Solid Propellant Micro-Voids for Burn Rate Control
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Solution Overview
Problem
Existing solid propellant rocket motors face challenges in controlling the burn rate and gas velocity due to uniform surface areas of energetic grain layers, leading to potential erosive burning and choking issues.
Innovation Solution
The implementation of a multi-layer structure with micro-voids and surface features, such as radially elongated slots and hollow micro-spheres, in the energetic grain layers to tailor the surface area for controlled burn rates and gas velocities, along with axially-spaced protrusions to manage flow and thrust.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform surface area of energetic grain layers is used, then manufacturing simplicity is maintained, but burn rate control and gas velocity management deteriorate
Solution Approach 1:
The patent introduces micro-voids at specific locations within the energetic grain layers to create local variations in surface area. These micro-voids are strategically positioned to control burn rate and gas velocity at critical regions without requiring complex overall grain geometry, thus maintaining manufacturing simplicity while achieving local burn rate control.
Solution Approach 2:
The energetic grain structure is segmented into multiple layers with different surface area characteristics. The first and second energetic grain layers are divided into regions with and without micro-voids, allowing independent control of burn rates in different sections of the propellant grain.
2Productivity
If micro-voids are introduced to control burn rate, then burn rate control improves, but manufacturing complexity increases
Solution Approach 1:
The patent incorporates micro-voids as porous structures within the dense energetic grain material. These micro-voids increase the effective surface area for combustion without significantly altering the overall grain structure or requiring complex manufacturing processes, as they can be formed through simple cavity creation during grain fabrication.
3Reliability
If surface area is increased to control gas velocity, then erosive burning is reduced, but propellant volume is consumed faster
Solution Approach 1:
The patent transitions from controlling gas velocity through two-dimensional grain surface geometry to three-dimensional micro-void structures embedded within the grain interior. This dimensional change allows substantial increases in effective combustion surface area without increasing the external dimensions of the propellant grain, thus preventing erosive burning without accelerating overall propellant consumption.
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 enhances the burn rate control, reduces the risk of erosive burning, and maintains desired gas velocities by selectively varying the surface area and geometry of the energetic grain layers, resulting in improved thrust and mechanical properties.
Implementation Method 1
tailor the surface area for controlled burn rates and gas velocities
Implementation Method 2
the bottom surface of the second energetic grain layer partially abuts the top surface of the first energetic grain layer at a predetermined geometry selected to define a predetermined flowpath via the micro-void
Implementation Method 3
Ignition at the bore surface of the solid propellant generates high pressure gas
Data Source
Figure 1~7A
Figure 2~7C
Figure 3A~3B
AI summary
A rocket motor (20) includes a nozzle (22) and a solid propellant (24) section in communication with the nozzle. The solid propellant section includes a first energetic grain layer (34) that has a top surface and a bottom surface, and a second energetic grain layer (32) that has a top surface and a bottom surface. The second layer is located on top of the first layer. The bottom surface of the second energetic grain layer partially abuts the top surface of the first energetic grain layer, and the bottom surface of the second energetic grain layer and the top surface of the first energetic grain layer define a micro-void therebetween.