COPV Combustion Chamber

Overview

The Solaris MkIII combustion chamber is a Type-V Composite Overwrapped Pressure Vessel (COPV) designed to withstand high chamber pressures while minimising structural mass. Unlike conventional metallic chambers, the COPV consists entirely of composite materials with aluminium threaded couplers at each end. This architecture reduces mass by over 60% relative to an equivalent aluminium chamber while still achieving a structural Factor of Safety above 3.

The chamber is manufactured using a hybrid laminate consisting of an inner fibreglass thermal barrier, eleven carbon-fibre structural plies, and an external abrasion-resistant sleeve. This laminated structure interfaces with Al7075-T6 threaded couplers, allowing the chamber to withstand pressures above 63 bar during operation.

Design & Layup Architecture

The COPV wall structure uses a multi-material laminate optimised for hoop strength, thermal isolation, and manufacturability within the available university workshop tooling. The layup is:

1 × Fibreglass inner ply for thermal protection
11 × 0/90 Carbon Fibre 3k twill structural plies
1 × External carbon-fibre sleeve for abrasion resistance
Al7075-T6 threaded couplers bonded into the laminate

The segmentation of the chamber into three modular composite sections reduces machining complexity, allows rapid fuel-grain swaps, and simplifies transport and setup during testing.

Manufacturing Process

The COPV is produced using a fully hand-layup composite process, refined through multiple sub-scale test articles. The workflow includes:

Mandrel preparation: deburring, degreasing, sealing and release agent application
Application of the fibreglass thermal barrier
Bonding and alignment of Al7075-T6 couplers
Sequential wet layup of carbon-fibre twill plies
Heat-shrink consolidation to maintain laminate pressure
High-temperature Technirez R2600 cure cycle (Tg ≈ 180°C)
Post-machining and dimensional inspection of couplers and threads

Structural Performance

Finite Element Analysis (ANSYS ACP + Static Structural) was conducted on the full wall layup, confirming a structural FoS above 3 at the expected 63.5 bar chamber pressure. Additional margin is provided by the fibreglass-first ply and outer sleeve, improving thermal performance and damage tolerance during integration.

Sub-scale COPV burst tests validated the laminate strength, manufacturing approach, and shrink-tape consolidation technique. These results closely correlated with simulation predictions, enabling final sign-off for the full-scale combustion chamber.

Testing & Validation

A multi-stage testing program was implemented to verify chamber strength, thermal performance, bonding quality, and interface integrity. This included:

Tensile dogbone testing of cured laminate coupons
Hydrostatic pressurisation of 60 mm sub-scale COPV vessels
Thread shear tests on Al7075 bonded coupler interfaces
Full-scale chamber hydrostatic testing to 1.5× MEOP

Conclusion

The Solaris MkIII Composite Overwrapped Combustion Chamber represents a significant leap in student-led hybrid rocket engine design. By leveraging a Type-V COPV architecture, the chamber achieves high structural performance while maintaining an exceptionally low mass. The combination of advanced composite layups, precision-machined aluminium couplers, and rigorous sub-scale and full-scale testing validated the chamber as flight-ready.

This COPV approach forms the backbone of future Monash HPR propulsion systems, enabling higher chamber pressures, longer burns, and more efficient vehicles.

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