Forced ignition in turbulent mixtures of sufficiently large Lewis numbers

刘易斯数足够大的湍流混合物中的强制点火

• 批准号: 411275182
• 负责人: Professor Dr. Christian Hasse
• 金额: --
• 依托单位: National Natural Science Foundation of China
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/411275182?language=en
• 关键词: Forced; ignition; turbulent; mixtures; sufficiently

The forced ignition of a turbulent premixed mixture is of relevance in many devices used in practice such as spark ignition engines/gas turbines, and in natural phenomena such as fires and explosions. It is therefore indispensable to understand the dynamics of ignition kernel evolution (IKE) in turbulent flows to improve the design of technical devices and to reliably control fires and explosions.A controlled forced ignition (or spark ignition) process consists of four phases: ignition kernel formation, ignition kernel growth, transition between ignition kernel and sustained flame kernel, and flame kernel development and flame stabilization. For the forced ignition of premixed reactants, the classic conclusion of turbulence effects on IKE is that turbulence renders ignition more difficult due to the turbulence-induced Kernel Dissipation (KD), which, however, neglects the effects of turbulence on the stretch of the ignition/flame kernel (Kernel Stretch, KS) during the growth and transition phases. However, facilitated ignition by turbulence for Le>1 was recently discovered in experiments. It was hypothesized that the turbulence-induced KS effect created flames with a wide range of positive and negative stretch rates. Negatively stretched flames with Le>1 are strengthened by differential diffusion, and this effect can potentially facilitate ignition. However, this important finding has not yet been analyzed using corresponding turbulent simulations that could reveal the detailed mechanism of turbulence effects on IKE when Le>1. Thus, understanding turbulence/kernel interaction in the forced ignition of turbulent premixed mixtures with Le>1 is an unresolved scientific issue. Closing this gap is the main objective of the project proposed here.The project is a close collaboration between TU Darmstadt (TUD) and Peking University (PKU). At PKU, Direct Numerical Simulations (DNSs) with detailed chemistry of laminar and turbulent forced ignition cases are performed and analyzed to gain a detailed understanding of IKE. The DNS database is used by TUD to develop, adapt and validate an advanced premixed flamelet model comprehensively accounting for negative/positive stretch, curvature, and preferential diffusion. Using this model, multidimensional flamelet tables will be created using at least progress variable, strain and curvature as parameters. The tables will be coupled with the flow solvers for simulations of turbulent forced ignition cases at both institutions: the results of Flamelet-DNS (PKU) and Flamelet-LES (TUD) will be compared to the DNS data with detailed chemistry.In summary, the project aims to contribute to the understanding of IKE in turbulent flows and to provide efficient modeling approaches for the design of next-generation high-efficiency, low-emission combustors.

湍流预混混合物的强制点火在实践中使用的许多装置（例如火花点火发动机/燃气轮机）中以及在自然现象（例如火灾和爆炸）中是相关的。研究湍流中点火核的演化规律，对于改进技术设备的设计和可靠地控制火灾和爆炸具有重要意义。受控强制点火（或火花点火）过程包括点火核形成、点火核生长、点火核与持续火焰核的过渡、火焰核发展和火焰稳定4个阶段。对于预混反应物的强制点火，湍流对IKE的影响的经典结论是，湍流使点火更加困难，由于湍流诱导的内核耗散（KD），然而，忽略了在增长和过渡阶段的点火/火焰内核的拉伸（内核拉伸，KS）的湍流的影响。然而，最近在实验中发现了Le>1的湍流促进点火。据推测，燃烧诱导的KS效应产生的火焰具有广泛的正拉伸率和负拉伸率。Le>1的负拉伸火焰通过微分扩散得到加强，这种效应可能有助于点火。然而，这一重要的发现还没有使用相应的湍流模拟来分析，可以揭示当Le>1时湍流对IKE的影响的详细机制。因此，理解Le>1的湍流预混混合物的强制点火中的湍流/内核相互作用是一个尚未解决的科学问题。该项目是达姆施塔特工业大学（TUD）和北京大学（PKU）的密切合作项目。在北京大学，直接数值模拟（DNSs）与层流和湍流强迫点火情况下的详细化学进行和分析，以获得详细的了解IKE。DNS数据库被TUD用于开发、调整和验证一个先进的预混火焰面模型，该模型综合考虑了负/正拉伸、曲率和优先扩散。使用这个模型，多维火焰表将创建至少使用进度变量，应变和曲率作为参数。这些表格将与两个机构的湍流强制点火情况模拟用的流动求解器相结合：Flamelet-DNS（PKU）和Flamelet-LES（TUD）的结果将与DNS数据进行详细的化学比较。总之，该项目旨在促进对湍流中IKE的理解，并为下一代高效，低排放的燃烧器