Fuel Injector Thermal Expansion Compensation via Controlled Tube Buckling
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Solution Overview
Problem
Fuel tubes in gas turbine engines fail due to differential thermal expansion between the injector support and the fuel tube, leading to high stresses at fixed connections, which can result in failure during engine operation, especially at increasing temperatures.
Innovation Solution
Designing a fuel injector where the injector support has a greater coefficient of thermal expansion than the fuel tube, allowing the fuel tube to buckle under compressive stress at room temperature, thereby accommodating differential thermal expansion without failure, using a braze cycle to fix the fuel tube at one end and allowing it to slide at the other, and controlling the buckling deformation to prevent catastrophic failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel tube is rigidly fixed at both ends in the injector support, then the fuel circuit is secure and stable, but differential thermal expansion causes high stresses and potential failure in the fuel tube
Solution Approach 1:
The fuel tube is designed with a dynamic connection at one end, allowing it to move axially within the injector support. This dynamic configuration enables the fuel tube to accommodate differential thermal expansion between the fuel tube and injector support, preventing excessive stress accumulation while maintaining fuel circuit integrity during engine operation
Solution Approach 2:
The invention changes the connection parameter from fixed-rigid to semi-fixed with controlled movement capability. By allowing controlled axial movement at one end while maintaining fixation at the other end, the system adapts to thermal expansion differences without compromising the fuel circuit's structural integrity
2Reliability
If coiled or helical fuel tube geometries are used to compensate for thermal expansion, then differential thermal growth is prevented, but manufacturing costs increase significantly
Solution Approach 1:
Instead of making the entire fuel tube coiled or helical (which increases manufacturing complexity and cost), the invention applies a localized solution by allowing movement only at one specific end of the fuel tube. The majority of the fuel tube remains straight and simple, maintaining ease of manufacture while achieving thermal expansion compensation at the critical connection point
Solution Approach 2:
The fuel tube connection system is segmented into two distinct zones: one end with fixed connection for structural stability and fuel circuit integrity, and the other end with movable connection for thermal expansion accommodation. This segmentation allows each zone to perform its specific function optimally without requiring complex geometries throughout the entire tube
3Reliability
If additional structures are added to the fuel tube to prevent thermal growth failure, then fuel circuit reliability improves, but device complexity and cost increase
Solution Approach 1:
The invention extracts the thermal expansion compensation function from the fuel tube geometry itself and relocates it to the connection interface between the fuel tube and injector support. By separating the compensation mechanism from the fuel tube structure, the fuel tube remains simple and straightforward, while the connection system handles the thermal expansion accommodation
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 solution allows for thermal expansion of the injector support during engine operation without straining the fuel tube, reducing the risk of failure and maintaining the fuel circuit integrity while using standard, straight fuel tubes without additional structures, resulting in cost savings.
Implementation Method 1
the injector support has a greater coefficient of thermal expansion than the fuel tube... differential thermal expansion of the fuel tube and the injector support during engine operation
Implementation Method 2
At room temperature the fuel tube is under compressive stress such that the fuel tube is buckled. As a result of differential thermal expansion of the fuel tube and the injector support during engine operation the fuel tube is relieved of compressive stress.
Data Source
AI summary
One embodiment includes a fuel injector for a gas turbine engine. The fuel injector has an inlet fitting for receiving fuel. The fuel injector also has an outlet fitting for delivering fuel through a nozzle to a combustor of the gas turbine engine. An injector support extends between the inlet fitting and the outlet fitting and has an internal bore therethrough. A fuel tube extends from the inlet fitting through the internal bore of the injector support to the outlet fitting. The injector support has a greater coefficient of thermal expansion than the fuel tube. At room temperature the fuel tube is under compressive stress such that the fuel tube is buckled. As a result of differential thermal expansion of the fuel tube and the injector support during engine operation the fuel tube is relieved of compressive stress.