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.     

高速煤粉射流火焰形态特征的实验研究

利用Hencken型平焰燃烧系统开展了高速煤粉射流燃烧实验,并结合煤粉射流火焰形态图谱对其火焰形态及主要影响因素进行分析.结果表明,射流速度提高促使煤粉火焰形态从群燃火焰向分散燃烧转变,在高速下呈现出较短、较暗的煤粉火焰,其中煤粉质量浓度下降和流场卷吸掺混增强均有影响.高Re数受限射流会引发强烈壁面回流,并裹挟边壁落粉...     

微通道内甲烷/氢气/氧气预混合火焰传播特性

在石英玻璃微圆管内,进行甲烷/氢气/氧气预混合火焰传播的实验研究,分析了管径、掺氢比、当量比及入口流速对火焰传播状态和稳定火焰位置的影响规律.结果表明:实验观测到的微火焰主要有管外射流火焰、脉动火焰、稳定火焰与反复熄燃火焰;随着管径增加,稳定火焰出现在更高当量比情况下,火焰位置更靠近燃烧室入口;掺氢比越高,形成稳定火焰对应的当量比越高,火焰位置更接近出口;高当量比时,稳定火焰仅在低入口流速下能够获得,随着当量比降低,火焰能在较高入口流速下稳定;低流速下,稳定火焰在当量比为1.85～1.925时更接近燃烧室入口,随着流速增加,火焰位置更接近出口;反复熄燃火焰在管径增加时对应的当量比维持在1.79～1.93,在掺氢比增加时对应的当量比为1.79～2.12.     

扼流式反向端烧嘴加热炉内气体流动的方式与节能

气体流动对火焰加热炉的传热过程、燃烧过程及其节能有着重要的影响.在火焰连续加热炉内存在着火焰充满炉膛及贴附金属表面以及炉内的气流如何影响到炉内的压力分布并从而影响到炉膛的吸风和冒火等等问题.这些问题归结为气流的混台和气流的分布问题.对于一定的炉型来说,它们将主要地决定于射流的作用和炉气所受到的浮力的作用.2 影响炉内气体流动的因素     

高温富氧空气下燃料射流自点火及火焰抬升特性研究

针对高温富氧空气中燃料射流的自点火现象及射流火焰的稳定机理,通过调节空气中的氧含量、射流速度和燃料稀释度,实验获得了自点火形成的射流火焰抬升高度变化规律.结果表明,随着空气中氧含量的提高,射流火焰抬升高度降低,吹熄极限速度增加;随着燃料射流速度增加,自点火后形成的火焰类型发生转变,火焰抬升高度会发生突增.通过将实验数据与现有抬升高度预测模型对比,得出了影响富氧自点火射流火焰稳定的主要因素.     

旋流杯下游流场经验关系式的进一步验证

利用得到的两种典型旋流杯结构(CFM-56燃烧室与某模型燃烧室)下游流场的实验数据,对已有经验关系式进行了改进,减少了关系式中的经验系数,使关系式能够较好地拟合两种旋流杯出口附近的轴向速度分布,各特征数据(如峰值位置、峰值哀减速度、回流区宽度及其沿下游的发展、回流速度及其衰减等)与实验数据十分相符,并给出了公式预测的误差范围在10%～20%之间,从而验证了公式的通用性.同时,给出了公式中不同的经验系数取值带来的变化,分析了与几何及工况参数之间可能的联系.分析表明,各经验系数的变化相互独立,且物理意义明确,可以方便地与结构参数联在一起.     

稳态湍流非预混燃烧的小火焰模拟

以甲烷/空气的湍流射流非预混燃烧为对象,建立二维稳态湍流非预混火焰的小火焰模型.利用湍流流动模型和小火焰模型耦合求解,计算出速度、混合分数、温度以及反应标量的摩尔分数在燃烧室内的分布,模拟结果表明小火焰模型能够用来描述燃烧室内燃烧机理.     

燃气轮机燃烧室振荡被动控制方法的数值研究

以预混燃烧方式工作的燃气轮机燃烧室易产生燃烧室振荡.应用非定常N-S方程、雷诺应力和紊流模型及涡团耗散燃烧模型,对该类型燃烧室在不同燃料喷注位置和空气流动速度下的气流流动特性和压力振荡特性进行了数值模拟.结果表明:采用CFD方法,可精确地获得放热与燃烧室声学特性之间的耦合关系,且与实验吻合较好.通过调整燃料喷注位置和空气的供给速度,可激发或抑制振荡.根据预混段流动时间及燃料喷注位置到火焰前沿的总流动时间均能可靠地预测稳定范围.     

火焰筒内环向多孔径向射流的流场研究

环向径向射流对燃烧室火焰筒内的流场有着重要的影响。本文采用三雏标准k-￡湍流模型详细模拟了燃烧室火焰筒内外的等温流场，给出了火焰筒不同截面位置的轴向速度和径向速度分布。并对数值模拟结果与实验数据进行了比较，结果符合较好，同时还分析了数值模拟结果与实验数据的差异。研究了火焰筒内多孔径向射流的流场特性，并比较了不同环向径向射流流量对火焰筒内流场的影响。研究结果表明：在射流孔附近，火焰筒内轴向速度和径向速度沿径向的梯度增大；而在火焰筒外，轴向速度沿径向的梯度变化不大，径向速度变化较大，但随着流体的流动，火焰筒外径向速度很快趋于均匀。当射流流量增加时，火焰筒内射流孔中心截面的两对称旋涡逐渐增大。     

二甲醚及癸烷层流火焰传播速度动力学模拟

燃料的火焰传播速度对燃烧,尤其在火焰传播、火焰驻定等方面具有重要影响。采用文献报道的详细机理进行计算,对可再生生物燃料二甲醚以及煤油的替代燃料癸烷的层流火焰传播速度进行数值模拟研究,分析了不同当量比、温度、压力对二甲醚和癸烷的层流火焰传播速度的影响,得到了包含温度、压力、当量比影响的火焰传播速度计算的经验关系式。结果表明,两种燃料的层流火焰传播速度均在当量比空间上近似呈现出抛物型分布,并均在1.1附近达到最大值;随着温度的增加而增大,且温度越高越敏感;随着压力的增加而减小,呈现出反比的关系。与文献中的实验结果对比表明,本文得到的经验公式可以在一定温度和压力范围内较准确的预测层流火焰传播速度。     

The influence of preferential diffusion and stretch on the burning intensity of a curved flame front with fuel spray

In our most recent paper on Bunsen spray flames, only a completely prevaporized mode of a normal Bunsen flame was considered; inverted Bunsen flame and droplet size effects had not been examined yet. In the present study, we consider two flame structures: normal and inverted Bunsen flames, and two spray modes: completely and partially prevaporized burning, by the method of large activation energy asymptotics. In this way, a complete parametric study of flame tip intensification or extinction (opening) can be conducted. Four parameters are used in the analysis. The first two are the droplet size and amount of liquid-fuel loading, which indicate internal heat loss for a rich spray but heat gain for a lean spray. The other two are the stretch and Lewis number (Le). Stretch is negative for a normal Bunsen flame but positive for an inverted Bunsen flame. Stretch strengthens (or weakens) the burning intensity of the Le>1 (or Le<1) normal Bunsen flame but decreases (or increases) the burning intensity of the Le>1 (or Le<1) inverted Bunsen flame. Burning intensity of the flame tip intensifies (or weakens) when the lean (or rich) spray has a smaller droplet size or a larger amount of liquid loading. For lean and rich ethanol-spray normal Bunsen flames with Le>1 or a rich methanol-spray inverted Bunsen flame with Le<1, closed-tip solutions are obtained. Conversely, stretch weakens the burning intensities of lean and rich ethanol-spray inverted Bunsen flames with Le>1, or rich methanol-spray normal Bunsen flames with Le<1, eventually leading to tip opening. Moreover, the opening becomes wider (or narrower) as the droplet size decreases or liquid loading increases for the rich (or lean) sprays. Note that for lean ethanol-spray normal (or inverted) Bunsen flame with Le>1, if liquid loading is large enough and droplet size is sufficiently small, there exists flame transition from normal (or inverted) Bunsen through planar to inverted cone (or normal Bunsen) flame. Finally, the critical value of droplet size, at which there exists a planar flame rather than a normal (or an inverted) Bunsen flame, increases with increasing liquid loading.     

Assessment of laminar flame velocity of producer gas from biomass gasification using the Bunsen burner method

Producer gas is a renewable fuel obtained from gasification processes. This fuel may be burned directly in furnaces to supply thermal demands, or used to run internal combustion engines or gas turbines. The characteristics of producer gas have been studied by various authors, however, most studies generally use mixtures of synthetic gases to represent Producer Gas. The main goal of this study is to evaluate the laminar flame velocity of Producer Gas obtained from gasifying eucalyptus wood in a two-stage downdraft gasifier using the Bunsen burner method and the Schlieren image visualization technique to register the profile of the flame. The Producer Gas volume fractions that were used in the tests were 20%, 16%, and 1.8% for CO, H₂, and CH₄, respectively. This resulted in a 4.9 MJ/Nm³ lower heating value. The registered laminar flame velocity at the stoichiometric point under optimal conditions was 0.33 m/s. The tests were carried out at standard atmospheric pressure and atmospheric temperature. The results were compared to studies of other authors, and this study shows that fractions of Hydrogen (H₂) and Carbon Monoxide (CO) in the Producer Gas result in increased laminar flame velocities, while fractions Nitrogen (N₂) and Carbon Dioxide (CO₂) result in reduced flame velocities.     

层流预混火焰传播速度与火焰稳定传播界限的测定

采用本生灯法和直管法测定了液化石油气（LPG）、甲烷与氢燃料质子交换膜燃料电池（PEMFC）阳极尾气与空气的三种不同浓度混合气的层流火焰传播速度。此外,对三种不同浓度可燃混合气火焰的稳定传播界限也进行了测定。实验结果为多燃料燃烧器的开发提供了设计依据。     

Aerodynamics of a slender axisymmetric Bunsen flame with large gas expansion

The flow around a stationary axisymmetric premixed flame attached to a plug flow Bunsen burner and propagating with a constant burning velocity relative to the fresh gas is analyzed for large values of the ratio of fresh gas injection velocity to flame burning velocity and small values of the burnt-to-fresh gas density ratio. The shape of the flame is close to a cone of small semiangle, and its presence induces only a small perturbation in the fresh gas. The velocity of the burnt gas is the superposition of a uniform axial velocity and the velocity induced by a line of sources on the axis of the burner. The pressure of the burnt gas on the flame is the sum of a uniform part that does not change the velocity of the fresh gas and a small variable part that causes a vertical acceleration of this gas and a slight deformation of the flame. Only a weak vorticity is generated at the flame. The analysis breaks down in small regions around the tip and the base of the flame where the assumption of a constant burning velocity is not valid.     

预混湍流火焰的根部脉动特性

采用平面激光诱导荧光的测试方法捕捉本生灯预混湍流火焰的瞬态形态,重点分析火焰根部的脉动特性及其对火焰稳定的影响.采用挡环和多孔板式湍流发生器,分别形成边界层湍流和位势流湍流.实验结果表明,对于这两种湍流发生器,射流火焰根部的脉动幅度都随来流速度的增大逐渐增强;增大湍流发生器的特征尺寸或者降低混气当量比,都会加大火焰根部的脉动幅度.挡环尺度的影响则表明了临界尺度的存在.当挡环尺度小于临界尺度时,火焰根部的脉动不利于火焰的稳定,即随着挡环尺度的增加,火焰吹熄速度降低.而当挡环尺度大于临界尺度时,随着挡环尺度的增加,吹熄速度变大.因此湍流的产生区域对火焰吹熄速度有着重要影响.     

Flame stretch analysis in diffusion flames with inert gas

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A theoretical study on Bunsen spray flames

The structure of Bunsen flame tip under the influence of dilute, monodisperse inert (water) or fuel (methanol) sprays is theoretically studied using large activation energy asymptotics. A completely prevaporized mode is identified, in which no liquid droplets exist downstream of the flame. Parameters for open and closed flame tips in the analysis consist of the amount of liquid loading indicating the internal heat loss for the water spray or the internal heat loss and heat gain for the rich and lean methanol-sprays, respectively, and the (negative) stretch coupled with Lewis number (Le) which strengthens the burning intensity of the Le>1 flame but weakens that of the Le<1 flame, respectively. For rich methane-air flames (Le>1) with water sprays (or lean methanol-spray flames with Le>1), closed-tip solutions are obtained. The burning intensity of the flame tip is enhanced with either decreasing liquid-water loading (or increasing liquid-fuel loading) or increasing stretch. Conversely, the negative stretch weakens the burning intensity of a lean methane-air flame (Le<1) with water sprays (or a rich methanol-spray flame with Le<1) and eventually leads to tip opening, i.e., flame extinction. The burning intensity is further reduced with either increasing liquid-water (or liquid-fuel) loading or increasing stretch. Moreover, the open flame tip is further widened when either the liquid-water loading (or liquid-fuel loading) or the upstream flow velocity is increased. It is noteworthy that the gradual increase of liquid-fuel loading strengthens the burning intensity of the lean methanol-spray flame (Le>1) and thus leads to the transition of flame configurations from conventional Bunsen cone through planar flame to inverted flame cone (a convex flame shape with respect to the upstream reactants). The critical value of liquid-fuel loading, at which there exists a planar flame rather than a Bunsen cone flame, is increased with either increasing upstream flow velocity or decreasing equivalence ratio.     

Burning velocities of chlorinated hydrocarbonmethaneair mixtures

Results are presented for the variation in burning velocities with equivalence ratio and reactant gases preheat temperature for a number of chlorinated hydrocarbon compounds in methane-air mixtures of different concentrations at atmospheric pressure. Flame velocity of the mixture is determined with a Bunsen burner by measuring the unignited mixture approach flow rates and the area of the flame front. The method provides acceptable results and compares favorably with widely published methane flame data. Activation energy for a particular chlorinated compound was calculated by relating the flame velocity to the overall combustion reaction rate. Results are compared with nonchlorinated compounds and the available data in the literature. The reasons for discrepancies are discussed. The results show that increasing chlorine content decreases flame velocity and shifts the maximum flame velocity from fuel rich toward fuel lean. The flame velocity increases with increasing gas preheat temperature.     

The synergistic effect of equivalence ratio and initial temperature on laminar flame speed of syngas

The laminar flame speed of syngas (CO:H₂ = 1:1)/air premixed gas in a wide equivalence ratio range (0.6–5) and initial temperature (298–423 K) was studied by Bunsen burner. The results show that the laminar flame speed first increases and then decreases as the equivalence ratio increasing, which is a maximum laminar flame speed at n = 2. The laminar flame speed increases exponentially with the increase of initial temperature. For different equivalent ratios, the initial temperature effects on the laminar flame speed is different. The initial temperature effects for n = 2 (the most violent point of the reaction) is lower than others. It is found that H, O and OH are affected more and more when the equivalence ratio increase. When the equivalence ratio is far from 2, the reaction path changes, and the influence of initial temperature on syngas combustion also changes. The laminar flame speed of syngas is more severely affected by H + O₂ = O + OH and CO + OH = CO₂ + H than others, which sensitivity coefficient is larger and change more greatly than others when the initial temperature and equivalence ratio change. Therefore, the laminar flame speed of syngas/air premixed gas is affected by the initial temperature and equivalence ratio. A new correlation is proposed to predict the laminar flame speed of syngas (CO:H₂ = 1:1)/air premixed gas under the synergistic effect of equivalence ratio and initial temperature (for equivalence ratios of 0.6–5, the initial temperature is 298–423 K).