A Review of NOxFormation Under Gas-Turbine Combustion Conditions

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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 NOv 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 NOv and CO regulations, a higher level of understanding of turbulence, chemical kinetics and their interactions is required. NOv in particular has become a pacing consideration, although other constraints are present. Selected NOv 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 NOv is formed in a distributed zone manner. Equilibrium and superequilibrium effects can broaden the NOv-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 NOv 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.