Engine Fuel Control System with Pressure Restrictor
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Solution Overview
Problem
Current fuel control systems for gas turbine engines face issues such as high hydromechanical loop instability, pump bearing integrity risks at low speeds, excessive internal leakages, and the need for larger actuators and servo-valves due to high pressure differentials, which can lead to increased heat input and sensitivity to external actuator off-take flows.
Innovation Solution
The system incorporates a restrictor in the fuel supply line to reduce the pressure difference between the pump outlet and the low-pressure source, allowing the fuel metering valve to receive fuel at a lower pressure, and a pressure limiting valve to bypass the restrictor when the pressure difference reaches a predetermined level, thereby separating HMU and actuator pressure rise requirements and reducing pump leakage and cavitation risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high pressure differential (HP-LP) is maintained to operate auxiliary engine devices and actuators, then actuator operation is ensured, but pump bearing integrity deteriorates at low speeds
Solution Approach 1:
The patent segments the pressure differential requirement into two separate functions: the restrictor maintains high pump outlet pressure (HPa) for actuator operation, while the fuel metering valve receives fuel at reduced pressure (HP). This segmentation allows the pump to operate at high pressure for reliability while the fuel system operates at lower pressure to protect pump bearings at low speeds.
Solution Approach 2:
The restrictor acts as an intermediary element between the pump outlet and the fuel metering valve. It creates a pressure drop that reduces the pressure at the fuel metering valve while maintaining high pressure at the pump outlet, thereby mediating between the conflicting requirements of actuator operation and pump bearing protection.
2Reliability
If a high pressure differential (HP-LP) is maintained to ensure actuator operation, then auxiliary devices can function correctly, but internal leakages in pump and HMU increase
Solution Approach 1:
The system segments the pressure differential function: the restrictor maintains high pump outlet pressure for auxiliary device operation, while the fuel metering valve operates at reduced pressure. This reduces the pressure differential across the HMU and minimizes internal fuel leakages while still providing sufficient pressure for actuators.
3Force
If a high pressure differential (HP-LP) is maintained to operate actuators, then actuator force is sufficient, but larger actuators and servo-valves are required
Solution Approach 1:
The patent segments the pressure supply: the restrictor maintains high pump outlet pressure (HPa) specifically for actuator operation, while the fuel metering valve receives fuel at reduced pressure (HP). This ensures sufficient pressure for actuator force while reducing the overall system pressure requirements.
4Reliability
If a high pressure differential (HP-LP) is maintained to ensure minimum pressure rise, then actuator operation is guaranteed, but hydromechanical loop instability increases
Solution Approach 1:
The system segments the pressure control function: the restrictor maintains high pump outlet pressure for actuator operation, while the fuel metering valve operates at reduced pressure with better stability. This segmentation reduces the feedback loop gain and improves hydromechanical loop stability while maintaining actuator 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 reduces pump bearing problems, decreases HMU leakage, and provides a more stable and efficient fuel delivery system by separating pressure rise requirements, allowing for smaller actuators and reduced sensitivity to off-take flows, while maintaining adequate pressure for actuator operation.
Implementation Method 1
a restrictor located in the supply line for passage of the fuel delivered by the pump arrangement therethrough, the restrictor being configured such that fuel exiting the restrictor for onward supply to the fuel metering valve is at a second high pressure (HP) which is lower than the first high pressure (HPa)
Implementation Method 2
a pressure limiting valve which is actuated when the pressure difference (HPa−LP) between the first high pressure and the low pressure reaches a predetermined level to open a flow path for fuel on the supply line to by-pass the restrictor, thereby limiting the pressure difference (HPa−LP)
Data Source
AI summary
An engine fuel control system is provided, including a supply line for the supply of fuel to a fuel metering valve which controls the flow of fuel to burners of an engine. Fuel is delivered at a first high pressure to the supply line by a pump arrangement. The engine fuel control system includes a restrictor located in the supply line for passage of the fuel delivered by the pump arrangement therethrough. The restrictor is configured such that fuel exiting the restrictor for onward supply to the fuel metering valve is at a second high pressure which is lower than the first high pressure. The engine fuel control system includes pressure limiting valves which actuate when the pressure difference between the first high and low pressure reaches a predetermined level to open a flow path for fuel on the supply line to by-pass the restrictor, thereby limiting the pressure difference.