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Investigation of turbulent combustion in humid air using a level-set flamelet library approach

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Author

Summary, in English

To meet the demands of high electrical efficiencies in combination with low emissions for gas turbine-based power plants, wet cycles have gained new interest. The combustion chamber is a key component in such a power plant. Detailed investigations are necessary to gain insight into the formation of hazardous emissions such as CO and NOx. In this paper, computational fluid dynamics (CFD) has been employed to perform the investigations. To examine the influence of humidity content in the inlet air stream on the mean flame position and CO and NOx emissions, the humidity content was varied from 0 to 31%. The CO emissions are a measure of incomplete combustion. The inlet temperature and the maximum flame temperature were held constant for all computations. The influence of different combustor loads was also investigated. This will influence the flame position, which is important for emission formation. The flame under investigation is a lean premixed propane flame, stabilized by a bluff body. The turbulent combustion has been modeled with the level-set flamelet library approach (FLA). This model includes a detailed chemical mechanism, which is of great importance when emissions are to be predicted. To illustrate this importance, the FLA model is compared with a simple eddy break-up model and validated against known experimental data at dry condition. The level-set flamelet library method shows very good agreement with the experimental data for both the temperature profile and the CO and NOx emissions. The simple eddy breakup model is only able to predict the temperature profile fairly well while the important emissions are being greatly overestimated. The computations have shown that the flame position, and hence the residence time, is most sensitive to the change in combustor load - while the degree of humidification appears to be of less importance. The CO emissions rise with an increase in the degree of humidification at constant load, while the opposite behavior is true for NOx emissions. At a constant level of humidification, the CO emissions fall with an increase in load and again, the opposite behavior is observed for NOx emissions. A map of emission indices for CO and NOx under different load conditions as a function of humidification can be generated. This map shows an operation window within which both the CO and NOx emissions are quite low.

Publishing year

2004

Language

English

Pages

215-224

Publication/Series

ASME Turbo Expo 2004: Power for Land, Sea, and Air

Volume

1

Document type

Conference paper

Publisher

American Society Of Mechanical Engineers (ASME)

Topic

  • Energy Engineering

Keywords

  • Inlet temperature
  • Turbulent combustion
  • Humid air
  • Level-set flamelet

Conference name

2004 ASME Turbo Expo

Conference date

2004-06-14 - 2004-06-17

Conference place

Vienna, Austria

Status

Published