CMC Heat Shield Mounting for Gas Turbine Combustors
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Solution Overview
Problem
The challenge in gas turbine engines is securing ceramic matrix composite (CMC) heat shields to metallic components without compromising their high-temperature capabilities, due to mismatched thermal expansion rates and the weakness of metal fasteners at CMC operating temperatures.
Innovation Solution
A combustor design featuring a metallic combustor shell with a ceramic matrix composite heat shield and a burner seal retainer made of metallic materials, allowing the burner seal to float radially and circumferentially to accommodate thermal expansion, and using a retainer flange to securely engage the heat shield without fasteners, ensuring stability and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal fasteners are used to secure CMC heat shields to metallic components, then the heat shield can be mounted to the combustor shell, but the metal fasteners lose strength and may melt at CMC operating temperatures
Solution Approach 1:
The patent removes metal fasteners from the mounting system entirely. Instead, the CMC heat shield is secured to the metallic combustor shell through direct contact and friction between the heat shield surface and the shell, or through thermal expansion interference fit, eliminating the fastener component that fails at high temperatures.
Solution Approach 2:
The patent introduces a thermal barrier coating or intermediate layer between the CMC heat shield and metallic combustor shell. This intermediary layer accommodates differential thermal expansion and provides a bonding interface that remains stable at high temperatures, replacing the function previously performed by metal fasteners.
2Reliability
If CMC heat shields are secured to metallic components, then the heat shield can be mounted to the combustor shell, but the mismatch in thermal expansion rates between CMC and metal creates binding stresses
Solution Approach 1:
The patent employs a dynamic mounting system where the CMC heat shield is allowed to expand and contract independently relative to the metallic combustor shell. This is achieved through flexible mounting features or clearance gaps that accommodate thermal movement, preventing the development of binding stresses from thermal expansion mismatch.
Solution Approach 2:
The patent modifies the mounting interface parameters to accommodate differential thermal expansion. This includes designing the mounting interface with appropriate clearance dimensions, friction coefficients, and geometric tolerances that allow the CMC and metal components to expand at different rates without creating excessive stresses.
3Strength
If metal fasteners are cooled to maintain strength at CMC operating temperatures, then the fastener strength is maintained, but the cooling requirements increase and temperature uniformity is reduced
Solution Approach 1:
The patent removes the need for active cooling of mounting components by eliminating metal fasteners entirely. The CMC heat shield mounting system is designed to operate passively at high temperatures without requiring external cooling energy, thereby maintaining temperature uniformity and reducing overall cooling requirements.
4Temperature
If CMC materials are used for heat shields, then the operating temperature can exceed metal alloy maximum use temperatures and cooling requirements are reduced, but the challenge of securing CMC to metal components arises
Solution Approach 1:
The patent simplifies the mounting system by removing complex high-temperature fasteners, cooling channels, and thermal management components. The CMC heat shield is mounted using a straightforward interface that leverages the inherent properties of CMC materials, such as low thermal expansion and high-temperature stability, to create a simple yet effective mounting solution.
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 configuration enhances the durability of CMC heat shields and burner seals by preventing binding stresses from thermal expansion mismatches, maintaining structural integrity at high temperatures and reducing emissions by minimizing cooling requirements.
Implementation Method 1
the burner seal is floating to allow movement of the burner seal radially and circumferentially relative to the dome panel and the burner seal retainer as the dome panel and the burner seal retainer grow thermally
Implementation Method 2
the heat shield is configured to shield a portion of the dome panel from the interior combustion space
Data Source
AI summary
A combustor for a gas turbine engine includes a combustor shell, a heat shield and a burner seal. The combustor shell includes metallic materials and is formed to define an interior combustion space. The heat shield includes ceramic matrix composite materials and is configured to shield a portion of the combustor shell from the interior combustion space. The burner seal includes ceramic matrix composite materials and is configured to extend through apertures formed in the combustor shell and the heat shield.