Characterization of Paraffin/LDPE Blends for Hybrid Rocket Fuel Grains

The performance of hybrid rocket engines is highly influenced by the regression rate of their solid fuels. Typically, paraffin fuel exhibits higher regression rates than conventional polymers such as HTPB due to the droplet entrainment mechanism from the liquid film formed on the surface during their melting and combustion. However, paraffin's low viscosity and mechanical fragility limit its application, creating challenges for processing, such as crack formation during solidification, and also for the structural integrity of the grains during combustion due to rocket acceleration forces. A promising approach to mitigate these limitations is the incorporation of polymeric additives into paraffin, enhancing the mechanical and viscous properties of the fuel matrix.
To this end, this work investigates paraffin blended with low-density polyethylene (LDPE). Three fuel blends were manufactured and tested in a total of 100 samples campaign, evaluating the influence of LDPE with concentrations of 0\%, 5\%, and 10\% on the grain regression rate.
This research aims to quantify the contribution of droplet entrainment and surface vaporization rates to the total regression rate of LDPE-blended paraffin, correlating it with the viscosity of the liquid film. The experiment was conducted on a planar burner to isolate the effects of the axisymmetric flow process, simplifying the analysis of the regression rate, flow behavior, and combustion characteristics. The results of this study contribute to a definitive choice of the fuel composition to satisfy specific flight mission requirements.