Telescoping-Piston Test Rig for Rocket Injector Stability

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Solution Overview

Problem

Existing subscale testing methods for rocket engine injectors fail to accurately assess full-scale performance due to limited understanding of combustion stability and the absence of predictive analytic models, leading to costly and time-consuming full-scale tests.

Innovation Solution

A subscale testing system with a continuously variable combustion volume, achieved by a moveable piston within the combustion chamber, allowing exposure of injector elements to a range of acoustic frequencies mimicking full-scale engine conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If conventional subscale testing is used, then testing cost and time are reduced, but accuracy of stability assessment deteriorates

Engineering Contradiction:

Improvetesting timeVSAvoidstability assessment accuracy

Core Design Contradiction:

Loss of timeVSMeasurement precision

Solution Approach 1:

The combustion chamber volume is made dynamically variable through a moveable piston that can be positioned at multiple axial locations. This allows the subscale chamber to dynamically adjust its volume to match different full-scale engine combustion chamber modes and acoustic frequencies, enabling accurate stability assessment across a range of operating conditions while maintaining the benefits of subscale testing.

Inventive Principle:

Principle #15Dynamics

2Measurement precision

If full-scale testing is used, then stability assessment accuracy is improved, but testing cost and time increase

Engineering Contradiction:

Improvestability assessment accuracyVSAvoidtesting time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

A subscale combustion chamber is used as a simplified copy of the full-scale engine combustion chamber. By making the subscale chamber volume variable through piston movement, it can replicate the acoustic modes and combustion conditions of full-scale engines without requiring actual full-scale testing, thereby reducing time and cost while maintaining assessment accuracy.

Inventive Principle:

Principle #26Copying

3Device complexity

If fixed combustion chamber volume is used, then device complexity is reduced, but adaptability to different acoustic frequencies deteriorates

Engineering Contradiction:

Improvechamber configuration complexityVSAvoidacoustic frequency range

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

4Device complexity

If injector plate is fixed, then device complexity is reduced, but ease of manufacturing different injector designs deteriorates

Engineering Contradiction:

Improvetesting system complexityVSAvoidinjector design iteration

Core Design Contradiction:

Device complexityVSEase of manufacture

Solution Approach 1:

The injector plate is designed as a separate, removable component that can be independently replaced with different injector designs. This segmentation allows the testing system to maintain simple overall structure while enabling easy iteration and comparison of different injector configurations through rapid exchange with the subscale combustion chamber and piston assembly.

Inventive Principle:

Principle #1Segmentation

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 system enables efficient, accurate, and cost-effective screening of injector stability across a range of acoustic frequencies, reducing the need for full-scale testing and minimizing risks to other engine components.

Implementation Method 1

The injector elements are thus exposed to acoustic modes of varying frequency, covering the range of acoustic modes expected in a full scale rocket engine

Methodology Applied

Scientific EffectAcoustic modes: Sound

Implementation Method 2

An annular gap between the piston and chamber sidewall provides a minimal cross-sectional flow area

Methodology Applied

Scientific EffectFlow through annular gap: Fluid Spray

Data Source

PatentUS20250290469A1Rocket injector subscale stability assessment with telescoping piston

Publication Date: 2025.09.18 BLUE ORIGIN MANUFACTURING LLC

AI summary

Systems and methods for subscale testing of rocket engine injector stability. The system includes a combustion chamber and a piston within the chamber that is continuously axially moveable via an actuator. An annular gap between the piston and a chamber sidewall provides a minimal cross-sectional flow area. A modular injector plate comprises one or more injector elements configured to inject a fuel and an oxidizer into the chamber. The piston is continuously translated, to thereby continuously vary a combustion volume of the chamber and to create a dynamically tunable downstream boundary. The injector elements are thus exposed to acoustic modes of varying frequency, covering the range of acoustic modes expected in a full scale rocket engine. The injector plate is removably attached to an upstream end of the chamber for replacement of the first injector elements with different, second injector elements for subsequent testing.