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/G057311/1
负责人：
Stylianos Rigopoulos
金额：
$ 17.45万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FG057311%2F1
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.

燃烧过程的建模仍然是一个杰出的技术问题，具有广泛的科学和实用性。到目前为止，我们能源的最大百分比是通过燃烧设备（例如汽车的内燃机，飞机涡轮机或用于发电的工业燃烧器）生产的。这些过程还解释了多种污染物（例如NOX和烟灰）以及温室气体的产生。人们普遍承认，改善这些过程的潜力很大，从而带来了巨大的环境利益。燃烧建模需要通过计算流体动力学（CFD）代码和全面的化学动力学模型来求解流体动力学方程，并通过计算流体动力学（CFD）代码求解。实用的燃烧设备始终是湍流，这需要进一步的元素，即湍流化学相互作用模型。将所有这些元素耦合导致了强大的计算问题，而瓶颈的主要原因是计算的化学动力学部分。全面的化学动力学包括大量物种和反应：即使对于最简单的燃料，例如甲烷，也需要50多种物种，而对于商业燃料来说，数百种物种和反应也很容易出现。每个物种都引入了问题的其他微分方程，并且由于这种系统经常表现出的过度刚度而进一步阻碍了整合。但是，如果要预测污染物的形成，则必须纳入综合机制。通过利用时间尺度的分离，可以显着简化燃烧的数学模型，以假设通常与中间物种相关的快速反应处于局部平衡状态。拟议的研究将探索一个有希望的概念，用于根据时间尺度的分离得出低维模型：速率控制的约束平衡（RCCE）。在这种方法中，可以根据相关的微分方程（包括原始详细机制的化学动力学）来发展动力学控制的物种，而平衡物种是通过最小化混合物的自由能来确定的，但要受到其他约束（分开）从质量，能量和元素的保护中，动力学控制物种必须保留其管理方程式给出的浓度。作者先前的工作提供了证据，表明RCCE有可能发展为理论上严格且实际上可行的方法，可用于将大型化学机制实施到CFD代码中。建立概念证明后，现在需要进一步的工作才能将RCCE带到准备在实际问题中应用的阶段。此外，关于RCCE基本面的几个重要问题仍未得到解答，例如它与其他减少机制的关系，例如计算奇异扰动（CSP）。这两种方法是互补的，它们的组合可能会证明是一种非常强大的工具。