Airfoil Last Chance Screen Geometry to Reduce Fuel Coking
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Solution Overview
Problem
Conventional last chance screens for aircraft fuel systems are susceptible to coking, leading to clogging and increased pressure drop, which can impact engine efficiency and cause downstream clogging in aircraft engines.
Innovation Solution
A method of manufacturing last chance screens with airfoil-shaped wall sections using electrical discharge machining (EDM) and abrasive flow machining (AFM), where the first and second ends of each hole are shaped to create convex curvatures, reducing surfaces normal to the fuel flow and minimizing coking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional woven wire mesh screens are used, then the screen can be easily manufactured, but the screen is highly susceptible to coking and clogging
Solution Approach 1:
The screen structure transitions from uniform woven mesh to a pattern with varying hole sizes and airfoil-shaped wall sections. The tapered wall sections create specific flow patterns at critical locations (hole entrances and exits) that prevent deposit accumulation, while maintaining manufacturing feasibility through stamping or EDM processes.
Solution Approach 2:
The wall sections between holes are given an airfoil-shaped cross-section with tapered contours instead of straight edges. This curvature design reduces flow separation and minimizes stagnant zones where deposits could accumulate, significantly reducing coking susceptibility while remaining manufacturable.
2Reliability
If airfoil-shaped wall sections are implemented, then coking is reduced, but the manufacturing process becomes difficult
Solution Approach 1:
Traditional mechanical stamping is supplemented or replaced with electrical discharge machining (EDM) processes. EDM can precisely create the complex airfoil-shaped tapered wall sections without the tool contact and tooling constraints of conventional stamping, making the difficult-to-manufacture geometry economically producible.
Solution Approach 2:
The manufacturing approach changes from single-step stamping to multi-step processes including EDM drilling and shaping. This parameter change in the manufacturing process enables precise control of the airfoil geometry, achieving the desired anti-coking surface profile that would be impossible with conventional methods alone.
3Object-affected harmful factors
If tapered hole shapes are created, then flow-orthogonal surface area is reduced, but traditional screen making techniques cannot achieve the shape
Solution Approach 1:
EDM processes replace traditional mechanical screen making techniques. The electrical discharge process can create complex tapered and airfoil-shaped hole geometries that are impossible to achieve with conventional stamping or punching, enabling the anti-coking surface area reduction while maintaining manufacturing capability.
Solution Approach 2:
The manufacturing process parameters are fundamentally changed from mechanical force-based forming to electrical energy-based material removal. This allows precise creation of the tapered hole shapes and airfoil wall sections that reduce flow-orthogonal surface area and minimize coking, which cannot be achieved with traditional screen making parameters.
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 airfoil-shaped last chance screens effectively reduce coking, prevent pressure drop, and extend the screen's lifespan by minimizing deposits and ensuring efficient fuel flow even at higher temperatures.
Implementation Method 1
forming an array of holes through a metal sheet with a wire electrode using electrical discharge machining
Implementation Method 2
applying a flow of an abrasive flow medium to the array of holes in a first direction, such that the first end of each hole is widened by the flow of the abrasive flow medium
Data Source
AI summary
A method of manufacturing a last chance screen for an aircraft engine includes forming an array of holes through a metal sheet with a wire electrode using electrical discharge machining. The array of holes comprises a plurality of holes. Each hole of the plurality of holes comprises a first end and a second end and is surrounded by a wall section such that the last chance screen is defined by the plurality of holes and the plurality of wall sections. The first and second end of each hole are widened by either applying a flow of an abrasive flow medium to the array of holes in two directions or using a conical sinker electrode on either side of the metal sheet. Shaping the first and second end of each hole results in an airfoil-shaped cross-section of each wall section.