Hypergolic ignition behaviors of 1-ethyl-3-methylimidazolium dicyanamide/nitromethane blends reacting with white fuming nitric acid

Hypergolic ionic liquids have wide range of potential applications in the propulsion field due to their low toxicity, high thermal stability, and safe handling; however, their high costs and unclear hypergolic ignition mechanisms have limited their development to date. In this work, nitromethane (NM), as an additive, was blended with 1-ethyl-3-methylimidazolium dicyanamide ([EMIm][DCA]) to obtain a new fuel with low viscosity and cost. The hypergolic ignition behaviors of [EMIm][DCA]/NM blends reacting with white fuming nitric acid (WFNA) were then investigated through drop tests. Two high speed cameras and a time-resolved infrared camera were used to record the macro and micro hypergolic ignition processes and the reaction region’s temperature evolution. The effects of the Weber number and NM blend ratio (α) on the hypergolic probability and ignition delay time (IDT) of the [EMIm][DCA]/NM blends were investigated. The results show that with increasing impact velocity, more smoke-like vapor and tiny droplets were formed, which promotes the hypergolic ignition probability and decreases the IDT. As increasing NM blend ratios, the hypergolic ignition performance is initially similar to pure [EMIm][DCA] (α ≤ 30 %) and then decreases rapidly (α > 30 %). This indicates that when α ≤ 30 %, fuels with excellent hypergolic ignition characteristics can be obtained, whose raw materials costs may be up to ∼25 % lower than pure [EMIm][DCA]. Finally, a hypothesized pre-ignition pathway of [EMIm][DCA]/NM was proposed based on the experimental data and physical characteristics of the system.