Droplet collision of hypergolic propellants

In the present mini-review,droplet impacting on a liquid pool,jet impingement,and binary droplet collision of nonreacting liquids are first summarized in terms of basic phenomena and the corresponding nondimensional parameters.Then,two representative hypergolic bipropellant systems,a hypergolic fuel of N,N,N′,N′-tetramethylethylenediamine(TMEDA)and an oxidizer of white fuming nitric acid(WFNA)and a monoethanolamine-based fuel(MEA-NaBH4)and a high-density hydrogen peroxide(H2O2),are discussed in detail to unveil the rich underlying physics such as liquid-phase reaction,heat transfer,phase change,and gas-phase reaction.This review focuses on quantifying and interpreting the parametric dependence of the gas-phase ignition induced by droplet collision of liquid hypergolic propellants.The advances in droplet collision of hypergolic propellants are important for modeling the real hypergolic impinging-jet(spray)combustion and for the design optimization of orbit-maneuver rocket engines.