Experimental and LES investigation of flame propagation in a hydrogen/air mixture in a combustion vessel

This work presents an experimental and numerical investigation of premixed flame propagation in a hydrogen/air mixture in a closed combustion vessel. In the experiment, high-speed schlieren video photography and pressure sensor are used to examine the flame dynamics and pressure transient. In the numerical study, a large eddy simulation （LES） based on a RNG sub-grid approach and a LES combustion model is applied to reproduce experi- mental observations. The effects of four physical phenomena on the burning velocity are considered in the combustion model, and the impact of grid type on the combustion dynamics is examined in the LES calculations. The flame experiences four stages both in experiment and LES calculations with structured and unstructured grids, i.e., spherical flame, finger-shaped flame, flame with its skirt in contact with the sidewalls, and tulip-shaped flame. The flame speed and pressure in the vessel develop with periodical oscillations in both the experiment and LES simulations due to the interaction of flame front with pressure wave. The numerical simulations compare well with the detailed experimental measurements, especially in term of the flame shape and position, pressure build-up, and periodical oscillation behaviors. The LES combustion model is successfully validated against the bench-scale experiment. It is put into evidence that mesh type has an impact to a certain extent on the numerical combustion dynamics, and the LES calculation on structured grid canpredict the flame dynamics and pressure rise more accu- rately than that on unstructured grid with the same mesh resolution. The flame shape is more asymmetrical in the LES on an unstructured grid than that on a structured grid, and both the flame speed and the pressure rise at the later flame stage are underestimated in the LES on the unstructured grid.     

预混火焰面附近的湍流特性测量

为考察预混火焰面附近的湍流特性,以及湍流与化学反应相互作用的机理,采用激光多普勒技术(laser Doppler anemometry,LDA)对本生火焰和V型火焰的流场进行了诊断。分别通过固体粉末和雾化硅油液滴进行无条件和条件示踪,研究了全场及反应物来流的流动特性。无条件示踪的测量结果表明,火焰区的流场存在湍流度迅速增大然后衰减的现象,而速度的测值呈现双峰分布。条件示踪测量结果表明,在火焰区内反应物来流的流动特性并没有发生明显的改变。在剪切流场中,火焰面的脉动和皱褶不显著影响上游反应物的流动特性。     

预混火焰面附近的湍流特性测量

为考察预混火焰面附近的湍流特性,以及湍流与化学反应相互作用的机理,采用激光多普勒技术(laser Doppleranem ometry,LDA)对本生火焰和V型火焰的流场进行了诊断。分别通过固体粉末和雾化硅油液滴进行无条件和条件示踪,研究了全场及反应物来流的流动特性。无条件示踪的测量结果表明,火焰区的流场存在湍流度迅速增大然后衰减的现象,而速度的测值呈现双峰分布。条件示踪测量结果表明,在火焰区内反应物来流的流动特性并没有发生明显的改变。在剪切流场中,火焰面的脉动和皱褶不显著影响上游反应物的流动特性。     

Microstructure of premixed propane/air flame in the transition from laminar to turbulent combustion

In order to explore the flame structure and propagation behavior of premixed propane/air in the transi-tion from laminar to turbulent combustion, the high speed camera and Schlieren images methods were used to record the photograph of flame propagation process in a semi-vented pipe. Meanwhile, the super-thin thermocouple and ionization current probe methods were applied to detect the temperature distribution and reaction intensity of combustion reaction. The characteristics of propane/air flame propagation and microstructure were analyzed in detail by the experimental results coupled with chemical reaction thermodynamics. In the test, the particular tulip flame behavior and the formation process in the laminar-turbulent transition were disclosed clearly. From the Schlieren images and iron current results, one conclusion can be drawn that the small-scale turbulent combustion also appeared in laminar flame, which made little influence on the flame shape, but increased the flame thickness obviously.     

2.5MW煤粉氧燃烧旋流火焰数值计算

为了准确地数值预报煤粉旋流火焰特征和主要烟气成分,比较扩展的涡耗散模型在多湍流模型下的预测性和影响,针对IFRF(国际火焰研究基地)2.5MW煤粉氧燃烧和空气燃烧实验,利用组分输运方程,结合7步改进的总包反应,对炉内煤粉氧燃烧进行数值计算,并与实验结果和空气燃烧基况对比.结果表明:氧扩散率、发射率和比热容等物性参数修正后,湿循环、氧预混二次流的煤粉氧燃烧扩散火焰温度场与空气燃烧总体一致,火焰稳定且为Ⅱ型火焰结构;EDC模型(涡耗散概念模型)对组分预测更为准确,尤在可实现k-ε模型下的缓慢反应CO生成和IRZ(中心内回流区)高温预测;而FRED模型(有限速率涡耗散模型)在多湍流模型下对炉内温度、组分、火焰结构预测亦较准确.     

Topological analysis of methane lean premixed flame in turbulent jet flow by direct numerical simulation

Direct numerical simulation is employed to investigate the premixed jet flame of methane in lean, combined with a detailed chemical kinetics including 17 species and 58 elemental steps and distinct Lewis numbers. Cold methane-air mixture at 0.55 equivalence ratio is injected into the coflow area with 9500 Reynolds number. The coflow ambient gas is set to be the burnt gas of the methane-air mixture in main jet and temperature is assigned to be the corresponding adiabatic flame temperature 1515 K. The whole s...     

Influence of rarefaction wave on premixed flame structure and propagation behavior

To explore the influence of rarefaction wave on the structure and propagation behavior of the premixed propane/air flame in a rectangle combustion pipe, the techniques of high speed Schlieren photograph method, pressure measurement and so on are used to study the interaction processes between rarefaction wave and flame. Two cases of rarefaction wave-flame interaction were performed in the experiment. The experimental result shows that both the rarefaction waves can cause the flame transition from laminar to turbulent combustion quickly. The cowflow rarefaction wave decreases the flame speed, while the counterflow rarefaction wave leads the flame propagation speed to increasing on the whole, accompanied with sharp vibration.     

Influence of rarefaction wave on premixed flame structure and propagation behavior

To explore the influence of rarefaction wave on the structure and propagation behavior of the premixed propane/air flame in a rectangle combustion pipe, the techniques of high speed Schlieren photograph method, pressure measurement and so on are used to study the interaction processes between rarefaction wave and flame. Two cases of rarefaction wave-flame interaction were performed in the experiment. The experimental result shows that both the rarefaction waves can cause the flame transition from laminar to turbulent combustion quickly. The cowflow rarefaction wave decreases the flame speed, while the counterflow rarefaction wave leads the flame propagation speed to increasing on the whole, accompanied with sharp vibration.     

两种沥青路面阻燃剂的阻燃效果研究

研究了氢氧化物阻燃剂和有机磷系阻燃剂对沥青的阻燃效果。采用热重分析仪、X射线光电子能谱仪、傅里叶变换红外光谱仪和扫描电子显微镜等设备表征两种阻燃剂的阻燃效果。研究结果表明,两种阻燃剂都能促进沥青表面生成具有阻燃效果的致密氧化层,从而起到阻燃作用。阻燃沥青热解产物中C―O和O＝C特征峰强度比纯沥青的大。无机阻燃剂质量分数为8%、有机阻燃剂质量分数为10%时,阻燃效果较好,并且有机阻燃剂的效果要优于无机阻燃剂。有机阻燃剂在热解前期就可以减少一部分芳香分和饱和分的挥发,同时,由于阻燃剂的黏连效果,氧化阻燃层较无机阻燃剂的更加致密。     

火焰在微细圆管中传播及其熄火现象

采用单步化学反应机理，假定流场满足Poiseuille分布，用热传导-组分扩散模型研究圆管中预混火焰传播特征和熄火条件。通过计算不同的壁面对流散热和气体流动速度下的火焰，得到火焰面形状的变化规律、火焰传播速度的曲线，分析出了微细圆管中熄火的规律：管道越细，熄火越容易；进口气流速度为0时的燃料消耗速率最小，但只有正的进口速度才有利于防止熄火。     

火焰在环形通道内形态演变的实验研究

采用实验方法研究环形通道内体积比为1∶3的乙烯/氧气混合气体以及体积比1∶2.5的乙炔/氧气/氩气混合气体的火焰形态演变过程.实验方面采用高速摄影观察环形通道内的火焰传播.火焰经历了四个主要阶段:球形火焰、手指型火焰、舌形火焰和爆轰,其中舌形火焰在整个爆燃到爆轰转变(deflagration to detonation transition,DDT)过程中占据了最长的时间,并且在爆轰起爆中占据重要作用.另外,舌形火焰与边界层的作用使得火焰表面积和火焰速度有所增加.也讨论了初始压力对DDT起爆距离的影响,对于同种气体,初始压力的增大有助于缩短DDT起爆距离.此外,在爆轰敏感性相同的前提下,不规则系统中的DDT起爆距离要短于规则系统中的DDT起爆距离.     

两种亚网格湍流模型的旋流扩散火焰大涡模拟

为研究旋流火焰结构,采用二阶矩亚网格(SOM-SGS)燃烧模型及Smagorinsky-Lilly和K方程亚网格湍流模型,对美国Sandia国家实验室测量的旋流火焰进行了大涡模拟,得到了与燃烧场速度、温度和温度脉动实测值相吻合的模拟结果。预报的瞬时温度分布云图与实际火焰的形状很相似。K方程亚网格湍流模型预报的瞬时温度分布比Smagorinsky-Lilly模型的预报结果更接近实际。燃烧火焰基本上位于回流区所在的位置,火焰在回流区被稳定。     

两种亚网格湍流模型的旋流扩散火焰大涡模拟

为研究旋流火焰结构,采用二阶矩亚网格(SOM-SGS)燃烧模型及Smagorinsky-Lilly和K方程亚网格湍流模型,对美国Sandia国家实验室测量的旋流火焰进行了大涡模拟,得到了与燃烧场速度、温度和温度脉动实测值相吻合的模拟结果。预报的瞬时温度分布云图与实际火焰的形状很相似。K方程亚网格湍流模型预报的瞬时温度分布比Smagorinsky-Lilly模型的预报结果更接近实际。燃烧火焰基本上位于回流区所在的位置,火焰在回流区被稳定。     

反应型阻燃剂中间体DOPO合成研究

以三氯化磷、邻苯基苯酚为主要原料,氯化锌为催化剂,合成阻燃剂9,10-二氢-9-氧杂-10-膦杂菲-10-氧化物(DOPO),分析反应过程中产生的黄色副产物并确定其结构,通过优化合成工艺,有效地抑制黄色副产物的生成,DOPO为白色固体且纯度达99.5%以上,满足应用要求.     

光滑管中预混火焰传播物理机理的实验研究

开展了常温常压下二元燃料氢气/丙烷和空气预混气体在光滑方管道中火焰传播物理机理的实验研究。采用压力-时间记录法和纹影法两种测试方法,获得火焰传播速度和火焰阵面结构沿管道变化情况。结果表明:两种方法所测得的火焰传播速度在所测量范围内都先增加后减小。火焰加速传播机理主要是前方未燃气体受到前驱压缩波作用而被加热和压缩的正反馈微分加速机制,之后在管端反射的压缩波影响下,火焰传播速度略有降低。     

Measurement of laminar burning velocities and analysis of flame stabilities for hydrogen-air-diluent premixed mixtures

The laminar burning velocities and Markstein lengths of the hydrogen-air-diluent mixtures were meas-ured at different equivalence ratios (0.4―1.5), different diluents (N2, CO2 and 15%CO2+85%N2) and di-lution ratios (0, 0.05, 0.10 and 0.15) by using the outwardly expanding flame. The influences of flame stretch rate on the flame propagation characteristics were analyzed. The results show that both the laminar burning velocities and the Markstein lengths of the hydrogen-air-diluent mixtures decrease with the ...     

Direct numerical simulation of hydrogen turbulent lifted jet flame in a vitiated coflow

The direct numerical simulation (DNS) method with 16 steps detailed chemical kinetics was applied to a lifted turbulent jet flame with H2/N2 fuel issuing into a wide hot coflow of lean combustion products,at temperature of 1045 K and low oxygen concentrations. The chemical reactions were handled by the library function of CHEMKIN which was called by the main program in every time step. Parallel com-putational technology based on message passing interface method (MPI) was used in the simulation. All the cases were run by 12 CPUs on a high performance computer system. Faver-averaged DNS re-sults were obtained by long time averaging the transient profile and compared with the experimental data. The roll-up and evolution of the vortices in jet flame were well captured. The vortices in the same rotating direction attracted each other and those in different rotating directions repulsed each other. Through complex interactions between vortices,the original symmetrical vortex structure could be converted into nonsymmetrical and more complex structures by combination,distortion and splitting of the vortices. The transient profiles of H,OH and H2O mass fraction at 5.76 ms showed the flame structure in jet flame,especially the autoignition regions clearly. The lift-off height was about 9 d―11 d,in agreement with the experimental observation. At the corner point of the flame sheet indicated by OH and H profiles,the combustion was always enhanced by the flame curvature and extended resident time. The profiles of turbulence intensities show that the flames were diffused from the original two outside flame sheets into the core. The DNS results can be considered in developing more accurate and more universal turbulence models.     

预混火焰中喷雾热分解制备纳米氧化钇

以硝酸钇的水溶液为前驱体,在甲烷和空气的预混火焰中喷雾热分解制备得到了结晶度高、具有较大比表面积的纳米氧化钇粉体。考察了反应过程中形成火焰的混合气体流量比咖以及雾化气体流量对生成的氧化钇晶型和比表面积的影响。研究表明,随着混合气体流量比咖的增加,得到的氧化钇粉体的比表面积在西为0．48附近出现了一个最大值32m^2／g;雾化气体流量对氧化钇粉体的比表面积的影响不大,不同雾化气流量下制备得到的氧化钇粉体的比表面积为30～33m^2／g。     

旋流稳焰瓦斯燃烧器湍流扩散火焰的数值模拟

为研究瓦斯燃烧器的火焰特性 ,采用k ε湍流模型、三气体扩散燃烧模型及综合辐射模型 ,对旋流稳焰瓦斯燃烧器湍流扩散火焰进行了数值模拟。研究结果表明 ,在旋流作用下 ,在火盆及其前端附近区域内形成了中心回流区 ,使燃气与助燃空气在此处发生剧烈掺混而被点燃 ,这有利于火焰稳定。在火焰前端仍存在一个高温尾流区 ,在选用和设计燃烧器时应充分考虑这一现象。燃气喷孔直径对火焰长度的影响非常显著 ,喷头顶部气孔位置和火盆锥口角对火焰长度影响较小。随着空气过剩系数和燃气中空气含量的增加 ,火焰长度明显减小。在实际应用中 ,应充分考虑燃烧器结构和操作条件的影响 ,以提高加热炉的效率和安全性。     

Conditional moment closure modeling of a lifted turbulent flame

The problems about reacting turbulent flows are made difficult because the rates of reaction of concern are highly nonlinear functions of reactive scalars. The turbu-lence in the flow engenders mixing of non-uniformities in species and temperature, and the rates of this mixing are usually not fast compared with the rates of reaction. As a consequence, large spatial and temporal fluctuations occur in the scalar quantities and efforts to express average rates of reaction in terms of average valu…