Ceramic-to-Metal Turbine Shaft Joint Relocation
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Solution Overview
Problem
The ceramic-to-metal attachment joint in gas turbine engines is temperature-limited, restricting operating temperatures below 800° K due to thermal gradients and stress, which hinders efficiency improvements and increased NOx reduction.
Innovation Solution
Relocating the ceramic-to-metal joint between bearings, increasing the ceramic shaft diameter, and using a connecting sleeve to form a strong joint, allowing for all-oil, all-air, or hybrid bearing systems to reduce thermal stress and enable higher operating temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the ceramic-to-metal attachment joint is located close to the turbine rotor, then the joint can be assembled, but the allowable operating temperature is limited below 800° K due to high thermal gradients and stress
Solution Approach 1:
The joint is relocated from a position close to the turbine rotor (axial dimension) to a position between the bearings, further from the heat source. This spatial repositioning in the axial dimension reduces exposure to thermal gradients while maintaining structural integrity and assembly feasibility.
Solution Approach 2:
A connecting sleeve is introduced as an intermediary component between the ceramic shaft and metal shaft. This mediator distributes thermal and mechanical stresses, protecting the ceramic material from direct exposure to extreme thermal gradients while enabling the joint to function reliably at higher temperatures.
2Strength
If the ceramic shaft diameter is increased to have proper stiffness, then the joint strength improves, but the device complexity increases
Solution Approach 1:
The ceramic shaft has a large diameter specifically at the joint region to provide proper stiffness and strength, while the shaft diameter can be reduced in other regions. This localized dimensional variation provides the necessary mechanical properties only where required, minimizing overall device complexity.
Solution Approach 2:
The shaft system uses a composite configuration combining ceramic and metal materials with different diameters. The ceramic portion provides high-temperature stability and stiffness at the joint, while the metal portion provides ductility and ease of manufacturing, creating a composite structure that balances strength and complexity.
3Temperature
If aggressive cooling is used to maintain allowable temperature at the joint, then the joint temperature is controlled, but the engine efficiency is reduced and size cannot be minimized
Solution Approach 1:
The joint is extracted from the high-temperature zone near the turbine rotor and repositioned between the bearings, away from the combustion chamber. This extraction removes the joint from the region requiring aggressive cooling, allowing the engine to operate at higher temperatures without compromising joint integrity, thereby improving efficiency and enabling compact design.
Data Source
AI summary
A metallic-ceramic joint for a turbo-compressor spool is disclosed. A temperature-limited joint is moved from outside the bearings to between the bearings and near the center of the shaft joining the turbine and compressor. This placement can lower the temperature at and around the joint and reduces the sharp gradient (and associated thermal stress) naturally occurring between the turbine rotor and the cooler joint. The bearing closest to the compressor can be an oil bearing and the bearing closest to the turbine an air bearing. The bearing closest to the compressor and the bearing closest to the turbine can both be an oil bearing. The bearing closest to the compressor and the bearing closest to the turbine can both be an air bearing. Moving the metallic-ceramic joint between the bearings can provide sufficient isolation to enable the all-air bearing solution.