LIMIT OF EQUIVALENCE RATIO ON MIXING ENHANCEMENT NEAR THE TUBE EXIT IN A TONE EXCITED RICH FLAME
✍ Scribed by Jin Kook Kim; Hyun Dong Shin
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 231 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0363-907X
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✦ Synopsis
An experimental investigation has been made with the objective of studying the limit of equivalent ratio () on mixing enhancement in a tone excited jet rich flame. The jet is pulsed by means of a loudspeaker-driven cavity and experiments are limited to very rich flames ('1•5). The excitation frequency is chosen for the resonant frequency identified as a pipe resonance due to acoustic excitation. Methane, propane and butane are used to examine the effect of mixture property on the limit of equivalence ratio. Mixing is always enhanced in a methane/air flame as the excitation intensity increases. In the case of propane/air and butane/air flames, mixing enhancement can be obtained only when the equivalence ratio lies in the range from a certain value (the equivalence ratio limit) to infinity (non-premixed flame), irrespective of mean mixture velocities. It is also found that the equivalence ratio limit is related to flame instability; the lower the Lewis number, the higher the equivalence ratio limit. As the excitation intensity increases, flame separation occurs below the equivalence ratio limit; an inner (premixed) flame is transformed into a cellular flame which then moves upstream, but the height of an outer (non-premixed) flame is not decreased. Acoustic pressure measurements using a microphone are made to quantify the oscillating velocity. The oscillating velocity amplitude at the cellular flame position is proportional only to mean mixture velocity regardless of fuel type.