Thermal-diffusive instabilities, soot and carbon nanotube formation in unstrained diffusion flames

无应变扩散火焰中的热扩散不稳定性、烟灰和碳纳米管的形成

• 批准号: RGPIN-2014-03622
• 负责人: Robert, Etienne
• 金额: $ 1.68万
• 依托单位: École Polytechnique de Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=663461
• 关键词: Thermal; diffusive; instabilities; soot; carbon

Combustion systems are complex machines in which a large number of chemical reaction take place simultaneously and closely coupled with fluid mechanics processes. It is therefore often useful to gather fundamental knowledge on each phenomenon in simple configuration uncoupled from perturbing influences. In this project we are using a unique experimental burner to investigate combustion-related phenomenon in unstrained diffusion flames. In this configuration, the reactants are provided separately to the reaction chamber and the flame has a one-dimensional inner structure which allows for direct quantitative comparison with theoretical models. Although this configuration can seem far from practical applications it is used extensively for the development of theoretical models, for instance on thermal-diffusive instabilities. It is also relevant to the flamelet concept, used extensively for the numerical modelling of the turbulent partially-premixed combustion encountered in gas turbines.**The research program presented here targets two main topics where the use of this unique tool can provide novel insight into complex combustion-related phenomena of particular interest for the canadian energy-conversion sector. In the context of the desire to reduce emissions from the combustion of hydrocarbons from fossil or biological origin, several products are the subject of intense research. For instance, carbon dioxide (CO2) is the dominant greenhouse gas, fine particulate such as soot are a serious health hazard and nitrogen oxides (NOx) are responsible for urban pollution and acid rain. However, attempts to reduce one of these emissions is often made at the expense of an increase in another or can result in an unacceptable decrease in performance.**The first research topic included in this proposal is the investigation of thermal-diffusive instabilities (TDIs) that form close to the extinction limit. The current trend to operate combustors with lean mixtures, a technique used extensively to to lower emissions in gas turbine applications, makes them more susceptible to the development of TDIs and research is necessary to to identify safe operating conditions in lean mixtures. Our work aims to provide experimental results for the quantitative validation of theoretical models for diffusion flame stability. The second research topic focuses on the formation and aggregation of soot particles in diffusion flame. These phenomena can be advantageously investigated using our experimental configuration where a stable soot layer can be formed and the residence time of the particles can be controlled precisely.**Additionally, two more research projects have been initiated following observation made in the burner mentioned above. The third research axis of this proposal focuses on the investigation of carbon nanotube formation in flame environments. More specifically, the unstrained and one dimensional nature of the flow in our reaction chamber offers unique conditions for the growth of a wide variety of carbon nano-structures, including nanotubes without catalysts. The fourth and final research axis of this proposal addresses the need to develop techniques to concentrate and sort aerosols, for instance as a function of the particle size. We are implementing an approach based of the use of acoustic forces to perform advanced concentration and sorting tasks on polydisperse sub-micron aerosols. Although initially motivated by our desire to separate the carbon nanotubes from the soot simultaneously produced by the flame, such acoustic-based techniques are relevant to a wide range of industrial applications in the energy conversion sector.

燃烧系统是复杂的机器，其中大量的化学反应同时发生并且与流体力学过程紧密耦合。因此，在不受扰动影响的简单配置中收集每种现象的基本知识通常是有用的。在这个项目中，我们使用独特的实验燃烧器来研究无应变扩散火焰中的燃烧相关现象。在这种配置中，反应物单独提供到反应室，火焰具有一维内部结构，可以与理论模型进行直接定量比较。尽管这种配置似乎与实际应用相去甚远，但它广泛用于理论模型的开发，例如热扩散不稳定性模型。它还与小火焰概念相关，广泛用于燃气轮机中遇到的湍流部分预混燃烧的数值模拟。**此处介绍的研究计划针对两个主要主题，在这两个主题中，使用这种独特的工具可以提供新颖的见解加拿大能源转换部门特别感兴趣的复杂燃烧相关现象。在希望减少化石或生物来源碳氢化合物燃烧排放的背景下，有几种产品成为深入研究的主题。例如，二氧化碳 (CO2) 是主要的温室气体，烟尘等细颗粒物严重危害健康，而氮氧化物 (NOx) 则造成城市污染和酸雨。然而，减少其中一种排放的尝试通常是以另一种排放的增加为代价的，或者可能导致性能出现不可接受的下降。**本提案中包含的第一个研究主题是热扩散不稳定性（TDI）的研究）形成接近灭绝极限。当前使用贫混合物运行燃烧室的趋势是一种广泛用于降低燃气轮机应用中排放的技术，这使得它们更容易受到 TDI 开发的影响，因此有必要进行研究以确定贫混合物中的安全运行条件。我们的工作旨在为扩散火焰稳定性理论模型的定量验证提供实验结果。第二个研究课题集中于扩散火焰中烟灰颗粒的形成和聚集。使用我们的实验配置可以有利地研究这些现象，在该配置中可以形成稳定的烟灰层并且可以精确控制颗粒的停留时间。**此外，在上述燃烧器中进行观察后，还启动了另外两个研究项目。该提案的第三个研究轴重点是研究火焰环境中碳纳米管的形成。更具体地说，我们的反应室中流动的无应变和一维性质为各种碳纳米结构的生长提供了独特的条件，包括没有催化剂的纳米管。该提案的第四个也是最后一个研究轴解决了开发浓缩和分类气溶胶技术的需求，例如作为颗粒尺寸的函数。我们正在实施一种基于声学力的方法，对多分散的亚微米气溶胶执行高级浓缩和分选任务。尽管最初的动机是我们希望将碳纳米管与火焰同时产生的烟灰分离，但这种基于声学的技术与能源转换领域的广泛工业应用相关。