Designing a More Efficient Altitude Compensating Rocket Nozzle

Voiceover

Presenter(s)

Ersel Serdar

Abstract or Description

Modern rocket engines use bell-shaped nozzles. Bell nozzle efficiency diminishes at high altitudes due to flow underexpansion, increasing mission cost and reducing payload capacity. Multiple altitude-compensating nozzles (ACN) have been developed as a solution to this problem. This project examines the performance of two ACNs (dual bell and plug nozzle) and develops a new hybrid nozzle that combines these concepts. The dual bell nozzle is a great ACN because of its simplicity and ease of manufacture, and the plug nozzle can adapt to different altitudes by moving its plug. The hybrid nozzle proposed in this project is a dual bell nozzle with a movable plug. Nozzles with a nozzle area ratio (NAR) of 434 were printed and tested in CU Boulder’s Engine Test room. The tests used liquid CO₂ at 1300 psi to simulate exhaust gases. The hybrid nozzle with the retracted plug produced more thrust at higher pressures than all of the other nozzles, including the dual bell nozzle. Because the dual bell nozzle is considered to be one of the best ACNs, these results suggest that the hybrid nozzle is potentially a more efficient alternative. A NAR between 5 and 20 would produce underexpanded flow, which is the condition where most ACNs are designed to operate at. Because the NAR in this project was much larger, the nozzles were highly overexpanded and flow separation inside the nozzle was likely. In the future, more tests of the hybrid nozzle with lower NAR should be performed.