Effects of oxidizing additives on the physical properties and ignition performance of hydrogen peroxide-based hypergolic propellants

Herein, the concept of novel hypergolic pairs for the enhanced ignition performance of hypergolic propellants is proposed. The proposed hypergolic combinations comprised ionic liquid fuels, namely, 1-ethyl-3-methyl-imidazolium-thiocyanate (EMIM SCN) and 1-butyl-3-methyl-imidazolium-thiocyanate (BMIM SCN), and hydrogen peroxide (H2O2) with oxidizing additives. LiNO3 and NH4NO3 were used as oxidizing additives, which were dissolved in 60-95 wt% H2O2 to enhance the physical properties and ignition performance. Adding the oxidizing additives decreased the theoretical performance of the hypergolic pairs, however, the presence of oxidizing additives drastically reduced the freezing point of the mixture with 95 wt% H2O2. Particularly, an abrupt change was observed in the freezing point of the mixture with the LiNO3 additive. At only 5 wt% LiNO3, the freezing point reached 30 degrees C. The ignition performance of the novel hypergolic pairs was significantly enhanced by the introduction of oxidizing additives. In the drop test, the LiNO3 additive exerted a substantially greater effect on the enhancement of ignition performance than that exerted by NH4NO3. Furthermore, this positive contribution was maximized with the decrease in the hydrogen peroxide concentration. Although the addition of NH4NO3 to 90 and 95 wt% H2O2 adversely affected the ignition performance, the combination of BMIM SCN and 60 wt% H2O2-containing LiNO3 extended the hypergolicity limit. This study is the first attempt to introduce nitrate salts as oxidizing additives in hydrogen peroxide with ionic fuels, including SCN anions. Nitrate salts exhibit potential to serve as additives that can be used with hydrogen peroxide to enhance the properties of oxidizers. The nitrate salt usage helps lower the freezing point of oxidizers. Further, it shortens the ignition delay time of the hypergolic pairs.