Simone Castellani , Gianmarco Lemmi , Pier Carlo Nassini , Roberto Meloni , Antonio Andreini
{"title":"A general formalism for determining the unburnt composition in multi-stream species transport-based CFD simulations","authors":"Simone Castellani , Gianmarco Lemmi , Pier Carlo Nassini , Roberto Meloni , Antonio Andreini","doi":"10.1016/j.combustflame.2025.114128","DOIUrl":null,"url":null,"abstract":"<div><div>The imperative to decarbonise combustion necessitates technical solutions that increasingly rely on the concurrent utilisation of different fuels and/or oxidisers. The complexity of the reactive mixture compositions in such scenarios poses additional challenges from a CFD modelling perspective. While species transport models can generally describe multi-stream combustion problems directly, the definition of turbulence-chemistry interaction closures or the proper comprehension of combustion regimes often requires the reconstruction of the non-reactive mixing field. This work proposes a general comprehensive formalism for determining the unburnt composition in multi-stream combustion environments. The method relies on the elemental mass fraction conservation for the definition of a linear system that can be solved at runtime to retrieve the local unburnt mixture composition. The introduced formalism allows to assess the number of auxiliary stream-tracking scalars <span><math><mrow><mi>a</mi><mo>−</mo><mi>p</mi><mi>r</mi><mi>i</mi><mi>o</mi><mi>r</mi><mi>i</mi></mrow></math></span>, thereby minimising computational efforts and effectively enabling the use of the inherent information within the set of transported species. The study presents an application example where a dual-fuel turbulent combustion scenario is numerically investigated. In this context, the consistency of the method with respect to the use of passive scalars has been discussed with and without the species equi-diffusivity assumption. A procedure for the <span><math><mrow><mi>a</mi><mo>−</mo><mi>p</mi><mi>r</mi><mi>i</mi><mi>o</mi><mi>r</mi><mi>i</mi></mrow></math></span> estimation of the error introduced by the species preferential diffusion has been proposed, providing insights about the expected uncertainty on the predicted mixture composition and the respective flame properties.</div><div><strong>Novelty and Significance Statement</strong></div><div>The determination of the non-reactive mixing field is crucial for understanding reactive CFD simulations based on species transport. Additionally, in turbulent combustion models, knowing the unburnt composition is often a pivotal requirement for the model closure. While recalculated mixture fractions can determine the unburnt composition in dual-stream problems, this approach is inappropriate for multi-stream problems. This research introduces a novel generalised method for determining unburnt mixture composition in multi-stream combustion scenarios using CFD calculations based on species transport. The proposed method minimises the need for additional passive scalars by efficiently utilising existing information from the solved equations and boundary conditions, leveraging elemental mass fraction conservation.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114128"},"PeriodicalIF":5.8000,"publicationDate":"2025-03-29","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/S001021802500166X","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 imperative to decarbonise combustion necessitates technical solutions that increasingly rely on the concurrent utilisation of different fuels and/or oxidisers. The complexity of the reactive mixture compositions in such scenarios poses additional challenges from a CFD modelling perspective. While species transport models can generally describe multi-stream combustion problems directly, the definition of turbulence-chemistry interaction closures or the proper comprehension of combustion regimes often requires the reconstruction of the non-reactive mixing field. This work proposes a general comprehensive formalism for determining the unburnt composition in multi-stream combustion environments. The method relies on the elemental mass fraction conservation for the definition of a linear system that can be solved at runtime to retrieve the local unburnt mixture composition. The introduced formalism allows to assess the number of auxiliary stream-tracking scalars , thereby minimising computational efforts and effectively enabling the use of the inherent information within the set of transported species. The study presents an application example where a dual-fuel turbulent combustion scenario is numerically investigated. In this context, the consistency of the method with respect to the use of passive scalars has been discussed with and without the species equi-diffusivity assumption. A procedure for the estimation of the error introduced by the species preferential diffusion has been proposed, providing insights about the expected uncertainty on the predicted mixture composition and the respective flame properties.
Novelty and Significance Statement
The determination of the non-reactive mixing field is crucial for understanding reactive CFD simulations based on species transport. Additionally, in turbulent combustion models, knowing the unburnt composition is often a pivotal requirement for the model closure. While recalculated mixture fractions can determine the unburnt composition in dual-stream problems, this approach is inappropriate for multi-stream problems. This research introduces a novel generalised method for determining unburnt mixture composition in multi-stream combustion scenarios using CFD calculations based on species transport. The proposed method minimises the need for additional passive scalars by efficiently utilising existing information from the solved equations and boundary conditions, leveraging elemental mass fraction conservation.
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.