| Summary: | Ionic liquids have a wide engineering application foresight due to their easy and safe storage and handling while are limited by the unclear mechanism of hypergolic ignition. In this study, three dicyanamide-based ionic liquids with different cations, 1-allyl-3-methyl imidazolium ([AMIm]), 1-ethyl-3-methylimidazolium ([EMIm]) and 1-butyl-3-methyl-imidazolium ([BMIm]), are prepared to react with white fuming nitric acid through drop tests. The diameter of ionic droplet is 2.2 mm, the impact velocities are controlled at 0.16/0.45/0.62/0.82/1.01 m s-1 by adjusting the dropping height, and the whole reacting process is recorded by three cameras to provide macroscopic, microscopic and infrared details. The promotion effect of impact velocity on hypergolic ignition probability is confirmed for all the ionic liquids, and the minimum impact velocity for successful hypergolic ignition of each ionic liquid was determined. The temperature evolution of hypergolic process shows a non-monotonic trend, and a four-stage process was performed to reveal the hypergolic mechanism. The experimental results indicate that short-chain alkyl and unsaturated substituents in cations are favored for hypergolic ignition, and the datasets are conducive for kinetic model construction.
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