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An understanding of the scalability of hybrid rocket regression models is critical for the enlargement and commercialization of small-scale engines developed within universities and similar research institutions. This paper investigates the fuel regression rates of recent 40 kN thrust-class motor experiments, which were designed based on fuel regression rate correlations of 2.5 kN thrust-class motors from previous research. The results show that fuel regression rates of the 40 kN experiments were within 26% of predictions made using correlations based on 2.5 kN experiments.

A recently developed reconstruction technique is used to investigate graphite nozzle erosion in two scales of hybrid rocket motors, 30N-thrust class and 2000N-thrust class, using oxygen as the oxidizer and high-density polyethylene as the fuel. Thermocouple measurements taken from within the nozzles are used to estimate nozzle throat wall temperature. Forty-four static firing tests were conducted under varying experimental conditions to confirm the validity of the reconstruction technique results, investigate the conditions at the onset of erosion and to formulate an empirical predictive model of nozzle erosion rate. Results show that a single formula that treats the combustion gas as a single oxidizing agent for which heterogenous rate constants are functions of equivalence ratio can satisfactorily replicate the

A nozzle throat erosion problem occurs in developing a 15 kN-thrust class motor. To obtain a history of the nozzle throat area in a hybrid rocket static firing test, a new method is developed. Although the specific heat ratio of the combustion gas, which depends on the oxidizer to fuel ratio ξ, is necessary to calculate a nozzle throat area, it is difficult to obtain temporal ξ in hybrid rockets. A reconstruction technique, which estimates temporal ξ, needs chamber pressure, oxidizer flow rate, and nozzle throat area as input data. These two equations are solved simultaneously to acquire two convergence calculations for nozzle throat area and ξ. The new method was applied to a static firing test. The results show a typical erosion history, showing the validity of this method.

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