Lynx V1 : Not being built

Lynx — Regeneratively Cooled Bipropellant Rocket Engine / Custom Thermal Sim

Propellants: N₂O / IPA
Cooling: Regenerative + Film
Analysis: RPA alongside a custom Python thermal model with spreadsheets for simple structural calculations.
Status: V2 design in progress

While I'm studying abroad in the UK for one semester, I want to try to build something really cool that is a bit different from my other projects. I decided a regeneratively cooled bipropellant engine would fulfil that requirement perfectly.

The project goals are derived from one master goal: learn as much as possible about the theory and practice of liquid rocketry:

Build a working regeneratively cooled rocket engine using Nitrous Oxide/Isopropyl Alcohol as propellants
- These propellants were chosen due to their suitability for future possible flight vehicles and their relative ease of use compared to cryogenic propellants.
Obtain a C* efficiency over 80%
Be able to change simple parameters such as Mass Ratio, film cooling mass ratio, etc
Be able to correlate data collected by this engine to a thermal sim I have developed myself
Have sufficient (>0.50) thermal margin for all thermal stress simulations
- 0.50 was chosen because the thermal sims have not been validated, and even though I believe it to be conservative, I want to have a solid amount of margin

All other requirements, like thrust, mass flow, chamber pressure, and inlet pressure, are derived from these requirements. Most importantly, I need to learn, and it would be ideal if it worked.

Lynx V2

I designed the first version of Lynx using RPA (Rocket Propulsion Analysis), NASA CEA for combustion properties, and a few custom spreadsheets I made myself for isentropic flow calculations, injector sizing, bolt sizing, and thermal stress calculations. Design reviews of Lynx V1 exposed several flaws, including manufacturability issues, narrow thermal margins, and, especially, an over-reliance on simulation tools without a sufficient first-principles foothold.

I took this advice to heart and wrote a thermal sim in Python (GitHub) over the course of a couple of weeks. The sim is mostly first-principles-based, while it does use some empirical calculations, such as the Bartz relation for heat transfer and film cooling based on NASA SP-8124, and also makes some pretty big assumptions, like assuming heat is only transferred into the coolant from one of the faces of the channels, and that gas properties are frozen (as I only have CEA calculate the gas properties at the chamber station)

Now that I've built my own model, I have a lot more control over the internals, and understand its underlying assumptions and limitations. Lynx V2 is currently in the design process, but I hope to have the design finalized by mid-October and ready by mid-November. This project will certainly take a large portion of my already slim free time up, but I am determined to have it ready on time.

When I fire the V2 engine, I hope to heavily instrument it, allowing me to match my thermal sim, which could make it a useful tool for design.

regensim output, visualized in google sheets

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