An experimental study on thermoacoustic instabilities in syngas-air premixed impinging jet flames

摘要

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% H-2 and 90% CO in volume, by varying equivalence ratio phi and Reynolds number Re-D. A flame stability map with a functional dependency on. and Re-D 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).