稀释燃烧的火焰稳定性

采用实验研究的方法探讨了反应物预热温度与稀释率两个因素对稀释燃烧火焰稳定性的影响.实验以氮气稀释的甲烷-空气对冲扩散火焰为研究对象,确定了不同反应物预热温度与氧化剂稀释率(氧气体积分数)时火焰的熄火极限,结果表明,增大反应物预热温度拓宽了火焰稳定燃烧区域,而增加氧化剂稀释率(降低氧气体积分数)会降低稀释火焰的稳定性,二者对火焰稳定性的影响作用相反.为了进一步分析反应物预热温度与稀释率对火焰稳定性的影响程度,引入了估算的Damkohler数,分析表明,在实验研究范围内,反应物预热温度对火焰稳定性的影响比稀释率的影响显著,是火焰稳定性的主要影响因素.     

强弱射流型MILD富氧燃烧器燃烧特性的数值分析

采用计算流体力学(CFD)数值模拟方法对一种强弱射流型MILD富氧燃烧器的流动和燃烧特性进行了分析.采用有限速率/涡耗散(FR/EDM)模型预测了丙烷MILD富氧燃烧过程中烟气速度场、温度场、组分体积分数分布和烟气内循环流量比等宏观特征,并与已有实验数据进行比较,验证了模型的准确性.在此基础上深入分析了MILD富氧燃烧的化学反应区结构、湍流和化学反应时间尺度等微观特征.结果表明:强烈的烟气内循环充分地稀释并预热主反应区内的反应物,减缓了化学反应速率,从而降低了火焰峰值温度,揭示了强弱射流型MILD富氧燃烧的低氧温和燃烧特征.     

氧煤在炉膛内的燃烧方式分析

采用高温预热氧化剂或提高射流速度的方式,可将氧煤燃烧和MILD燃烧相结合,氧煤燃烧可以得到较高CO_2浓度的烟气,约90%,便于实现燃煤过程的CO_2捕集和封存(CCS),而MILD燃烧模式下的氧浓度整体水平较低,从而降低了煤的化学反应速率。利用煤粉的反应动力学参数,建立了氧煤燃烧炉膛的辐射传热模型,同时对不同氧浓度下煤粉燃尽时间和炉膛温度分布进行了计算。结果表明:煤炭颗粒的燃尽时间随着氧浓度和燃烧温度的降低而延长,且在低氧浓度下(10%),氧浓度的变化对燃尽时间的影响程度增大,而燃烧温度的变化对燃尽率的影响不大。煤样固定碳含量高,则炉膛介质温度整体提高,随着氧浓度的降低,燃烧峰值降低且位置稍有延后,且温度分布趋于均匀化。     

预热空气温度对丙烷无焰燃烧特性的影响

在20 kW燃烧实验台上,采用丙烷气体为燃料,研究了不同的空气预热温度对无焰燃烧下炉内温度分布和污染物排放的影响规律。结果表明,预热空气会提高炉膛平均温度并降低炉内温度波动;预热空气会使炉膛氧浓度峰值的位置提前,同时炉膛尾部氧浓度降低,整个炉膛氧浓度在0.4%～5%;预热空气会使炉膛尾部烟气中NO_x排放增加;预热空气使炉膛尾部CO峰值升高,但无焰燃烧下最终排烟中CO浓度为0。     

循环流化床锅炉低氮燃烧的CPFD数值模拟

针对某75 t/h循环流化床锅炉炉膛出口NOx排放超标问题进行分析探讨,以合理的低氮燃烧控制技术为主,辅以SNCR烟气脱硝技术,争取达到NO x超净排放要求。采用CPFD计算方法对循环流化床锅炉炉膛内的气固流动和燃烧特性进行数值模拟,运用低过量空气燃烧法和空气分级技术对锅炉进行低氮燃烧控制,研究一、二次风配比、二次风射流、过量空气系数、循环倍率和颗粒粒径等因素对炉内燃烧及NO x排放的影响。结果表明:通过低氮燃烧控制后,炉内速度场和温度场分布均匀,炉膛出口处烟气流速增加,炉膛平均烟温和出口氧浓度降低,还原性气体CO浓度和优化前基本相同,炉膛出口NOx浓度降低,减排效果显著,为以后的锅炉运行提供实际指导经验。     

烟气再循环技术研究现状及发展趋势

烟气再循环技术是实现高温空气燃烧、富氧燃烧、无焰燃烧等新型燃烧方式的重要手段。通过对烟气再循环实现形式、循环温度、循环量的合理设计可有效改善燃烧,起到降低污染物排放和提高燃烧效率的作用,是未来节能减排的重要方法。综述了烟气再循环技术在工业燃烧器、锅炉、内燃机、燃气轮机和斯特林发动机上的研究与应用。国内外研究表明:可以通过不同的方式来实现烟气的再循环;烟气回流量的控制是烟气再循环燃烧的技术难点。     

进一步提高高温空气燃烧余热回收率

目前，高温空气燃烧的排烟温度在200℃左右，为了进一步提高余热回收率，对降低排烟温度到50℃的可能性作了分析及实验，理论计算表明，降低排烟温度后，余热回收率可以提高6%～10%，由于天然气的烟气中含有较多的水蒸气，利用其冷凝热为进一步提高余热回收效率提供了更大的空间，烟气中的污染物可被冷凝的水分吸收，减少污染物排放。计算天然气烟气燃烧产物露点后，建议在蓄热体低温部分采取防止低温腐蚀的措施。     

基于燃烧风预热下铜精炼炉烟气热损失研究

根据能量平衡原理，建立了基于燃烧风预热下铜精炼阳极炉高温烟气热损失数学模型，并根据不同预热燃烧风温度对铜精炼阳极炉氧化期高温烟气热损失数学模型进行计算。结果表明，随着燃烧风预热温度增加，铜精炼阳极炉氧化期重油流量和高温烟气热损失减少趋势十分明显，节能效果显著。此外，给出了一些合理化建议，有利于铜精炼阳极炉氧化期节能效果进一步提高。     

CO_2稀释对不同燃料无焰燃烧及NO生成特性的影响

为探讨CO_2稀释对不同燃料无焰燃烧机理的影响,通过实验和数值模拟研究了CO_2稀释率对CH_4、C_3H_8和H_2扩散燃烧的火焰温度、NO排放摩尔分数及无焰燃烧的影响.结果表明:随着CO_2稀释率的增大,峰值温度和NO排放摩尔分数逐渐下降,峰值温度距燃烧器喷嘴的距离逐渐增大,炉内温度分布更加均匀,更有利于达到无焰燃烧状态;相同稀释率下,CO_2稀释对降低炉内峰值温度及出口NO排放摩尔分数的效果由好到坏依次为:H_2燃烧、CH_4燃烧、C_3H_8燃烧;当CO_2稀释率足够大时,炉内燃烧处于无焰燃烧状态.     

HTAC燃烧特性及环境特性分析

HTAC(High Temperature Air Combustion)与传统燃烧方法比较，可使燃烧范围扩大，燃烧过程稳定，燃烧温度分布均匀，并可抑制NOx的生成，减少CO2的排放。理论计算证明了CO2稀释空气对改善燃烧特性及减少污染物的生成均有成效。     

稀燃和EGR对汽油发动机性能影响研究

基于一台带有低压废气再循环系统的1.5 L涡轮增压直喷汽油发动机进行了稀燃和废气再循环(EGR)影响发动机燃烧性能的试验研究。结果表明,随着稀释率的上升,EGR和稀燃均导致发动机滞燃期、燃烧持续期延长,燃烧重心提前,有效燃油消耗率下降,排气温度下降,平均绝热指数上升。相同稀释率下,相比稀燃,EGR的滞燃期长,燃烧重心提前,两者燃烧持续期基本相等,稀释极限低,绝热指数小,排气温度低。在稀释率分别为20%、35.9%时,最大可减小有效燃油消耗率4.7%、7.2%。热容对燃油经济性的影响占主导地位,相同稀释率下,循环变动系数小于3%时,相比稀燃,EGR具有更好的燃油经济性。     

预热室结构对多段式自预热燃烧器内燃烧及NOx排放特性的影响

提出了一种多段式自预热燃烧器及其4种典型的预热室结构,通过计算流体力学（CFD）方法研究了燃烧室内流场、烟气卷吸率、温度场、燃气燃尽率以及NOx体积分数,并与传统燃烧器的情况进行了对比．结果表明：与传统燃烧器相比,多段式自预热燃烧器改变了燃烧室内流场,对低热值燃料适应性强,其预热室结构同时影响烟气卷吸率和预热效果,并最终影响燃尽率与NOx体积分数;此外,燃烧器负荷对燃尽率影响甚微,但对NOx体积分数影响较大．     

Thermal management and catalytic combustion stability characteristics of premixed methane/air in heat recirculation meso‐combustors

In order to illuminate heat recirculation effect on catalytic combustion stability and further improve energy conversion efficiency in meso‐combustor, the catalytic combustion characteristics of the combustor with/without preheating channels are numerically studied at steady conditions. It is found that methane conversion rate and combustion efficiency increases by 2% to 3% and approximately 9% in the heat recirculation meso‐combustor, indicating that heat recirculation effect facilitates more complete combustion of methane and medium components. Preheating channels show positive effects on improving combustion stability in the heat recirculation meso‐combustor. On one hand, preheating channels facilitate heat recirculation effect, and heat recirculation rate exceeds 10% for all cases and reaches 31.8% with an inlet velocity of 0.5 m/s, leading to significant increment of methane‐specific enthalpy at the preheating channel outlet. On the other hand, Rh(s)/O(s) ratios of catalytic surface and catalytic surface temperature in main reaction zone are enlarged by the preheating channels, facilitating methane adsorption at catalytic surface. Specially, most of fuels are consumed in a shorter distance with higher methane conversion speed, which brings benefits to promote combustion efficiency and may be helpful to inhibit the combustion instability in heat recirculation meso‐combustors.     

预热对陶瓷燃烧器燃烧过程的影响

应用计算机模拟技术研究了不同空气和煤气预报温度对陶瓷燃烧过程的影响,通过研究发现不同的预热度对燃烧火焰的长度影响显著,配置合理的温度是热风炉操作一个有效的调节手段。     

Numerical study of EGR effects on reducing the pressure rise rate of HCCI engine combustion

The effects of the inert components of exhaust gas recirculation (EGR) gas on reducing the pressure rise rate of homogeneous charge compression ignition engine combustion were investigated numerically by utilizing the CHEMKIN II package and its SENKIN code, as well as Curran’s dimethyl ether reaction scheme. Calculations were conducted under constant volume combustion and engine combustion (one compression and one expansion only, respectively) conditions. Results show that with constant fuel amount and initial temperature and pressure, as EGR ratio increases, combustion timings are retarded and the duration of thermal ignition preparation extends non-linearly; peak values of pressure, pressure rising rate (PRR), and temperature decrease; and peak values of heat release rate in both low temperature heat release (LTHR) and high temperature heat release decrease. Moreover, maximum PRR decreases as CA50 is retarded. With constant fuel amount, mixtures with different EGR ratios can obtain the same CA50 by adjusting the initial temperature. Under the same CA50, as EGR ratio increases, the LTHR timing is advanced and the duration of thermal ignition preparation is extended. Maximum PRR is almost constant with the fixed CA50 despite the change in EGR ratio, indicating that the influence of EGR dilution on chemical reaction rate is offset by other factors. Further investigation on the mechanism of this phenomenon is needed.     

Numerical study of Mild combustion with entrainment of burned gas into oxidizer and/or fuel streams

A numerical study has been performed to obtain basic knowledge of Mild combustion in which the fuel stream is preheated and diluted with various amounts of burned gas as well as the oxidizer stream. This situation occurs in application of Mild combustion in furnaces in which the burned gas might entrain into fuel and/or oxidizer streams via internal recirculation. For this purpose, a numerical model has been employed which consists of a network of plug flow reactors, counterflow diffusion flame solver and an equilibrium solver for generation of the burned gas. Detailed chemistry and multi-component transport model including Soret and Dufour effects have been used for the calculations. Stationary behavior of the model shows a considerable decrease in flame peak temperature with increasing dilution ratio for fuel dilution case as well as oxidizer dilution case. A decrease of the flame peak temperature is accompanied by a decrease of the NO formation. Further analysis of the NO reaction kinetics turned out that the prompt NO route plays a dominant role in the total NO formation. These observations were the motivation to investigate the autoignition behavior of each dilution case to study consequences of the application of each case. It appears that the most reactive mixture fraction is highly dependent on the dilution case and it can occur in a wide range of mixture fractions for different dilution cases. For a detailed comparison of autoignition behavior of dilution cases, the role of chemical and diffusion effects in this behavior has been clarified. Dilution ratio has been founded as a dominant parameter to control chemical effects and strain rate as a parameter to control diffusion effects. Dilution ratio appears to be an important parameter to determine the order of autoignition between dilution cases. Increasing strain rate delays the autoignition of dilution cases differently for each dilution case.     

Experimental investigation on the kinetics of biomass combustion in vertical tube reactor

The paper presents results of experimental investigation performed in order to examine kinetics of loose biomass combustion in vertical tube reactor. The investigation conducted included continuous measurement of the fuel mass loss rate, with two biomass combustion models (piston and batch model) proposed, each relying on appropriate theoretical postulates. Results obtained indicated that piston combustion model had shown better agreement between theoretical and experimental data and was therefore used to further analyse effects of excess-air on the combustion kinetics, as well as associated effects of flue gas recirculation. Recirculation of cold flue gases is used to lower peak temperature inside the furnace, as well as to reduce a zone where ash melting problems may potentially occur. During the investigation performed, effects of flue gas recirculation on the combustion process were simulated by simultaneously injecting nitrogen and air flows into the furnace. This was deemed appropriate to simulate real-life conditions prevailing in the furnace with gas recirculation. Experiments were conducted on specially designed and constructed apparatus that enabled kinetic parameters to be determined for the combustion of different types of biomass. Results obtained have indicated that quantity of air affects kinetics of biomass combustion and that increased recirculation leads to reduced biomass reaction rate. The same conclusion was reached based on the results of experiments conducted with two different types of agro-biomass, namely wheat straw and corn stalks, which are most commonly used for energy generation. Results achieved are deemed particularly important when it comes to design of new plants that utilize cigarette type combustion system, but also for development of numerical models used to simulate combustion of biomass bales, with special emphasis placed on the impact of recirculation gases on the combustion kinetics.     

Effect of Different Configurations on Small Pellet Combustion Systems

The combustion of pellets in small stoves is a complex issue in which many factors must be considered. The University of Vigo has developed a 24 kWt fixed bed stove pilot plant for studying pellet combustion in which different configurations and operational conditions can be tested. An extensive experimental study using the statistical analysis approach is presented. Analyses of the main control factors involved in the performance of stoves of this kind and their optimization are also presented, including preheating of air, secondary air supply and gas recirculation. The influence of air and pellet feeding rates and stove temperature as part of a group of energy and environmental variables is analyzed in detail. The study establishes that the use of secondary air and, especially, the recirculation of gases considerably reduce CO emissions.     

废气再循环率及点火时刻对天然气发动机燃烧和排温的影响

基于一台当量比燃烧的天然气发动机,采用三维燃烧分析与发动机一维热力学计算相结合的方式开展了废气再循环(exhaust gas recirculation,EGR)率及点火时刻对缸内燃烧过程和发动机排温的影响研究。研究结果表明:随着EGR率的增加,燃烧相位后移,燃烧持续期延长,放热率峰值减小,最大压升率、缸内最高燃烧压力和最高平均燃烧温度均降低,再循环废气的稀释作用和热容效应能够抑制混合气的燃烧。随着点火时刻的提前,燃烧重心(CA50)前移,燃烧持续期缩短,最大压升率、缸内压力和放热率峰值均增大。排温随EGR率的增大和点火时刻的提前而降低。保持空气和燃气进气量不变,EGR率增大至23%,点火时刻提前至-18°能够将原机标定功率提升7.4 kW,有效燃料消耗率降低4 g/(kW·h)。当空气和燃气进气量增加11.6%,EGR率大于19%,点火时刻早于-10.5°时,可将原机标定功率提升36 kW并且将排温控制在760℃以内。     

燃气轮机燃烧室柔和燃烧热力学与燃料条件的计算分析

本文通过零维数值模拟,对基于烟气循环的不同级别燃气轮机燃烧室中实现柔和燃烧的条件进行了计算分析。结果表明燃气轮机燃烧室柔和燃烧主要受回流烟气和燃料、空气的混合物温度的影响,烟气回流起到缩短混合物点火延迟时间的作用。由于不同燃料和不同负荷条件下混合物自燃温度变化不大,柔和燃烧具有较好的燃料适应性和变负荷性能。分析还表明未完全反应的烟气不会影响柔和燃烧工况范围。