Combustion characteristics of skeleton polymer reinforced paraffin-wax fuel grain for applications in hybrid rocket motors

Paraffin-based fuel is a promising and low-cost alternative for hybrid rocket motor applications due to its advantage of high regression rate. Meanwhile, paraffin fuel alone has poor mechanical strength that cannot meet the requirements in practical applications. Embedding skeleton polymer into paraffin-wax fuel can effectively enhance the mechanical properties and keep the advantage of high regression rate. In this paper, the mechanical and combustion characteristics of different polymer materials were comprehensively evaluated by using SEM, TG, TDG, mechanical test and flame propagation speed measurement experiments. A type of polymer reinforced paraffin-wax fuel grain has been fabricated and tested using a newly-designed optically accessible solid fuel tubular combustor. Combustion efficiency of the polymer reinforced paraffin fuel grain was further measured using a lab-scaled hybrid rocket motor. As a result, ABS is a better candidate that can be used in polymer reinforced paraffin fuel grain in terms of favorable combustion and mechanical properties. The flame propagation speed of polymers printed by SLS technique are much higher than those printed by SLA technique due to its rougher surface. Moreover, Paraffin liquid droplets and columns were clearly observed during the combustion process of the new proposed polymer reinforced paraffin fuel due to the entrainment and shearing of oxidizer flow, leading to higher regression rate and better mixing efficiency, which turns in higher combustion efficiency in fuel rich conditions compared with literature results.