The effect of hydrogen enrichment on the forced response of CH4/H2/Air laminar flames. (6th July 2021)

• Record Type: Journal Article
• Authors: Lim, Zhengli; Li, Jingxuan; Morgans, Aimee S.
• Is Part Of: International journal of hydrogen energy. Volume 46:Number 46(2021)
• Page Start: 23943
• Page End: 23953
• Publication Date: 2021-07-06
• Subjects: Combustion instabilities -- Flame describing function -- Level set approach -- Hydrogen; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2021.04.171
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: Hydrogen-enrichment of conventional natural gas mixtures is an actively-explored strategy for reducing pollutant emissions from combustion. This study investigates the effect of hydrogen enrichment on the unsteady flame response to perturbations, with a view to understanding the implications for thermoacoustic stability. The Level Set Approach for kinematically tracking the flame front was applied to a laminar conical premixed methane/hydrogen/air flame subjected to 2D incompressible velocity perturbations. For hydrogen enrichment levels ranging from 0% to 80% by volume, the resulting unsteady heat release rate of the flame was used to generate the Flame Describing Functions (FDFs). This was performed across a range of perturbation frequencies and levels at ambient pressure. The mean heat release rate of the flame was fixed at Q ̇ ¯ = 2.69 k W and the equivalence ratio was set to ϕ = 1.08 for all hydrogen enrichment levels. Hydrogen-enrichment was found to shift the FDF gain drop-off to higher frequencies, which will increase propensity to thermoacoustic instability. It also reduced the effective flame time delay. Sensitivity analyses at ϕ = 0.8 revealed that the changes in FDF were driven predominantly by the flame burning speed, and were insensitive to changes in Markstein length. Highlights: Hydrogen-enriched premixed combustion is simulated with the flame front tracking achieved using the Level Set Approach. Flame Describing Functions were generated to map the response of perturbed flames across varying hydrogen levels. Hydrogen enrichment leads to an increased threshold frequency for gain drop-off and global reduction in the phase lag. Changes to the flame response are driven primarily by changes to the base laminar flame speed of the mixture. Changes caused by the different Markstein lengths of the mixtures were found to be negligible.