Böttler, Hannes (2024)
Modeling of ignition and flame propagation in lean and rich hydrogen-air mixtures.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00027271
Dissertation, Erstveröffentlichung, Verlagsversion
Kurzbeschreibung (Abstract)
Green hydrogen holds significant promise as a sustainable alternative to traditional fossil fuels in mitigating global warming. Its direct thermal conversion via combustion is one of the most cost-efficient ways of power generation. To advance the development of technical combustion chambers for green hydrogen, detailed knowledge of its combustion dynamics, which differ significantly from that of conventional fuels, is required. Simulation-aided design processes that incorporate predictive and computationally efficient models have become indispensable in the development of combustion chambers. To enable simulation-aided design processes for hydrogen, established models must be adapted to the distinct characteristics of hydrogen flames. In particular, the high reactivity and diffusivity of hydrogen cause mixture inhomogeneities near the reaction zones due to an imbalance in the diffusive mass and heat fluxes, known as differential diffusion. This also leads to a strong sensitivity to flame front distortions known as flame stretch, which in turn can be classified into strain and curvature effects. In lean hydrogen-air flames, the interplay of differential diffusion and stretch effects leads to strongly corrugated flame fronts with cellular structures, as they are subject to thermo-diffusive instabilities. These instabilities change the flame dynamics and are not yet captured by the existing models.
In this thesis, various physical phenomena in premixed hydrogen-air flames are analyzed, focusing on differential diffusion, flame stretch, and thermo-diffusive instabilities. Flames with arbitrary combinations of strain and curvature are systematically investigated using a composition space model that reveals sensitive changes in global flame properties, flame structures and reaction pathways. Based on this analysis, a novel flamelet-based modeling approach is developed that incorporates a tabulated manifold, differential diffusion, and a coupling method through the transport of major species. Rigorous evaluations demonstrate the accuracy of the model in predicting ignition characteristics, flame propagation and flame structure in different hydrogen-air mixtures. The model shows significantly improved predictions for the flame structure observed in laminar and turbulent thermo-diffusively unstable hydrogen-air flames when extended by strain and curvature variations. In summary, this work introduces a novel model that showcases improved predictability of premixed hydrogen-air flames in different configurations and marks a substantial advancement toward the predictive simulation of technical hydrogen combustors.
| Typ des Eintrags: | Dissertation | ||||
|---|---|---|---|---|---|
| Erschienen: | 2024 | ||||
| Autor(en): | Böttler, Hannes | ||||
| Art des Eintrags: | Erstveröffentlichung | ||||
| Titel: | Modeling of ignition and flame propagation in lean and rich hydrogen-air mixtures | ||||
| Sprache: | Englisch | ||||
| Referenten: | Hasse, Prof. Dr. Christian ; Chen, Prof. Dr. Zheng | ||||
| Publikationsjahr: | 13 Mai 2024 | ||||
| Ort: | Darmstadt | ||||
| Kollation: | 166 Seiten in verschiedenen Zählungen | ||||
| Datum der mündlichen Prüfung: | 23 April 2024 | ||||
| DOI: | 10.26083/tuprints-00027271 | ||||
| URL / URN: | https://tuprints.ulb.tu-darmstadt.de/27271 | ||||
| Kurzbeschreibung (Abstract): | Green hydrogen holds significant promise as a sustainable alternative to traditional fossil fuels in mitigating global warming. Its direct thermal conversion via combustion is one of the most cost-efficient ways of power generation. To advance the development of technical combustion chambers for green hydrogen, detailed knowledge of its combustion dynamics, which differ significantly from that of conventional fuels, is required. Simulation-aided design processes that incorporate predictive and computationally efficient models have become indispensable in the development of combustion chambers. To enable simulation-aided design processes for hydrogen, established models must be adapted to the distinct characteristics of hydrogen flames. In particular, the high reactivity and diffusivity of hydrogen cause mixture inhomogeneities near the reaction zones due to an imbalance in the diffusive mass and heat fluxes, known as differential diffusion. This also leads to a strong sensitivity to flame front distortions known as flame stretch, which in turn can be classified into strain and curvature effects. In lean hydrogen-air flames, the interplay of differential diffusion and stretch effects leads to strongly corrugated flame fronts with cellular structures, as they are subject to thermo-diffusive instabilities. These instabilities change the flame dynamics and are not yet captured by the existing models. In this thesis, various physical phenomena in premixed hydrogen-air flames are analyzed, focusing on differential diffusion, flame stretch, and thermo-diffusive instabilities. Flames with arbitrary combinations of strain and curvature are systematically investigated using a composition space model that reveals sensitive changes in global flame properties, flame structures and reaction pathways. Based on this analysis, a novel flamelet-based modeling approach is developed that incorporates a tabulated manifold, differential diffusion, and a coupling method through the transport of major species. Rigorous evaluations demonstrate the accuracy of the model in predicting ignition characteristics, flame propagation and flame structure in different hydrogen-air mixtures. The model shows significantly improved predictions for the flame structure observed in laminar and turbulent thermo-diffusively unstable hydrogen-air flames when extended by strain and curvature variations. In summary, this work introduces a novel model that showcases improved predictability of premixed hydrogen-air flames in different configurations and marks a substantial advancement toward the predictive simulation of technical hydrogen combustors. |
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| Alternatives oder übersetztes Abstract: |
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| Freie Schlagworte: | Combustion, flamelet manifolds, thermo-diffusive instabilities, differential diffusion, strain, curvature | ||||
| Status: | Verlagsversion | ||||
| URN: | urn:nbn:de:tuda-tuprints-272719 | ||||
| Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau | ||||
| Fachbereich(e)/-gebiet(e): | 16 Fachbereich Maschinenbau 16 Fachbereich Maschinenbau > Fachgebiet Simulation reaktiver Thermo-Fluid Systeme (STFS) |
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| Hinterlegungsdatum: | 13 Mai 2024 13:25 | ||||
| Letzte Änderung: | 14 Mai 2024 07:50 | ||||
| PPN: | |||||
| Referenten: | Hasse, Prof. Dr. Christian ; Chen, Prof. Dr. Zheng | ||||
| Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 23 April 2024 | ||||
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| Suche nach Titel in: | TUfind oder in Google | ||||
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