Additive Fuel Grain Rifling for Hybrid Rocket Regression
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Solution Overview
Problem
Conventional hybrid rocket engines using cast-molded solid fuels like HTPB and paraffin wax suffer from low regression rate, excessive vibration, high fuel waste, poor specific impulse, and inconsistent thrust performance, making them unsuitable for applications requiring vibration-free, high-performance rocket propulsion.
Innovation Solution
An additively manufactured solid fuel grain with a cylindrical shape featuring a center combustion port formed by a stack of fused concentric ring-shaped beads, designed to increase surface area and induce axial oxidizer-fuel gas flow, improving combustion efficiency and reducing fuel waste, manufactured using additive manufacturing technologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional cast-molded solid fuel grains are used, then the manufacturing process is simple and reliable, but the regression rate is low and thrust performance is inconsistent
Solution Approach 1:
The fuel grain is segmented into multiple layers with distinct functional zones: a core region with higher fuel concentration for sustained combustion, and an outer region with optimized regression characteristics. This segmentation allows different portions of the fuel grain to contribute differently to the combustion process, achieving both high regression rate and consistent thrust performance throughout the burn duration.
Solution Approach 2:
The fuel grain exhibits local quality variations in its composition and structure. The core region has different fuel concentration and binder distribution compared to the outer regions, creating localized combustion characteristics that optimize both regression rate and thrust consistency. This non-uniform distribution allows the fuel to burn more efficiently at different stages of combustion.
2Ease of manufacture
If conventional solid fuels like HTPB and paraffin wax are used, then the fuel is easy to manufacture and handle, but excessive vibration and fuel waste occur
Solution Approach 1:
The fuel grain uses a composite material system combining organic binder (such as HTPB) with inorganic particles (such as metal powders or ceramic particles). This composite structure reduces vibration by dampening combustion oscillations, decreases fuel waste through more complete combustion, while maintaining ease of manufacture through proven casting processes. The inorganic particles act as vibration dampers and combustion promoters simultaneously.
3Device complexity
If conventional fuel grain designs are used, then the engine structure is simple, but specific impulse is poor and combustion efficiency is low
Solution Approach 1:
The fuel grain design incorporates three-dimensional internal structures including radial and axial variations in composition and porosity. This dimensional complexity is embedded within the fuel grain itself rather than requiring complex external engine components. The 3D structure optimizes oxidizer-fuel mixing and combustion efficiency, achieving high specific impulse while maintaining relatively simple engine overall structure.
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 achieves higher regression rates, improved thrust consistency, enhanced specific impulse, and reduced vibration, while maintaining the safety and mechanical simplicity of hybrid rocket engines, enabling their use in applications previously unsuitable for conventional hybrid rockets.
Implementation Method 1
Depending upon the type of solid fuel used, phase change will occur either from a solid to a gas or from a solid to entrained liquid droplets along the exposed surface area of the solid fuel grain port wall
Implementation Method 2
as each plurality of such ring-shaped beaded structures forming layers cool and solidify, likewise a fusion bond develops between the layers
Data Source
AI summary
An additively manufactured solid fuel grain for a hybrid rocket engine having a cylindrical shape, defining a center combustion port and comprising a stack of fused layers of polymeric material suitable for hybrid rocket fuel. Each layer is formed as a plurality of fused abutting concentric beads of solidified material arrayed around the center port. An oxidizer is introduced into the solid fuel grain through the center port, with combustion occurring along the exposed surface area of the solid fuel grain center port wall. Each concentric bead possesses a surface pattern that increases the combustion surface area and when stacked forms a rifling pattern of undulations that induces oxidizer-fuel gas axial flow to improve combustion efficiency. The port wall surface pattern persists during the rocket engine's operation as the fuel phase changes from solid to gas and is ablated.