Lewis number effects on lean premixed combustion characteristics of multi-component fuel blends

Zitouni, S., Pugh, D. ORCID: https://orcid.org/0000-0002-6721-2265, Crayford, A. ORCID: https://orcid.org/0000-0002-6921-4141, Bowen, P. J. ORCID: https://orcid.org/0000-0002-3644-6878 and Runyon, J. ORCID: https://orcid.org/0000-0003-3813-7494 2022. Lewis number effects on lean premixed combustion characteristics of multi-component fuel blends. Combustion and Flame 238 , 111932. 10.1016/j.combustflame.2021.111932

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Abstract

Variation in natural gas composition, alongside the potential for H2 enrichment, creates the potential for significant changes to premixed flame behaviour. To strengthen fundamental understanding of lean multi-component alternative fuel blends, an outwardly propagating spherical flame was employed to measure the flame speeds and Markstein lengths of C1single bondC4 hydrocarbons, alongside precisely mixed blends of CH4/C2H6, CH4/C3H8 and CH4/H2. Theoretical relationships between Markstein length and Lewis Number are explored alongside effective Lewis number formulations. Under lean conditions, equal volumetric additions of H2 and C3H8 (30% vol.) to CH4 resulted in similar augmentation of burning velocity, however, opposite susceptibility to preferential diffusional instability was noted. At a fixed equivalence ratio of 0.65, limited changes in composition provide a marked change in the premixed flame response with the addition of C2H6 and C3H8 to CH4. For lean CH4/H2 mixtures, a diffusional based Lewis Number formulation yielded a favourable correlation, whilst a heat-release model resulted in better agreement for lean CH4/C3H8 blends. Modelling work suggests that measured enhancement of lean CH4 flames upon H2 or C3H8 is strongly correlated to changes in volumetric heat release rates and production of H radicals. Furthermore, a systematic analysis of the flame speed enhancement effects (thermal, kinetic, diffusive) of H2 and C3H8 addition to methane was undertaken. Augmented flame propagation of CH4/H2 and CH4/C3H8 was demonstrated to be principally an Arrhenius effect, predominantly through reduction of associated activation energy. Finally, plausible short-term variations in composition with hydrogen-enriched multi-component natural gas flames were investigated experimentally and numerically. At the leanest conditions, small variations in CH4:C3H8 content at a fixed H2 fraction resulted in discernible changes in stretch related behaviour, a reflection of the thermo-diffusive behaviour of each fuel's response.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Engineering
Publisher:	Elsevier
ISSN:	0010-2180
Date of First Compliant Deposit:	17 January 2022
Date of Acceptance:	8 December 2021
Last Modified:	09 Jan 2024 17:14
URI:	https://orca.cardiff.ac.uk/id/eprint/146449

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