烧室优化设计提供有用的设计依据,适合于工程应用。     

Experimental study on combustion characteristics of Chinese RP-3 kerosene

In order to illustrate the combustion characteristics of RP-3 kerosene which is widely used in Chinese aero-engines, the combustion characteristics of RP-3 kerosene were experimentally investigated in a constant volume combustion chamber. The experiments were performed at four different pressures of 0.1 MPa, 0.3 MPa, 0.5 MPa and 0.7 MPa, and three different temperatures of 390 K,420 K and 450 K, and over the equivalence ratio range of 0.6–1.6. Furthermore, the laminar combustion speeds of a surrogate fuel for RP-3 kerosene were simulated under certain conditions. The results show that increasing the initial temperature or decreasing the initial pressure causes an increase in the laminar combustion speed of RP-3 kerosene. With the equivalence ratio increasing from 0.6 to 1.6, the laminar combustion speed increases initially and then decreases gradually.The highest laminar combustion speed is measured under fuel rich condition(the equivalence ratio is 1.2). At the same time, the Markstein length shows the same changing trend as the laminar combustion speed with modification of the initial pressure. Increasing the initial pressure will increase the instability of the flame front, which is established by decreased Markstein length. However, different from the effects of the initial temperature and equivalence ratio on the laminar combustion speed,increasing the equivalence ratio will lead to a decrease in the Markstein length and the stability of the flame front, and the effect of the initial temperature on the Markstein length is unclear. Furthermore, the simulated laminar combustion speeds of the surrogate fuel agree with the corresponding experimental datas of RP-3 kerosene within 10% deviation under certain conditions.     

Large-eddy simulation and linear acoustic modeling of entropy mode oscillations in a model combustor with coolant injection

Lean-burn combustor is particularly susceptible to combustion instability and the unsteady heat release is usually considered as the excitation of the self-maintained thermo-acoustic oscillations. The transverse coolant injection is widely used to reduce the temperature of burnt gas, but on the other hand, it will introduce temperature fluctuation inside the combustor. Therefore, it is necessary to consider the influence of the coolant injection on combustion instability, and evaluate its dynamic feature. In this paper, Large-Eddy Simulation (LES) of the self-excited pressure oscillations in a model combustor with coolant injection is carried out. The analysis of transient flow characteristics and the identification of the pressure modes confirm that one of the low frequency pressure oscillations is related to entropy fluctuations, which is known as rumble combustion instability. The LES results show that transient coolant injection is another excitation of temperature fluctuation other than unsteady combustion. The amplitude of the entropy mode oscillation increases with increasing coolant air mass whereas the change of its frequency is insignificant. According to the major feature of entropy wave oscillation caused by coolant injection, a compact coolant injection model is proposed and applied in the One Dimensional (1D) Acoustic Network Method (ANM). Key correlations used in the model match well with LES data in low frequency range. This means that the coolant injection model is a complex one reflecting the interaction of the fluctuating coolant mass, pressure and temperature. Finally, the combustion instability frequencies and modes predicted by acoustic network method are also in good agreement with LES results.     

固体火箭冲压发动机燃烧性能评价方法

通过对固体火箭冲压发动机的工作特点分析,提出了适用于评价固体火箭冲压发动机燃烧性能的方法。对气动法、燃气分析法、台架推力法等燃烧性能评价方法进行了分析,并对其优缺点进行了说明。     

液氧/甲烷火焰和燃烧不稳定性试验

为了解液氧/甲烷火焰在外界扰动作用下的表现,增进对燃烧不稳定性的理解,分别对两种喷剪切同轴式喷嘴结构进行了试验,试验采用单喷嘴矩形模型燃烧室,液氧以液态从中心喷嘴喷注,甲烷以气态从同轴的环形腔喷注。试验中,压力调节装置上的齿轮间断性地堵住和打开安装在燃烧室底部和主喷管旁边的辅助喷管出口,分别向燃烧室输入高频扰动。采用高速照相机记录火焰的OH辐射量,并采用阴影和纹影技术记录液氧的喷雾过程。试验成功激发起了燃烧室一阶横向和一阶纵向振型,在高频扰动作用下,还产生了两次强低频振荡。讨论了分离火焰的特征及其液氧射流在外界扰动作用下的表现和影响参数。     

固体火箭冲压发动机补燃室燃烧过程显示

采用二维开窗式固体火箭冲压发动机试验系统,对补燃室内的燃烧现象进行观察,以火焰图像的形式直观形象地描述了进气道位置对补燃室内燃烧过程的影响,试验所采用的装药为含硼贫氧推进剂。并通过高速数字摄影仪摄取补燃室内部某个时刻瞬时火焰图像,借助于光学理论和计算机图像处理技术计算出整个补燃室内部的温度分布。     

超声速燃烧凹槽火焰稳定的研究动态

高超声速气流在燃烧室的停留时间非常短，使得超燃冲压发动机燃烧室内燃料与气流的混合及其燃烧变得非常困难。目前集燃料喷射、混合及火焰稳定为一体的凹槽有望改进这一情况而受到了普遍关注。介绍了超声速气流流过凹槽的自激振荡及其控制、停留时间和阻力等特性，总结、分析了近几年凹槽在超声速气流中增强混合及燃烧的实验与数值研究，指出了在把凹槽用于提高超燃冲压发动机性能方面存在的问题和进一步研究的方向。     

Influence of thermal inhibitor position and temperature on vortex-shedding-driven pressure oscillations

Vortex-acoustic coupling is one of the most important potential sources of combustion instability in solid rocket motors (SRMs). Based on the Von Karman Institute for Fluid Dynamics (VKI) experimental motor, the influence of the thermal inhibitor position and temperature on vortex-shedding-driven pressure oscillations is numerically studied via the large eddy simulation (LES) method. The simulation results demonstrate that vortex shedding is a periodic process and its accurate frequency can be numerically obtained. Acoustic modes could be easily excited by vortex shedding. The vortex shedding frequency and second acoustic frequency dominate the pressure oscillation characteristics in the chamber. Thermal inhibitor position and gas temperature have little effect on vortex shedding frequency, but have great impact on pressure oscillation amplitude. Pressure amplitude is much higher when the thermal inhibitor locates at the acoustic velocity anti-nodes. The farther the thermal inhibitor is to the nozzle head, the more vortex energy would be dissipated by the turbulence. Therefore, the vortex shedding amplitude at the second acoustic velocity antinode near 3/4L (L is chamber length) is larger than those of others. Besides, the natural acoustic frequencies increase with the gas temperature. As the vortex shedding frequency departs from the natural acoustic frequency, the vortex-acoustic feedback loop is decoupled. Consequently, both the vortex shedding and acoustic amplitudes decrease rapidly.