Aero-Engine Fuel Pumping Unit with Differential Speed Gearing
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Solution Overview
Problem
The existing fuel pumping system for aero-engines, which uses two centrifugal pumps in series, faces inefficiencies due to both pumps operating at the same speed, making it difficult to optimize their operation for varying engine power settings and multiphase flows.
Innovation Solution
A fuel pumping unit with a gear arrangement that allows the low-pressure and high-pressure centrifugal pumps to be driven at different speeds using a single drive input, incorporating a bevel gear drive and a selector valve for mode selection, enabling efficient operation across different power settings and reducing the size and weight of the high-pressure pump.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If two centrifugal pumps are mounted on a common journal shaft driven by a single drive shaft, then the structure is simplified and both pumps can be driven by a single input, but both pumps operate at the same speed making it difficult to operate both pumps efficiently
Solution Approach 1:
A gear arrangement is introduced as an intermediary mechanism between the single drive shaft and the two centrifugal pumps. The gear arrangement includes a drive gear on the drive shaft that meshes with first and second driven gears on the low-pressure and high-pressure pump shafts respectively, allowing differential speed control while maintaining a single drive input
Solution Approach 2:
The common drive mechanism is segmented into separate drive paths for each pump through the gear arrangement. The drive gear can be selectively engaged with either the first driven gear or the second driven gear, allowing independent speed control of each pump while maintaining structural integration
2Weight of moving object
If the high pressure pump is run at high speeds, then the pump size and weight can be reduced, but the low pressure pump needs to run at slow speeds to handle multiphase flows and low inlet pressures
Solution Approach 1:
The system dynamically adjusts pump speeds based on operational requirements. The low-pressure pump can run at slow speeds for multiphase flows and low inlet pressures, while the high-pressure pump runs at high speeds to reduce size and weight. The gear arrangement enables this dynamic speed differentiation
Solution Approach 2:
The operational parameters of each pump are independently optimized - the low-pressure pump operates at lower speeds to handle multiphase flows and low inlet pressures, while the high-pressure pump operates at higher speeds to minimize size and weight. This parameter differentiation resolves the contradiction between weight reduction and operational adaptability
3Weight of moving object
If the high pressure centrifugal pump is used, then the pump size and weight are reduced compared to positive displacement pumps, but centrifugal pumps typically vary in efficiency with rotational speed
Solution Approach 1:
The high-pressure centrifugal pump operates dynamically at optimized high speeds where its efficiency characteristics are maximized. The gear arrangement allows the pump to run at speeds that reduce its size and weight while maintaining high efficiency, avoiding the energy losses associated with operating at suboptimal speeds
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 configuration improves pump efficiencies, reduces heat rejection to the fuel, and allows for efficient operation at low engine power settings, enhancing the heat sink capability of the fuel for cooling engine oil while maintaining compactness and reducing unit size and weight.
Implementation Method 1
a gear arrangement being operatively located between the drive input and the low and high pressure pumps such that the low and high pressure pumps are driven at different speeds by the drive input
Implementation Method 2
the LP pumping stage comprises a centrifugal impeller pump
Data Source
AI summary
A fuel pumping unit has a low pressure centrifugal pump and a high pressure centrifugal pump. In use, the low pressure pump supplies fuel at a boosted pressure to the high pressure pump for onward supply to a fuel metering unit. The pumping unit further has a drive input which drives the low and high pressure pumps. A gear arrangement is operatively located between the drive input and the low and high pressure pumps such that the low and high pressure pumps are driven at different speeds by the drive input.