Ignition study of hypergolic solid fuels through counterflow experiment using hydrogen peroxide spray

Hypergolic solid fuels provide rapid and reliable ignition for hybrid rockets, offering significant advantages over conventional methods. However, a practical experimental approach is necessary to study ignition and combustion behavior under realistic oxidizer flow conditions. This study introduced a novel counterflow spray experiment using 90 % rocket-grade hydrogen peroxide sprays applied to low-density-polyethylene-based fuel pellets embedded with sodium borohydride and manganese acetate tetrahydrate. The results showed that sodium borohydride caused vigorous reactions, damaging the pellets, while the addition of manganese acetate tetrahydrate moderated this effect. Hypergolic ignition and sustained combustion were achieved at oxidizer mass flow rates of 0.38-0.57 g/s, with ignition delay times of 15 to 30 ms, consistent with droplet test results. In addition, reignition was successful under the same flow conditions, although the char layer formed on pellet surface after the first ignition limited the surface additive reactivity, leading to longer ignition delay times. 3D surface analysis provided quantitative data on surface roughness across various fuel compositions and flow rates. This novel counterflow spray experiment is expected to be both effective and simple, with the ability to offer valuable insights into hypergolic ignition and combustion process.