Acoustic and heat release signatures for swirl assisted distributed combustion

Abstract

The acoustic signal and heat release fluctuations are examined from a swirl combustor using methane as the fuel. The focus was on flame stability and noise emission that have direct relevance in further developing distributed combustion for gas turbine applications and oxy-fuel combustion. Three regimes are examined in this paper, the first being a swirl mode at equivalence ratios between 0.9 and 0.55. The second one being distributed combustion, achieved through N2/CO2 dilution to reach oxygen concentration below 15%, fostering distributed reaction. The third was oxy-fuel flame using increased amounts of CO2 dilution to reach distributed reaction. For the first case, lowering the equivalence ratio led to a reduction in the peak sound pressure level around 500Hz and a decrease in heat release fluctuations. For all the equivalence ratios, close coupling between acoustic signature and heat release fluctuations existed around 200Hz. Distributed combustion, achieved at oxygen concentration below 15%, showed a much lower peak sound pressure levels at the 500Hz range with no coupling between heat release fluctuations and acoustic signal, outlining the flame stability at this regime. Also, the noise emission levels were significantly reduced under this mode. For the third regime, increase in CO2 dilution resulted in high heat release fluctuations and an unstable flame which oscillated between two different flame modes, a feature that did not exist in the first two regimes. Further increase in CO2 led to achieving distributed reaction and a much more stable flame as compared to its oscillatory behavior at lower CO2 amounts, along with reduced noise emission levels. This outlines the possibility of achieving distributed combustion in a stable manner via CO2 dilution in oxy-fuel flames.