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In this work, six energetic complexes were prepared and used as promoters for the hypergolic reaction of 1-ethyl-3-methylimidazolium cyanoborohydride [EMIM][BH3CN] and 90% H2O2. The structures of these compounds were studied by FT-IR spectroscopy, powder XRD, and single crystal X-ray diffraction. The results revealed that all the compounds were iso-structural and each metal centre was coordinated with four organic ligands and two counter ions. The decomposition temperatures of these compounds ranged from 169.6-255.9 °C. After adding 10 wt.% of prepared complexes to an ionic liquid, [EMIM][BH3CN], the shortest ignition delay time achieved was 94 ms. Moreover, the formed homogenous catalytic fuels had similar densities, thermal stabilities, as well as specific impulses similar to that of pure [EMIM][BH3CN]. The simple preparation method, excellent yield, as well as high performance of these compounds make them promising promoters for use in green hypergolic bipropellants.

Hybrid rocket propulsion can contribute to reduce launch costs by simplifying engine design and operation. Hypergolic propellants, i.e. igniting spontaneously and immediately upon contact between fuel and oxidizer, further simplify system integration by removing the need for an ignition system. Such hybrid engines could also replace currently popular hypergolic propulsion approaches based on extremely toxic and carcinogenic hydrazines. Here we present the first demonstration for the use of hypergolic metal-organic frameworks (HMOFs) as additives to trigger hypergolic ignition in conventional paraffin-based hybrid engine fuels. HMOFS are a recently introduced class of stable and safe hypergolic materials, used here as a platform to bring readily tunable ignition and combustion properties to hydrocarbon fuels. We present an experimental investigation of the ignition delay (ID, the time from first contact with an oxidizer to ignition) of blends of HMOFs with paraffin, using White Fuming Nitric Acid (WFNA) as the oxidizer. The majority of measured IDs are under 10 ms, significantly below the upper limit of 50 ms required for functional hypergolic propellant, and within the ultrafast ignition range. A theoretical analysis of the performance of HMOFs-containing fuels in a hybrid launcher engine scenario also reveals the effect of the HMOF mass fraction on the specific impulse (Isp) and density impulse (ρIsp). The use of HMOFs to produce paraffin-based hypergolic fuels results in a slight decrease of the Isp and ρIsp compared to that of pure paraffin, similar to the effect observed with Ammonia Borane (AB), a popular hypergolic additive. HMOFs however have a much higher thermal stability, allowing for convenient mixing with hot liquid paraffin, making the manufacturing processes simpler and safer compared to other hypergolic additives such as AB.

Combined with a common fuel binder, solid hypergols can simplify the overall complexity of hybrid rocket engines, as the fuel grain can be ignited and reignited without any external power source or...

The advance of space technology is deeply affected by the breakthrough of high-performance fuels. Hypergolic ionic liquids (HILs) are one of the most potential fuels for bipropellant systems. However, high viscosity value and low specific impulse of traditional N-based HILs limit their application. Recently, boron-based HILs with low viscosity become the new candidates, and their derivatives are also found to promote the hypergolicity as additives in HILs. Here, the synthesis, physical chemical properties and thermal performance of boron-based HILs and HIL-additive system are reviewed.

This paper describes the testing and pulse performance analysis of a 45 N thruster, designated A45, using a 19.78% monomethylhydrazine–80.22% hydrazine fuel blend with mixed oxides of nitrogen cont...

We present a straightforward formulation predicting the characteristic velocity and specific impulse for bipropellant thrusters as a direct function of injection conditions, propellant combination,...

The development of hypergolic materials has aroused great interest due to their important applications in aerospace technology. In this work, six new energetic complexes were prepared and comprehensively characterized. All energetic complexes had isostructural characteristics, which made them ideal candidates for studying their structure-performance relationships. These energetic complexes had good thermal stabilities and excellent specific impulses. The vacuum-specific impulses were in the range 264.0-271.9 s, which was greater than most reported solid hypergolic materials. Moreover, the hypergolic performance of these compounds was examined by using 100% HNO3 as the oxidizer, and their catalytic performance in the hypergolic reaction of typical energetic ionic liquids and 90% H2O2 was comprehensively studied. All compounds displayed excellent hypergolic performance with the shortest ignition delay time of 4 ms. The examined copper-containing energetic complexes displayed excellent catalytic activities for the hypergolic reaction between energetic ionic liquids and 90% H2O2. The shortest ignition delay time of the examined hypergolic reactions was 31 ms. The suitable physicochemical properties, excellent energetic properties, and high catalytic activity of the hypergolic reactions have demonstrated the great potential of these energetic complexes as promoters for the development of green hypergolic bipropellants.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2021-07-18, 資料番号: PA2210010000

Task-specific dicyanamide anion ([DCA]−), cyanoborohydride anion ([CBH]−) and 1-ethyl or 1-allyl-3-methylimidazolium cations ([EMIM]+ or [AMIM]+) were mixed in different ratios to form hypergolic ionic mixtures. Their viscosities, densities, decomposition temperatures, specific impulses were determined and calculated. Ignition delay time was obtained by a drop test recorded by a high-speed camera. Theoretical calculations and molecular dynamics simulations were applied for exploring their energy and microstructure. The results indicated that ionic nature and ionic ratio in mixtures were two decisive factors for properties of ionic mixtures. Specially, mixture [EMIM][CBH]0.7[DCA]0.3 possessed the shortest ignition delay time of 3 ms with white fuming nitric acid (WFNA) as oxidizer, which was shorter than that of pure ionic liquid [EMIM][DCA] (32 ms) or [EMIM][CBH] (8 ms). However, with a reverse ratio of anions, mixture [EMIM][CBH]0.3[DCA]0.7 possessed a very long ignition delay time of 373 ms and showed a different phenomenon in ignition process. Thermogravimetric analysis indicated that mixture [EMIM][CBH]0.7[DCA]0.3 decomposed faster than mixture [EMIM][CBH]0.3[DCA]0.7. The radial distribution functions (RDFs) suggested that the H-bond interactions in mixtures obviously were influenced by ionic ratios. As a new design strategy, hypergolic ionic mixtures can not only combine properties of different ions, but also show more prominent performances in a specific ionic ratio than each parent ionic liquid.

A hypergolic system is a combination of organic fuel and oxidizer that ignites spontaneously upon contact without any external ignition source. Although their main usage pertains to rocket bipropellants, it is only recently that hypergolics have been established from our group as a revolutionary preparative method for the synthesis of different types of carbon nanostructures depending on the organic fuel-oxidizer pair. In an effort to further enrich this concept, the present work describes new hypergolic pairs based on 1,3-cyclohexadiene and 1,3-cyclooctadiene as the organic fuels and fuming nitric acid as the strong oxidizer. Both carbon-rich compounds (ca. 90% C) share a similar chemical structure with unsaturated cyclopentadiene that is also known to react hypergolically with fuming nitric acid. The particular pairs ignite spontaneously upon contact of the reagents at ambient conditions to produce carbon nanosheets in suitable yields and useful energy in the process. The nanosheets appear amorphous with an average thickness of ca. 2 nm and containing O and N heteroatoms in the carbon matrix. Worth noting, the carbon yield reaches the value of 25% for 1,3-cyclooctadiene, i.e., the highest reported so far from our group in this context. As far as the production of useful energy is concerned, the hot flame produced from ignition can be used for the direct thermal decomposition of ammonium dichromate into Cr2O3 (pigment and catalyst) or the expansion of expandable graphite into foam (absorbent and insulator), thus demonstrating a mini flame-pyrolysis burner at the spot.

Conventional hypergolic propellant combinations, using hydrazine and its derivatives as fuels and dinitrogen tetroxide based oxidizers, have been applied in spacecraft for attitude and roll control systems for more than 50 years. However, due to their high toxicity and carcinogenic potential, investigations into alternative green propellants are an active field in current research efforts. Promising alternative propellant candidates are combinations of hydrogen peroxide and suitable hypergolic room-temperature ionic liquids. In this work, imidazole thiocyanate ionic liquids are tested in drop tests with hydrogen peroxide. For this purpose, a newly developed automated drop test setup was designed and implemented. As a result, 1-ethyl-3-methylimidazolium thiocyanate (EMIM SCN) and 1-butyl-3-methylimidazolium thiocyanate (BMIM SCN) turned out to be hypergolic with highly concentrated hydrogen peroxide (96.1%). The ignition delay time on average is 31.7 ms for EMIM SCN and 45 ms for BMIM SCN. Theoretical performance of the two ionic liquids was calculated with NASA CEA and compared to a conventional hypergolic propellant combination (monomethyl hydrazine/dinitrogen tetroxide). The specific impulse of the green propellants is nearly 5% lower, but the density specific impulse is increased by 10%. Furthermore, the ignition delay time was reduced by dissolving a catalytic additive, copper thiocyanate, in the EMIM SCN. The lowest average ignition delay time of 13.9 ms was achieved for EMIM SCN and 5 wt% of copper thiocyanate. For higher copper concentration the ignition delay time is not further reduced. The fuel with EMIM SCN and 5 wt% of copper thiocyanate and the pure EMIM SCN were further characterized by thermal and spectroscopic methods. Fluid properties like density, viscosity and surface tension were also determined in laboratory investigations.

As potential hypergolic fuels, hypergolic ionic liquids have attracted much attention since their development. Herein, a series of hypergolic ionic liquids based on asymmetric [bis(imidazolyl)-BH2]+ cations were synthesized. The asymmetric structure of these hypergolic ionic liquids was further confirmed by NMR, infrared (IR), and high-resolution mass spectrometry-electron spray ionization (HRMS-ESI). Moreover, these hypergolic ionic liquids possess a high density of over 1.00 g cm−3, a comprehensive liquid range from −60 °C to 20 °C, and a density-specific impulse performance ranging from 305.4 to 357.8 s g cm−3, which is superior to that of unsymmetrical dimethylhydrazine. Remarkably, (1-allyl-1H-imidazol-3-ium-1-yl)(1-methyl-1H-imidazol-3-ium-1-yl) dihydroboronium dicyandiamide had the best ignition-delay time (18 ms), a high density (1.114 g cm−3), and a high value for heat of formation (400 kJ mol−1/1.48 kJ g−1). This work provides the possibility of a promising and green hypergolic fuel as rocket propellant.

Paraffin-based fuels incorporating solid amine boranes are investigated to identify formulations suitable for use as hypergolic hybrid rocket propellants. Their ignition delays are measured followi...

We investigate the potential of sodium borohydride (NaBH4) as reactive additive for ignition and combustion of boron and boron-paraffin wax solid fuels using hydrogen peroxide (H2O2) as liquid oxidizer. The new hybrid propellant system (solid fuel and liquid oxidizer) is investigated for a gas generator in ducted ramjets in which, the fuel-rich hot gases would be used for ramjet. Measurements of ignition delays along with visualizations of the ignition and combustion events were conducted by high-speed imaging on three propellant configurations; oxidizer drop on boron powder, oxidizer drop on boron-paraffin solid fuel slab, and oxidizer spray on a hollow cylindrical boron-paraffin fuel grain. These investigations revealed that the hypergolicity of boron with H2O2 is controlled by catalytically driven exothermic decomposition of H2O2 into superheated steam and oxygen in the presence of magnesium (∼5%) such that ignition and combustion of boron is delayed inordinately (7 s at 1.0 MPa). Boron hypergolicity improved dramatically by adding only 1% NaBH4 due to higher exothermicity of NaBH4 H2O2 reaction. This reaction driven hypergolicity is very fast (∼1 ms at 1.0 MPa), rapidly gasifies boron oxide layer, and enables sustained combustion of boron. Ignition of boron-paraffin wax solid fuel slab with a single drop of oxidizer was achieved with mean delay ∼5.4 ms at 1.0 MPa. The optimum NaBH4 concentration (5.7 wt%) for achieving ignition and spontaneous burning of boron was evaluated as a baseline formulation. The spray-on-hollow cylindrical fuel grain achieved combustion of boron during ignition and reignition tests with an ignition delay of 12–15 ms under normal ambient conditions. Our investigations prove the feasibility of utilizing liquid H2O2 for the hypergolic combustion of boron based solid fuels for a green and energy efficient propulsion system.

The attainment of the efficient ignition of traditional liquid hydrocarbons of scramjet combustors at low flight Mach numbers is a challenging task. In this study, a novel chemical strategy to improve the reliable ignition and efficient combustion of hydrocarbon fuels was proposed. A directional hydroboration reaction was used to convert hydrocarbon fuel into highly active alkylborane, thereby leading to changes in the combustion reaction pathway of hydrocarbon fuel. A directional reaction to achieve the hypergolic ignition of 1-octene was designed and developed by using Gaussian simulation. Borane dimethyl sulfide (BDMS), a high-energy additive, was allowed to react spontaneously with 1-octene to achieve the hypergolic ignition of liquid hydrocarbon fuel at -15 °C. Compared with the ignition delay time of pure 1-octene (565 °C), the ignition delay time of 1-octene/BDMS (9:1.2) decreased by 3850% at 50 °C. Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry confirmed the directional reaction of the hypergolic ignition reaction pathway of 1-octene and BDMS. Moreover, optical measurements showed the development trend of hydroxyl radicals (OH·) in the lower temperature hypergolic ignition and combustion of 1-octene. Finally, this study indicates that the enhancement of the low-temperature ignition performance of 1-octene by hydroboration in the presence of BDMS is feasible and promising for jet propellant design with tremendous future applications.

INTRODUCTION: Hypergolic propellants can be released in large amounts during space launch contingencies. Whether propellant-contaminated suit fabric poses a significant risk to rescue crews, due to off-gassing, has not been explored in detail. In this study, we addressed this issue experimentally, exposing space suit fabric to propellants (dinitrogen tetroxide [N2O4] and monomethyl hydrazine [MMH]).METHODS: The NASA Space Shuttle Program Advanced Crew Escape System II (ACES II) is similar to the NASA Orion Crew Survival System (OCSS) and was utilized here. Suit fabric was placed and sealed into permeation cells. Fabric exterior surface was exposed to constant concentrated hypergolics, simulating permeation and leakage. Fabric was rinsed, and permeation and off-gassing kinetics were measured. Experimental parameters were selected, simulating suited flight crewmembers during an evacuation transport without cabin air flow.RESULTS: The fabric allows for immediate permeation of liquid or vaporized MMH and N2O4. NO2 off-gassing never exceeded the AEGL-1 8-h level (acute exposure guideline level). In contrast, MMH off-gassing levels culminated in peak levels, approaching AEGL-2 10-min levels, paralleling the drying process of the fabric layers. DISCUSSION: Our findings demonstrate that MMH off-gassing is promoted by the drying of suit material in a delayed fashion, resulting in MMH concentrations having the potential for adverse health effects for flight and rescue crews. This indicates that shorter decontamination times could be implemented, provided that suit material is either kept moist to prevent off-gassing or removed prior to medical evacuation. Additional studies using OCSS or commercial crew suits might be needed in the future.Schwertz H, Roth LA, Woodard D. Propellant off-gassing and implications for triage and rescue. Aerosp Med Hum Perform. 2020; 91(12):956961.

The paper presents the results of drop tests performed to measure ignition delay for ionic liquids under various experimental conditions. Factors that strongly affect correct determination of ignition delay are indicated. Processes preceding ignition upon contact between various quantities of a fuel and an oxidizer are explained. It is argued that well-defined experimental conditions are required to ensure correct comparison when using benchmark fuels.

In this paper, four kinds of guanidinium dicyanamide-based energetic salts were prepared and investigated as energetic additives to hypergolic ionic liquid 1-ethyl-3-methyl imidazolium dicyanamide ...

On the basis of hypergolic dicyandiamide (DCA) and cyanoborohydride (CBH) anions, 1-methyl-1,2,4-triazole (MTZ) ligand, and transition metal (Co/Ni/Cu) cations, five hypergolic coordination compoun...

Atomically precise o-carboranealkynyl-protected clusters [Ag14(C4B10H11)12(CH3CN)2]·2NO3 (CBA-Ag) and [Cu6Ag8(C4B10H11)12Cl]NO3 (CBA-CuAg) have been found to exhibit hypergolic activity, such that ...

A unique, versatile, and material-independent approach to manipulate contactlessly and merge two chemically distinct droplets suspended in an acoustic levitator is reported. Large-amplitude axial oscillations are induced in the top droplet by low-frequency amplitude modulation of the ultrasonic carrier wave, which causes the top sample to merge with the sample in the pressure minimum below. The levitator is enclosed within a pressure-compatible process chamber to enable control of the environmental conditions. The merging technique permits precise control of the substances affecting the chemical reactions, the sample temperature, the volumes of the liquid reactants down to the picoliter range, and the mixing locations in space and time. The performance of this approach is demonstrated by merging droplets of water (H2O) and ethanol (C2H5OH), conducting an acid-base reaction between aqueous droplets of sodium hydroxycarbonate (NaHCO3) and acetic acid (CH3COOH), the hypergolic explosion produced via merging a droplet of an ionic liquid with nitric acid (HNO3), and the coalescence of a solid particle (CuSO4·5H2O) and a water droplet followed by dehydration using a carbon dioxide laser. The physical and chemical changes produced by the merging are traced in real time via complementary Raman, Fourier-transform infrared, and ultraviolet-visible spectroscopies. The concept of the contactless manipulation of liquid droplets and solid particles may fundamentally change how scientists control and study chemical reactions relevant to, for example, combustion systems, material sciences, medicinal chemistry, planetary sciences, and biochemistry.

Analytical reagent (AR)-grade nitric acid (69.3% by mass) and lithium–aluminum–hydride (LAH) as an additive to paraffin wax are evaluated as green propellant substitutes for state-of-the-art propel...

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2020-02-23, 資料番号: PA2010025000

The exploration of environmentally friendly hypergolic combinations of ionic liquid fuels and hydrogen peroxide as an oxidizer offers opportunities to replace commonly used conventional toxic, corrosive and carcinogenic hydrazine-based liquid hypergolic combinations. Various research opportunities await regarding the detailed investigations of green hypergolic ionic liquids (HILs) with rocket grade hydrogen peroxide (RGHP, >85% H2O2). In this work, the combustion of HILs 1-ethyl-3-methyl imidazolium cyanoborohydride ([EMIM][BH3CN]) and 1-allyl-3-ethyl imidazolium cyanoborohydride ([AEIM][BH3CN]), and HIL-additive mixtures with 95% H2O2 has been investigated. A new additive, 1,3-dimethyl imidazolium copper iodide ([diMIM]n[Cu2I3]n) was synthesized successfully; a structural investigation was performed through the use of single-crystal x-ray diffraction analysis through which a crystal density of 3.22 g/cm3 was revealed. The physicochemical properties (density, viscosity, and decomposition temperature) as well as performance parameters (ignition delay and specific impulse) of 2 to 15 wt% of [diMIM]n[Cu2I3]n in [EMIM][BH3CN] were determined. A 15 wt% of [diMIM]n[Cu2I3]n exhibited ignition delay time (IDT) values of 13 and 29 ms under fuel-rich and oxidizer-rich conditions, respectively; these IDT values are 100 times lower than those for [EMIM][BH3CN]. Interestingly, [diMIM]n[Cu2I3]n-[EMIM][BH3CN] combinations revealed high density (>0.98 g/cm3), good thermal (>200 °C) and chemical stability, and 5.6–6.0% higher density specific impulse than those found for unsymmetrical dimethyl hydrazine. The additive-promoted hypergolic combustion of HIL with RGHP opens a new avenue to the replacement of conventional toxic hypergolic combinations.

When a sphere of one reactant is placed in the medium of another reactant with which it is hypergolic, a chemical reaction (modeled here as a zeroth-order one-step irreversible Arrhenius reaction) ...

High viscosity and cost limit the performances and applications of hypergolic ionic liquids as propellant fuels. In this paper, several highly viscous hypergolic ionic liquids were prepared and mix...

This study focuses on the stepwise procedure involved in the development of a numerical model of a bi-propellant hypergolic chemical propulsion system using key features and performance characteristics of existing and planned (near future) propulsion systems. The study targets specific impulse of 100 N delivery performance of thrust chambers which is suitable for primary propulsion and attitude control for spacecraft. Results from numerical models are reported and validated with the Rocket Propulsion Analysis (RPA) computation concept. In the modelling process, there was proper consideration for the essential parts of the thruster engine such as the nozzle, combustion chamber, catalyst bed, injector, and cooling jacket. This propulsion system is designed to be fabricated in our next step in advancing this idea, using a combination of additive manufacturing technology and commercial off the shelf (COTS) parts along with non-toxic propellants. The two non-toxic propellants being considered are Hydrogen Peroxide as the oxidiser and Kerosene as the fuel, thus making it a low-cost, readily available and environmentally-friendly option for future microsatellite missions.

The combination of Energetic Ionic Liquid (EIL) “green” fuels and high test peroxide (>90% H2O2; HTP), as a “green” oxidizer, is a very promising platform for the development of fully “green” bipropellants for space exploration. In this work, two new “tandem-action” promoters – [FcCH2N(CH3)3+]2[Cu2I42−] (P1) and [FcCH2N(CH3)3+]n[Cu2I3−]n (P2) – and two reference “single-action” promoters, [FcCH2N(CH3)3+][H3BCN−] (P3) and [CH3N(CH2CH3)3+]n[Cu2I3−]n (P4), were prepared, comprehensively characterized and evaluated for their ability to significantly shorten the Ignition Delay (ID) times of hypergolic reactions between a series of EILs and H2O2. These promoters exhibited high solubility and long-term chemical stability in a typical EIL fuel – 1-ethyl-3-methylimidazolium dicyanamide (F1). Upon screening the performance of promoter–EIL formulations, the best ID result of 31 ms was observed for the combination of 1-ethyl-3-methylimidazolium cyanoborohydride (F2) fuel and promoter P2 (10 wt%), with H2O2 (95%), whereas an ID time of 58 ms was observed for the F2/P2 formulation with commercially available H2O2 (70%), respectively. Remarkably, the latter formulation remained fully homogeneous even at −40 °C, and showed an ID time of 66 ms at this temperature with H2O2 (95%), indicating the advantages of our approach for the development of novel fully “green” bipropellants.

Boron based compounds have been looked upon as possible replacements to conventional toxic hypergolic fuels in propellant system. In an attempt to add to the pool of boron based hypergols, a series of new amine borane/ cyanoborane zwitterionic compounds were developed. Their hypergolic reactivity, performance parameters and physico-chemical properties were examined, in detail. The unsymmetrical dimethyl hydrazine (UDMH) based zwitterions, UDMH-borane and UDMH-bisborane displayed strikingly lower ignition delay times of 2.2 and 2 ms, respectively and high specific impulse 241 and 245 s, respectively. The pyridinium-cyanoborohydride exhibited high heat of formation (146 kJ/mol) than UDMH. While all the developed compounds exhibited higher density than the UDMH. Chemical stability of UDMH-borane was investigated at different environmental conditions; it was found to be stable for longer duration. Low ignition delay, good thermal and chemical stability, positive heat of formation, high specific impulse, ease of synthesis, and commercially available starting materials are the promising features of these compounds which make them attractive prospects in revolutionizing the area of green hypergolic fuel in liquid as well as hybrid rocket propulsion.

We demonstrate a co-crystal-based strategy to create new solid hypergols, that is, materials exhibiting spontaneous ignition when in contact with an oxidant, from typically non-hypergolic fuel molecules. In these materials, the energy content and density can be changed without affecting the ignition delay. The use of an imidazole-substituted decaborane as a hypergolic "trigger" component in combination with energy-rich but non-hypergolic nitrobenzene or pyrazine yielded hypergolic co-crystals that combine improved combustion properties with ultrashort ignition delays as low as 1 ms.

The hypergolic ignition induced by the head-on collision of TMEDA and WFNA droplets was experimentally investigated with emphasis on the effect of droplet size on the ignitibility and the ignition delay time. The ignitibility regime nomogram in We - d O space indicates that the reduction of droplet size tends to suppress the hypergolic ignition. The ignition delay time, which was precisely determined by using grayscale level analysis, becomes shorter for smaller droplets. The seemingly conflicting size effects were resolved by means of time scaling analysis to reveal the size dependence of the three pre-ignition processes, which were identified as the first stage of droplet collision, deformation and intermixing, the second stage of droplet heating from interior to surface, and the third stage of droplet vaporization subject to heat loss by convective cooling.