A REVIEW OF NOX FORMATION UNDER GAS-TURBINE COMBUSTION CONDITIONS

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(x) 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(x) and CO regulations, a higher level of understanding of turbulence, chemical kinetics and their interactions is required. NO(x) in particular has become a pacing consideration, although other constraints are present. Selected NO(x) 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(x) is formed in a distributed zone manner. Equilibrium and superequilibrium effects can broaden the NO(x)-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(x) 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.