Fluid reaction surfaces (i.e. – impellers) – Interrelated controls for impeller and drive means – Pitch adjustment related to drive brake or clutch operation
Reexamination Certificate
1998-11-23
2001-05-15
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Interrelated controls for impeller and drive means
Pitch adjustment related to drive brake or clutch operation
C415S049000, C415S118000
Reexamination Certificate
active
06231306
ABSTRACT:
TECHNICAL FIELD
This invention relates to the control of gas turbine compressors and more particularly to a control system for detecting and preventing an impending compressor stall.
BACKGROUND ART
The phenomenon of compressor stall has become an important limiting factor in the operation of gas turbine engines as their performance characteristics have improved. In modern gas turbine engines, upon acceleration or under high altitude and lower speed flight conditions, unstable flow may develop in the compressor which can lead to a stall with a resultant increase in turbine temperature and mechanical vibration along with a simultaneous reduction in cooling air supplied to the turbine wheel. These conditions describe “compressor stall” and can lead to turbine failure if the compressor stall is not recognized and corrective action not taken. Turbine failure during engine operation can lead to severe engine and aircraft damage.
To avoid such damage, control systems have been proposed to detect the onset of compressor stall and either signal the aircraft pilot or automatically compensate to bring the engine out of the stall condition. It has been found that functions of certain engine operating parameters can provide an indication of stalled engine conditions. Systems have been designed which monitor these parameters to detect compressor stall. Several previous attempts to develop stall warning indicators have used either engine operating pressures, pressure ratios, speed or temperatures as input parameters.
DISCLOSURE OF THE INVENTION
A primary object of the present invention is the provision of a control system for preventing a compressor stall.
A further object of the present invention is the provision of such a control system for preventing stall that uses only one sensed compressor pressure parameter to determine an impending stall condition.
Another object of the present invention is the provision of a control system, that does not unnecessarily increase the compressor stall margin and thereby negatively effect engine efficiency.
The present invention is predicated on the fact that low pressure compressor disturbances occur at different engine operating conditions. However, the low pressure compressor or fan disturbances are detrimental only if amplified by deteriorated compressor stages that have been adversely affected as they have large tip clearances. The present invention utilizes a signal indicative of the amplified low pressure compressor or fan disturbance to predict an impending stall. Thus, the present invention is designed to predict an impending stall and maintain an adequate compressor stall margin.
According to the present invention, a control system for preventing a compressor stall includes means for sensing a signal indicative of compressor pressure, which signal has a frequency that is a function of the fan or low pressure compressor speed. The control system also includes means for processing the sensed pressure signal by: (1) isolating the relevant frequencies of the sensed signal; (2) calculating the magnitude of the relevant frequency portions of the sensed signal; and (3) comparing the sensed signal to a predetermined threshold indicative of a healthy compressor. The control system also provides a processed signal indicative of an impending stall condition. The control system further includes means, responsive to the processed signal, for providing an output signal to initiate corrective action to prevent the impending stall condition. For example, the engine control means which is a part of the control system, in response to the output signal, increases stall margin by either adjusting the compressor variable airflow geometry or by modulating the compressor bleed valve.
The present invention has utility in that it allows for an indication of an impending stall condition sufficiently in advance such that corrective action may then be taken to prevent the stall from occurring. The present invention is simple to implement as it uses only one sensed engine operating parameter to indicate an impending stall condition. The simplicity of the present invention allows for it to be practical for engine fleet retrofitability. Further, the present invention provides a higher relative engine efficiency because the mechanisms to increase the stall margin are not employed until required to ensure safe engine operation below the surge line. Thus, the control system results in savings in the amount of fuel consumed by the engine.
The foregoing and other objects, features and advantages of the present invention will become more apparent in the following detailed description of the best mode for carrying out the invention and from the accompanying drawings, which illustrate an embodiment of the invention.
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Look Edward K.
McAleenan James M
McCormick Paulding & Huber LLP
United Technologies Corporation
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