Combustion performance of hybrid rocket fuels loaded with MgB2 and carbon black additives

Paraffin-based fuel has a great potential for several innovative missions, including space tourism, due to its safety, low environmental impact, high performance and low cost. Despite the fact that liquefying solid fuels increases the regression rate of hybrid rocket motors, incorporating energetic materials into solid fuel can still improve the performance. The objective and scope of this study is to increase the performance characteristics of the paraffin-based fuel by using magnesium diboride (MgB₂) and carbon black (CB) additives. The cylindrical-port fuel grains were manufactured with various additives percentages in mass (wt%: CB-2% and MgB₂-10%) and tested using a laboratory-scale ballistic hybrid motor under gaseous oxygen. The mechanical performance results revealed that adding CB and MgB₂ improved the ultimate strength and elastic modulus of paraffin-based fuels. The addition of these fillers increased the hardness of fuel by developing a strong interaction in the paraffin matrix. Thermogravimetry (TG) results showed that CB inclusion improved the thermal stability of the paraffin matrix. The average regression rates of fuels loaded with CB and MgB₂ were 32% and 52% higher than those of unmodified paraffin wax, respectively. The characteristic velocity efficiency was found in the range of 68%–79% at an O/F ratio of 1.5–2.6. The MgB₂ oxidation/combustion in the paraffin matrix was described by a four-step oxidation process ranging from 473 K to 1723 K. Finally, a combustion model of MgB₂ in the paraffin matrix was proposed, and four-step oxidation processes were discussed in detail.