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A mixture of 1-ethyl-3-methylimidazolium ethyl sulfate ([Emim][EtSO4]) and hydroxylammonium nitrate (HAN) is an energetic monopropellant potentially suitable in a multimode chemical-electric microt...

Gas-hybrid rockets get thrust by combusting the mixture gas of a fuel-rich hot gas and an atomized liquid oxidizer. Many kinds of liquid oxidizers are used for the gas-hybrid rockets. These are very difficult to handle because they have toxins or is not liquid at ordinary temperatures and pressures. In this study, we focused on hydroxylammonium nitrate (HAN) liquid as the liquid oxidizer for the gas-hybrid rockets. HAN liquid is easy to handle because it has very few toxins and is a stable substance at ordinary temperatures and pressures. It is important to observe single droplet because atomized HAN liquid oxidizer consist of many droplets. And it is considered that HAN concentration affect ignition characteristics of the HAN droplets. Therefore, we investigated relationships between HAN concentration and ignition characteristics of the HAN droplets by obtaining the decomposition delay time of the HAN droplets (τde).

The combustion characteristics of hydroxylammonium nitrate aqueous solution were studied. It was found that the role of the two-phase region is very important and the boiling of water by superheat is responsible for the high burning rate. The evaluated bubble nucleation rate coincides with burning rate at very high region. Further, the combustion mechanism of propellant solution is discussed. The hydrodynamic instability was taken into the discussion, and the estimation of hydrodynamic instability supports the observed phenomena. These discussions of hydrodynamic instability and bubble nucleation solution are summarized, and the combustion mechanism of the propellant solution is described in detail.

The study and development of new monopropellants as hydrazine substitutes for propulsion applications are currently investigated to reduce handling and storage costs and to increase engine performance. The most cited meri t of these new propellants is their reduced toxicity and low vapour pressure and keywords as “non-toxic propellants” or “green propellants” are extensively used in literat ure and proceedings. Aqueous energetic ionic liquids comprising an ionic oxidizer, an ioni c or molecular fuel and water as solvent, are currently proposed and investigated as new monopropellants and possible hydrazine substitutes. The main advantages of these new propellant formulations versus hydrazine are: (i) lower melting points, (ii) higher densities, (i ii) higher volumetric impulses for equivalent specific impulses and (iv) generally accessible on a semi-industrial scale. But different challenges have to be overcome before the practical development and production of new thrusters using these propellants. In the present p aper, A batch reactor has been used to study the thermal and catalytic decompositions of binary aqueous hydroxylammonium nitrate (HAN: [NH 3OH] + [NO 3] ) and ternary aqueous HAN-H2O2 mixtures. The activity of different catalysts has been evaluated by determini ng the reaction products.

The combustion characteristics and reaction mechanism of a HAN-based liquid propellant (HANGLY26, consisting of 60% HAN, 14% glycine and 26% water by weight) were investigated. Combustion tests of liquid strands formed in test tubes were performed in an optically accessible strand burner. Thermocouples were also installed in the strand to measure the temperature distribution of the reaction zone. The burning rate of HANGLY26 exhibited four burning rate regimes for pressures ranging from 1.5 to 14.5 MPa. No luminous flame was observed in any combustion tests. The product temperatures were found to be at the water boiling points at the test pressures below 8.8 MPa. For pressures above 8.8 MPa, the product temperatures were found to be lower than the boiling points of water. Slope break points for burning rate were found to coincide with those of concentration curve versus pressure. The reaction mechanism changes between adjacent burning rate regimes dictate the slope break phenomenon observed in burning rates. Major species found from the recovered liquid residues are nitrogen, nitric oxide, carbon dioxide, and formaldehyde. Two threshold temperatures of 473 and 673 K were found in the pyrolysis study of the liquid propellant. The decomposition mechanism of glycine was also studied. INTRODUCTION Hydroxylammonium nitrate (HAN)-based liquid monopropellants have been considered as potential candidates for the next-generation space propulsion applications because of their high density, low toxicity, and low freezing point''. In these propellants, HAN acts as the oxidizing component and fuel-rich components are added to achieve higher energy release H-N-O-H* NO Figure 1. Chemical structure of HAN. and higher flame temperature. Water is added to adjust the properties, such as viscosity and flame temperature. The chemical structure of HAN is shown in Figure 1. HAN itself can be considered as a monopropellant. The combustion characteristics and the reaction mechanism of HAN have been extensively studies by various researchers. Vosen studied the apparent burning rate of aqueous HAN solution with different concentrations. He found that the apparent burning rate first decreased with increasing pressure, then remained constant once the pressure exceed a threshold value. Reaction kinetics of HAN and HAN-based liquid propellants (LP) have been studied by various researchers. Lee and Thynell and Thynell and Kim studied the thermal decomposition of solid HAN and HAN-water solutions and found that HAN decomposition consists of several stages: 1) proton transfer and subsequent reactions occurring while water evaporates as the sample heats up. As the critical concentration of HAN is reached, the reaction rate is greatly accelerated, forming a pool of highly reactive HONO and HNO species; 2) evolution of gaseous Hs H H \ / ,O +H H H

This paper presents the initial research, development and testing of a novel rocket monopropellant which has potentially higher performance, significantly less toxic and environmentally benign compared with hydrazine, which is the current state-of-the-art. The new monopropellant is based on the oxidizer Ammonium Dinitramide (ADN). Swedish Space Corporation (SSC) has since 1995 been working on new chemical propulsion systems for small spacecraft. In 1997, SSC in cooperation with the Swedish Defence Research Establishment (FOA) and Chalmers University of Technology began research and development of ADN-based liquid monopropellants for small rocket engines. The objectives of the work presented here, have been research of the basic principals, design and experimental tests of critical functions and characteristic. The outcome of this work was formulation of a new ADNbased monopropellant candidate, LMP-101, consisting of 61% ADN, 26 % water and 13% glycerol. LMP-101 has a theoretical vacuum specific impulse of 2420 Ns/kg (exp. ratio 50) and an adiabatic combustion temperature of 1970 K. LMP-101 has been tested in different experimental rocket engines and operated both pulsed in steady state. "Proof of concept" has been demonstrated, i.e. the propellant ignites rapidly and is capable of a sustained, complete combustion with clean exhaust gases (i.e. approximately 50% water, 30% nitrogen and 20% carbon dioxide). Restarts have been performed without observed degradation in ignition characteristics. A two-year development phase of a flight-like rocket engine is planned to start during 2000. The work was supported by the Swedish National Space Board and the European Space Agency (ESA). INTRODUCTION Hydrazine and hydrogen peroxide have been recognized as rocket propellants for more than 50 years. During the 1950's and 1960's the use of hydrogen peroxide decreased due to its inferior storage stability and hazards in production and handling. Simultaneously, the hydrazine propulsion system technology developed. With the development of a reliable and long lived catalyst, hydrazine-based monopropellant propulsion system became commonly used for space propulsion applications. Hydrazine emerged as the standard liquid monopropellant. Since then, hydrazine-based systems have performed a vast number of space flights demonstrating the capability of millions of pulses and mission duration of more than 20 years. Moreover, there are today a wide range of qualified commercial off the shelf components suitable for hydrazine based propulsion systems. Personnel safety and recent increased environmental awareness are, and will continue to be, important issues in the context of propulsion system handling and operation. There is also an increased awareness on how safety and handling contributes to the vehicles overall costs. This is of particular importance for small spacecraft handled and operated by organizations not having the infrastructure to handle a propellant such as hydrazine. In the past decades, the payload cost has decreased while the cost of fuelling a spacecraft has increased along with the repeated lowering of the limit value of hydrazine exposure. Over the past few years, hydroxylammonium nitrate (HAN)based monopropellants have emerged as "Green Propellant" candidates for space propulsion '''. Although other candidates such as hydrogenperoxide also could be envisaged as a "Green Propellant" candidate, SSC decided at an early stage to focus on ADN-based monopropellants as the "Green Propellant" candidate for the work described in this paper. For the successful development of a new propellant, it must lead to a more cost effective overall propulsion system. * Head of Dept. Propulsion R&D t Research Engineer, Dept. Propulsion R&D I Research Engineer, FOA Defense Research Establishment Copyright 2)2, is a solid oxidizer salt, mainly intended for high performance solid rocket propellants. It is synthesized from mixed acid (nitric and sulfuric acid), ammonia and salts based on sulfamicacid. All components are standard industrial chemicals. No solvents, except water, are needed to produce ADN. All waste chemicals are recycled. ADN is highly hygroscopic which makes it possible to formulate a liquid monopropellant by dissolving ADN in water and adding a suitable fuel. The amount of ADN that can be dissolved in a solvent depends on the temperature at which the blend is saturated. E.g. at room temperature measurements have shown that it is possible to dissolve 80% ADN in water, while at 0 °C, 70% ADN can be dissolved. Hence, low temperature requirements on the propellant will decrease the specific impulse and the density of the propellant. Figure 4 shows a Differential Scanning Calorimeter (DSC) curve of ADN. The DSC used was a Mettler DSC 30 with a ceramic sensor. The curve shows the endotherm melting peak at 91 °C, followed by an exothermal decomposition at 154 °C. Table 1 gives of the basic properties of ADN. Melting point Heat of formation Density Molecular weight Enthalpy of melting Oxygen balance 91 °C -148kJ/mol 1.81 g/cm 1 24.056 g/mol 140 J/g +25.79 % Table 1: Basic properties of ADN

This investigation was focused on the combustion behavior of XM46. The regression rate of XM46 has been characterized up to 207 MPa, displaying a complex burning behavior with both negative pressure exponent and plateaulike behavior. The e ame structure displayed three different stages: 1 ) nearly simultaneous decomposition of both hydroxylammonium nitrate (HAN) and triethanol ammonium nitrate initiating in the liquid to produce gases around 300 ±C, 2) breakdown of heavy opaque intermediate molecules into transparent species, and 3 ) reaction of transparent species to form e nal products in the luminous e ame. The feeding tests showed peculiar e ashback phenomena, believed to be related to the interaction between gas-phase radicals and unburned liquid propellant. Pyrolysis tests of XM46 were conducted in a specially designed pyrolyzer used in conjunction with a gas chromatograph/mass spectrometer. The major pyrolysis products observed were NO, N 2O, N2, CO2, CO, H2O, HCN, and C2H4 when pyrolyzed at temperatures between 130 and 540 ± C. The pressure dependency of the burning rate of the HAN-based liquid propellant is highly nonlinear. Water evaporation has a noticeable effect on combustion characteristics of XM46. Gas dissolution/desorption could also affect the burning rate. The type of fuel ingredient was found to have a signie cant effect on the overall burning characteristics.

The impact of the performance and density of on-board propellants on science payload mass of Discovery Program class missions is evaluated. A propulsion system dry mass model, anchored on flight-weight system data from the Near Earth Asteroid Rendezvous mission is used. This model is used to evaluate the performance of liquid oxygen, hydrogen peroxide, hydroxylammonium nitrate, and oxygen difluoride oxidizers with hydrocarbon and metal hydride fuels. Results for the propellants evaluated indicate that the state-of-art, Earth Storable propellants with high performance rhenium engine technology in both the axial and attitude control systems has performance capabilities that can only be exceeded by liquid oxygen/hydrazine, liquid oxygen/diborane and oxygen difluoride/diborane propellant combinations. Potentially lower ground operations costs is the incentive for working with nontoxic propellant combinations.

Measurements have been made to investigate the isothermal decomposition characteristics of hydroxylammonium nitrate (HAN) in the condensed phase over the temperature range from 120 to 180 C. Experiments were conducted at atmospheric pressure in a nitrogen environment using confined rapid thermolysis (CRT)TFTIR spectroscopy. Results show that the major IR-active decomposition species of HAN-water mixtures are H2O, N2O, NO, NO2, and HNO3. For solid HAN, N2O is the dominant species formed, and HNO3 concentration is somewhat higher than that in solution state at the same temperature. It is conjectured that the evolution of species from the HAN-water mixture can be split into three general separate regions: 1) proton transfer is initiated and subsequent reactions form a pool of the highly reactive species HONO and HNO, 2) these species are involved in many subsequent reactions causing the evolution of gas-phase species and depletion of HAN, and 3) reactions in the condensed phase occur among products from HAN decomposition. Foils exposed to rapid thermolysis of HAN experienced essentially no pitting or fracturing over the range of temperatures studied.

HAN is one of the high energy materials and chemical formula is NH 3 (OH)NO a , hydroxylammonium nitrate. HAN is easily soluble in the water and it is the stable material and the combustion performances of HAN propellents are relatively high. So it has been used the oxidizer of liquid gun propellants. HAN has been studied as the liquid gun propellants""61, however not studied as an oxidizer of solid propellants. In this study theoretical combustion performances and decomposition characteristics of HAN propellants were obtained. In theoretical study HTPB(hydroxyl terminated polybutadiene) was used and the concentration of it was 14 percents and the concentration of HAN and aluminum (Al) were 86 percents. The calculating conditions were that the pressure in the chamber was 5 MPa and the nozzle expansion ratio was the optimum at sea level. The specific impulse (Isp) of HAN/HTPB/A1 propellant reached

The growing cost of space missions, the need for increased mission performance, and concerns associated with environmental issues are changing rocket design and propellant selection criteria. Whereas a propellant's performance was once defined solely in terms of specific impulse and density, now environmental safety, operability, and cost are considered key drivers. Present emphasis on these considerations has heightened government and commercial launch sector interest in Hydroxylammonium Nitrate (HAN)-based liquid propellants as options to provide simple, safe, reliable, low cost, and high performance monopropellant systems.