Liquid Bipropellants Research Articles

EVALUATION OF SOLID ROCKET PROPELLANTS FOR LOW EARTH ORBIT

In contemporary aerospace technology, solid rocket propellants are commonly employed in the thriller and boost of space cargoes to LEO. These are reliable, uncomplicated, and high in thrust; and thus, can be used in both military as well as civil space ventures. This paper provides a comprehensive evaluation of five prominent solid rocket propellants: Five categories namely Ammonium Perchlorate Composite Propellant (APCP), Double-Base Propellant, Composite Modified Double Base (CMDB) Propellant, Hydroxyl-terminated polybutadiene (HTPB)-Based Propellant, and Ammonium Nitrate Composite Propellant (ANCP) have been identified. This also falls under the evaluation and includes aspects such as historical bases to see how the formulation of the propellant has changed over time regarding the development of propellant technology. In the case of each propellant, the chemical properties of the mix and reactions that its fundamental are analyzed. It also shares details regarding the changes and advancements made in the little while to enhance capability, safety, and environmental compatibility of these fuels, such as synthesizing fuels for liquid bipropellants. Some of the modern applications of technologies within the active spectrum of aerospace operations are explained in more detail to provide clients with the most versatile and essential information. Among the essentials of this work, the complex calculation of thrusts developed by the specific propellant with corresponding graphics has significant importance. These estimations afford chances of comparing the efficiency of the propellant in terms of producing thrusts as well as achieving the indicated optimal performance. Thus, the main objective of this study is to identify which of the solid rocket propellants to use in LEO missions and if any, what modifications could be made to improve them. Thus, the purpose of this paper is to contribute to the development of the constantly evolving branch of rocket propulsion by discussing the benefits and shortcomings of each propellant. These findings and recommendations could be useful in perfecting the recipes for the propellants and improving the efficiency of the subsequent missions to planets. Keywords: Aerospace, Solid rocket propellants, Thrust, Low earth orbit.

Cationic effect on properties related to thermal stability and ignition delay for hypergolic ionic liquids

Hypergolic ionic liquids (HILs) are considered as a promising alternative of toxic hydrazine derivatives in the field of liquid bipropellants. The anionic structure plays an important role in determining the hypergolic performance of HILs. Nevertheless, the structure–activity relationship between the cationic structure and ignition properties is still unclear. In this study, the aromaticity, electrostatic potentials (ESPs), natural bond orbital (NBO) analysis, and molecular orbital gap of 25 ionic liquids based on dicyanamide anion were studied to gain more insight into the correlation between cationic structure and hypergolic properties. For the HILs based on the same type of cation with different substituents, better aromaticity leads to better thermal stability of HILs. For the HILs with different types of cations, when the ESPs distribution is relatively concentrated around a certain value, the thermal stability of HILs is relatively higher. The second-order perturbation energy (E(2)) would be responsible for ignition delay (ID) time. The larger the E(2), the more stable the system, and the longer the ID time of HILs. It is also proved for the first time that the energy gap between the HOMO of cations and LUMO of HNO3 could not be used as a method to determine whether this cation-based IL is hypergolic. All these results can be fully justified with experimental data and have important theoretical instructive significance in the design of new high-performance HILs.

Theoretical Study on Hydrolytic Stability of Borohydride-Rich Hypergolic Ionic Liquids.

Hypergolic ionic liquids (HILs) are a new kind of green rocket fuels, which are used as potential replacements for toxic hydrazine derivatives in liquid bipropellants. These functional HILs can react with oxidizers and release a large amount of heat in a very short time, finally leading to ignition of the propellant system. Among them, most borohydride-rich HILs were very sensitive to water, but a few special examples displayed good hydrophobicity and remained very stable in air even after a month or more. However, the reasons behind their hydrolytic stability are unclear. In this study, several calculation methods including electrostatic potentials (ESPs), molecular orbital energy gaps, and interaction energy were used to explore the water stability of eight typical borohydride-rich HILs. The obtained results demonstrated that negatively charged anions with high absolute ESP values usually reacted more easily with positively charged water. The large molecular orbital energy gap with BPB-, BCNBCN-, CTB-, and BTB- indicates the high degree of difficulty of interactions between anions and water, leading to a better hydrolytic stability of borohydride-rich anions. During the analyses of interaction energy, the relatively water-sensitive borohydride-rich anions (BH4-, BH3CN-, etc.) generally had lower interaction energy with water than stable anions such as BPB- and BCNBCN-. Studies on their stepwise hydrolysis mechanism demonstrate that, in the case of all the reactions, the first step is the rate-determining step and high energy barrier values of anions correspond to good hydrophobicity. This study will help us understand the hydrolysis of borohydride-rich HILs and provide a guide for the development of new HILs with promising properties.

Towards N-Alkylimidazole Borane-based Hypergolic Fuels.

Over the past few decades, toxic and highly volatile hydrazine derivatives have been the main fuel choices for liquid bipropellants, especially in traditional hypergolic rocket engines. The search for new hypergolic fuels as replacements for hydrazine derivatives is of great interest to researchers. In this study, a series of N-alkylimidazole borane compounds has been synthesized and characterized. Interestingly, these compounds display promising applications as potential hypergolic fuels owing to their excellent physiochemical properties including low melting points, high thermal stability, low viscosities, and unique hypergolic reactivity. Compared with popular hypergolic ionic liquids, the cost-effective and scaling-up advantages of these materials highlight their promising potential as high-performance fuels in liquid bipropellant formulations.

Towards Safer Rocket Fuels: Hypergolic Imidazolylidene‐Borane Compounds as Replacements for Hydrazine Derivatives

Currently, toxic and volatile hydrazine derivatives are still the main fuel choices for liquid bipropellants, especially in some traditional rocket propulsion systems. Therefore, the search for safer hypergolic fuels as replacements for hydrazine derivatives has been one of the most challenging tasks. In this study, six imidazolylidene-borane compounds with zwitterionic structure have been synthesized and characterized, and their hypergolic reactivity has been studied. As expected, these compounds exhibited fast spontaneous combustion upon contact with white fuming nitric acid (WFNA). Among them, compound 5 showed excellent integrated properties including wide liquid operating range (-70-160 °C), superior loading density (0.99 g cm(-3) ), ultrafast ignition delay times with WFNA (15 ms), and high specific impulse (303.5 s), suggesting promising application potential as safer hypergolic fuels in liquid bipropellant formulations.

Direct Dynamics Simulation of the Activation and Dissociation of 1,5-Dinitrobiuret (HDNB)

Certain room-temperature ionic liquids exhibit hypergolic activity as liquid bipropellants. Understanding the chemical pathways and reaction mechanisms associated with hypergolic ignition is important for designing new fuels. It has been proposed (J. Phys. Chem. A 2008, 112, 7816) that an important ignition step for the hypergolic ionic liquid bipropellant system of dicyanamide/nitric acid is the activation and dissociation of the 1,5-dinitrobiuret anion DNB(-). For the work reported here, a quasiclassical direct dynamics simulation, at the DFT/M05-2X level of theory, was performed to model H(+) + DNB(-) association and the ensuing unimolecular decomposition of HDNB. This association step is 324 kcal/mol exothermic, and the most probable collision event is for H(+) to directly scatter off of DNB(-), without sufficient energy transfer to DNB(-) for H(+) to associate and form a highly vibrationally excited HDNB molecule. Approximately 1/3 of the trajectories do form HDNB, which decomposes by eight different reaction paths and whose unimolecular dynamics is highly nonstatistical. Some of these paths are the same as those found in a direct dynamics simulation of the high-temperature thermal decomposition of HDNB (J. Phys. Chem. A 2011, 115, 8064), for a similar total energy.

Simulation of Earth-Storable Liquid Bipropellants With Gaseous Reactants

It is shown that to duplicate the combustion products of earth-storable liquid propellants by the combustion of a gaseous fuel and oxidizer combination which is at the same initial temperature, the only two conditions that must be satisfied are: (a) the elemental composition (i.e., atomic species and their proportions) of the liquid and gaseous propellants must be the same; (b) the initial energies (i.e., total enthalpies) of the two propellant combinations must be the same. An illustrative example of the simulation of the liquid propellant combination of N2O4/50 percent N2H4-50 percent UDMH at an O/F = 2 is given.

Influence of injectant properties for fluid injection thrust vector control

A linearized model of fluid-injection thrust vector control is developed. The analysis provides a very simple expression for injectant effective specific impulse and clearly shows effects of injectant and propellant properties on performance. Results compare favorably with a body of gas and liquid injection data available in the open literature. Aerothermochemical aspects are examined by predicting performance of selected injectants in combination with a hypothetical rocket propellant and nozzle. These injectants fall into six classes: inert gases, inert liquids, reactive gases, dissociative liquids, reactive liquids, and liquid bipropellants. Results are discussed in detail.

Combustion of liquid monopropellants and bipropellants in droplets

Combustion of liquid monopropellants and bipropellants in droplets

Surface properties of liquid bipropellants and their effects on the kinetics of ignition

Surface properties of liquid bipropellants and their effects on the kinetics of ignition