White Fuming Research Articles

Multiple Diagnostics of Hybrid Rocket Ignition and Effect of Hypergolic Additive Granulometry

The ignition delay and surface-temperature evolution of ammonia-borane-doped paraffin wax exposed to white fuming nitric acid are measured in oxidizer-drop tests. The ammonia borane granulometry is varied to investigate the limits of hypergolic ignition and its underlying mechanisms. High-speed visible, Schlieren, and midinfrared optical systems are used simultaneously to observe the phenomena occurring between the first contact and the appearance of a flame. The experiments reveal the usefulness of both Schlieren and midinfrared high-speed imaging as diagnostic tools for hybrid hypergolic experiments, specifically for the detection of preignition events not observable through visible light emission. A strong relationship is found between the granulometry of the ammonia-borane additive and the ignition delay of the fuel pellets. At 25% ammonia borane by weight, pellets made with a granulometry of 600–710 μm ignited in 15.4 ms, whereas those made with a granulometry of 53–106 μm ignited in 60.1 ms on average. Granulometry also affects preignition phenomena such as gas-release velocity and surface-temperature evolution. These results reveal that the acid drop acts as a heat sink for the hypergolic ignition of the hybrid rocket fuel and that a minimum additive particle size is needed to avoid quenching.

N-Alkyl-1,2,4-triazole–Borane Complexes as High-Density Hypergolic Materials

AbstractHydrazine and its derivatives have served as a conventional bipropellant fuel for several decades. However, their extremely acute toxicity and carcinogenicity, high volatility, and environmental impact have attracted significant attention. In order to synthesize green bipropellant fuels with high density, high specific impulse, and good thermal stability, three novel N-alkyl-1,2,4-triazole–borane complexes were successfully synthesized by reacting alkylated 1,2,4-triazole coordinated with sodium borohydride in the presence of ammonium sulfate. During the droplet test with white fuming nitric acid, there was a relatively short ignition delay time of 98 ms. Additionally, these hypergolic fuels possessed a high density exceeding 1.10 g cm–3, and the specific impulse is ranging from 187 to 199 s, and the highest decomposition temperature reaches 153.4 °C. These results demonstrate their great potential as hypergolic fuels or hypergolic ionic liquid additives in the field of hypergolic materials.

Droplet collision of hypergolic propellants

AbstractIn the present mini‐review, droplet impacting on a liquid pool, jet impingement, and binary droplet collision of nonreacting liquids are first summarized in terms of basic phenomena and the corresponding nondimensional parameters. Then, two representative hypergolic bipropellant systems, a hypergolic fuel of N,N,N′,N′‐tetramethylethylenediamine (TMEDA) and an oxidizer of white fuming nitric acid (WFNA) and a monoethanolamine‐based fuel (MEA‐NaBH4) and a high‐density hydrogen peroxide (H2O2), are discussed in detail to unveil the rich underlying physics such as liquid‐phase reaction, heat transfer, phase change, and gas‐phase reaction. This review focuses on quantifying and interpreting the parametric dependence of the gas‐phase ignition induced by droplet collision of liquid hypergolic propellants. The advances in droplet collision of hypergolic propellants are important for modeling the real hypergolic impinging‐jet (spray) combustion and for the design optimization of orbit‐maneuver rocket engines.

Synthesis and Energetic Characterization of Borane-Amines on High-Nitrogen Heterocycles.

Borane-amines have garnered attention over the last several decades in a variety of applications, ranging from hydrogen storage materials to hypergolic fuel systems. An investigation into the synthesis of borane-amines with high-nitrogen content heterocycles was undertaken in this work. Borane-amines were formed by the reaction of BH3·Me2S in tetrahydrofuran (THF) with the requisite nitrogen-containing heterocycle and isolated by placing the crude reaction mixture in hexanes to precipitate the product. X-ray crystallography, thermogravimetric analysis (TGA), high resolution mass spectroscopy (HRMS), 1H NMR, 13C NMR, and 11B NMR were utilized for product characterization, while impact and friction sensitivity testing were conducted to identify sensitivity in the synthesized compounds. Most isolated borane-amines, except one, were found to decompose in the atmosphere and were more sensitive to mechanical stimuli than their starting materials; however, all synthesized compounds were found to be hypergolic in the presence of white fuming nitric acid (WFNA).

Ignition delay and performance of sorbitol based hypergolic hybrid fuels

The ignition delay of ammonia-borane-doped sorbitol and paraffin-based fuel pellets exposed to white fuming nitric acid is measured in oxidizer drop tests. Various mixtures of sorbitol, paraffin and ammonia-borane are tested to investigate the effect of sorbitol concentration on the ignition behavior of hypergolic hybrid fuels. High-speed visible, Schlieren, and mid-infrared imaging techniques are used to study the ignition behavior in a non-intrusive manner. The experiments demonstrate that the ignition flame appears faster and is larger with fuel pellets made of sorbitol compared to those made of paraffin. Sorbitol pellets containing 10 percent ammonia-borane by mass ignited in 8.20 ms on average, while paraffin pellets containing 10 percent ammonia-borane ignited in 60.25 ms. The average ignition flame intensity was measured to be approximately 6 times greater in sorbitol-based pellets than in paraffin-based ones. Ignition delay and oxygen bomb calorimeter tests are also performed using aged pellets and showed that exposure to ambient air negatively impacts the storage stability of sorbitol-based fuel samples. Theoretical performance calculations revealed that sorbitol-ammonia-borane mixtures can reach density-specific impulses similar to those of paraffin-ammonia-borane mixtures. This makes sorbitol-ammonia-borane a rare hypergolic hybrid fuel that is liquefying while also having high propulsive density and a very short ignition delay.

Different Ignition Modes and Temperature Evolution of Typical Hypergolic Ionic Liquids

The hypergolic ignition behaviors of three ionic liquids [BMIm][DCA], [EMIm][DCA], and [EMIm][CDB] reacting with white fuming nitric acid (WFNA) were investigated using the drop test approach. Two high-speed cameras with/without a long-distance microscope and a time-resolved infrared camera were used to simultaneously record the hypergolic ignition process and the reaction region temperature evolution. Results showed two distinct hypergolic ignition modes. Specifically, for [BMIm][DCA] and [EMIm][DCA], some “vapor smoke” is generated after the fuel droplet contacts the WFNA pool, followed by sudden ejection of liquids induced by microexplosion. The measured temperature in the observation window is found to first increase, then decrease, and rise again. For [EMIm][CDB], no microexplosion is observed and the temperature monotonically increases before hypergolic ignition. It is inferred that microexplosion is caused by sufficient accumulation of gaseous intermediates or products underneath the liquid surface, and the monotonic or nonmonotonic increasing temperature is a characteristic of ignition modes. A conceptual model is proposed to illustrate the two ignition modes. In addition, the droplet impact velocity (U0) was varied from 1.1 to 2.1 m/s in the experiment. It is found that the vapor delay time (VDT), explosion delay time (EDT), and ignition delay time (IDT) are all reduced with U0 by at most 50%. For a given U0, the three time scales decrease in the order [BMIm][DCA], [EMIm][DCA], and [EMIm][CDB] (IDT as low as 14.4 ms).

Hypergolic ignition of paraffin-based hybrid rocket fuels by sprays of liquid oxidizer

An experimental study is conducted to measure the ignition delay of ammonia borane doped paraffin wax with sprays of white fuming nitric acid as oxidizer. The injection pressure and injector diameter are varied to investigate the effects of spray characteristics on the ignition dynamics. A range of Weber (We) number for the oxidizer jet covering 100 < We <2700 and Reynolds (Re) number 1300 < Re <8900 is investigated, whereas the We number at the droplet scale varies from 0.8 < Wedrop <24.1. The sprays are characterized using phase-doppler anemometry to obtain the size and speed distribution of the oxidizer droplets across multiple positions. In addition to conventional high-speed imaging, the hypergolic ignition is also observed using Schlieren imaging and a high-speed mid-infrared camera. The results show that the ignition delay of a hypergolic hybrid fuel under spray conditions is unaffected by the mean droplet size of the oxidizer. The ignition delay decreases with increasing We number at the droplet scale and increasing droplet velocity. The variability in the ignition delay also decreases with Weber number and droplet velocity. The values obtained for the ignition delay when using a spray are generally higher than those from simple oxidizer drop experiments, highlighting the need to investigate the hypergolic ignition in configurations representative of engine conditions.

Comparison of quantitative removal efficiency of the prevention systems for white fume and odor from textile tenter process by using light scattering method

Comparison of quantitative removal efficiency of the prevention systems for white fume and odor from textile tenter process by using light scattering method

Green Hypergolic Ionic Liquids: Future Rocket Propellants

Hydrazine and its derivatives have been used as standard propellants for spacecraft propulsion systems since the 1960s, despite being highly toxic and carcinogenic. The propellant synthesis community has constantly been looking for green alternatives for the same. Hypergolic ionic liquids (HILs) with several attractive properties, such as high energy content, high bulk density, low vapor pressure, and low toxicity, have been proposed as an alternative to hydrazine and its derivatives. In the present study, the theoretical performance of sixty-eight HILs was studied at a combustion chamber pressure of 3 MPa and a nozzle expansion ratio of 40. The specific impulse and density specific impulse of the HILs were calculated with white fuming nitric acid (WFNA), inhibited red fuming nitric acid (IRFNA), and nitrogen tetroxide (NTO) as oxidizers. The specific impulse of 2,2-dimethyltriazanium nitrate (HIL-1) was found to be 23 s higher than monomethylhydrazine (MMH), whereas its density-specific impulse was found to be 123 g-s/cm3 higher than MMH. The gains in the specific impulse and density specific impulse coupled with other desirable “green” properties for several HILs are expected to establish them as potential replacements for hydrazine and its derivatives.

An experimental study on the hypergolic process enhanced by pre-ignition heat release: [AMIM][DCA]/furfuryl alcohol blends reacting with white fuming nitric acid

The hypergolic ignition behaviors of [AMIM][DCA] (1-allyl-3-methylimidazolium dicyanamide)/furfuryl alcohol (FA) blends reacting with white fuming nitric acid (WFNA) are investigated using drop test approach. Morphology results from two high speed cameras and temperature profiles from an infrared camera are combined in analyzing the hypergolic process. A typical hypergolic process observed in this work involves a mixing dominant stage, a stage with moderate temperature rising and vapor/secondary droplets emerging, and a stage with violent temperature rising accompanied by flame occurrence. Two kinds of delay times are used to characterize the hypergolic process which are found to be nonmonotonic with the variations of FA fractions. FA, though not hypergolic with WFNA, exhibits extensive pre-ignition heat release due to its physical and chemical properties, which enhances the hypergolic process of [AMIM][DCA]/FA blends with WFNA.

Characterization of Galvanizing Flue Dust and Recycling Possibilities

Waste generation is a part of every technological process, including galvanizing. The presented paper deals with the characterization of flue dust generated in the process of hot-dip galvanizing, and proposes possible methods for zinc recycling. The flue dust is released into the atmosphere as a white fume above the zinc bath, which is caused by the decomposition of ammonium chloride and zinc chloride present in the flux. This dust is classified as hazardous waste and is a material with a particle size below 90 µm. In addition to zinc and iron compounds, it contains water vapor and oils. The presented elemental, phase, and other characteristic methods of flue dust are important for the subsequent selection of a suitable method for processing the material. At present, this waste is not processed separately due to its low production, which is approximately 0.3 kg per 1 tonne of galvanized steel. The proposed hydrometallurgical recycling method enables the processing of flue dust on a small scale and enables the recovery of high-purity zinc in the form of metallic zinc or zinc oxide.

An Experimental Study on the Hypergolic Process Enhanced by Pre-Ignition Heat Release: [Amim][Dca]/Furfuryl Alcohol Blends Reacting with White Fuming Nitric Acid

An Experimental Study on the Hypergolic Process Enhanced by Pre-Ignition Heat Release: [Amim][Dca]/Furfuryl Alcohol Blends Reacting with White Fuming Nitric Acid

Experimental study on hypergolic ignition and non-ignition for dicyanamide-based ionic liquids at low impact velocity conditions

Ionic liquids have a wide engineering application foresight due to their easy and safe storage and handling while are limited by the unclear mechanism of hypergolic ignition. In this study, three dicyanamide-based ionic liquids with different cations, 1-allyl-3-methyl imidazolium ([AMIm]), 1-ethyl-3-methylimidazolium ([EMIm]) and 1-butyl-3-methyl-imidazolium ([BMIm]), are prepared to react with white fuming nitric acid through drop tests. The diameter of ionic droplet is 2.2 ​mm, the impact velocities are controlled at 0.16/0.45/0.62/0.82/1.01 ​m ​s-1 by adjusting the dropping height, and the whole reacting process is recorded by three cameras to provide macroscopic, microscopic and infrared details. The promotion effect of impact velocity on hypergolic ignition probability is confirmed for all the ionic liquids, and the minimum impact velocity for successful hypergolic ignition of each ionic liquid was determined. The temperature evolution of hypergolic process shows a non-monotonic trend, and a four-stage process was performed to reveal the hypergolic mechanism. The experimental results indicate that short-chain alkyl and unsaturated substituents in cations are favored for hypergolic ignition, and the datasets are conducive for kinetic model construction.

Synthesis and properties of borane‐containing ionic liquids based on biferrocene

AbstractTo develop a new type of energetic ionic liquid (EIL) that has a catalytic effect on the thermal decomposition of ammonium perchlorate (AP) and can be ignited in white fuming nitric acid (WFNA), six borane‐containing ionic liquids based on biferrocene were successfully synthesized, and their structures were determined by x‐ray crystallography. Except for iodized salts, four EILs with high thermal stability burned rapidly in WFNA, one of which, bis[1‐(ferrocenylmethyl)imidazole‐3‐yl] dihydroboronium cyanoborohydride, [Fcmim][BH3CN], produced the shortest ignition delay (ID) time of 5 ms. However, iodized salts demonstrated a better catalytic effect on AP than did BH3CN−‐ or N(CN)2−‐based EILs and bis[1‐(ferrocenylmethyl)benzimidazole‐3‐yl] dihydroboronium iodide, [Fcbemim][I], could advance the final thermal decomposition temperature of AP by 50°C. Anions have a significant effect on the structures and performances of ionic liquids.

From heart drug to propellant fuels: Designing nitroglycerin-ionic liquid composite as green high-energy hypergolic fluids

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.

High-Energy Metal–Organic Frameworks with a Dicyanamide Linker for Hypergolic Fuels

In this study, a hypergolic linker (dicyanamide, DCA) and a high-energy nitrogen-rich ligand (1,5-diaminotetrazole, DAT) were applied to construct high-energy metal-organic frameworks (HEMOFs) with hypergolic property. Three novel metal-organic frameworks (MOFs) were synthesized via a mild method with fascinating 2D polymeric architectures, and they could ignite spontaneously upon contact with white fuming nitric acid (WFNA). The gravimetric energy densities of the three HEMOFs all exceeded 26.2 kJ·g-1. The cupric MOF exhibits the highest gravimetric and volumetric energy density of 27.5 kJ·g-1 and 51.3 kJ·cm-3, respectively. By adjusting the metal cations, high-energy ligands and hypergolic linkers can improve the performance of hypergolic MOFs. This work provides a strategy for manufacturing MOFs as potential high-energy hypergolic fuels.

AN EXPERIMENTAL STUDY OF FACTORS AFFECTING HYPERGOLIC IGNITION OF AMMONIA BORANE

Hypergolic hybrid motors are advantageous for rocket propulsion due to their simplicity, reliability, low weight, and safety. Many hypergolic hybrid fuels with promising theoretical performance are not practical due to their sensitivity to temperature or moisture. Ammonia borane (AB) has been proposed and studied as a potential hypergolic hybrid fuel that provides both excellent performance and storability. This study investigates the effect of droplet impact velocity, pellet composition, and storage humidity on ignition delay of AB with white fuming nitric acid as the oxidizer. Most ignition delays measured were under 50 ms with many under 10 ms and some even under 2 ms, which is extremely short for hybrid systems. Higher droplet velocities led to slightly shorter ignition delays, and exposing samples to humidity slightly increased ignition delay. An AB pellet composition of at least 20% epoxy binder was found to minimize ignition delay. The epoxy facilitates ignition by absorbing or adhering the oxidizer and slowing the reaction with the fuel, preventing oxidizer expulsion and holding it close to the fuel. These results emphasize the importance of binder properties in hypergolic hybrids. Pellets varying in composition and storage method were extinguished and reignited with the oxidizer to demonstrate reignition capability.

Hypergolic ionic mixtures with task-specific ions: A new strategy to improve performances of ionic liquids as propellant fuels

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.

High-speed multi-spectral imaging of the hypergolic ignition of ammonia borane

Recently, ammonia borane (a hydrogen-dense solid fuel) has received increased attention as a potential fuel for use in hybrid rocket systems due to its potential for higher performance. Ammonia borane (AB) is also highly hypergolic with white fuming nitric acid (WFNA) while lacking the health hazards associated with more conventional hypergolic fuels (e.g. hydrazine and its derivatives). To date, there remains a lack of information regarding the combustion behavior of ammonia borane. This work makes use of simultaneous visible and infrared multi-spectral imaging to study the combustion behavior of AB during a hypergolic ignition event (with reagent grade nitric acid droplets applied to the AB as the oxidizer). Using optical filters corresponding to previously reported spectral bands, emission from BO, BO2, HBO2, and the B-H stretch mode of AB were selectively imaged. A two-step ignition process consisting of an initial gas evolution step followed by a separate, seemingly premixed flame propagation step was observed. Observation of HBO2 emission during the pre-ignition/gas evolution phase suggests that rapid formation of HBO2 occurs even at the lower temperatures present prior to ignition. This initial formation of HBO2 (and the subsequent heat release associated with it) may be a major driver of AB/nitric acid decomposition. Emission intensity profiles obtained after the AB samples began burning with the ambient air suggests some degree of HBO2 consumption within the flame front, seemingly counter to the current understanding that HBO2 is a stable product species. This may indicate that boron combustion via boranes may proceed to more complete combustion than is typical for more conventional boron fuels. The ignition dynamics and sequence of boron product formation was well-captured by the multi-spectral imaging technique applied to this reaction system for the first time. This technique could be applied for further study of other boron systems.

Experimental Study of Factors Affecting Hypergolic Ignition of Ammonia Borane

Hypergolic hybrid motors are advantageous for rocket propulsion due to their simplicity, reliability, low weight, and safety. Many hypergolic hybrid fuels with promising theoretical performance are not practical due to their sensitivity to temperature or moisture. Ammonia borane (AB) has been proposed and studied as a potential hypergolic hybrid fuel that provides both excellent performance and storability. This study investigates the effect of droplet impact velocity, pellet composition, and storage humidity on ignition delay of AB with white fuming nitric acid as the oxidizer. Most ignition delays measured were under 50 ms with many under 10 ms and some even under 2 ms, which is extremely short for hybrid systems. Higher droplet velocities led to slightly shorter ignition delays, and exposing samples to humidity slightly increased ignition delay. An AB pellet composition of at least 20% epoxy binder was found to minimize ignition delay. The epoxy facilitates ignition by absorbing or adhering the oxidizer and slowing the reaction with the fuel, preventing oxidizer expulsion and holding it close to the fuel. These results emphasize the importance of binder properties in hypergolic hybrids. Pellets varying in composition and storage method were extinguished and reignited with the oxidizer to demonstrate reignition capability.