Gas Turbine Fuel Control System Torque Runaway Detection
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Solution Overview
Problem
Existing fuel control systems for gas turbine engines face challenges in accurately distinguishing between real fuel flow upward runaway events and spurious torque spikes, leading to potential incorrect activation of emergency fuel reductions, and there is a need to reduce torque thresholds while minimizing the risk of incorrect activations.
Innovation Solution
A fuel control system that includes a metering valve, a first engine sensor to determine power output, a control unit to compare the power output with a power threshold, and a second engine sensor to measure the rate of change of rotational speed of the core engine spool, allowing the control unit to adjust the power threshold based on the measured rate of change, thereby confirming fuel flow upward runaway with an additional parameter and reducing the risk of incorrect activations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power threshold is reduced to lower torque limits, then the risk of unacceptably high torques in the propeller system is reduced, but the risk of incorrect activation due to spurious torque spikes increases
Solution Approach 1:
The invention introduces an intermediary parameter (rate of change of core engine spool speed) that mediates between the power threshold comparison and the emergency fuel chop decision. This intermediary provides additional verification to distinguish real fuel flow runaway from spurious torque spikes, resolving the contradiction by adding a filtering layer that maintains sensitivity while reducing false activations
Solution Approach 2:
The invention changes the parameter used for verification from a static power threshold alone to a dynamic combination of power threshold and rate of change of speed. By monitoring how quickly the core engine spool speed is changing, the system can differentiate between genuine fuel flow problems (which cause rapid acceleration) and spurious signals (which do not), thus resolving the detection accuracy issue while maintaining reliable torque control
2Reliability
If the power threshold is set low to prevent high torques, then torque control is improved, but false activation from electrical interference increases
Solution Approach 1:
The rate of change of core engine spool speed serves as an intermediary verification parameter that filters out spurious activations from electrical interference. Since electrical interference does not cause actual changes in engine spool speed, the intermediary parameter effectively blocks false signals while allowing genuine torque problems to trigger the emergency fuel chop
Solution Approach 2:
The system uses feedback from the core engine spool speed sensor to verify whether a power threshold exceedance is genuine. The feedback loop continuously monitors the rate of change of spool speed and uses this information to confirm or reject the need for emergency fuel reduction, thereby eliminating false activations from electrical interference while maintaining effective torque control
Data Source
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AI summary
A fuel control system is provided for a gas turbine (26, 6) engine having a core engine (2) comprising at least one core engine (2) spool in which a compressor (4) and a turbine (26, 6) are interconnected by a shaft (28, 8). The system includes a first engine sensor (42, 44) which determines a power output of the engine. The system further includes a control unit (38) which is configured to compare the determined power output with a value of a power threshold, and to command a reduction in fuel supplied to the engine when the determined power output exceeds the power threshold value. The system further includes a second engine sensor (42, 44) which measures the rate of change of rotational speed of the core engine (2) spool. The control unit (38) is further configured to adjust the power threshold value as a function of the measured rate of change of speed of the core engine (2) spool.