Gas Turbine Fuel Injector Nozzle Thermal Expansion Bellows
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Solution Overview
Problem
In fuel injectors for gas turbine engines, the formation of carbon in insulating gaps between moving parts leads to reduced insulation effectiveness and potential blockage, causing fuel accumulation and diminished nozzle service life due to differential thermal expansion and fuel leakage into these gaps.
Innovation Solution
The integration of an annular bellows within the insulating gap to isolate a portion from fuel entry, with sealing attachments to internal and external walls, prevents fuel from entering and accumulating in the gap, maintaining effective insulation and accommodating thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the insulating gap is left open to accommodate differential expansion, then thermal expansion is accommodated, but fuel enters the gap causing carbon buildup and insulation degradation
Solution Approach 1:
The insulating gap is segmented into two distinct zones: a first insulating gap between the internal wall and bellows, and a second insulating gap between the external wall and bellows. This segmentation allows each gap to be independently managed while maintaining overall insulation effectiveness and accommodating thermal expansion without fuel ingress.
Solution Approach 2:
The bellows acts as an intermediary component that separates the internal and external walls, creating a protected insulating space. The bellows interface with both walls through sealing attachments that prevent fuel from entering the insulating gaps while allowing thermal expansion movements.
2Stress or pressure
If the walls are anchored at one end and free at the other for relative movement, then differential expansion is minimized, but fuel can still pass into the air gap through the free end interface
Solution Approach 1:
The bellows is constructed as a flexible, convoluted structure that can expand and contract to accommodate thermal movements of the internal and external walls. The flexible bellows maintains sealing attachments to both walls while allowing relative movement, preventing fuel from entering the insulating gaps without constraining thermal expansion.
Solution Approach 2:
The bellows introduces dynamic flexibility to the insulating gap configuration, allowing the system to adapt to thermal expansion and contraction of the walls. The convoluted structure of the bellows enables it to move with the walls while maintaining the sealing function that prevents fuel ingress.
3Stability of the object's composition
If carbon builds up in the insulating gap, then insulation is reduced, but the gap structure remains in place
Solution Approach 1:
The bellows effectively extracts or removes the harmful function of the insulating gap by preventing fuel from entering it in the first place. The sealing attachments at the bellows interfaces eliminate the source of carbon buildup, thereby preserving both the gap structure integrity and insulation performance.
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 bellows effectively prevents carbon buildup and fuel accumulation, enhancing the insulation efficiency and extending the service life of the nozzle by maintaining the integrity of the insulating gap and allowing for differential expansion without fuel ingress.
Implementation Method 1
accommodate differential expansion of the internal and external walls while minimizing thermally induced stresses
Implementation Method 2
insulating gap from an interface whereat fuel may enter the insulating gap
Data Source
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AI summary
A fuel injector for a gas turbine engine comprises a housing stem and a nozzle, the nozzle including an internal wall in heat transfer relation with fuel flowing through the nozzle, and an external wall in heat transfer relation with ambient air. The internal and external walls have downstream tip ends that are relatively moveable at an interface due to relative thermal growth during operation of the engine. An internal insulating gap is disposed between the internal and external walls to provide a heat shield for the internal wall, and a bellows internal to the injector has an upstream end sealingly attached to an upstream portion of one of the internal and external walls, and a downstream end sealingly attached to a downstream portion of the other wall to fluidly separate the insulating gap from any fuel entering into the nozzle through the interface.