Sloughing Prediction in Paraffin-Based Lattice-Augmented Hybrid Rocket Fuels

Fuel sloughing, a phenomenon in which fragments of the fuel grain detach and eject from the chamber without burning, is a problem in paraffin-based hybrid rockets due to their low mechanical strength. Sloughing can cause nozzle blockage and overpressurization, thus risking motor failure. Embedding polymer lattices within paraffin wax has emerged as a promising strategy to enhance its strength and mitigate sloughing. However, the fundamental mechanisms that lead to sloughing and quantifying the mechanical strength enhancement due to the lattice remain limited. The current work aims to address these gaps through combined experimental and modeling efforts. First, the viscoelastic behavior of paraffin wax is characterized using rheological testing. Second, shear testing is performed on paraffin wax to evaluate the influence of lattice volume fractions on shear strength. Finally, a one-dimensional transient heat conduction model is developed to predict temperature distributions within the solid fuel grain during operation. The measured shear strengths are compared with aerodynamic shear stresses induced by oxidizer flow, establishing a criterion for the onset of sloughing. The combined results from the rheological, mechanical, and thermal analyses provide a framework for predicting sloughing, offering a pathway to improved design and reliability of paraffin-based hybrid rocket fuels.