About This Project

Nozzle flow separation is a condition where exhaust gases in a rocket nozzle cause severe pressure fluctuations that can damage a spacecraft. The Schmucker Criterion provides insight as to where this flow separation occurs, but it tends to become inaccurate at smaller scales. Using a small scale composite combustion chamber, we want to use vibration data and nozzle extensions to determine exactly what nozzle expansion ratio causes damage to our carbon fiber material during test.

Ask the Scientists

What is the context of this research?

Fundamental texts about liquid rocket engines focus primarily on larger, more complicated engines such as the RS-25 or F-1, meaning that the data they provide on pressure ratio, area ratio and Mach number (Figure 1-6) is more difficult to apply to smaller engines in the 100 to 1,000lbf thrust range. Additionally, these texts also tend to focus on combustion chambers made out of copper or nickel alloys (Section 8.4). Amateurs and space startups operate on a shoestring budget, making the high thrust and manufacturing methods described in these texts inaccessible. Ablative composite chambers are cheap and easy to make, and by testing a critical way in which these chambers can fail, we can provide data to these communities to improve their own designs that these texts don't provide.

What is the significance of this project?

Second stage engines have extremely large expansion ratios to optimize their exhaust for the vacuum of space, but testing these engines on the ground requires large infrastructure to simulate a high altitude or a stub-nozzle. Stub-nozzles are cheaper, however they fail to characterize the real pressure conditions the engine would be exposed to. Using our composite engine, we're aiming to map where cracks and stresses on the combustion chamber occur and how this damage causes hot spots inside the engine. This is important because these hot spots can cause parts of the ablative inside the engine to erode faster than other parts, which can lead to even more severe internal stresses. Using this data, more robust composite engines can be made.

What are the goals of the project?

This project has two main goals. First, we want to know exactly what expansion ratio causes flow separation on our engine. We'll use multiple nozzle extensions and compare our empirically determined expansion ratio to predicted values from the Schmucker Criterion. Second, we'll document where our composite chamber accrues the most damage when flow separation occurs. We'll use accelerometers positioned on the injector and nozzle extension flange and perform detailed inspections to create a map of this damage. Using temperature data, we'll also determine if this correlates to any localized hot spots on the chamber wall. Our test plan includes 3 tests with varying nozzle extensions, 1 test to confirm results we saw in the first 3, and an additional 4 tests for damage mapping.