A Review of NO_x Formation Under Gas-Turbine Combustion Conditions

Abstract

Gas turbines offer very high cycle efficiency, exceeding 50% in modern 250 MW-class combined-cycle units for power generation, as well as very low NO_v in the lean premixed combustion mode with natural gas fuel. They also account for virtually all commercial aeropropulsion systems, in which case kerosene-based fuel is used. To meet future NO_v and CO regulations, a higher level of understanding of turbulence, chemical kinetics and their interactions is required. NO_v in particular has become a pacing consideration, although other constraints are present. Selected NO_v data obtained at laboratory and machine conditions with gaseous fuel are reviewed here. Although the important chemical reactions cover a wide range in effective Damkohler number, the measure of turbulence-chemistry interactions, it appears that NO_v is formed in a distributed zone manner. Equilibrium and superequilibrium effects can broaden the NO_v-forming zones beyond the fine scales of turbulence, even in non-premixed flames. Pressure and the structure of the turbulent flowfield have a diminishing effect on NO_v emissions in progressively leaner premixed combustion. Generalizations such as these cannot be made for the related problems of CO emissions and combustion-driven pressure oscillations.