An experimental study on thermoacoustic instabilities in syngas-air premixed impinging jet flames. (1st December 2019)

• Record Type: Journal Article
• Authors: Kim, Jae Hyeon; Kim, Seul Gi; Lee, Kee Man; Park, Jeong
• Is Part Of: Fuel. Volume 257(2019)
• Publication Date: 2019-12-01
• Subjects: Flame oscillation -- Frequency analysis -- Impinging jet flame -- Thermoacoustic instability; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2019.115921
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Thermoacoustic instability, originated from a flame oscillation being followed by a flow instability, is a new finding. The differences between two distinct noisy flames are analyzed and discussed. The Strouhal number for oscillatory flame-flow interaction decreases with Reynolds number while it increases (decreases) with equivalence ratio in regime II-1 (II-2). Such an oscillatory behavior is quite different from those in known jet-flow instability results. Abstract: Experiments on combustion instabilities via flame-flow interaction (thereby thermoacoustic instabilities) were conducted for syngas-air premixed impinging jet flames with the mixing ratio of 10% H2 and 90% CO in volume, by varying equivalence ratio ϕ and Reynolds number ReD . A flame stability map with a functional dependency on ϕ and ReD was presented. Such flame behaviors were classified into four regimes: attached flame, lifted flame, flash-back, and blow-out. Lifted flame was also divided into two sub-regimes: silent flame (SF, regime I) and noisy flame (NF, regime II). NF are again divided into two sub-regimes: II-1 and II-2. The present main concerns focused on combustion instabilities via flame-flow interaction accompanied by two types of noises. When the cold jet is ignited in regime II-1, the flame oscillation was first started, subsequently being followed by jet-flow instability. While in regime II-2, both the flame and flow oscillations were simultaneously started. The noisy flame in regime II-1 exhibited a strong flame-flow interaction. While that in regime II-2 was identified to a relatively weak interaction of flow instability with the oscillating flame. Both noise level and oscillatory flame-flow interaction could be characterized by functional dependencies on Reynolds number and equivalence ratio, respectively. Both noise levels in regimes I and II increase with Reynolds number and equivalence ratio. Differently from well-known jet-flow instability results showing that Strouhal number is proportional to Re D 1 / 2, the Strouhal number for oscillatory flame-flow interaction decreases with Reynolds number while it increases (decreases) with equivalence ratio in regime II-1 (II-2).