Experimental investigation on thermal behavior and regression rate characteristics of paraffin-polyethylene wax blends as hybrid rocket fuels

This paper focuses on the effects of polyethylene wax (PE wax) addition on the thermophysical properties and regression rate performance of paraffin-based hybrid rocket fuels. The thermal properties of paraffin-PE wax blends with varying ratios were systematically characterized using TGA/DSC measurements, while the dynamic viscosity of the fuels in the molten-state was determined using a viscometer. Rheological characterization confirmed that PE wax addition increases the molten-state viscosity of the fuel. The thermal analyses revealed increased melting temperature and thermal stability with PE wax addition, manifested by pyrolysis peak temperature shifting approximately 10°C toward higher values. Subsequent to performance characterization, a series of firing tests were carried out using a lab-scale hybrid rocket motor with gaseous oxygen (GOX) as the oxidizer and fuel formulations containing 0–20 % PE wax. A novel instantaneous internal ballistic reconstruction technique (IBRT) was developed to characterize the transient regression behavior, providing significantly improved statistical reliability compared to traditional mass-loss methods. Experimental results demonstrated that increasing PE wax content from 0 % to 20 % reduces thrust performance by 13 % and regression rate by 33 % under similar operating conditions. The IBRT indicated continuous decreases in both regression rate and oxidizer mass flux during the burning duration, due to port area growth, with the regression rate exhibiting greater sensitivity to mass flux variations than that of classical hybrid fuels. The regression rate reduction mechanism was attributed to increased molten-state viscosity and melting temperature, which inhibited Kelvin-Helmholtz instability (KHI) responsible for droplet entrainment. This study evaluated the effect of PE wax content on the thermochemical performance properties and regression characteristics of paraffin-based fuels, thereby establishing a foundation for designing hybrid rocket fuels that effectively balance combustion performance with mechanical requirements.