Method for determining nozzle throat erosion history in hybrid rockets

The authors introduce a new reconstruction technique titled Nozzle Throat Reconstruction Technique or NTRT to estimate nozzle throat erosion history and oxidizerto-fuel mass ratio history in hybrid rockets. Nine five-second static firing tests were carried out on a 2kN-class Cascaded Multistage Impinging-jet type hybrid rocket motor under varying oxidizer flowrates to evaluate the accuracy of NTRT results. Nozzle throat erosion histories calculated by NTRT agreed well with measured values for initial and final nozzle throat radius, and successfully reconstructed the case where no measureable amount of nozzle throat erosion occurred. For equivalence ratios 0.6-1.4, the relationship between nozzle throat erosion rate and equivalence ratio determined by NTRT displays a trend consistent with chemical kinetic limited heterogeneous combustion theory, as well as predictions made by previous researchers. A numerical simulation was carried out to investigate the applicability of an alternative computational technique which uses a nozzle exit pressure measurement as input data, and revealed that pressure in vicinity of the static pressure port is likely to deviate from centerline pressure by up to 0.1 [MPa] or 30%.