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.