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RATE-CONTROLLED CONSTRAINED EQUILIBRIUM: A BASIS FOR EFFECTIVE COUPLING OF COMPREHENSIVE CHEMICAL KINETICS AND CFD

速率控制约束平衡：综合化学动力学与 CFD 有效耦合的基础

基本信息

批准号：
EP/G057311/2
负责人：
Stylianos Rigopoulos
金额：
$ 11.78万
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FG057311%2F2
关键词：
RATE CONTROLLED CONSTRAINED EQUILIBRIUM BASIS

项目摘要

Modelling of combustion processes remains an outstanding technical problem with wide implications, both scientific and practical. By far the largest percentage of our energy is produced via combustion equipment such as internal combustion engines for cars, turbines for aircraft or industrial burners for power generation. These processes also account for the generation of a wide variety of pollutants, such as NOx and soot, as well as for the generation of greenhouse gases. It is widely acknowledged that there is large potential for improvement of those processes, resulting in great environmental benefits. Combustion modelling requires the coupling of fluid dynamics equations, solved numerically through a Computational Fluid Dynamics (CFD) code, with a comprehensive chemical kinetics model. Practical combustion devices are invariably turbulent, which necessitates a further element, the turbulence-chemistry interaction model. Coupling all of these elements results in a formidable computational problem, and the main cause of the bottleneck is the chemical kinetics part of the calculation. Comprehensive chemical kinetics include very large numbers of species and reactions: even for the simplest fuels, such as methane, more than 50 species are necessary, while for commercial fuels hundreds of species and reactions can easily be present. Each species introduces an additional differential equation to the problem, and integration is further hampered by the excessive stiffness that is often exhibited by such systems. Yet the incorporation of comprehensive mechanisms is essential if the formation of pollutants is to be predicted. The mathematical modelling of combustion can be significantly simplified by taking advantage of the time scale separation to assume that fast reactions, typically associated with intermediate species, are in a state of local equilibrium. The proposed research will explore a promising concept for deriving the low-dimensional models on the basis of time-scale separation: Rate-Controlled Constrained Equilibrium (RCCE). In this approach, the kinetically controlled species are allowed to evolve according to the relevant differential equations including the chemical kinetics of the original detailed mechanism, whilst the equilibrated species are determined by minimising the free energy of the mixture, subject to the additional constraints (apart from conservation of mass, energy and elements) that the kinetically controlled species must retain the concentrations given by the solution of their governing equations. Previous work by the authors has provided evidence that RCCE has the potential to develop into a method that is both theoretically rigorous and practically feasible for the implementation of large chemical mechanisms into CFD codes. Having established proof of concept, further work is now required to bring RCCE to the stage where it is ready for application in practical problems. Furthermore, several important questions about the fundamentals of RCCE remain unanswered, such as its relation to other methods of mechanism reduction such as Computational Singular Perturbation (CSP). The two methods are complementary and it is possible that a combination of them will prove a very powerful tool.

燃烧过程的模拟仍然是一个突出的技术问题，具有广泛的科学和实用意义。到目前为止，我们能源的最大比例是通过燃烧设备产生的，例如汽车的内燃机、飞机的涡轮机或用于发电的工业燃烧器。这些过程还导致了各种污染物的产生，如NOx和烟尘，以及温室气体的产生。人们普遍认为，这些工艺有很大的改进潜力，从而产生巨大的环境效益。燃烧模型需要通过计算流体动力学(CFD)程序数值求解的流体动力学方程与全面的化学动力学模型相耦合。实际的燃烧装置总是湍流的，这就需要另一个元素，湍流-化学相互作用模型。将所有这些元素耦合在一起会导致一个可怕的计算问题，而瓶颈的主要原因是计算中的化学动力学部分。全面的化学动力学包括非常大量的物种和反应：即使是最简单的燃料，如甲烷，也需要超过50种物种，而对于商业燃料，可以很容易地存在数百种物种和反应。每一个物种都给问题引入了一个额外的微分方程，而这种系统经常表现出的过度僵硬进一步阻碍了积分。然而，如果要预测污染物的形成，纳入综合机制是必不可少的。通过利用时间尺度分离假设通常与中间物种相关的快速反应处于局部平衡状态，可以显著简化燃烧的数学模型。这项研究将探索基于时间-尺度分离的低维模型的一个有前途的概念：速率控制约束均衡(RCCE)。在这种方法中，允许受动力学控制的物种根据包括原始详细机理的化学动力学在内的相关微分方程式演化，而平衡的物种是通过最小化混合物的自由能来确定的，受附加约束(除了质量、能量和元素守恒之外)，受动力学控制的物种必须保持其控制方程的解所给出的浓度。作者以前的工作提供了证据，表明RCCE有潜力发展成为一种理论上严格且实际可行的方法，用于在CFD程序中实现大型化学机理。在确定了概念证明之后，现在需要进一步的工作，以使RCCE达到准备在实际问题中应用的阶段。此外，关于RCCE基本原理的几个重要问题仍然没有得到回答，例如它与其他机构简化方法的关系，如计算奇异摄动(CSP)。这两种方法是相辅相成的，它们的结合可能会被证明是一个非常强大的工具。