Aircraft Engine Fuel Flow Control Assembly with Dynamic Metering
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Solution Overview
Problem
Modern aircraft gas turbine engines require higher fuel pressures and temperatures, leading to increased load on journal bearings, which are addressed using hybrid pressure pads, but this results in parasitic fuel flow output loss at low rotational speeds, necessitating larger pumps or inefficient fuel flow at start-up conditions.
Innovation Solution
A fuel flow control assembly with a gear arrangement and bearing structure, including a pressure pad with a radially extending port and a flow metering device that restricts fuel flow at low pressure conditions and increases it at high pressure conditions, managed by a method that regulates fuel flow using a fuel metering device to optimize fuel supply to journal bearings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hybrid pressure pads are used to increase load carrying capability through increased fuel film thickness, then journal bearing size and weight are reduced, but parasitic pump fuel flow output loss occurs at cranking conditions
Solution Approach 1:
The pressure pad system transitions from static to dynamic operation through a metering valve that responds to rotational speed changes. At low speeds (cranking), the valve restricts fuel flow to minimize parasitic loss. At high speeds (operational), the valve opens to provide full pressure pad support, enabling the system to adapt its fuel consumption characteristics to actual load requirements
Solution Approach 2:
The system changes the operational parameters of the pressure pad by using a metering valve to control fuel flow rate based on rotational speed. The valve transitions from a restricted state at low speeds to an open state at high speeds, dynamically adjusting the fuel film thickness and pressure characteristics to match operational requirements
2Strength
If hybrid pressure pads are used to meet journal bearing load requirements, then bearing size and weight are reduced, but fuel flow output is insufficient at low rotational speeds
Solution Approach 1:
The metering valve creates a dynamic fuel supply system that adjusts flow rate based on rotational speed. During cranking and low-speed operations, the valve opens to maximize fuel flow output. During high-speed operations, the valve restricts flow to minimize parasitic loss while maintaining adequate lubrication, thus optimizing the trade-off between fuel flow output and parasitic loss across the operational range
Solution Approach 2:
The system exhibits periodic behavior where the metering valve alternates between open and restricted states based on rotational speed thresholds. This periodic switching ensures adequate fuel flow during startup/cranking phases while minimizing parasitic losses during steady-state 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 wasteful fuel leakage, minimizes pump size and weight, maintains fuel temperature as an effective heat sink, and ensures adequate engine restart capabilities by precisely controlling fuel flow, especially during windmill starts.
Implementation Method 1
The load of the gear shafts is supported by journal bearings operating on both the hydrostatic pressure and the hydrodynamic pressure from a thin film of fuel
Implementation Method 2
The load of the gear shafts is supported by journal bearings operating on both the hydrostatic pressure and the hydrodynamic pressure from a thin film of fuel
Implementation Method 3
The metering valve is in flow communication with the port of the pressure pad to restrict the fuel flow at a low pressure operating condition and open the port to increase the fuel flow at a high pressure operating condition
Data Source
Figure 1
Figure 2~3
AI summary
A fuel flow control assembly for an aircraft engine. The assembly includes a gear arrangement (14, 16) having a shaft (12, 18). Also included is a bearing structure (26) operatively coupled to the shaft. Further included is a pressure pad (32) disposed adjacent the bearing structure, the pressure pad having a radially extending port (40) for receiving a fuel flow. Yet further included is a flow metering device (36) in flow communication with the port of the pressure pad to restrict the fuel flow at a low pressure operating condition and open the port to increase the fuel flow at a high pressure operating condition.