Fuel Metering Unit Push Piston for Low Speed Fuel Flow
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Solution Overview
Problem
Existing fuel systems for aerospace applications face challenges in delivering sufficient fuel flow during low engine speeds, such as windmill relight conditions, due to parasitic leakage losses, and existing solutions are complex and can affect dynamic performance under other operating conditions.
Innovation Solution
A fuel metering unit with a metering valve controlling the supply to a pressure raising valve's delivery chamber, where a push piston is moved by pressure from a control chamber communicating with a valve control port, allowing reliable operation during low speed conditions without adding extra components, and suitable for various pumping arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the pumping arrangement operates at low engine speed, then the engine can run at low speeds, but parasitic leakage losses increase significantly reducing fuel flow delivery
Solution Approach 1:
The pressure raising valve incorporates a push piston that dynamically adjusts the valve opening based on operating conditions. At low engine speeds, the push piston responds to pressure differential changes to increase the valve opening, thereby reducing parasitic leakage losses and ensuring adequate fuel flow delivery to the burner manifold.
2Stress or pressure
If the pressure raising valve maintains high system pressure, then fuel-draulic devices operate correctly, but parasitic losses increase reducing fuel flow at low speeds
Solution Approach 1:
The pressure raising valve uses a push piston mechanism that changes the effective valve opening parameter in response to pressure differential changes. This allows the system to dynamically adjust between maintaining adequate pressure for fuel-draulic device operation and reducing pressure-related parasitic losses to ensure sufficient fuel flow at low engine speeds.
3Quantity of substance
If existing techniques reduce system pressure rise at start, then adequate fuel flow is delivered to the engine, but the arrangements become complex and may adversely affect PRV operation under other conditions
Solution Approach 1:
The invention merges the pressure reduction function with the existing pressure raising valve by incorporating a push piston into the PRV assembly. This integration eliminates the need for separate pressure control devices, reducing system complexity while ensuring adequate fuel flow delivery during windmill relight conditions and maintaining proper PRV operation under other operating conditions.
4Speed
If the push piston is supplied with fuel under pressure from the larger gear pump, then the PRV opens at low speeds, but the arrangement is only suitable for twin gear pump systems
Solution Approach 1:
The pressure raising valve with push piston is designed to respond to pressure differential changes regardless of the specific pumping arrangement configuration. The push piston mechanism universally responds to the pressure conditions created by any pumping arrangement (single or twin gear pumps, variable or fixed displacement), making the solution adaptable and versatile across different engine start configurations without requiring pump-specific design modifications.
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 ensures reliable fuel flow during engine start-up at low speeds by reducing parasitic leakage losses and maintaining system stability across different operating conditions, including engine shut-down, without compromising dynamic performance.
Implementation Method 1
a push piston movable under the influence of the pressure within a control chamber to urge the valve member towards its open position
Data Source
AI summary
A fuel metering unit (FMU) comprising a metering valve operable to control the supply of fuel to a delivery chamber of a pressure raising valve (PRV), the PRV including a valve member movable under the influence of the pressure within the delivery chamber between a closed position and an open position in which fuel is able to flow from the delivery chamber to an outlet port, and a push piston movable under the influence of the pressure within a control chamber to urge the valve member towards its open position, wherein the control chamber communicates with a valve control port.