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Ammonium dinitramide-based ionic liquids (ADN-EILPs) are a promising alternative to hydrazine monopropellants. Continuous wave (CW) laser heating using carbon wools is an effective approach to attain the rapid ignition of ADN-EILPs. This study aims to verify the influence of the dispersibility of carbon additives in ADN-EILPs on their ignition. The investigation was performed by performing fluorescence microscopy of samples imitating the mixture of ADN-EILPs with carbon additives and CW laser ignition tests of ADN-EILPs with several yarn-lengths of carbon wools. Based on these results, the dispersity mechanism of carbon additives in ADN-EILPs is proposed, which indicates that the use of high-power laser is not an effective approach to ignite ADN-EILPs consisting of carbon additives with high dispersibility. During sample preparation for the ignition tests, it was verified that the difference in the length of carbon yarns affects the bulk density and morphology of the prepared samples, and dispersibility of carbons. The results of the ignition tests indicate that samples whose morphology altered into a liquid-like morphology cannot be ignited and the ones who retained their original one can be ignited. The physical distribution of the residue of samples with a liquid-like morphology, observed after the ignition tests, agrees with the discussion regarding the dispersibility mechanism of carbon additives, obtained through fluorescence microscopy. Moreover, for the samples exhibiting an ignition capacity, the bulk density of additives would be crucial to be considered to achieve the effective ignition. [ABSTRACT FROM AUTHOR]

Two-dimensional numerical simulations with the particle tracking method were conducted to analyse the dispersion behind the detonation front and its mean structure. The mixtures were 2H $_2$ –O $_2$ –7Ar and 2H $_2$ –O $_2$ of increased irregularity in ambient conditions. The detonation could be described as a two-scale phenomenon, especially for the unstable case. The first scale is related to the main heat release zone, and the second where some classical laws of turbulence remain relevant. The dispersion of the particles was promoted by the fluctuations of the leading shock and its curvature, the presence of the reaction front, and to a lesser extent transverse waves, jets and vortex motion. Indeed, the dispersion and the relative dispersion could be scaled using the reduced activation energy and the $\chi$ parameter, respectively, suggesting that the main mechanism driving the dispersion came from the one-dimensional leading shock fluctuations and heat release. The dispersion within the induction time scale was closely related to the cellular structure, particles accumulating along the trajectory of the triple points. Then, after a transient where the fading transverse waves and the vortical motions coming from jets and slip lines were present, the relative dispersion relaxed towards a Richardson–Obukhov regime, especially for the unstable case. Two new Lagrangian Favre average procedures for the gaseous detonation in the instantaneous shock frame were proposed and the mean profiles were compared with those from Eulerian procedure. The characteristic lengths for the detonation were similar, meaning that the Eulerian procedure gave the mean structure with a reasonable accuracy. [ABSTRACT FROM AUTHOR]

The inner flow containing the ignition process of a throatless and diverging (constant diverging angle α = 5 deg) rotating detonation engine (RDE) was experimentally investigated by both optical observation and pressure measurement. An RDE that had an acrylic engine wall with a length of 70 mm and an inlet diameter of 20 mm was tested under a low back pressure condition using gaseous C 2 H 4 − O 2 as the propellants. A high-speed camera captured the ignition process, of which there were two types: deflagration-to-detonation transition and direct initiation. In addition to the visualizations of the inner flow, the pressure values in an RDE with an acrylic wall were compared with those of an RDE having a stainless steel wall with 8 pressure ports in the axial direction. The comparison revealed that the RDE exhaust flow was supersonic. A strong self-luminescence and CH* luminosity area near the injector surface during combustion suggested that the short completion of detonation combustion enabled the thermal choking of the subsonic propellant gases even when the channel was diverging. Moreover, the axial position of the erosion in the acrylic wall indicated that the heat release region was near the injector surface. Finally, a theoretical flow model for the RDE was compared to the experimental data, and the results suggested that the inner flow in the RDE can be reasonably described as a quasi-one-dimensional steady flow. [ABSTRACT FROM AUTHOR]

Ammonium dinitramide–based energetic ionic liquid propellants (ADN‐EILPs) exhibit the advantages of high energy density, low toxicity, and handling safety, and are therefore promising monopropellants. Herein, we characterized the ignition of ADN‐EILPs induced by CW laser heating in the presence of carbon fibers, clarifying the effect of laser power and suggesting that ignition reproducibility is influenced by the difference of ADN‐EILP osmotic state in carbon fibers or carbon fiber configuration. The observed ignition behavior allowed one to conclude that (i) high‐power CW laser heating causes the formation of bubbles on the surface, which disturbs further heating; and (ii) an Arrhenius‐type relationship exists between ignition delay and heating rate, suggesting that the strategy of foreshortening ADN‐EILP ignition delay by increasing CW laser power has certain limits. [ABSTRACT FROM AUTHOR]

The ignition system for ammonium dinitramide‐based non‐solvent ionic liquids (ADN‐EILPs) with a continuous‐wave (CW) laser was investigated. The efficiency of conversion from CW laser power to ignition energy for ADN‐EILPs is important, and carbon additives are expected to enhance the efficiency of conversion. The impact of additive shapes on ADN‐EILP ignition by CW lasers is discussed herein by comparing the results of the ignition behavior observation using a high‐speed infrared camera. The shapes of the carbon additives are of two different types: fine fiber mass, called carbon wool, and powder of graphite. The ignition delay of carbon wool mixed ADN‐EILPs is shorter than that of the sample with graphite powder. The difference in these results might depend on the low dispersibility in ADN‐EILPs of carbon wools and the presence of local heat spots owing to the CW laser. The addition of carbon wools in ADN‐EILPs is expected to facilitate their ignition by CW laser heating. [ABSTRACT FROM AUTHOR]