Effects of intense strain on flame structure and NOx generation in turbulent counterflow lean-premixed hydrogen flames

IF 6.2 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-09-26 DOI:10.1016/j.combustflame.2025.114459

Mohamad Fathi, Stefan Hickel, Nguyen Anh Khoa Doan, Ivan Langella

{"title":"Effects of intense strain on flame structure and NOx generation in turbulent counterflow lean-premixed hydrogen flames","authors":"Mohamad Fathi, Stefan Hickel, Nguyen Anh Khoa Doan, Ivan Langella","doi":"10.1016/j.combustflame.2025.114459","DOIUrl":null,"url":null,"abstract":"<div><div>Direct numerical simulations (DNS) are conducted for reactants-to-products counterflow configurations at turbulent conditions to understand how strain affects the structure and NOx emissions of lean premixed hydrogen flames. Two nominal equivalence ratio conditions, 0.5 and 0.7, are investigated. Under unstretched conditions, the Markstein length is negative for the former and slightly positive for the latter, indicating distinct responses of heat release rate and flame consumption speed to strain in each case. For each equivalence ratio condition, three levels of applied strain rate are considered, resulting in a total of six DNS. Results indicate that overall NOx emissions decrease with increasing strain at turbulent conditions, consistent with recent results for laminar conditions presented in Porcarelli et al. (2024). However, the relative decrease of NOx with strain is faster under turbulent conditions because turbulent mixing limits the occurrence of super-adiabatic temperatures. Moreover, the decrease of NOx is strongly correlated only to the mean applied tangential strain rate, while local fluctuations of strain due to vortices exhibit more stochastic behaviour. The detailed analysis presented in this article indicates that the applied strain can be used to substantially decrease NOx emissions in premixed hydrogen flames under practical conditions.</div><div><strong>Novelty and Significance statement:</strong></div><div>This work examines for the first time in detail the coupled effects of strain and turbulence in hydrogen flames, for various conditions spanning different signs of the Markstein length and increasing applied strain levels. In particular, it clarifies the different roles of applied strain, turbulence-driven strain, and curvature on both flame structure and NOx generation. Results further show for the first time that both in-flame and post-flame NOx can be suppressed at high strain levels under turbulent conditions. This result is of paramount importance as it implies that NOx can be suppressed at combustor-relevant conditions by straining the flame.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"282 ","pages":"Article 114459"},"PeriodicalIF":6.2000,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Combustion and Flame","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0010218025004961","RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ENERGY & FUELS","Score":null,"Total":0}

引用次数: 0

Abstract

Direct numerical simulations (DNS) are conducted for reactants-to-products counterflow configurations at turbulent conditions to understand how strain affects the structure and NOx emissions of lean premixed hydrogen flames. Two nominal equivalence ratio conditions, 0.5 and 0.7, are investigated. Under unstretched conditions, the Markstein length is negative for the former and slightly positive for the latter, indicating distinct responses of heat release rate and flame consumption speed to strain in each case. For each equivalence ratio condition, three levels of applied strain rate are considered, resulting in a total of six DNS. Results indicate that overall NOx emissions decrease with increasing strain at turbulent conditions, consistent with recent results for laminar conditions presented in Porcarelli et al. (2024). However, the relative decrease of NOx with strain is faster under turbulent conditions because turbulent mixing limits the occurrence of super-adiabatic temperatures. Moreover, the decrease of NOx is strongly correlated only to the mean applied tangential strain rate, while local fluctuations of strain due to vortices exhibit more stochastic behaviour. The detailed analysis presented in this article indicates that the applied strain can be used to substantially decrease NOx emissions in premixed hydrogen flames under practical conditions.

Novelty and Significance statement:

This work examines for the first time in detail the coupled effects of strain and turbulence in hydrogen flames, for various conditions spanning different signs of the Markstein length and increasing applied strain levels. In particular, it clarifies the different roles of applied strain, turbulence-driven strain, and curvature on both flame structure and NOx generation. Results further show for the first time that both in-flame and post-flame NOx can be suppressed at high strain levels under turbulent conditions. This result is of paramount importance as it implies that NOx can be suppressed at combustor-relevant conditions by straining the flame.

查看原文本刊更多论文

湍流逆流贫预混氢火焰中强应变对火焰结构和NOx生成的影响

对湍流条件下的反应物-生成物逆流构型进行了直接数值模拟（DNS），以了解应变如何影响贫预混氢火焰的结构和NOx排放。研究了0.5和0.7两个标称等效比条件。在非拉伸条件下，前者的Markstein长度为负，后者的Markstein长度略为正，表明在每种情况下，放热速率和火焰消耗速度对应变的响应都是不同的。对于每个等效比条件，考虑了三个水平的施加应变率，从而得到6个DNS。结果表明，在湍流条件下，总氮氧化物排放量随着应变的增加而减少，这与Porcarelli等人（2024）最近在层流条件下的结果一致。然而，在湍流条件下，由于湍流混合限制了超绝热温度的发生，NOx随应变的相对下降速度更快。此外，NOx的减少仅与施加的平均切向应变率密切相关，而由于涡旋引起的局部应变波动表现出更多的随机行为。本文的详细分析表明，在实际条件下，施加应变可以大大减少预混氢火焰中的NOx排放。新颖性和意义声明：这项工作首次详细研究了氢火焰中应变和湍流的耦合效应，在各种条件下跨越不同的马克斯坦长度标志和增加的应用应变水平。特别地，它阐明了施加应变、湍流驱动应变和曲率对火焰结构和NOx生成的不同作用。研究结果首次表明，在湍流条件下，在高应变水平下，火焰内和火焰后的NOx都可以被抑制。这一结果是至关重要的，因为它意味着氮氧化物可以在燃烧器相关条件下通过压缩火焰来抑制。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

求助全文

约1分钟内获得全文求助全文

来源期刊

Combustion and Flame 工程技术-工程：化工

CiteScore

9.50

自引率

20.50%

发文量

631

审稿时长

3.8 months

期刊介绍： The mission of the journal is to publish high quality work from experimental, theoretical, and computational investigations on the fundamentals of combustion phenomena and closely allied matters. While submissions in all pertinent areas are welcomed, past and recent focus of the journal has been on: Development and validation of reaction kinetics, reduction of reaction mechanisms and modeling of combustion systems, including: Conventional, alternative and surrogate fuels; Pollutants; Particulate and aerosol formation and abatement; Heterogeneous processes. Experimental, theoretical, and computational studies of laminar and turbulent combustion phenomena, including: Premixed and non-premixed flames; Ignition and extinction phenomena; Flame propagation; Flame structure; Instabilities and swirl; Flame spread; Multi-phase reactants. Advances in diagnostic and computational methods in combustion, including: Measurement and simulation of scalar and vector properties; Novel techniques; State-of-the art applications. Fundamental investigations of combustion technologies and systems, including: Internal combustion engines; Gas turbines; Small- and large-scale stationary combustion and power generation; Catalytic combustion; Combustion synthesis; Combustion under extreme conditions; New concepts.