Bimetallic Piston Ring Holder for CMC Liner Thermal Expansion
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Solution Overview
Problem
Gas turbine engines face challenges in maintaining a seal between ceramic matrix composite (CMC) liners and metal components due to differing coefficients of thermal expansion, leading to difficulties in attaching and sealing the aft ends of the liners.
Innovation Solution
A piston ring assembly with a bimetallic piston ring holder, comprising materials with different coefficients of thermal expansion, is used to accommodate the thermal expansion mismatch between CMC liners and metal components, ensuring a secure seal and increased useful life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a piston ring holder is made of a single metal material to attach to the outer casing, then the structural strength and ease of manufacture are improved, but the sealability with CMC liners deteriorates due to mismatched thermal expansion coefficients
Solution Approach 1:
The piston ring holder is constructed as a composite structure with a metal substrate providing structural strength and a ceramic coating layer (such as CMC or CBN) on the sealing surface that matches the thermal expansion coefficient of the CMC liner. This composite material approach allows the holder to simultaneously achieve mechanical strength from the metal and thermal compatibility from the ceramic coating, resolving the contradiction between structural strength and sealability.
Solution Approach 2:
The piston ring holder employs different materials for different regions: the bulk structure uses metal for overall strength, while the specific sealing surface uses a ceramic coating with matched thermal expansion properties. This local differentiation of material properties allows the single component to satisfy both structural requirements and sealing requirements at different locations.
2Temperature
If CMC liners are used to withstand extreme temperatures, then the temperature resistance is improved, but the ease of sealing with metal components deteriorates due to differing coefficients of thermal expansion
Solution Approach 1:
The ceramic coating on the piston ring holder acts as an intermediary layer between the metal structural components and the CMC liner. This intermediate ceramic layer has thermal expansion properties that bridge the gap between metal and CMC materials, facilitating proper sealing while allowing the CMC liner to maintain its high-temperature resistance capabilities.
Solution Approach 2:
By applying a ceramic coating to the metal piston ring holder, the system creates a composite structure where the ceramic outer layer provides thermal compatibility with the CMC liner, while the metal substrate maintains structural integrity. This enables effective sealing between CMC components without compromising the temperature resistance benefits of using CMC liners.
3Device complexity
If traditional metal piston ring holders are used, then the device complexity is reduced, but the useful life of the seal deteriorates due to thermal expansion mismatch
Solution Approach 1:
The piston ring holder uses a composite structure with metal substrate and ceramic coating, which appears more complex than traditional single-material holders. However, this composite design eliminates seal failure due to thermal expansion mismatch, dramatically extending the useful life of the sealing system and reducing maintenance requirements, thereby justifying the increased manufacturing complexity.
Solution Approach 2:
The ceramic coating changes the thermal expansion parameters of the piston ring holder's sealing surface to match those of the CMC liner. This parameter modification prevents differential thermal expansion during operation, eliminating a primary cause of seal degradation and extending the operational life of the sealing system.
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 bimetallic piston ring assembly effectively maintains a seal and accommodates thermal expansion, reducing the risk of seal failure and extending the assembly's useful life by matching the thermal expansion characteristics of CMC and metal components.
Implementation Method 1
A piston ring holder including a first portion formed of a first material having a first coefficient of thermal expansion, αH1, and a second portion formed of a second material having a second coefficient of thermal expansion, αH2. The first coefficient of thermal expansion, αH1, is different than the second coefficient of thermal expansion, αH2.
Data Source
AI summary
A gas turbine engine is provided having a combustion section with a liner extending between a forward end and an aft end. A structural member is positioned in or around at least a portion of the combustion section. Additionally, a piston ring holder is provided attached to the structural member at a first end and positioned proximate to the aft end of the liner at a second end. The piston ring holder is a bimetallic member including a first portion formed of a first material and a second portion formed of a second material. A coefficient of thermal expansion of the first material is different than a coefficient of thermal expansion of the second material.