Variable-Composition Fins for Rocket Motor Combustion Chambers
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Solution Overview
Problem
The assembly of a rocket engine combustion chamber with a copper alloy longitudinal wall and a nickel or iron alloy outer shell is challenging due to difficulties in welding these materials, leading to complex and unreliable brazing processes and long manufacturing cycles with potential defects.
Innovation Solution
The fins are made with a composition that gradually varies from a copper alloy at the base to a more weldable and mechanically stronger alloy at the tip, allowing for easier attachment of a nickel or iron alloy shell, enhancing weldability and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the longitudinal wall and fins are made of copper alloy to maximize heat exchange, then thermal conduction is improved, but weldability with the nickel or iron alloy shell deteriorates
Solution Approach 1:
The fin is designed with non-uniform material composition: the base portion (proximal to the longitudinal wall) is made of copper alloy for optimal thermal conduction, while the distal portion (tip) is made of a different alloy with superior weldability. This local differentiation allows each region of the fin to optimize its function - heat transfer at the base and welding at the tip - resolving the contradiction between thermal performance and manufacturability.
Solution Approach 2:
The fin is constructed as a composite structure combining two different alloys: a copper-based alloy at the base for thermal conductivity and a nickel- or iron-based alloy at the tip for weldability and mechanical strength. This composite approach allows the fin to simultaneously achieve both high heat exchange efficiency and ease of attachment to the shell, directly resolving the technical contradiction.
2Strength
If the shell is made of nickel or iron alloy to ensure structural integrity, then mechanical strength is improved, but weldability with copper alloy fins deteriorates
Solution Approach 1:
The fin's material composition varies locally: the base maintains copper alloy for thermal properties while the tip transitions to nickel or iron alloy matching the shell material. This local material optimization allows the shell-fin assembly to achieve both high mechanical strength (through compatible shell-tip materials) and good weldability (through material compatibility at the joint).
Solution Approach 2:
The fin acts as a composite transition element between the copper alloy longitudinal wall and the nickel/iron alloy shell. By incorporating both material types within the fin structure, it provides both thermal conduction pathways and mechanically strong, weldable connection points, resolving the contradiction between strength and manufacturability.
3Ease of manufacture
If brazing is used to attach the shell to the fins, then assembly is achieved, but process complexity and reliability deteriorate due to differential stresses
Solution Approach 1:
By making the fin tip material match the shell material (both nickel or both iron alloy), the joint region has uniform material properties that eliminate differential thermal expansion and stress issues during brazing. This local material matching simplifies the brazing process and improves reliability compared to joining dissimilar metals.
Solution Approach 2:
The fin tip and shell are made of the same alloy composition, creating a homogeneous joint region. This material homogeneity eliminates the problems of differential stresses and complex brazing procedures associated with joining dissimilar metals, thereby reducing process complexity and improving assembly reliability.
4Reliability
If electrolytic deposition or thermal spraying is used to seal channels, then sealing is achieved, but manufacturing time increases due to multiple operations
Solution Approach 1:
The fin tip is pre-formed with the same material as the shell during the fin manufacturing process itself, rather than applying a separate coating layer afterward. This preliminary integration of the sealing function into the base structure eliminates subsequent coating, curing, and cleaning operations, significantly reducing manufacturing cycle time while maintaining reliable channel sealing.
Solution Approach 2:
The structural function of the fin and the sealing function of the channel closure are merged into a single integrated component. The fin tip itself, made of shell-matching material, serves both as the structural end of the fin and as the sealing surface for the coolant channels, eliminating the need for separate sealing operations and reducing manufacturing complexity.
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 approach simplifies the manufacturing process, ensures satisfactory mechanical strength, and reduces the risk of defects by facilitating the welding of the shell to the fins, while also improving the thermal conduction and structural integrity of the combustion chamber.
Implementation Method 1
improving the thermal conduction and structural integrity of the combustion chamber
Data Source
Figure 1~2
AI summary
The invention relates to a combustion chamber (1) for a rocket motor extending along a longitudinal axis A and comprising a longitudinal envelope, this longitudinal envelope comprising a longitudinal internal wall (10) made of a first alloy which is a copper alloy and which is extended on its radially outer face (15) by a plurality of fins (20) extending radially outwards, each one of these fins having a proximal portion (22), a median portion (25) and a distal portion (28), and comprising an external shell (30) surrounding this longitudinal internal wall (10) and these fins (20), this shell (30) being made of a third alloy different from the first alloy. The proximal portion (22) is made of this first alloy and the distal portion (28) is made of a second alloy which is an alloy different from the first alloy, the median portion (25) of the fin (20) between the proximal portion (22) and the distal portion (28) having a composition that varies gradually with radial distance from the longitudinal axis A from 100% of first alloy at the interface between the proximal portion (22) and the median portion (25) to 100% of second alloy at the interface between the median portion (25) and the distal portion (28), the weldability of the second alloy with the third alloy being better than the weldability of the first alloy with this third alloy, and/or the mechanical strength of the second alloy being greater than that of the first alloy.