Variable Displacement Pump Fuel Flow Limiting for Over-Thrust Protection
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Solution Overview
Problem
Modern jet aircraft engines face challenges in preventing engine over-thrust during control system failures and managing fuel system heat, particularly due to increased heat generation from larger fuel pumps, which can lead to loss of aircraft control and icing issues.
Innovation Solution
A fuel delivery system utilizing a variable displacement pump with two distinct pump displacement settings, a high mass flow setting for starting and takeoff, and a low mass flow setting for cruising and descent, along with a metering valve for regulating fuel delivery, which can be automatically switched to the low flow setting in case of control system failure to prevent over-thrust and minimize heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a larger capacity fuel pump is used to meet increased fuel flow requirements, then fuel delivery capability is improved, but heat generation increases
Solution Approach 1:
The patent employs a variable displacement fuel pump that can dynamically adjust its displacement between a first setting (higher flow capacity) and a second setting (lower flow capacity). This dynamic adjustment allows the pump to deliver higher fuel flow when needed (improving productivity) while reducing heat generation during normal operation by operating at lower displacement, thus resolving the contradiction between fuel delivery capability and heat generation.
2Power
If full fuel pump flow is delivered to the engine combustor, then engine power output is improved, but engine over-thrust occurs during control system failure
Solution Approach 1:
The patent implements a fail-safe mechanism where the variable displacement pump is pre-configured with two distinct displacement settings. In the event of control system failure, the pump automatically transitions to the second displacement setting which limits fuel flow to a safe level, preventing engine over-thrust. This preliminary action ensures engine control safety while still allowing full power output when the control system is functioning normally.
3Reliability
If additional hardware features are added to bypass pump delivered flow, then engine over-thrust protection is improved, but device complexity increases
Solution Approach 1:
The patent makes the variable displacement pump multi-functional by enabling it to serve both as the primary fuel delivery mechanism and as the over-thrust protection device. The pump's ability to switch between two displacement settings allows it to provide both full power fuel delivery and limited flow protection without requiring separate bypass hardware or additional control components, thus improving reliability while maintaining simplicity.
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
The system effectively prevents engine over-thrust by limiting fuel flow and reduces heat generation, thereby enhancing safety and preventing fuel system icing, without the need for additional control hardware, while maintaining efficient fuel delivery across various operational conditions.
Implementation Method 1
The variable displacement pump has a first displacement setting for a first desired mass flow of fuel and a second displacement setting for a second desired mass flow of fuel
Implementation Method 2
A metering valve downstream of the variable displacement pump selectively regulates fuel delivery
Data Source
AI summary
A fuel delivery system (10) comprises a variable displacement pump (20) for pressurizing fuel. The variable displacement pump has a distinct first pump displacement setting for a first desired mass flow of fuel and a distinct second pump displacement setting for a second desired mass flow of fuel. The variable displacement pump operates in only one of the first and second pump displacement settings. A fuel control (22) with a metering valve downstream of the variable displacement pump selectively regulates fuel delivery.