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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/G057311/1
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，我们最大比例的能源是通过燃烧设备产生的，例如汽车内燃机、飞机涡轮机或发电用工业燃烧器。这些过程还导致多种污染物的产生，例如氮氧化物和烟灰，以及温室气体的产生。人们普遍认为，这些工艺的改进潜力巨大，可以带来巨大的环境效益。燃烧建模需要将通过计算流体动力学 (CFD) 代码进行数值求解的流体动力学方程与综合化学动力学模型相结合。实际的燃烧装置总是处于湍流状态，这需要另一个元素，即湍流化学相互作用模型。所有这些元素的耦合会导致巨大的计算问题，而瓶颈的主要原因是计算的化学动力学部分。综合化学动力学包括大量的物质和反应：即使对于最简单的燃料，例如甲烷，也需要超过 50 种物质，而对于商业燃料，可以很容易地存在数百种物质和反应。每个物种都会为问题引入一个额外的微分方程，并且此类系统经常表现出的过度刚度进一步阻碍了积分。然而，如果要预测污染物的形成，则必须采用综合机制。通过利用时间尺度分离来假设通常与中间物质相关的快速反应处于局部平衡状态，可以显着简化燃烧的数学模型。拟议的研究将探索一个有前途的概念，用于在时间尺度分离的基础上推导低维模型：速率控制约束平衡（RCCE）。在这种方法中，允许动力学控制的物质根据相关的微分方程（包括原始详细机制的化学动力学）演化，而平衡的物质是通过最小化混合物的自由能来确定的，受到额外的约束（除了质量、能量和元素守恒之外），即动力学控制的物质必须保留由其控制方程的解给出的浓度。作者之前的工作提供了证据，表明 RCCE 有潜力发展成为一种理论严谨且实践可行的方法，可将大型化学机制实施到 CFD 代码中。建立概念验证后，现在需要开展进一步的工作，使 RCCE 达到可应用于实际问题的阶段。此外，关于 RCCE 基本原理的几个重要问题仍未得到解答，例如它与其他机制简化方法（例如计算奇异扰动（CSP））的关系。这两种方法是互补的，它们的组合可能会成为一个非常强大的工具。