Impinging jet ignition studies of hydrogen peroxide with gelled fuel rendered hypergolic by addition of reactive particles

Impinging jet experiments were conducted using doublet, triplet, and quintuplet injector configurations to measure ignition delay of hydrogen peroxide (H₂O₂) with gelled hydrocarbon fuel containing reactive particles. The addition of this material, sodium borohydride, renders the reactants hypergolic. Variation of fuel chemical properties (reactive particle size), and impinging jet characteristics (equivalence ratio, impingement velocity, velocity ratio, momentum ratio, and momentum flux ratio) were investigated to determine their effect on ignition delay. Cold flow and impinging jet ignition experiments were coupled to develop an understanding of system startup transient effects as well. Gelled fuels containing sieved particles indicate first light times are independent of particle size, while average ignition onset times decreased when the particle size was reduced. Increasing the target flow velocity range (the ratio of fuel/oxidizer velocities being held constant) from approximately 0.8 to 14.6 m/s (fuel velocity), indicated first light times consistently decreased while ignition delay decreased with increasing velocity until a plateau was achieved around 5 m/s. Investigation of global equivalence ratio effects, and experiments in which the oxidizer flow conditions were varied relative to the fuel conditions (at a fixed target equivalence ratio) also showed a relative independence of such conditions on the ignition delay time. Doublet and triplet injector configurations produced comparable first light and ignition onset times, while the average ignition time for the quintuplet injector configuration was nearly doubled. The quintuplet injector configuration produced a conical flow structure down stream of impingement, while the doublet and triplet configurations produced fans. Transition of flow conditions 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, reducing the local volumetric energy density. These results indicate more complex multi-injector geometries are not necessary to achieve short ignition delay times for this system.