Combustion Chamber Mounting Lugs for Aircraft Engine Assembly
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Solution Overview
Problem
The existing assembly of an annular combustion chamber in aircraft engines is costly due to complex geometry and requires expensive machining for flat surfaces, leading to high mass and aerodynamic pressure drops.
Innovation Solution
A simpler assembly using regularly distributed fixing lugs with grooves in the casing, where the lugs engage with hooks, reducing the surface area obstructing airflow and allowing for thermal expansion, with clamping that changes with temperature to minimize stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a complex annular connecting piece with conical section and flanges is used to connect the combustion chamber to the diffuser housing, then the combustion chamber is securely positioned and retained, but the system mass increases and aerodynamic pressure losses occur due to the large surface area obstructing airflow
Solution Approach 1:
The single complex annular connecting piece is segmented into multiple discrete fixing lugs (typically 6-12 lugs distributed circumferentially). Each lug is a simple U-shaped or hook-shaped element that engages with a corresponding groove in the diffuser housing. This segmentation reduces the total mass of the connecting structure while maintaining secure retention through distributed attachment points around the combustion chamber periphery.
Solution Approach 2:
The conical section and extended flanges that created aerodynamic drag and blocked airflow are completely removed from the design. The connecting function is extracted and performed solely by the minimal necessary fixing lugs that engage in grooves, eliminating the harmful aerodynamic features while preserving the mechanical connection function.
2Use of energy by moving object
If the conical section with windows is used to allow airflow to the turbine cooling system, then cooling air passage is provided, but the complex geometry increases manufacturing cost and machining requirements
Solution Approach 1:
The conical section with windows is completely removed from the connecting piece design. The airflow passage function is extracted and redirected through alternative paths that do not require complex geometric features. The fixing lugs provide clearances and flow paths for cooling air without requiring machined windows or conical sections.
Solution Approach 2:
Instead of creating airflow passages through windows in a conical section, the design inverts the approach by using the spaces between and around the simple fixing lugs as the airflow paths. The grooves in the housing and clearances in the lug design naturally provide channels for cooling air to reach the turbine without requiring positive airflow features.
3Strength
If flat contact surfaces are machined on the flanges to ensure proper connection, then the combustion chamber is securely connected to the housing, but manufacturing cost increases due to expensive machining requirements
Solution Approach 1:
The single large flange connection is segmented into multiple discrete lug-groove engagement points distributed around the combustion chamber. Each lug engages with its corresponding groove through a simple hook-shaped geometry that requires minimal machining - essentially only the groove geometry in the housing needs to be precision-machined, while the lugs themselves can be formed with simple bending or casting operations.
Solution Approach 2:
Instead of machining flat contact surfaces on large flanges to achieve connection strength, the design inverts the approach by using interference-fit hook-shaped lugs engaging in grooves. The connection strength is achieved through the geometric interlock and potential interference fit of the lug in its groove, eliminating the need for expensive flat surface machining on both mating parts.
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 solution reduces the system's mass and aerodynamic pressure drops while maintaining structural integrity and reducing assembly costs, enhancing operational efficiency.
Implementation Method 1
The downstream end 12 of the outer wall 14 of the combustion chamber is connected to the wall of the diffuser housing 16 by a connecting piece 17. This connecting piece is welded to the said downstream end 12.
Implementation Method 2
The tabs are shaped so that, when cold, a clamping force is exerted between the end of each tab and the radially outermost surface of the groove or an adjacent area of the inner surface of said housing.
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The combustion chamber module comprises a combustion chamber the front end of whose external wall is attached to an annular bracket (17) with radial bars (36) which fit into a groove in the wall of a frame (16). An independent claim is included for turbomachines fitted with the module.