Hypergolic ignition of hydrogen peroxide/gel fuel impinging jets

Impinging jet experiments were conducted using doublet, triplet, and quintuplet injector configurations to measure ignition delay of hydrogen peroxide with gel hydrocarbon fuel containing sodium borohydride (NaBH4) particles. Rheological characterization and surface tension measurements of gel fuel mixtures were obtained to demonstrate their non-Newtonian shear thinning behavior and determine the influence of NaBH4 addition. Cold-flow experiments were conducted to elucidate system startup transients. First light times decreased with increasing reactant flow velocity, whereas ignition delay decreased until a plateau was achieved beyond 5 m/s. Variation of reactant flow and global equivalence ratios exhibited a relative independence of such conditions on ignition delay. Doublet and triplet injector configurations produced comparable first light and ignition onset times, whereas the average ignition time for the quintuplet injector configuration was nearly doubled. Transition of flow conditions (from fans to a more conical flow structure) downstream of impingement may have detrimentally influenced ignition for the quintuplet configuration by affecting the overall reactive surface area and volume in which the reactants are distributed. These results indicate that more complex multi-injector geometries are not necessary to achieve short ignition delay times for this system, and reactant flows may be varied to optimize for performance without adversely affecting ignition delay.