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Abstract The effect of an N-alkyl substituent R on the characteristics of ignition of hypergolic ionic liquids (ILs) upon contact with white fuming nitric acid (WFNA) is examined by a modified drop test method that simultaneously combines high-speed shadow imaging with high-speed two-color pyrometry. The number of carbon atoms in the synthesized N-alkylated propargyl-imidazolium dicyanamide with alkyl substituents varied from 1 to 7. The ILs under study can be grouped in two categories depending on the initial location of the flame zone. When R has 1 to 3 carbon atoms, ignition is visualized as a glow inside a bubble (formed after droplet fall) and above the liquid surface. When the number n of carbon atoms in R is 4 to 6, no glow is recorded inside the bubble. In the case of a heptyl substituent, ignition does not occur since no flame is observed during approximately one minute. It is shown that the value of ignition delay can be interpreted as an Arrhenius-type function where the exponent depends linearly on n. An analysis of high-speed video records shows that the evaporation starting time of WFNA measured from the first IL–WFNA contact is also an Arrhenius-type function of n. Furthermore, it is found that the time for a bubble to reach its maximum diameter is independent of n. A possible mechanism of reaction between ILs of this class and WFNA is suggested and discussed. [ABSTRACT FROM AUTHOR]

Abstract. Detonation and deflagration initiation under focusing conditions in a lean hydrogen-air mixture was experimentally investigated. The experiments were carried out in a shock tube equipped with the laser schlieren system and pressure transducers. Two-dimensional wedges (53° and 90°), semi-cylinder and parabola, were used as the focusing elements. The peculiarities of mild and strong ignition inside the reflector cavity were visualized. A hydrogen-nitrogen mixture was taken for comparison between reactive and inert mixture. It was found that mild ignition inside the reflector cavity can lead to detonation initiation outside the cavity. Schlieren pictures of the process were obtained and the dependence of the distance of detonation initiation on Mach number of the incident shock wave was established. [ABSTRACT FROM AUTHOR]

Synthesis of new highly energetic ionic liquids (ILs) is described, and their hypergolic ignition properties are tested. The synthesized ILs combine the advantages of conventional rocket propellants with the energy characteristics of acetylene derivatives. To this end, N-alkylated imidazoles (alkyl = ethyl, butyl) have been synthesized and alkylated with propargyl bromide. The desired ionic liquids have been produced by metathesis using Ag dicyanamide. Modified hypergolic drop tests with white fuming nitric acid have been performed for N-ethyl (IL-1) and N-butyl propargylimidazolium (IL-2) ionic liquids. In the modified drop tests, high-speed shadowgraph imaging is used to visualize the process, and the temperature rise due to ignition is monitored with a two-color photodetector. It is shown that the ignition delay is shorter for IL-1 as compared to IL-2. The ignition of IL-1 occurs in two stages, whereas the combustion of IL-2 proceeds smoothly without secondary flashes. [ABSTRACT FROM AUTHOR]