Velocity and turbulence effects on high intensity distributed combustion

Abstract

High intensity distributed combustion assists to provide substantial performance improvement for gas turbine applications for our quest to simultaneously seek improved pattern factor, ultra-low emission of NOx and CO, low noise, enhanced stability, fuel flexibility and higher efficiency. In such combustion method, controlled mixing between the injected air, fuel and hot reactive gases from within the combustor prior to mixture ignition must occur to achieve distributed reactions in the entire combustion chamber. Near zero emission of NO and CO has been achieved using methane as the fuel under distributed combustion conditions at high heat (energy) release intensity of 22–36MW/m3atm. The conditions to form distributed reaction in the combustor are further investigated through variation of air injection velocity with the output parameters focused on pollutants emission and combustor performance. The isothermal flowfield is examined using particle image velocimetry (PIV) to determine key features associated with the flowfield and its effects on pollutants emission and stability. The results showed higher entrainment and turbulence at increased injection velocity. Increase in injection velocity decreased NO emissions by some 20–48% with minimal impact on CO emission under premixed fuel–air condition. Less than 4ppm of NO was achieved at an injection velocity of 46m/s at an equivalence ratio of 0.7 and heat (energy) release intensity of 31.5MW/m3atm using normal temperature air. High injection velocity at the same operating condition decreased NO emission by some 20% to 3.2ppm. Higher injection velocity under preheated inlet air condition further decreased NO to 2ppm (48% reduction) at an equivalence ratio of 0.5. The results under non-premixed combustion conditions showed similar behavior. The reduction of NO with single injection parameter is attributed to improved distributed reaction condition from direct entrainment and rapid mixing of reactive species present in the combustion zone under high intensity combustion conditions.