Fuel Nozzle Heat Shield With Thermal-Closing Axial Gap
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Solution Overview
Problem
Conventional heat shields for fuel injectors in gas turbine engines form gaps due to differential thermal growth, allowing high-temperature gases to ingress and reducing thermal protection effectiveness.
Innovation Solution
A heat shield design that forms an axial gap configured to decrease in hot conditions relative to cold conditions, reducing the ingress of high-temperature gases by accommodating differential thermal growth between the heat shield and nozzle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional heat shield is used to provide thermal protection, then thermal insulation is achieved, but differential thermal growth causes gaps that allow high-temperature gas ingress
Solution Approach 1:
The heat shield is designed to utilize differential thermal expansion between itself and the fuel injector components. The shield expands at a different rate than the nozzle and stem, causing the gap to close under hot operating conditions rather than open, thereby maintaining thermal protection effectiveness while accommodating thermal growth differences
Solution Approach 2:
The gap between the heat shield and fuel injector components is designed to be dynamic rather than static. The gap size changes with temperature, closing under hot conditions when thermal protection is most needed, and opening under cold conditions to accommodate manufacturing tolerances and assembly requirements
2Temperature
If the heat shield is positioned close to the nozzle to minimize gap, then thermal protection is improved, but differential thermal growth causes contact or excessive gap under operating conditions
Solution Approach 1:
The heat shield and fuel injector components are designed with different thermal expansion characteristics. The shield is positioned to be slightly spaced from the nozzle at assembly temperature, but the differential expansion causes the gap to close to an optimal size under hot operating conditions, simultaneously achieving thermal protection and accommodating thermal growth
Solution Approach 2:
The gap dimensions are designed as temperature-dependent parameters rather than fixed dimensions. The initial cold gap is deliberately set to account for expected thermal expansion, ensuring that the hot gap achieves the optimal size for thermal protection while accommodating the temperature-induced dimensional changes
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
Enhances thermal protection of fuel injectors by minimizing the entry of high-temperature gases, thereby reducing coking and auto-ignition risks, and maintaining effective thermal insulation.
Implementation Method 1
The distal end of the heat shield is spaced from the lip to form an axial gap that is configured to decrease in a hot condition relative to a cold condition operatively associated with the injector
Data Source
AI summary
An injector includes a mount, a stem, a nozzle, and a heat shield. The heat shield extends from the mount to surround the stem and at least a portion of the nozzle. The nozzle includes an exterior annular body. The distal end of the heat shield is spaced from a lip extending from the exterior annular body or a cap surrounding the nozzle to form an axial gap.