初始温度/压力对天然气层流燃烧速率的影响

在定容燃烧弹内利用高速纹影摄像法研究了不同初始温度和初始压力下不同当量比的天然气-空气混合气的火焰传播过程,并结合火焰传播照片分析了初始压力和初始温度对混合气层流燃烧速率的影响.研究表明,天然气-空气混合气的无拉伸火焰传播速率和无拉伸层流燃烧速率随当量比的增加先增大后减小,且最大值出现在化学当量比附近.火焰传播速率和层流燃烧速率均随着初始压力的升高而降低,随着初始温度的升高而提高.     

高温高压下二甲醚—空气预混层流燃烧特性研究

在定容燃烧弹内研究了初始压力为0.5 MPa时,不同初始温度和燃空当量比下二甲醚-空气混合气预混层流火焰的层流燃烧速率和马克斯坦长度,分析了火焰拉伸对火焰传播速率的影响.基于容弹燃烧的双区模型计算了预混层流燃烧的燃烧特性参数.结果表明:随着初始温度的增加,二甲醚-空气预混合气的无拉伸火焰传播速率和无拉伸层流燃烧率增加;对于给定的初始温度,在化学当量比偏浓混合气一侧存在一个层流燃烧速度的峰值;随初始温度和当最比增加,马克斯坦长度值减小,火焰前锋面的不稳定性增加;最大燃烧压力随初始温度的增加而下降,压力升高率随初始温度的增加而降低.     

不同初始压力下掺氢天然气的燃烧特性

在定容燃烧弹内研究了不同初始压力下天然气-氢气-空气混合气的火焰传播规律,得到了不同掺氢比例和初始压力下,不同燃空当量比时混合气的层流燃烧速率,并分析了火焰的稳定性及其影响因素.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,而马克斯坦长度值则随着掺氢比例的增加而减小,即火焰的稳定性下降.不同初始压力下,随着燃空当量比的增加,马克斯坦长度值在不同掺氢比例下均增加,显示火焰的稳定性增加.无拉伸层流燃烧速率随着初始压力的增加略有减小,且在化学当量比附近,变化的初始压力和掺氢比对无拉伸层流燃烧速率的影响最为明显.     

用光学纹影摄影术观察分析定容燃烧室内氢燃料的燃烧过程

论述了采用纹影摄影术和高速摄影法观察分析氢气和空气预混合燃料在定容燃烧室内的火花点火燃烧过程,定性地分析了预混合氢气燃料的火焰形态和变化过程,以及燃烧室内的初始压力和空燃比对火焰传播速度及其燃烧压力的影响,通过采用纹影摄影术方法,初步揭示了预混合氢气燃料在定容燃烧室内燃烧时火焰初期紊流产生的机理,以及由开始的层流状火焰发展到湍流状火焰的过程,研究结果表明,预混合氢气燃料燃烧的火焰传播速度及燃烧压力明显地受燃烧室内的初始压力和空燃比的影响。     

氮气稀释气对天然气燃烧特性的影响

为获得氮气稀释气对天然气燃烧特性的影响规律,在定容燃烧反应器中对不同当量比与初始压力下天然气的火焰传播特性、燃烧稳定性及燃烧特性进行了试验测试,并分析了氮气稀释度对天然气火焰传播特性、燃烧稳定性及燃烧特性的影响规律。研究结果表明:随着初始压力与氮气稀释度的升高,火焰前锋面将出现细小裂纹,火核逐渐向定容燃烧反应器上部漂移,火焰稳定性变差;随着初始压力的提高,马克斯坦长度明显变短,火焰稳定性变差,无拉伸火焰传播速度与层流燃烧速度明显降低,但最大燃烧压力显著升高。随着当量比的提高,层流燃烧速度与最大燃烧压力出现先增加后降低的趋势,两者的最大值出现在当量比为1.0时。马克斯坦长度随氮气稀释度的增加逐渐变短,表明火焰逐渐趋于不稳定;同时,无拉伸火焰传播速度、层流燃烧速度与最大燃烧压力随氮气稀释度的增加显著降低。     

EGR中二氧化碳对氢气层流燃烧特性的影响

为了更深入地理解废气中二氧化碳对掺氢燃料燃烧特性的影响,在定容燃烧弹中利用高速摄像系统研究了不同燃空当量比φ(0.6～1.4)和稀释比(0%～40%)下CO2稀释氢气-空气混合气的层流燃烧特性.结果表明:氢气-空气混合气的火焰传播速率随着燃空当量比的增大而增大;马克斯坦长度随着当量比的增大而增大,即火焰的稳定性增强;随稀释比的增大,无拉伸火焰传播速率S1明显减小;同时得到层流火焰燃烧速率,并分析了稀释比对火焰稳定性的影响.通过对试验结果数据拟合,获得了计算氢气-CO2-空气混合气的无拉伸层流燃烧速率的拟合多项式.     

稀释气对掺氢天然气层流预混燃烧燃烧速率的影响

在定容燃烧弹内研究了初始压力为0.1 MPa、初始温度为285 K时掺氢天然气-空气-稀释气体混合气层流预混燃烧的火焰传播规律,获得了分别使用氮气和二氧化碳作为稀释气时,在不同掺氢比、稀释度和当量比下的无拉伸层流燃烧速率,并分析了氮气和二氧化碳稀释气对燃烧速率的影响.结果表明:无拉伸层流燃烧速率随着掺氢比的增加而增加,随着稀释度的增加而减小,二氧化碳对燃烧速率的作用强于氮气.     

异丁醇/辛酸甲酯混合燃料预混层流火焰速度的研究

针对生物柴油与醇类混合燃料燃烧机理研究的需求,采用高速纹影光学诊断方法和定容燃烧弹系统试验研究了异丁醇/辛酸甲酯混合燃料的预混层流燃烧特性。测量了不同当量比和初始压力条件下的不同配比混合燃料—空气预混合气的层流燃烧火焰速度,火焰拉伸率以及马克斯坦长度。分析了燃烧初始条件及异丁醇掺混比例对混合燃料的无拉伸层流燃烧速度及火焰不稳定性的影响规律。结果表明:异丁醇/辛酸甲酯混合燃料的拉伸层流火焰传播速度和层流火焰燃烧速度随着当量比的增加先增加后减少,随着初始压力的增加而减小;马克斯坦长度随着当量比和初始压力的增加而减小;异丁醇掺混比例的增加加快了层流火焰燃烧速度,但使得火焰的不稳定性倾向增加。     

初始压力对甲烷-空气预混气体燃烧特性的影响研究

试验采用高速纹影系统和压力传感器对甲烷-空气预混气体定容燃烧特性进行了研究,分析了不同初始压力对火焰传播特性的影响以及定容燃烧弹中压力的变化规律。试验结果表明:随着初始压力的增加,火焰的传播速度变化不大,并且有减小的趋势,当初始压力超过0.14 MPa后火焰的燃烧速度会发生突变而增大;初始压力的变化对定容燃烧弹中燃烧压力的影响十分显著,当初始压力为0.10 MPa时,最大燃烧压力Pmax=0.703MPa;而在初始压力为0.16 MPa时,最大燃烧压力Pmax=1.42 MPa;随着初始压力的增加,火焰变得愈发的不稳定。     

甲醇-空气-氮气混合气预混球型火焰的试验研究

利用高速纹影摄像法在定容燃烧弹内研究了不同燃空当最比、初始压力、初始温度和气体稀释度下甲醇-空气-氮气混合气预混球型火焰的发展特性以及3种火焰锋面的不稳定性.获得了不同初始状态下的层流燃烧速度、质量燃烧流量和马克斯坦长度.高的初始压力时,火焰锋面生成的裂纹发展并形成细胞状结构.稀混合气时,浮力和电极的冷却作用对火焰的发展有重要影响.当量比在化学计量比附近时,随着初始温度的提高,流体动力学不稳定性被抑制.随着初始压力的增加,流体动力学不稳定性增强.稀释气的加入抑制了火焰锋面流体动力学的不稳定性.     

Combustion characteristics of methanol–air and methanol–air–diluent premixed mixtures at elevated temperatures and pressures

Combustion characteristics of the methanol–air premixed mixtures were studied in a constant volume bomb at different equivalence ratios, initial pressures and temperatures, and dilution ratios. The results show that the combustion pressure, the mass burning rate and the burned gas temperature get the maximum value at the equivalence ratio of 1.1 while the flame development duration and the combustion duration get the minimum value at the equivalence ratio of 1.1. The flame development duration, the combustion duration and the peak combustion pressure decrease with the increase of the initial temperature, while the maximum burned gas temperature increases with the increase of the initial temperature. The peak combustion pressure and temperature increase with the increase of the initial pressure. The flame development duration and combustion duration increase with the increase of the dilution ratio, while the peak combustion pressure and temperature decrease with the increase of the dilution ratio.     

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。     

高温高压条件下乙醇-空气-稀释气预混合气层流燃烧特性研究

利用定容燃烧弹和高速纹影摄像手段研究了不同初始压力、初始温度、气体稀释度和燃空当量比下乙醇-空气-稀释气预混层流燃烧特性的基础特征参数,如绝热火焰温度、层流燃烧速度、层流燃烧质量流量、层流燃烧火焰厚度和已燃气体Markstein长度。研究结果表明:在给定初始压力、初始温度和气体稀释度的情况下,绝热火焰温度、质量燃烧流量和层流燃烧速度的最大值均出现在当量比1.0～1.1,层流火焰厚度在当量比1.1处取得最小值;已燃气体Markstein长度随当量比的增加呈下降趋势;在给定当量比条件下,绝热火焰温度随初始压力、初始温度的增加而增加,随氮气稀释度的增加而降低;层流燃烧速度随初始压力和氮气稀释度增加而降低,随初始温度增加而增加;层流质量燃烧流量随初始压力和初始温度的增加而增加;随氮气稀释度增加而减小;层流火焰厚度和已燃气体Markstein长度随初始压力和初始温度的增加而减小,随氮气稀释度的增加而增加。     

Effects of initial pressure and hydrogen concentration on laminar combustion characteristics of diluted natural gas–hydrogen–air mixture

In this study, the experiment study about the laminar burning velocity and the flame stability of CO₂ diluted natural gas–hydrogen–air mixture was conducted in a constant volume combustion vessel by using the high-speed schlieren photography system. The unstretched laminar burning velocity and the Markstein length at different hydrogen fractions, dilution ratios and equivalence ratios and with different initial pressures were obtained. The flame stability was studied by analyzing the Markstein length, the flame thickness, the density ratio and the flame propagation schlieren photos. The results showed that the unstretched laminar burning velocity would be reduced with the increase of the initial pressure and dilution ratio and would be increased with the increase of the hydrogen fraction of the mixture. Meanwhile, the Markstein length would be increased with the increase of the equivalence ratio and the dilution ratio. Slight flaws occurred at the early stage. At a specific equivalence ratio, a higher initial pressure and hydrogen fraction would cause incomplete combustion.     

Experimental study on premixed combustion of spherically propagating methanol-air-nitrogen flames

The outward propagation and development of surface instability of the spark-ignited spherical premixed flames for methanol-air-nitrogen mixtures were experimentally studied by using a constant volume combustion chamber and a high-speed schlieren photography system. The laminar burning velocities, the mass burning fluxes, and the Markstein lengths were obtained at different equivalence ratios, dilution ratios, initial temperatures, and pressures. The laminar burning velocities and the mass burning fluxes give a similar curve versus the equivalence ratios. They increase with the increase of initial temperature and decrease with the increase of dilution ratio. The laminar burning velocity decreases with elevating the initial pressure, while the mass burning flux increases with the increase of the initial pressure. Markstein length decreases slightly with the increase of initial temperature for the rich mixtures. High initial pressure corresponds to low Markstein length. Markstein length increases with the increase of dilution ratio, which is more obvious when the mixture becomes leaner. Equivalence ratio has a slight impact on the development of the diffusive-thermal cellular structure at elevated initial pressures. The initial pressure has a significant influence on the occurrence of the flame front cellular structure. At the elevated pressures, the cracks on the flame surface branch and develop into the cell structure. These cells are bounded by cracks emitting a bright light, which may indicate soot formation. For very lean mixture combustion, the buoyancy effect and cooling effect from the spark electrodes have a significant impact on the flame propagation. The hydrodynamic instability, inhibited with the increase of initial temperature around the stoichiometric equivalence ratio, is enhanced with the increase of initial pressure and suppressed by mixture dilution.     

Experimental study on premixed combustion of spherically propagating methanol-air-nitrogen flames

The outward propagation and development of surface instability of the spark-ignited spherical premixed flames for methanol-air-nitrogen mixtures were experimentally studied by using a constant volume combustion chamber and a high-speed schlieren photography system. The laminar burning velocities, the mass burning fluxes, and the Markstein lengths were obtained at different equivalence ratios, dilution ratios, initial temperatures, and pressures. The laminar burning velocities and the mass burning fluxes give a similar curve versus the equivalence ratios. They increase with the increase of initial temperature and decrease with the increase of dilution ratio. The laminar burning velocity decreases with elevating the initial pressure, while the mass burning flux increases with the increase of the initial pressure. Markstein length decreases slightly with the increase of initial temperature for the rich mixtures. High initial pressure corresponds to low Markstein length. Markstein length increases with the increase of dilution ratio, which is more obvious when the mixture becomes leaner. Equivalence ratio has a slight impact on the development of the diffusive-thermal cellular structure at elevated initial pressures. The initial pressure has a significant influence on the occurrence of the flame front cellular structure. At the elevated pressures, the cracks on the flame surface branch and develop into the cell structure. These cells are bounded by cracks emitting a bright light, which may indicate soot formation. For very lean mixture combustion, the buoyancy effect and cooling effect from the spark electrodes have a significant impact on the flame propagation. The hydrodynamic instability, inhibited with the increase of initial temperature around the stoichiometric equivalence ratio, is enhanced with the increase of initial pressure and suppressed by mixture dilution.     

利用火花点火式快速压缩装置进行天然气直喷分层燃烧可行性的研究

利用快速压缩装置进行了天然气直喷分层燃烧可行性的研究。结果表明 :天然气分层燃烧具有短的初期火焰发展期和主燃期以及高的燃烧压力。分层燃烧可使稀燃极限延伸到很小的当量比。由于过度分层 ,CO在当量比大于 0 .8时急剧增加 ,而 NOx 的峰值也因充量分层而出现在小当量比处。燃烧效率在当量比处于0 .1～ 0 .9范围时高于 0 .92 ,在极小当量比时由于未燃混合气淬熄 ,在当量比时由于过度分层而使燃烧效率降低。根据燃烧产物计算的燃烧效率与根据放热分析获得的燃烧效率一致。因此 ,天然气直喷分层燃烧在宽广的当量比范围内可望实现高效燃烧火花助燃发动机的宽广的高效燃烧。     

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EG R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...     

Measurements of laminar burning velocities and flame stability analysis for dissociated methanol–air–diluent mixtures at elevated temperatures and pressures

The laminar burning velocities and Markstein lengths for the dissociated methanol–air–diluent mixtures were measured at different equivalence ratios, initial temperatures and pressures, diluents (N₂ and CO₂) and dilution ratios by using the spherically outward expanding flame. The influences of these parameters on the laminar burning velocity and Markstein length were analyzed. The results show that the laminar burning velocity of dissociated methanol–air mixture increases with an increase in initial temperature and decreases with an increase in initial pressure. The peak laminar burning velocity occurs at equivalence ratio of 1.8. The Markstein length decreases with an increase in initial temperature and initial pressure. Cellular flame structures are presented at early flame propagation stage with the decrease of equivalence ratio or dilution ratio. The transition positions can be observed in the curve of flame propagation speed to stretch rate, indicating the occurrence of cellular structure at flame fronts. Mixture diluents (N₂ and CO₂) will decrease the laminar burning velocities of mixtures and increase the sensitivity of flame front to flame stretch rate. Markstein length increases with an increase in dilution ratio except for very lean mixture (equivalence ratio less than 0.8). CO₂ dilution has a greater impact on laminar flame speed and flame front stability compared to N₂. It is also demonstrated that the normalized unstretched laminar burning velocity is only related to dilution ratio and is not influenced by equivalence ratio.