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• Characterization of a novel hypergolic fuel, PAHyp 3. • Identification of an ignition envelope addressing hypergolicity and chemical stability. • By drop/impinging jet tests, fast ignitions were measured. • High-quality images revealed a new atomization mode, termed catalytically decomposition-assisted atomization. Since the beginning of this century, the space industry has been searching for stable non-toxic propellants to replace hydrazine-based fuels. In this paper, we introduce a novel eco-friendly self-igniting fuel, denoted PAHyp 3, which comprises a blend of N,N,N′,N′-tetramethylethylenediamine (TMEDA) and N-methylethanolamine (MMEA) catalyzed with a copper-based catalyst. This promising formulation is coupled with hydrogen peroxide as the oxidizer. To map near-optimal formulations in terms of performance and chemical stability, we varied the proportions of MMEA and TMEDA, each catalyzed with copper nitrate trihydrate concentrations ranging from 0.25% to 3% by weight. Drop tests revealed that a 50:50 mixture of TMEDA and MMEA, catalyzed with 2 wt% copper nitrate trihydrate, exhibited a rapid ignition delay time (IDT) of approximately 14 ms when paired with 94% hydrogen peroxide. This composition was subsequently chosen for evaluation using an impinging jet apparatus capable of capturing simultaneous visible and shadowgraph high-speed imaging, facilitating the detailed study of the ignition process. Screenshots from impinging jet firing tests unveiled that the majority of ignition events, utilizing 94% hydrogen peroxide, occurred downstream less than 20 ms after impingement. Subsequently, foam-like structures engulfed the vaporized and combusted liquid sheet, emitting stable orange/green flames. These promising outcomes indicate that PAHyp 3 presents novel prospects in aerospace propulsion, with the potential to replace hazardous and toxic hydrazine-based propellants. Moreover, a model was proposed to explain how bubble nucleation and growth from hydrogen peroxide decomposition can enhance atomization, leading to a new atomization mode we have termed "catalytic decomposition-assisted atomization". [Display omitted] [ABSTRACT FROM AUTHOR]

This work presents an experimental study on the hypergolic behavior of variants of N,N,N',N'-tetramethylethylenediamine (TMEDA)/N,N-dimethylethanolamine (DMEA) system, named PAHyp 0, with 93 wt% hydrogen peroxide. Two different copper-based catalyst and one cobalt-based catalytic agent were dissolved in the fuels to trigger the pre-ignition reactions. When employing copper chloride dihydrate, the resultant fuel requires methanol (ternary system) as a stabilizing agent, whereas both carboxylic salts of copper and cobalt dissolved in TMEDA/DMEA deliver a stable formulation (binary system) without the need for any organic solvent. Shadowgraph high-speed imaging was used to capture the ignition process and pressure wave development of over 30 fuel samples in a modified drop test. An ignition/stability envelope was proposed to map the safe and unstable formulations. It was demonstrated that the concentration of TMEDA should be no more than 50% in the binary system, while the amount of methanol should fall within a concentration window of 33 to 50% in the ternary system. Lower loadings of catalyst, ranging from 0.5 to 1.0 wt%, are required to deliver stable fast-igniting fuels. Three promising formulations catalyzed with 1 wt% copper salts were selected to perform impinging jet fire experiments. Impinging jets yielded significantly lower ignition delay times than drop tests due to the better mixing conditions. However, it was verified that ignition may fail for low values of jet velocities, below 0.8 m/s, and for high jet velocities, exceeding 14 m/s. An attempt to explain the ignition and non-ignition events was made by using the fundamentals of explosion limits of the hydrogen/oxygen system and oxidation reactions at low temperature. Remarkably, ultra-fast ignitions of about 10 ms were measured by the impinging jet setup within near-optimal operational conditions. Therefore, TMEDA/DMEA-based fuels with reduced catalyst loadings (0.5–1.0 wt%) offer new opportunities in aerospace propulsion and should be further studied. [ABSTRACT FROM AUTHOR]

New-generation green bipropellants based on ionic liquids for aircraft have attracted the attention of researchers. However, the major defects of ionic liquid propellants are their low specific impulse and incomplete combustion, which limits their practical application. In this work, a series of novel hypergolic fluids were prepared by mixing oxygen-rich nitroglycerin (NG) with fuel-rich dicyanamide-based ionic liquids. The complete dissolution of NG in ionic liquids makes these hypergolic fluids became self-supplying oxygen composite fuels, which generate much less solid residual products than pure hypergolic ionic liquids (HILs). Moreover, the addition of NG inhibited the micro-explosion between fuel and white fuming nitric acid (WFNA), extended the contact time between fuel and oxidizer. And a proper amount of NG in the fuel could suppress the secondary combustion. These composite fuels have high density (>1 g cm−3), low viscosity (as low as 13.49 cP), wide liquid operating ranges and acceptable ignition delay time. Additionally, the specific impulses of the composite fuels were higher than pure HILs. For the first time, this work provides a simple and reliable method to control the ignition properties of HIL by adding oxygen-enriched additives. [ABSTRACT FROM AUTHOR]