Electro-mechanical Backup Fuel Control for Overthrust Arrest
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Solution Overview
Problem
Existing fuel control systems for gas turbine engines face challenges in managing thrust imbalances caused by overthrust conditions, often leading to engine shut-down, which is not acceptable in all flight conditions, particularly during landing approaches, as it can create unsafe thrust asymmetries.
Innovation Solution
An engine fuel control system with an electro-mechanical backup control system that includes a detector for overthrust events, a controller to determine the rate and offset of a pullback signal, and an electromagnetically operated control servo valve to gradually reduce fuel flow, preventing overshoot and maintaining engine operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the default response to overthrust is engine shut-down, then engine protection from overspeed failure is improved, but thrust control and safety during critical flight phases deteriorates
Solution Approach 1:
The system dynamically adjusts the response to overthrust conditions based on flight phase detection. During critical phases like landing approach, the system maintains engine operation with controlled fuel flow reduction rather than immediate shut-down, adapting the protection strategy to the operational context to avoid harmful thrust asymmetry
Solution Approach 2:
The detector arrangement continuously monitors engine parameters to detect overthrust events and flight conditions. This feedback enables the control system to distinguish between normal operational variations and actual overthrust malfunctions, and to select appropriate responses (shut-down vs. controlled fuel flow reduction) based on the detected flight phase
2Speed
If immediate fuel flow reduction is applied upon overthrust detection, then thrust control response time is improved, but engine flameout risk increases
Solution Approach 1:
The system applies a predetermined rate of increase to the pullback signal upon overthrust detection, rather than immediately applying maximum fuel flow reduction. This preliminary controlled action begins the thrust reduction process while maintaining engine operation, preventing the abrupt fuel flow changes that could cause flameout
Solution Approach 2:
The control system modifies the pullback signal parameter at a controlled rate of increase rather than making abrupt changes. This gradual parameter adjustment allows the engine to respond smoothly to the overthrust condition while maintaining stable combustion and continuous operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively arrests upward runaway fuel flow, prevents engine flameout, and ensures smoother thrust control, allowing for stable engine operation during overthrust conditions without immediate shut-down, thus enhancing safety and control during critical flight phases.
Implementation Method 1
an electro-mechanical backup control system which, in the event of an engine overthrust event, is controllable by an electrical pullback signal to operate the pressure drop control arrangement
Data Source
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AI summary
An engine fuel control system includes a fuel metering valve operable to control the flow of fuel between a supply line and a delivery line. The fuel control system further includes a pressure drop control arrangement operable to regulate a pressure drop across the metering valve, the pressure drop control arrangement maintaining in normal use a substantially constant pressure drop across the metering valve. The fuel control system further includes an electro-mechanical backup control system which, in the event of an engine overthrust event, is controllable by an electrical pullback signal to operate the pressure drop control arrangement, such that increasing the pullback signal reduces the flow of fuel between the supply line and the delivery line. The fuel control system further includes a detector arrangement which detects a start of an engine overthrust event, and detects a time at which an upward runaway caused by the overthrust event is arrested. The fuel control system further includes a controller which (i) determines, at the time of the overthrust detection, a rate of increase of the pullback signal and an offset of the pullback signal, (ii) sends the pullback signal to the backup control system at the determined rate of increase, and (iii), when the upward runaway is arrested, reduces the pullback signal sent to the backup control system by the determined offset.