Accuracy and Applicability of a Reconstruction Technique for Determining Nozzle Throat Erosion History in Hybrid Rockets

摘要

Uncertainty analysis of a reconstruction technique for determining nozzle throat erosion history in hybrid rockets is carried out using results from a 2kN-class Cascaded Multistage Impinging-jet Hybrid Rocket Motor static firing test. Measurement bias and conceptual bias are examined to identify best practices for future experimental investigations using this technique. The uncertainty in results for nozzle throat erosion history and oxidizer to fuel mass ratio are seen to remain below ± 9% of nominal values for most of the firing test, whereas nozzle discharge coefficient and c* efficiency vary less than ± 3%. A linearly time-dependent c* efficiency, which varies between upper and lower measurement bias values, is used to estimate uncertainty in nozzle throat erosion rate. Results suggest that the assumption of constant c* efficiency leads to an uncertainty in the solution for nozzle throat erosion rate of less than ± 10%. In conclusion, the precision limit of final nozzle throat radius and chamber pressure measurements are shown to be the most important considerations for future applications of this reconstruction technique.