Method for Determining Nozzle-Throat-Erosion History in Hybrid Rockets

Abstract

The authors of this paper introduce a new reconstruction technique titled Nozzle Throat

Comprehensive Data Reduction for N2O/HDPE Hybrid Rocket Motor Performance Evaluation

“…Kamps et al recently introduced a method, titled the "Nozzle Throat Reconstruction Technique (NTRT)," for determining both A t and ξ histories through the data reduction of commonly measured experimental values with the aim of enabling hybrid rocket researchers to accurately and cost-effectively investigate nozzle erosion experimentally [26]. The two governing equations of this method are the thrust equation shown by (1), and the characteristic exhaust velocity equation shown by (2):…”

“…where ∆t represents the sampling rate of the experimental measurement history in s, and t b is the burn time in s. Burn time is defined as the duration of time from the moment the (gauge) chamber pressure reaches 10% of the maximum value to the time at the aft-bisector of the pressure drop at the end of burning. This designation is outlined in [31] (p. 459), and was used in [26,27]. The fuel port radius in Equation 9is calculated based on the fuel mass, M fu , fuel density, ρ fu , and the outer diameter and length of the fuel, D fu and L fu¬ , according to Equation 11:…”

“…The chamber was purged with N 2 for a minimum of 30 s, both to extinguish the combustion of fuel and to cool the nozzle to less than 500 K for handling. The uncertainty introduced by applying such moving averages is much smaller than the precision limits of the sensors used, and therefore will not be addressed in detail in this paper (refer to [26]). Initial and final nozzle throat diameter measurements, d t,o and d t,f , were taken by the image analysis of digital photographs of the nozzle before and after firing.…”

“…Carmicino and Sorge, and Nagata et al alleviated the need to treat η * as a constant by measuring thrust and incorporating the thrust equation [24,25]. Most recently, Kamps et al combined these works, incorporating both the c * and thrust equations, and treating η * as a constant in order to determine the history of the nozzle throat area in an effort to investigate nozzle throat erosion [26]. This ballistic reconstruction technique was titled "Nozzle Throat Reconstruction Technique" or "NTRT," and was later used in a follow-on study by Kamps et al, which demonstrated how to use the results of the NTRT with thermocouple measurements from within the nozzle to determine the wall temperature history at the nozzle throat [27].…”

Hybrid Rockets as Post-Boost Stages and Kick Motors

“…The third technology is the use of an erosion-resistant material at the nozzle throat. For example, Kamps et al reported that coating the throat of a conventional graphite nozzle with SiC prevented erosion completely in a five second firing test [43]. D'lia et al [44] and Whitmore et al [45] achieved erosion reduction in longer firing durations using throat inserts made of customized erosion-mitigating materials with varying degrees of success.…”