An account of fuel/air unmixedness effects on NOx generation in gas turbine combustors
Difficulties associated with the calculation of gaseous emissions of total oxides of nitrogen (NOx), total unburned hydrocarbons (UHC) and carbon monoxide (CO) from aircraft gas turbine engines are briefly reviewed. The study concentrates on one of these difficulties, the effects of fuel/air unmixedness on emissions. By means of a characteristic time analysis of actual engine combustors, it is shown Damkohler Numbers are such that NOx emissions are especially sensitive to fuel/air unmixedness effects on eddy length-scales down to the Kolmogorov scale. It is proposed that in any regions of non-premixed reaction, the liquid fuel introduced burns, after evaporation, with a Gaussian distribution of equivalence ratios about the local mean equivalence ratios. Collected values of the Fletcher/Heywood statistical mixing parameter for a variety of practical gas turbine combustors are used to provide standard deviations for Gaussian distributions of local equivalence ratio as a function of mean equivalence ratio. These distributions and the resulting fuel flows, together with two reduced chemical reaction mechanisms for Jet-A fuel, are used on a parallel array of n-identical, well-stirred reactors, to establish NOx correction factors. The NOx correction factor is a multiplier to the NOx calculated at identical operating conditions but with perfectly-premixed fuel and air. It is indicated how the NOx correction factor might be applied to post-process a CFD solution or a well-stirred reactor network representing a given combustor. The NOx correction factor calculations are provided for a typical gas turbine engine compression characteristic from 4 to 29 atmospheres combustion pressure, and over a range of mean equivalence ratios from 0.2 to 2.3. It is shown that fuel/air unmixedness results in regions of both NOx amplification and NOx suppression. The complex curves resulting provide insight into various emission-reduction strategies that have been employed on engines. The magnitudes of the correction factor are particular to the reaction mechanism used, but, depending on mechanism and conditions, can range from 0.1 to several hundred.
- Research Organization:
- Innovative Scientific Solutions, Inc., Dayton, OH (US)
- OSTI ID:
- 20002755
- Resource Relation:
- Conference: 33rd Intersociety Energy Conversion Engineering Conference, Colorado Springs, CO (US), 08/02/1998--08/06/1998; Other Information: 1 CD-ROM. Operating system required: Windows 3.x; Windows 95/NT; Macintosh; UNIX. All systems need 2X CD-ROM drive.; PBD: 1998; Related Information: In: Proceedings of the 33. intersociety energy conversion engineering conference, by Anghaie, S. [ed.], [2800] pages.
- Country of Publication:
- United States
- Language:
- English
Similar Records
The role of reactant unmixedness, strain rate, and length scale on premixed combustor performance
Effect of pressure and fuel-air unmixedness on NO{sub x} emissions from industrial gas turbine burners