Optimization of the Spatial and Temporal Fuel Distribution for Stable Combustion in Lean Premixed Combustors

Speaker(s): 
Date: 
November 30, 2000 - 12:00pm
Location: 
Bldg. 90

The limited success that has been achieved to date in suppressing unstable combustion in lean premixed combustors has been based on the use one of three approaches: a pilot flame, active combustion control using either primary or secondary fuel flow modulation, or modification of the fuel time lag. What these approaches have in common is that they all involve changing the spatial and/or temporal fuel distribution in a manner, which suppresses a given instability. In this presentation, results are presented from an experimental study of the effect of the spatial and temporal fuel distribution on unstable combustion in a laboratory scale lean premixed combustor. Such information is essential for the development of strategies for defining the optimum spatial and temporal fuel distribution for suppressing a given instability, where in general the notion of optimum must include maximizing noise suppression while minimizing the NOx penalty, which may result from any deviation from perfectly premixed conditions. The experiments were conducted in a unique combustor facility, which provides the capability to extensively vary the spatial and temporal fuel distribution. The combustor inlet fuel distribution was characterized using planar laser induced fluorescence while the time and location where the fuel actually burns was determined using chemiluminescence imaging. In addition the instabilities were characterized in detail, using high frequency response pressure transducers, infrared absorption equivalence ratio measurements and phase-synchronized chemiluminescence imaging. The results of these measurements reveal the mechanism by which a given fuel distribution suppresses a given instability and in turn provides the insights and understanding which is necessary for the development of a methodology for making an a priori determination of the optimum fuel distribution for a given instability.

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