热厚材料表面的近极限火焰传播特性

利用窄通道实验系统对低速气流中聚甲基丙烯酸甲酯(PMMA)平板表面逆风传播火焰的熄灭极限和传播速度进行了研究,主要实验参数为气流速度(≤10,cm/s)和氧气体积分数(≤50%,).实验发现,当气流速度和氧气体积分数接近火焰熄灭边界时,连续火焰分裂成为独立的、可稳定传播的小火焰,该现象的存在使材料的可燃范围扩大到连续火焰边界之外.分析表明,经典的热区火焰传播理论不能很好地预测火焰在低速流动中的传播速度,其偏差随着气流速度和氧气体积分数的减小而增大.     

液化石油气层流燃烧火焰特性分析

应用实验测试的方法对常温常压下不同配比的液化石油气/空气的燃烧特性进行研究,获得了水平管内火焰传播速度、火焰中心温度、火焰高度等随着液化气体积分数的变化规律。结果表明:火焰传播速度随着液化石油气体积分数的增大先增大后减小,最大值出现在体积分数为2. 78%处,即当量比为0. 98;不同燃烧方式火焰中心温度沿高度方向变化规律不同,扩散火焰的温度分布均匀;半预混火焰温度沿高度方向先上升后下降;全预混火焰中心温度随火焰高度的增加而下降;火焰高度随着液化石油气体积分数变化而变化,在当量比小于1时,火焰高度随着液化石油气体积分数的减小而降低,当接近化学当量比时达到最低;当量比大于1后,随着液化石油气体积分数减小,火焰高度增加。     

地沟油生物柴油与正丁醇/乙醇混合燃料燃烧火焰特性

为研究不同配比下生物柴油混合燃料燃烧特性,设计了一套生物质液体燃料雾化蒸发燃烧系统,该系统可产生生物柴油及其混合燃料层流预混火焰,结合OH-PLIF平面激光诱导荧光技术测定并分析燃烧火焰的高度和锋面面积以及层流预混火焰的传播速度和OH-PLIF总信号强度等燃烧特性.结果表明随着正丁醇或乙醇添加比例的增大,两种混合燃料燃烧火焰高度、火焰锋面面积呈下降趋势;火焰传播速度呈上升趋势.在混合燃料中,正丁醇的体积分数越大,燃烧火焰OH-PLIF总信号强度越大,而乙醇的体积分数越大,混合燃料燃烧火焰OH-PLIF总信号强度越小.     

同轴射流非预混火焰闪烁特性及非线性分析

以同轴射流燃烧器为研究对象,对6 mm、11.4 mm和17.4 mm 3种燃烧器直径下的甲烷空气同轴射流扩散火焰进行数值模拟,研究了氧气质量分数在23%～48%内扩散火焰的闪烁特性。结果表明:使火焰稳定的伴流速度比值U_r随着燃烧器直径的增大而增加,3种燃烧器直径下抑制火焰振荡所对应的U_r值分别为0.647、2.2和11.4;作用在火焰面外部的涡旋随着U_r的增大逐渐向火焰下游推移,同时峰值闪烁频率增加,而火焰的振荡幅度逐渐减小,流动与换热特性由周期性振荡转变为混沌状态;火焰的振荡幅度随着氧气质量分数的增加而减小,当氧气质量分数为48%时,火焰的闪烁峰值频率为10 Hz,且火焰闪烁的峰值频率不随氧气质量分数发生变化。     

某重型燃气轮机燃烧室进气速度变化对燃烧流动特性影响规律的数值研究

燃气轮机燃烧室进气速度变化是引起燃烧不稳定的主要因素之一,本文以某重型燃气轮机单管燃烧室为研究对象,建立了不同燃烧室进气速度条件下的单管燃烧室三维数值模型,研究了预混燃烧模式下燃烧火焰面随燃烧室进气速度的变化规律。燃料和氧化剂分别为甲烷和空气,燃空当量比为0.481。基于燃气轮机实际运行流量变化试验数据,燃烧室进气速度分别取103.9 m/s、94.8 m/s、85.7 m/s、76.5 m/s、67.2 m/s。研究结果表明燃烧室进气速度越大,燃烧火焰面越长,且燃烧火焰面所包裹的体积与燃烧室进气速度基本呈正比线性关系;在进气速度为103.9 m/s时,燃烧火焰面所包裹的体积较速度为67.2 m/s增加了23.8%。     

低氧稀释条件下煤粉颗粒燃烧特性实验研究

在平面扩散火焰煤粉燃烧实验系统上采用光纤光谱仪和CMOS相机分别测量了不同燃烧气氛(O_2/N_2、O_2/CO_2)、热协流温度(1 473～1 873 K)和氧气体积分数(5%～20%)下烟煤煤粉燃烧火焰的辐射光谱和火焰图像,获得了不同燃烧条件下煤粉颗粒温度沿程分布和燃烧特性。结果表明:在O_2/N_2或O_2/CO_2气氛下,随着热协流温度和氧气体积分数的降低,火焰颜色由亮黄色逐渐转变为暗红色,煤粉颗粒温度降低;随着热协流氧气体积分数的下降,煤粉颗粒温度波动系数减小了37%,颗粒温度分布更均匀;与O_2/N_2气氛相比,O_2/CO_2气氛下煤粉火焰光强减弱,煤粉着火距离增加,煤粉颗粒的平均温度降低了24～103 K,颗粒温度波动系数最大减小了24%。     

七氟丙烷与火焰作用过程中产生的氟化氢研究

采用激光吸收光谱分析法,测试了不同体积分数七氟丙烷与杯式燃烧器火焰作用过程中氟化氢产生量,研究了七氟丙烷体积分数对氟化氢产生量的影响规律.测试了七氟丙烷在不同灭火速度下熄灭杯式燃烧器火焰时的氟化氢产生量,考察了灭火速度对氟化氢产生量的影响.结合试验测试结果,分析了七氟丙烷灭火时的热分解过程及灭火机理.结果表明,七氟丙烷与燃烧杯火焰作用过程中,在七氟丙烷体积分数远远小于临界灭火体积分数(8.4％,乙醇火)时,其体积分数越高,产生的氟化氢质量体积分数越大,当七氟丙烷体积分数增大到1.3％时,氟化氢质量浓度超过4000 mg/m3.使用七氟丙烷熄灭燃烧杯火焰时,灭火速度越快,灭火剂与火焰的作用时间就越短,产生的氟化氢质量浓度就越低.     

逆风和静止环境中火焰沿柱状燃料传播的实验研究

本文测量不同直径的ＰＭＭＡ燃料捧在逆风和静止环境中的火焰传播速度，裂解长度和火焰形状，实验结果表明，在相同的燃料直径下，逆流风速越大，火焰传播速度较小，裂解区长度越小。火焰形状越平；在相同的逆流风速下，（１）当逆流风速于０．７ｍ／ｓ时，燃料直径越大，火焰传播速度越小；（２）当逆流风速大于０．７ｍ／ｓ时，燃料直径越大，火焰传播速度越大，当逆流风速较大时，不同直径燃料的无因次裂解长度趋现一致。     

可燃固体颗粒堆中的逆向火焰传播

本研究考察了火焰在可燃固体颗粒堆中的传播过程．选取5 mm直径PMMA小球作为特征可燃物,以氧气和氮气的混合气作为氧化剂,在不同氧浓度和流速条件下对火焰传播速度和固体质量消耗速率进行了测量．研究表明,氧通量是影响火焰传播和质量消耗的主导因素．氧通量保持不变时,增大流速会缩短火焰前锋的气相预热长度,使其传播速度降低;同时,固相预热长度拉长导致质量消耗速率升高,使火焰传播速度与质量消耗速率呈现相反的变化趋势．     

环境压力对热厚固体材料表面火焰传播的影响

通过实验对热厚聚甲基丙烯酸甲酯(PMMA)平板表面向上和向下传播火焰进行观测,研究了环境压力和氧气浓度对火焰传播和熄灭的影响.对于向下传播火焰,火焰传播速度与压力和氧气浓度之间的关系为■;利用Damk?hler数将火焰传播速度随压力的变化划分成了两个区域:化学反应控制区和传热控制区.对于向上传播火焰,存在与氧气浓度有关的临界环境压力,将火焰传播划分成两种模式.当环境压力小于临界压力时,火焰为根部退后传播模式;当环境压力大于临界压力时,火焰为燃料退化燃烧模式.两种传播模式的转变压力随着氧气浓度的增加而降低.     

Effect of initial pressure,temperature and equivalence ratios on laminar combustion characteristics of hydrogen enriched natural gas

In this study, the flame propagation characteristics of premixed natural gas–hydrogen–air mixtures were studied in constant volume combustion bomb by using the high-speed schlieren photography system. The flame radius, laminar flame propagation speed and the flame stretch rate were obtained under different initial pressure, temperature, equivalence ratios and hydrogen fractions. Meanwhile, the flame stability and their influencing factors were obtained by analyzing the Markstein length and the flame propagation schlieren photos under various combustion conditions. The results show that the stretched laminar propagation speed increases with the increase of the initial temperature and hydrogen fraction of the mixture, and will decreases with the increase of the initial pressure. Meanwhile, according to the Markstein length and the flame propagation pictures, the flame stability decreases with the increase of the temperature and hydrogen fraction, and the slight flaws occurred at the early stage; at larger flame radius, the flame stability is more sensitive to the variation of the initial temperature and hydrogen fraction than to that of initial pressure and equivalence ratio.     

Soot formation, spray characteristics, and structure of jet spray flames under high pressure

Coaxial jet spray flames of kerosene and oxygen are experimentally studied over a pressure range of 0.1–1.0 MPa to determine the relationship between flame structure, droplet behavior, and soot formation region, which varies with changes in pressure. The direct images and chemiluminescence spectra show that the spray flames have three regions: the blue flame region, which has a peak of CH* and C₂* radical chemiluminescence, luminous flame region caused by soot emission, and blue emission region caused by CO₂ emission. With increase in ambient pressure, the flame length shortens drastically, the luminous flame region envelopes the blue flame region, and the blue emission becomes more intense. The result of phase-Doppler anemometry shows that a large number of small droplets evaporate and disappear near the burner, and the evaporation of large droplets also occurs rapidly under high pressure. The result of temperature measurements shows that high-temperature regions appear near the burner. The flame temperature drastically decreases along the central axis, and a minimum temperature point appears. This point moves upstream with increase in ambient pressure because evaporation of the droplets occurs further upstream. A laser-induced incandescence measurement shows that the soot volume fraction does not monotonously increase or decrease with increase in ambient pressure. The soot volume fraction at the central axis becomes low upstream and high downstream. As pressure increases, the vertical position at which the peak of soot volume fraction appears at the central axis moves upstream.     

Effect of initial pressure on laminar combustion characteristics of hydrogen enriched natural gas

Flame propagation of premixed natural gas–hydrogen–air mixtures was studied in a constant volume combustion bomb. Laminar burning velocities and mass burning fluxes were obtained under various hydrogen fractions and equivalence ratios with various initial pressures, while flame stability and their influencing factors (Markstein length, density ratio and flame thickness) were obtained by analyzing the flame images at various hydrogen fractions, initial pressures and equivalence ratios. The results show that hydrogen fraction, initial pressure as well as equivalence ratio have combined influence on both unstretched laminar burning velocity and flame instability. Meanwhile, according to flame propagation pictures taken by the high speed camera, flame stability decreases with the increase of initial pressures; for given equivalence ratio and hydrogen fraction, flame thickness is more sensitive to the variation of the initial pressure than to that of the density ratio.     

Laminar burning velocity and Markstein length of nitrogen diluted natural gas/hydrogen/air mixtures at normal,reduced and elevated pressures

Flame propagation of premixed nitrogen diluted natural gas/hydrogen/air mixtures was studied in a constant volume combustion bomb under various initial pressures. Laminar burning velocities and Markstein lengths were obtained for the diluted stoichiometric fuel/air mixtures with different hydrogen fractions and diluent ratios under various initial pressures. The results showed that both unstretched flame speed and unstretched burning velocity are reduced with the increase in initial pressure (except when the hydrogen fraction is 80%) as well as diluent ratio. The velocity reduction rate due to diluent addition is determined mainly by hydrogen fraction and diluent ratio, and the effect of initial pressure is negligible. Flame stability was studied by analyzing Markstein length. It was found that the increase of initial pressure and hydrogen fraction decreases flame stability and the flame tends to be more stable with the addition of diluent gas. Generally speaking, Markstein length of a fuel with low hydrogen fraction is more sensitive to the change of initial pressure than that of a one with high hydrogen fraction.     

亚/超临界环境下燃料的喷雾燃烧特性研究

采用高温高压定容燃烧弹系统对亚/超临界环境下燃料在纯氧中的喷射燃烧现象进行试验研究,通过高速相机和阴影法进行燃烧图像信息的采集,研究在相同的超临界温度下,正己烷和乙醚两种燃料喷射燃烧火焰特性随环境压力和喷油脉宽的改变而呈现的差异性。试验结果表明:在亚临界压力下,两种燃料在不同喷油脉宽下的燃烧时间均随着环境压力的升高而升高,火焰发展后期基本保持较为稳定的形态和亮度,符合传统的喷射燃烧过程。正己烷在临界压力点下火焰长度最短,形态较为规则;超临界压力下,火焰形态有稳定趋势但仍有轻微波动,且火焰长度略短于亚临界;喷油脉宽改变时,燃烧时间在临界压力附近呈现出不同的趋势。乙醚的燃烧时间随压力的升高而增大,在临界压力处达到最大值,后随着压力的继续升高而下降,不同压力条件下火焰形态略有差别。燃烧现象存在差异性主要是由于亚/超临界坏境下燃料的物性参数和破碎蒸发机理不同。     

天然气/氢气燃烧特性研究

在定容燃烧弹中研究了不同氢气掺混比例、燃空当量比和初始压力下的大然气／氢气混合气的燃烧特性,建立了适合用于容弹计算的准维双区模型。研究结果表明：在各种当量比和初始压力下,随着掺氢比例的增加,混合气的质量燃烧速率明显增加,燃烧持续期和火焰发展期娃著缩短。随着掺氢比例的增加,短的燃烧持续期所对应的当量比范围变宽,稀混合气和浓混合气条件下天然气掺氢对火焰发展期缩短的效果更明显。化学计量比附近（1．0—1．1）掺氢燃烧对燃烧最大压力值影响不大,浓混合气（燃空当量比大于1．1）和稀混合气燃烧时,随着掺氢比例的增加,最大燃烧压力值增加。     

Measurements of laminar burning velocities and onset of cellular instabilities of methane–hydrogen–air flames at elevated pressures and temperatures

An experimental study on laminar burning velocities and onset of cellular instabilities of the premixed methane–hydrogen–air flames was conducted in a constant volume combustion vessel at elevated pressures and temperatures. The unstretched laminar burning velocity and Markstein length were obtained over a wide range of hydrogen fractions. Besides, the effects of hydrogen addition, initial pressure and initial temperature on flame instabilities were analyzed. The results show that the unstretched flame propagation speed and the unstretched laminar burning velocity are increased with the increase of initial temperature and hydrogen fraction, and they are decreased with the increase of initial pressure. Early onset of cellular instability is presented and the critical radius and Markstein length are decreased with the increase of initial pressure, indicating the increase of hydrodynamic instability with the increase of initial pressure. Flame instability is insensitive to initial temperature compared to initial pressure. With the increase of hydrogen fraction, significant decrease in critical radius and Markstein length is presented, indicating the increase in both diffusional-thermal and hydrodynamic instabilities as hydrogen fraction is increased.     

Soot and NO formation in methane–oxygen enriched diffusion flames

NO and soot formation were investigated both numerically and experimentally in oxygen-enriched counterflow diffusion flames. Two sets of experiments were conducted. In the first set, the soot volume fraction was measured as a function of oxygen content in the oxidizer jet at constant strain rate (20 s⁻¹). In the second set of experiments, the soot volume fraction was measured as a function of strain rate variation from 10 to 60 s⁻¹ and at constant oxygen content on the oxidizer side. A soot model was developed based on a detailed C₆ gas phase chemistry. The soot and molecular radiation were taken into account. Numerical results were verified against experimental data. The soot volume fraction was predicted with the maximum discrepancy less than 30% for all cases considered. It was found that oxygen variation significantly modified the diffusion flame structure and the flame temperature, resulting in a substantial increase of soot. The temperature increase promotes aromatics production in the fuel pyrolysis zone and changes the relative contributions of the thermal and Fenimore mechanisms into NO formation. As the strain rate increases, the residence time of incipient soot particles in the high temperature zone is reduced and the total amount of soot decreases. High concentration of soot in the flame leads to enhancement of radiant heat exchange: the reduction of temperature due to radiation was found to be between 10 and 50 K. This caused a reduction of peak NO concentrations by 20%–25%. The increase of oxygen content in the oxidizer stream resulted in a reduction of the distance between the plane of the maximum temperature and the stagnation plane.     

天然气-氢气-空气混合气的层流燃烧速度测定

在定容燃烧弹内研究了常温常压下天然气-氢气-空气混合气的火焰传播规律,得到了不同掺氢比例（氢气在天然气中的体积掺混比例为0％～100％）和燃空当量比（0．6～1．4）下混合气的层流燃烧速率和马克斯坦长度,通过对马克斯坦长度的测量,分析了拉伸对火焰传播的影响。结果表明,随着天然气中掺氢比例的增加,混合气的燃烧速率呈指数规律增加,马克斯坦长度值减小,火焰的稳定性下降。各掺氢比例下,随当量比的增加,马克斯坦长度值增加,火焰的稳定性增强。通过对试验结果的数据拟合,得到了计算天然气-氢气-空气混合气层流燃烧速率的关系式。     

天然气-氢气-空气混合气火焰传播特性研究

在定容燃烧弹内研究了初始条件为常温常压的灭然气-氢气-空气混合气火焰传播规律,得到了不同掺氢比例和燃空当量比下混合气的层流燃烧速率、质量燃烧流量和马克斯坦长度,结合火焰传播照片,分析了火焰的稳定性并预测了大尺寸火焰稳定性的演变趋势。研究结果表明,随着天然气中掺氢比例的增加,混合气的燃烧速率增加,且增长速率逐渐加快,马克斯坦长度值减小,火焰的稳定性下降。各种掺氢比例下,随当量比的增加,马克斯坦长度值增加,火焰的稳定性增加。掺氢比例高于80％时,随着火焰的传播,其不稳定性将明显增加。