交流和直流电场对天然气贫燃火焰的影响

对常温、常压下定容燃烧弹中的甲烷/空气预混贫燃火焰的传播和燃烧特性进行了研究, 对比了相同电压有效值下15 kHz高频交流电压和直流电压对火焰的影响。结果表明:两种电压加载方式下, 火焰形状均发生变形, 当过量空气系数一定时, 交流电场作用下的火焰在水平方向上的拉伸比直流电场下的剧烈, 且混合气越稀, 两者差异越明显;与未加载电压相比, 当过量空气系数为1.2、1.4和1.6时, 交流电场作用下的平均火焰传播速度分别提高49.14%、76.54%、117.65%, 直流电场下分别提高41.38%、58.02%、62.75%, 交流电场下压力峰值增幅分别为9.48%、11.48%、14.20%, 直流电场下增幅分别为4.46%、5.25%、8.76%。因此, 相同电压有效值下, 15 kHz高频交流电场对火焰的促进作用较直流电场更明显。     

负直流电场对不同初始压力预混甲烷/空气火焰的影响

在定容燃烧弹中研究了常温（298 K）,初始压力P_initial为0.1～0.5 MPa,加载U=-5、-10 kV直流电场对甲烷/空气预混火焰燃烧特性的影响。结果表明：不同初始压力下,加载电压,火焰主要在水平方向发生拉伸变形,加载电压幅值越高,火焰变形越明显,初始压力越高,火焰不稳定性增加,火焰面褶皱增加。加载电压后,火焰传播速率明显提高,电压幅值增大,其提高程度逐渐明显,初始压力增大,其提高程度更加明显,电场对火焰的促进效果更加明显,λ=1.4,U=-10 kV,P_initial=0.1～0.5 MPa时,平均火焰传播速率分别提高35.67%～52.71%。相对于未加载电压,加载电压后,各初始压力下质量燃烧率均增大,随电压幅值升高而升高,且初始压力越大,质量燃烧率变化越明显;火焰的初始燃烧期和主燃烧期均缩短,初始压力越高,缩短程度也越明显,二者相比,初始燃烧期缩短的程度更为明显。     

内/外烟气再循环对天然气燃烧NOx生成的影响

烟气再循环作为一种有效抑制NO_x生成的技术,广泛应用于化工、制药和酿酒等行业的天然气低氮燃烧过程,其作用机理是学术界和工业界关注的热点。本文根据内/外烟气再循环的作用不同,设计了弱/强内烟气再循环两种扩散式燃烧器,结合外烟气再循环技术,在0.8MW中试实验台上研究了内/外烟气再循环对天然气燃烧过程NO_x生成的影响规律,同时开展了Fluent数值模拟。结果表明：内烟气再循环能够有效抑制NO_x的生成,同时保证燃烧稳定。相同工况下,带内烟气再循环燃烧器初始排放远低于传统低氮燃烧器。同时结合外烟气再循环技术,可使NO_x排放量维持在30mg/m³以下。Fluent模拟结果显示了外烟气再循环能够显著地降低天然气燃烧火焰区的温度和O₂浓度。其中温度的降低对于NO_x生成的抑制起到了决定性的作用。当NO_x降低到约30mg/m³时,快速型NO_x对整体NO_x生成的贡献超过热力型NO_x,此情况下必须考虑对快速型NO_x进行抑制。     

天然气催化燃烧催化剂的研究进展

分析了以天然气作能源燃烧时,催化燃烧具有火焰燃烧不可比拟的优越性;进而对天然气催化燃烧使用的催化剂进行了研究探讨;提出了今后研究开发燃烧催化剂的努力方向。     

天然气成分波动对其预混火焰传播特性的影响

利用定容燃烧弹试验平台和CHEMKIN PRO气相化学动力学软件,研究了常温常压和化学计量比下天然气成分变化对其层流燃烧速度和火焰不稳定性的影响规律。结果表明,天然气的层流燃烧速度随乙烷、丙烷和正丁烷含量的增加而上升,且乙烷的影响效果最为显著。天然气-空气火焰的不稳定性随着乙烷、丙烷和正丁烷含量的增加而降低,正丁烷对火焰综合不稳定性的抑制能力与丙烷相近,且都强于乙烷。火焰结构分析表明,天然气成分波动时H基浓度峰值的变化最为显著,天然气的层流燃烧速度与火焰中OH基和H基浓度之和的最大值之间有较强的相关性。层流燃烧速度敏感性分析和净反应速率分析表明,天然气成分变化会影响其燃烧过程中重要基元反应的进行,通过正影响的基元反应和负影响的基元反应之间的竞争,火焰中H基的浓度峰值发生变化,乙烷含量变化对H基浓度的影响最大。     

电场对甲烷-空气混合气燃烧特性的影响

利用定容燃烧弹研究了外加电场对甲烷-空气混合气燃烧特性的作用。加载电压为0、-5、-10和-12 kV,混合气的过量空气系数λ分别为0.8、1.0和1.6,代表浓燃、当量比和稀燃三种混合气状态。结果表明,电场方向上的火焰发展半径和火焰传播速度明显增加,原先近似圆球形的火焰形状发生变化。特别是稀燃混合气,电场作用下火焰的传播状况增加最为显著,火焰近似呈圆柱形。在加载电压为-12 kV时,对于λ=0.8、1.0和1.6的混合气,火焰拉伸速度最大值分别增加了42.3%、29.7%和111.7%。同时,混合气燃烧压力的发展明显加快,压力峰值出现的时间明显提前。对于浓燃和当量比浓度的混合气,压力峰值变化不大,而稀燃混合气的压力峰值增加较为明显。在-12 kV电压作用下,浓燃、当量比和稀燃三种状态下混合气的压力峰值时间提前了13.4%、7.5%和24.6%,相应的燃烧压力峰值增大了2.2%、1.0%和8.1%。本文应用外加电场对燃烧火焰产生的离子风效应及其对传播火焰形成的拉伸作用对试验结果进行了说明。     

配风方式对燃煤锅炉掺烧污泥影响的数值模拟研究

燃煤耦合污泥发电技术研究主要聚焦在掺混比等条件的影响,而主燃区过量空气系数等因素的影响规律尚不清晰。鉴于此,采用涡耗散模型对600 MW四角切圆煤粉锅炉掺烧市政污泥进行数值模拟研究,分析了污泥掺混比例、主燃区过量空气系数以及二次风配风方式对燃煤锅炉内污泥掺混燃烧及NOx生成的影响。结果表明:随着污泥掺混比增加,炉膛整体温度下降,影响燃烧稳定性,同时炉膛出口NOx浓度有所降低。当污泥掺混比例增长至20%,炉膛出口温度约下降100 K,NOx浓度减少53.2%。而污泥掺混比例对于炉膛内速度场分布影响较小。随着主燃区过量空气系数由0.72增加至0.96,炉膛出口温度增幅较小,仅增加15 K左右,而NOx浓度则大幅增长,由174.39 mg/m3增长至352.09 mg/m3,约增长50.4%。在本文过量空气系数范围内,考虑温度和NOx浓度,推荐主燃区过量空气系数0.84。不同二次风配风对燃煤锅炉掺烧污泥影响差异较大。5种配风方式下,炉膛出口温度和NOx浓度有较大变化。鼓腰配风下炉膛出口温度最低,为1 289 K,而倒塔配风温度最高,为1 341 K。同时鼓腰配风下NOx浓度较高,为207.77 mg/m3,束腰配风NOx浓度较低,为156.42mg/m3。综合温度和NOx浓度,本文二次风配风推荐采用束腰配风方式。     

工业燃烧室天然气湍流扩散火焰长度影响因素分析

通过1.3MW级工业燃烧器实验验证商用CFD软件计算天然气湍流扩散火焰长度的有效性。以天然气（含有95%CH4和5%N2）为燃料,以直径为300mm、长度为1200mm的圆筒形燃烧室中、燃气孔径基本尺寸2mm的同轴射流扩散火焰为研究对象。采用数值计算的方法研究了燃气流量、喷孔孔径、助燃风特性等多种因素对火焰长度的影响规律。研究结果表明：在天然气湍流扩散火焰中,当孔径不变燃气流量增加一倍,火焰长度由652mm增加到782mm,增长19.9%。当燃气流量不变孔径增加一倍,652mm增加到1012mm,增长55.2%。改变燃气孔径是控制湍流扩散火焰长度的有效手段;在一定氧含量范围内,与助燃风氧含量相比,湍流火焰长度对助燃风速度的变化更加敏感。该研究对评估天然气燃烧装备性能和优化燃烧室设计具有重要的应用价值。     

压力对管道天然气泄漏扩散影响的数值模拟

利用Fluent软件的物质传输模型和湍流模型模拟了不同压力下天然气管道的泄漏扩散。通过对比分析模拟结果,得到了不同泄漏压力对天然气扩散的影响效果。模拟结果可为天然气泄漏事故的处理提供一定参考。     

进口甲烷再燃烧对煤粉燃烧以及NOx生成影响的数值模拟

A full two-fluid model of reacting gas-particle flows and coal combustion is used to simulate coal combustion with and without inlet natural gas added in the inlet. The simulation results for the case without natural gas burning is in fair agreement with the experimental results reported in references. The simulation results of different natural gas adding positions indicate that the natural gas burning can form lean oxygen combustion enviroment at the combustor inlet region and the NOx concentration is reduced. The same result can be obtained from chemical equilibrium analysis.     

微型定容燃烧腔内C2~C4烷烃/空气火焰传播

在直径35 mm、高度2 mm光学可视的定容燃烧腔内,实验研究了常温常压静止乙烷/空气、丙烷/空气和正丁烷/空气预混气在燃烧腔中心由电火花点燃后向外传播的火焰传播特性。结果表明：3种燃料空气混合气可形成火焰传播的当量比范围不同,范围由大到小排序为乙烷>丙烷>正丁烷;3种燃料均存在由光滑火焰面向褶皱火焰面转变的传播形态;在微型定容燃烧腔内,3种燃料的火焰传播速度均低于常规尺度下定容燃烧弹内火焰传播速度,且火焰传播速度随半径增加而减小;随着当量比增加,火焰锋面容易出现褶皱和断裂现象,在高当量比情况下,火焰传播会出现短暂停滞。     

Experimental and numerical study of CH4/CH3Cl/O2/N2 premixed flames under oxygen enrichment

A comprehensive experimental and numerical study has been conducted to understand the influence of CH₃Cl addition on CH₄/O₂/N₂ premixed flames under oxygen enrichment. The laminar flame speeds of CH₄/CH₃Cl/O₂/N₂ premixed flames at room temperature and atmospheric pressure are experimentally measured using the Bunsen nozzle flame technique with a variation in the amount of CH₃Cl in the fuel, equivalence ratio of the unburned mixture, and level of oxygen enrichment. The concentrations of major species and NO in the final combustion products are also measured. In order to analyze the flame structure, a detailed chemical kinetic mechanism is employed, the adopted scheme involving 89 gas-phase species and 1017 elementary forward reaction steps. The flame speeds predicted by this mechanism are found to be in good agreement with those deduced from experiments. Chlorine atoms available from methyl chloride inhibit the oxygen-enhanced flames, resulting in lower flame speeds. This effect is more pronounced in rich flames than in lean flames. Although the molar amount of CH₃Cl in the methane flame is increased, the temperature at the post flame is not significantly affected, based on the numerical analysis. However, the measured concentration of NO is reduced by about 35% for the flame burning the same amount of methyl chloride and methane at the oxygen enrichment of 0.3. This effect is due to the reduction of the concentration of free radicals related to NO production within the flame. In the numerical simulation, as CH₃Cl addition is increased, the heat flux is largely decreased for the oxygen-enhanced flame. It appears that the rate of the OH + H₂ → H + H₂O reaction is reduced because of the reduction of OH concentration. However, the function of CH₃Cl as an inhibitor on hydrocarbon flames is weakened as the level of oxygen enrichment is increased from 0.21 to 0.5. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 103–111, November–December, 2006.     

微小型凹腔燃烧器内甲烷/空气预混火焰特性

对有凹腔的微细通道内甲烷/空气的预混燃烧进行了实验研究,并与无凹腔的情况进行了比较。结果表明,无凹腔时,只出现了稳定或振荡的倾斜火焰;有凹腔时,在很宽的速度范围内火焰均能被有效地稳定,当进气速度接近吹出极限时,火焰锋面发生弯曲和脉动。当量比为0.8、0.9和1.0时有凹腔的微细通道的吹出极限分别为0.8、1.35和1.75 m·s^-1,是对应进气条件下燃烧速度的几倍,这表明凹腔具有很强的稳燃能力。数值模拟结果表明,凹腔的斜壁与下游的水平壁面之间的转折点存在很大的速度梯度和剪应力,导致了火焰在高速下被拉断而吹出。总之,有凹腔的微细通道内火焰的稳定性主要由反应区和流场之间的相互作用决定。     

Effects of initial temperature on the structure of laminar CH4-air premixed flames

The growing popularity of natural gas as a eco-friendly fuel, is of paramount motivation of present investigation. In the present paper, the effect of initial temperature on the flame structure have been investigated in which laminar one-dimensional planar propagating flames of CH₄/air mixtures is simulated numerically using detailed chemical kinetic scheme and realistic transport models. The burning velocities are fundamentally important in developing models to predict progress of combustion. Hence, the burning velocities as a function of initial temperature of unburnt gas have been computed for stoichiometric mixture. The present predictions of burning velocities are compared with reported experimental data of Stone et al. [Combust. Flame. 114 (1998) 546], Hill and Huang [Combust. Sci. Technol. 60 (1980) 7] and Rallis and Garforth [Combust. Flame 31 (1978) 53]. The present prediction lies within the scatter of experimental data. A correlation in the form of S_u/S_u,0=(T_u/T_u,0)^1.575 has been developed to describe the dependence of initial temperature on the burning velocity for stoichiometric mixture. The structures of flame are investigated in details for initial temperature of 300 and 600 K which clearly indicate that detailed chemical kinetics are essential for prediction of the effects of initial temperature on the burning velocities. The present study will help in designing and developing the regenerative combustion systems.     

O2/CO2气氛中水蒸气预混CH4燃烧特性与烟气余热梯级利用方案

对O2/CO2气氛中甲烷预混水蒸气燃烧特性及主要污染物生成进行了数值模拟研究,在加湿燃烧的基础上提出一种全新的清洁燃烧方式,即在保证甲烷流量一定时,通过改变入口处水蒸气的质量分数,研究水蒸气预混比Rf(0, 0.1, 0.2, 0.3, 0.4和0.5)对燃烧流场、燃烧组分和污染物浓度的影响。结果表明,随Rf增大,燃烧反应速率上升、燃烧效率提高且污染物排放量降低。模拟所得甲烷预混水蒸气的最优气氛为81%CH4/19%H2O,提出了一种高效节能的O2/CO2气氛下水蒸气预混CH4燃烧与烟气余热梯级利用方案。     

Effects of diluents on NO x formation in coflow CH4/air diffusion flames

The effect of diluent addition on NO _x formation in a laminar CH₄/air coflow diffusion flame was investigated by numerical simulation with experimental verification. The hydrocarbon fuel stream was diluted with N₂, CO₂, and Ar. The volume fraction of diluents systematically changed from 0.0 to 0.5. The simulation data agree well with the experimental one. The computational results indicate that overall the three diluents reduce the formation of NO and the effects vary from weak to strong in the order: N₂, Ar and CO₂. Differences between the influences of the various diluents are discussed in terms of the thermal, the dilution and the direct chemical effects, respectively. Further, the addition of CO₂ reduces the formation of NO₂, while the addition of N₂ or Ar has little effect on it. However, the formation rate of N₂O increases by each of the added diluents.