低热值C2H4-AIR-N2预混气体在多孔介质内的燃烧特性研究

利用自行设计的多孔介质实验台,对C_2H_4-AIR-N_2预混气体在多孔介质燃烧器内的燃烧特性进行了实验研究,分析燃料当量比、预混气体流速以及N_2稀释比对预混气体的可燃极限、火焰传播方向、火焰温度分布以及污染物排放的影响。研究表明:随着稀释比的上升,预混气体的可燃极限范围缩小,火焰向上游传播的工况逐渐减少;燃烧器内最高火焰温度与当量比以及气体流速正相关,与稀释比负相关;CO的排放量随着稀释比的上升而增加,与当量比以及气体流速负相关;实验中的NO排放量小于20 mg/m~3。     

有序堆积床内预混气体燃烧特性实验研究

为研究预混气体在多孔介质燃烧器中的火焰燃烧特性,设计了一种新型多孔介质燃烧器,其中多孔介质区域由氧化铝圆柱体有序堆积而成.分别研究了当量比和入口速度对甲烷/空气预混气体在多孔介质燃烧器中的火焰温度分布、火焰最高温度以及火焰传播速度的影响.结果 表明:在当量比0.162～0.324、入口速度0.287～0.860 m/s...     

两层多孔介质燃烧器的数值模拟

通过一维数值模拟研究了预混气体在两层多孔介质燃烧器内的燃烧特性,着重研究两层多孔介质燃烧器中的超绝热燃烧和火焰的稳定区域。结果表明,预混气体在两层多孔介质内可以发生一定程度的超绝热燃烧,贫燃极限可以扩展到0.45。两层多孔介质能够在较宽的流速范围内将火焰稳定在它的交界面上。数值预测的最小和最大火焰传播速度与实验取得了相同的趋势,其火焰传播速度至少是自由空间中的3倍。     

渐变型多孔介质中预混燃烧温度分布试验

进行了预混天然气在等孔隙率渐近变孔径的多孔介质中的燃烧试验，用热电偶测量了燃烧室温度分布，并与单一孔径（d=1mm）的均匀多孔介质中燃烧结果进行了比较。结果表明，渐变型多孔介质燃烧器比均匀型多孔介质燃烧器具有更多的优点：燃烧室温度分布更加均匀，燃烧更加稳定，并能更好的适应当量比和流量／功率的变化，由于孔径的变化，多孔介质中气流扰动增加，有利于火焰的稳定，当量比和流速变化范围增大。     

多入口多孔介质燃烧器的数值模拟

在多入口燃烧器内加入多孔介质,以甲烷/空气为燃料,采用非预混燃烧的数值模拟方法,探究多入口燃烧器的燃烧情况.对比多孔介质燃烧与空间自由燃烧,分析了"超焓燃烧"现象;在多孔介质燃烧基础上,探究不同当量比对燃烧温度的影响;在多孔介质燃烧和不同当量比的基础上探究污染物CO和CO_2的排放情况.结果表明:多孔介质燃烧可以实现"超焓燃烧"特性,燃烧火焰温度高于自由空间燃烧温度;当量比对燃烧温度影响很大,随着当量比的增大,燃烧器内最高燃烧温度升高,但燃烧过程存在一个最佳当量比0.6,超过该当量比后最高温度将不再变化;多入口多孔介质燃烧有助于减少CO和CO_2的生成量.     

惰性多孔介质中预混燃烧的研究进展

预混气体在惰性多孔介质中的燃烧具有燃烧速度快、燃烧效率高、温度分布均匀、贫燃极限宽、节约能源、污染物排放低等优点。介绍了惰性多孔介质中预混气体单向流动燃烧和往复流动燃烧的原理和特点,详述了火焰传播与驻定的机理,以及火焰传播中的不稳定现象,分析了影响火焰传播的因素,讨论了数值模拟中的物理模型、控制方程、边界条件、反应机理和求解方法,回顾了预混气体多孔介质燃烧技术的应用情况,分析指出了有待进一步研究的问题。     

天然气在渐变型多孔介质中的预混燃烧启动特性

针对天然气在渐变型多孔介质燃烧器中的点火启动过程进行了试验研究,通过监测燃烧器壁面或气体温度在点火后的变化,得到了影响启动时间的因素及特性,对特定的燃烧器而言,启动时间与预混气体当量比、流速以及点火位置有关,在冷态下点火,随着当量比接近理论当量比,启动时间减小;混合气体流速增大,启动时间增大;点火位置从燃烧器外移到燃烧器人口时,启动时间可大大缩小,采用小流速、近理论当量比条件下点火,对多孔介质层预热,有利于火焰迅速向上游移动,然后再调整到需求当量比或流速,可以大大减小燃烧器启动时间,采用孔径变化率高的渐变型多孔介质结构,也可以达到缩短启动时间的目的。     

甲烷-空气预混火焰稳定特性的实验研究

基于本生灯实验,测试分析了甲烷-空气预混火焰的稳定燃烧特性。试验研究了预混气体火焰闪回和吹熄极限随燃空当量比的变化关系。研究发现,甲烷-空气混合气体的闪回极限的最大值出现在接近化学当量比处,并且呈现出类似抛物线的变化规律;而火焰的吹熄极限随着当量比的增加而逐渐增大。试验通过采用13 mm和11 mm两种不同口径的本生灯,研究了本生灯孔径对甲烷-空气预混火焰的稳定燃烧区间的影响关系,实验证明,随着孔径的增大,闪回极限将会减小,而吹熄极限随之增大。通过实验获取这些参数,能够为设计和优化燃烧系统提供理论支撑。     

天然气在渐变型多孔介质中的预混燃烧

设计了孔径沿程变化的渐变型多孔介质(GVPM)燃烧器，为了解天然气在其中的预混燃烧特性，对燃烧室气体、固体温度分布和CO、NO；污染物排放进行了测量．试验研究了渐变型多孔介质中燃烧的温度场分布、火焰移动、污染物排放、稳定性及多孔介质孔径结构对燃烧特性的影响规律．将研究结果与几种均匀型多孔介质(HPM)中的燃烧进行比较，发现渐变型多孔介质中的燃烧可以有更多的优点，包括均匀温度场分布、极低污染物排放、高火焰速度、高稳定性、宽燃烧极限和有很大的负荷调节范围等．     

变功率下Rijke预混燃烧器的热声不稳定

为探索燃烧过程中热声不稳定的产生机理,对Rijke预混燃烧器热声不稳定进行了试验研究.Rijke预混燃烧器为直径40 mm、管长1 066 mm的不锈钢圆管,下端封闭,上端开口;致密堇青石材质的多孔介质稳燃体位于燃烧器1/4管长处,甲烷与空气的预混气体在稳燃体上方燃烧形成平面火焰作为加热热源.试验发现,Rijke预混燃烧器的燃烧温度和热声不稳定强度都随功率的变化而线性变化,获得的声压级位于132～143 dB.另外,Rijke预混燃烧器内热声不稳定的主峰频率几乎不受功率的影响,但幅值为最大峰值一半时的高频率和低频率之差随着功率的增大而不断减小,说明燃烧功率越大时,热声不稳定的声能就越集中于主峰频率.     

多孔介质中预混式燃烧的数值研究

本文考虑向燃烧室中插入高孔隙率的多孔介质的燃烧过程,根据气固两相局部非热平衡假设,建立了混合气体在惰性多孔介质中预混燃烧的一维数学模型,模拟了不同条件下甲烷-空气的预混合气在多孔介质中燃烧时的温度分布及气体流速、当量比和吸收系数对燃烧室气体温度峰值的影响.结果表明,多孔介质的存在明显改善了燃烧室的换热性能,强化了对新鲜混合气的预热,加速了燃烧反应的进行,燃烧室利用率提高.     

Analytical and experimental study of premixed methane–air flame propagation in narrow channels

This study investigates analytically and experimentally the influence of preheat temperature on flame propagation and extinction of premixed methane–air flame in single quartz tubes with inner tube diameters of 3.9, 3, 2 and 1 mm respectively. The effects of preheat temperature, tube diameter, equivalence ratio and mixture flow rate on the flame speed and extinction conditions are determined. The analytical results show that high preheat temperature of the mixture can effectively suppress flame quenching, and the occurrence of stable solution in the slow flame branch extends the flammability limit leading to possible flame propagation in mini channels. Experimental results confirm that the flame speed increases and the flammability limit shifts toward the fuel lean direction either through increasing the preheat temperature or decreasing the mixture flow rate, or both. Decrease of propagating flame speed is observed before the stoichiometric equivalence ratio at high preheat temperatures. The analytical model provides insights into how propagating flame in mini channels can be sustained; however, the model is only good at predicting flame speed near the fuel lean branch. Influence of Cu²⁺ ions exchanged zeolite 13X catalyst on flame speed is also addressed. It is noted that the zeolite based catalyst can lower the preheat temperature requirement in order to sustain the flame propagation in narrow channels.     

Direct simulation vs volume-averaged treatment of adiabatic, premixed flame in a porous medium

For the case of flame thickness being of the order of the pore linear dimension, the flame structure and speed in adiabatic, premixed methane-air combustion in porous media are examined. The local, volume-averaged conservation equations that assume a local thermal equilibrium between the solid and the gas phases (i.e. the single-medium treatment) or allow for a thermal nonequilibrium (i.e. the two-medium treatment) are used along with the direct application of the pointwise conservation equation to a two-dimensional porous medium model (ordered arrangement of discrete or connected square cylinders). The effective properties of the porous medium in the volume-averaged treatments, including the interfacial Nusselt number, are found by applying the local volume-averaging principles. The results show that, although significant variations of the temperature and species concentrations occur over a pore, the flame structure, thickness, speed, and excess temperature (i.e. local gas temperature in excess of the adiabatic temperature) are fairly well predicted by the two-medium model (the single-medium treatment is unable to predict the local excess temperature). However, the volume-averaged treatments are unable to predict the pore-level, local high temperature region in the gas phase (which can be up to 40% above the adiabatic temperature), and the pore-level variation in the flame speed with respect to the flame location in the pore (which can vary by up to 20%). Other shortcomings of the volume-averaged treatments are also revealed through a parametric examination involving the pore-geometry variables, solid to gas conductivity ratio, equivalence ratio, porosity, and flame location within the pore.     

预混气体在多孔介质中往复式超绝热燃烧的数值研究

根据气、固两相局部非热平衡假设,建立了RSCP系统的二维非稳态数学模型,对于固体能量方程中的辐射源项采用辐射传递的有限体积法求解,研究了当量比、换向半周期、混合气流速对温度分布、辐射热流量和放热率的影响,考察了最高温升和可燃极限与这些参数之间的关联．研究表明,燃烧室内温度呈梯形分布,高温区较宽;气体的最高温度明显高于绝热火焰温度;贫可燃极限显著扩展,对提高燃烧效率和节约能源有重要作用。     

Experimental analysis of the effects of porous wall on flame stability and temperature distribution in a premixed natural gas/air combustion

In the present analysis, the flame stabilization and temperature distribution within a premixed burner contain porous wall are studied experimentally. The effects of inner diameter, length, and pore density of the porous wall, thermal load, equivalence ratio, and the inlet velocity of the fuel‐air mixture on these are studied. The fuel used in this study is natural gas and the porous wall is SiC (silicon carbide) ceramic foam. The experimental results clearly indicate that the axial temperature along the porous wall increases when the inner diameter of the porous wall decreases and its length increases. The porous wall temperature with an inner diameter of 40 mm, length of 66 mm, and pore density of 30 PPI (pores per inch) has the highest temperature among the examined states. The results of studying the effect of the porous wall on flame stability show that the flame stability limit has a direct relationship with the length and pore density of porous wall and an inverse relationship with the inner diameter of the porous wall. Also, it is found that the porous wall has the highest temperature causes the maximum flame stability limit.     

On a porous medium combustor for hydrogen flame stabilization and operation

In this study, the characteristics of hydrogen flame stabilization in porous medium combustor were investigated. The flame was observed in a quartz tube. The porous medium was oxide-bonded silicon carbide (OB-SiC) or aluminum oxide (Al₂O₃) with 60 PPI and 30 PPI pore size distributions. The results indicated that under a low equivalence operation, the flame would transform from surface combustion to interior combustion with an increased heating value. Under a high equivalence ratio, both interior combustion and flashback transition existed at the same time. The thermal conductivity of silicon carbide is higher than that of aluminum oxide. Thus, interior combustion region was more extensive under a low equivalence ratio operation with a high premixed gas velocity. Flashback was apparent for Al₂O₃ under high an equivalence ratio with low a premixed gas velocity. Consequently, hydrogen flame stability could be controlled by the pore size distribution and thermal conductivity of the porous media, input heating value and input equivalence ratio.     

CH4/air预混气体双层多孔介质燃烧特性数值模拟研究

基于局部热平衡假设,定义了无量纲参数——火焰宽度比,在过量空气系数为1.2条件下,研究了CH_4/air预混气体在双层多孔介质中浸没燃烧和表面燃烧的燃烧特性。结果表明:表面燃烧具有更高的烟气出口温度以及更高的火焰宽度比。浸没燃烧火焰轮廓类似抛物线,而表面燃烧的火焰宽度比则基本不变;入口速度不同时,距离着火面同一位置浸没燃烧火焰宽度基本保持不变,火焰轮廓仍类似于抛物线;而对于表面燃烧,相同位置的火焰宽度比在很小范围内(约为0.03)呈现先增大后减小的变化规律。同时研究也表明表面燃烧具有更高的NO_x排放,且随着速度的增加两种燃烧方式NO_x排放变化规律一致,均呈现先增大后减小再增加的变化规律。在速度为1.1～1.2μm/s左右时,两种燃烧方式NO_x排放大致相当,这表明在不扩大污染的条件下,可以使用表面燃烧获得更多的对外辐射以节约能源。