{"title":"The extinction limits and the radical index of non-premixed counterflow flames of methane/ammonia/nitrogen versus high-temperature air","authors":"Yuki Murakami, Takuya Tezuka, Hisashi Nakamura","doi":"10.1016/j.combustflame.2024.113540","DOIUrl":null,"url":null,"abstract":"<div><p>The extinction limits of non-premixed counterflow flames of methane (CH<sub>4</sub>)/ammonia (NH<sub>3</sub>)/nitrogen (N<sub>2</sub>) versus high-temperature air (<em>T</em><sub>Air</sub> = 700 K and 1000 K) were investigated both experimentally and numerically. Extinction stretch rates of non-premixed counterflow flames of CH<sub>4</sub>/NH<sub>3</sub> mixtures decreased greatly as the ammonia mixing ratio increased. Recent chemical kinetic models could well predict measured extinction limits of non-premixed counterflow flames of CH<sub>4</sub>/NH<sub>3</sub> mixtures, especially for <em>T</em><sub>Air</sub> = 1000 K. Chemical kinetic analyses indicated that the nature of NH<sub>3</sub> consuming active radicals but not regenerating them through its oxidation is the primary reason for the drastic decreases in extinction stretch rates of non-premixed counterflow flames of CH<sub>4</sub>/NH<sub>3</sub> mixtures. Furthermore, the combined metric of the transport weighted enthalpy (<em>TWE</em>) and the radical index (<em>RI</em>) is introduced for non-premixed counterflow flames of CH<sub>4</sub>/NH<sub>3</sub> mixtures. The OH-radical index (<em>RI</em><sub>OH</sub>), previously used in the combined metric for extinction limits of non-premixed counterflow flames of large hydrocarbons, expresses linear relationships with extinction limits for both <em>T</em><sub>Air</sub> conditions. According to further investigations on heat releases from individual reactions, the contribution to heat releases from a reaction involving O radicals, i.e., CH<sub>3</sub> + O ⇄ CH<sub>2</sub>O + H, becomes large in addition to reactions involving OH radicals, i.e., CO + OH ⇄ CO<sub>2</sub> + H and H<sub>2</sub> + OH ⇄ H + H<sub>2</sub>O. Based on the analyses, a new radical index based on the combination of OH and O radicals (<em>RI</em><sub>OH&O</sub>) is proposed. The <em>RI</em><sub>OH&O</sub> better expresses the linear relationship between extinction limits and the combined metric of <em>RI</em><sub>OH&O</sub> and <em>TWE</em>.</p></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":null,"pages":null},"PeriodicalIF":5.8000,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0010218024002499/pdfft?md5=30f6fc89999ac63b449dd015a6b0b595&pid=1-s2.0-S0010218024002499-main.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Combustion and Flame","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0010218024002499","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
The extinction limits of non-premixed counterflow flames of methane (CH4)/ammonia (NH3)/nitrogen (N2) versus high-temperature air (TAir = 700 K and 1000 K) were investigated both experimentally and numerically. Extinction stretch rates of non-premixed counterflow flames of CH4/NH3 mixtures decreased greatly as the ammonia mixing ratio increased. Recent chemical kinetic models could well predict measured extinction limits of non-premixed counterflow flames of CH4/NH3 mixtures, especially for TAir = 1000 K. Chemical kinetic analyses indicated that the nature of NH3 consuming active radicals but not regenerating them through its oxidation is the primary reason for the drastic decreases in extinction stretch rates of non-premixed counterflow flames of CH4/NH3 mixtures. Furthermore, the combined metric of the transport weighted enthalpy (TWE) and the radical index (RI) is introduced for non-premixed counterflow flames of CH4/NH3 mixtures. The OH-radical index (RIOH), previously used in the combined metric for extinction limits of non-premixed counterflow flames of large hydrocarbons, expresses linear relationships with extinction limits for both TAir conditions. According to further investigations on heat releases from individual reactions, the contribution to heat releases from a reaction involving O radicals, i.e., CH3 + O ⇄ CH2O + H, becomes large in addition to reactions involving OH radicals, i.e., CO + OH ⇄ CO2 + H and H2 + OH ⇄ H + H2O. Based on the analyses, a new radical index based on the combination of OH and O radicals (RIOH&O) is proposed. The RIOH&O better expresses the linear relationship between extinction limits and the combined metric of RIOH&O and TWE.
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.