Undulating Fuel Injector Tube Structure for Thermal Fatigue Relief
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Solution Overview
Problem
Pressure atomizing fuel injectors for gas turbine engines experience premature fatigue failure due to thermal expansion and vibration resonance, leading to costly repairs from cracking at the metallurgical braze joints, especially in the primary fuel tube.
Innovation Solution
The fuel injector design incorporates an elongated fuel tube with an undulating surface that is in contact with another surface within the housing, reducing stress and fatigue failure by providing increased axial compliance and thermal transfer characteristics, and includes a secondary fuel tube with an undulating surface to support the primary fuel tube and reduce contact areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the primary fuel tube is rigidly supported by metallurgical braze joints at both ends, then the structural support and positioning are improved, but the fatigue life deteriorates due to thermal expansion and vibration resonance stresses
Solution Approach 1:
The patent changes the physical state and geometric parameters of the primary fuel tube by introducing an undulating configuration instead of a straight rigid tube. This geometric parameter change allows the tube to flex and accommodate thermal expansion while maintaining structural support through the undulating shape's inherent flexibility and contact points with the secondary fuel tube.
Solution Approach 2:
The patent transforms the static rigid structure into a dynamic system where the primary fuel tube can move relative to the secondary fuel tube. The undulating tube allows controlled movement and flexing to absorb thermal expansion stresses and vibration resonance, while the contact points provide dynamic support rather than rigid fixation.
2Temperature
If the primary fuel tube is made cooler by secondary fuel flow, then the thermal stability is improved, but the thermal gradient stresses increase causing fatigue failure at braze joints
Solution Approach 1:
The patent changes the geometric parameters of the primary fuel tube to an undulating configuration, which modifies the thermal conduction path and reduces thermal gradient stresses. The undulating shape increases the surface area and distributes thermal stresses more evenly along the tube length, preventing concentration at the braze joints while maintaining the cooling function.
3Ease of manufacture
If straight fuel tubes are used with metallurgical joints, then the manufacturing simplicity is improved, but the resistance to fatigue failure deteriorates under thermal expansion and vibration
Solution Approach 1:
The patent modifies the geometric parameter of the fuel tube from straight to undulating, which can be manufactured through forming or bending processes after assembly. This parameter change maintains manufacturing feasibility while dramatically improving fatigue resistance by allowing the tube to flex and absorb thermal and vibrational stresses without failing at the braze joints.
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 design significantly reduces fatigue failure at the metallurgical joints, minimizes resonant frequencies, and enhances the structural support of fuel delivery tubes, thereby increasing the fatigue life and reducing maintenance costs of the fuel injector.
Implementation Method 1
said undulating tube surface being in contact with another surface disposed in said housing at one or more locations of said undulating tube surface
Implementation Method 2
During high power engine operation, the fuel injector undergoes thermal expansion and vibration resonance, which generate internal stresses
Data Source
AI summary
The subject matter of this specification can be embodied in, among other things, a fuel injector for a gas turbine engine includes a fuel injector housing, and an elongated fuel tube held in position in said housing by spaced apart joints and including an undulating tube surface along at least a portion of its length between said joints, said undulating tube surface being in contact with another surface disposed in said housing at one or more locations of said undulating tube surface.