Browse Topic: Hydrazines
The race is on for leadership in cislunar space, considered a gateway to the future of space exploration. Yet operating in this domain introduces unique challenges for propulsion systems. In contrast to low-Earth orbit (LEO), the cislunar environment requires higher precision propulsion solutions; these are necessary to enable rapid and accurate maneuvering of spacecraft and long-term sustainability. Propellants like hydrazine and nitrogen tetroxide offer the high energy density required for cislunar missions, but they must be handled very differently from the inert, non-reactive gases at play in LEO systems.
Future legislations such as EPA27 [1] and EURO VII [2] are further reducing NOx emission limits. At the same time, the focus of emission compliance over a broad range of operation conditions is becoming more stringent; with a specific focus onto the cold start. The reduction of NOx is reached over a Selective Catalytic Reduction (SCR) system, with NH3 as a reductant. NH3 is derived over the processing of Urea Water Solution (UWS) to NH3. The conversion of UWS to NH3 is a highly complex process, with the danger of deposit formation, which is especially challenging in Compact Urea Processing Units (CUPU). One of the key factors for the successful development of Compact Urea Processing Units is the precise application of simulation and testing methods. Therefore, existing testing methods e.g. for the determination of the urea processing capability or the deposit formation were optimized, new testing methods are being introduced and the parameters evaluated are being broadened. For the simulation it is mandatory to use validated models to ensure a good correlation between simulation and testing. For this reason, the simulation tools, e.g. for the determination of the NH3 distribution, were evaluated and adjusted to deliver reliable results. The results gained in testing and simulations are not only evaluated individually, but in combination amongst each other. This leads to a full picture and an in-depth understanding of the UWS processing in a CUPU. Moreover, it leads to a fuller understanding of the impacting parameters of NH3 distribution, NH3 yield and deposit formation, which can afterwards be used for an optimal application of the unit within the required boundary conditions in customer projects.
A highly miniaturized, MR-143, green monopropellant thruster was developed for 1N thrust. Testing indicated the initial catalyst bed heater was insufficient. In subsequent development, the thruster was equipped with a more efficient catalyst bed heater. For reliable ignition of the advanced, non-toxic, AF-M315E monopropellant, the catalyst needs to be preheated. This preheat temperature is much higher than what hydrazine thrusters require. Moreover, the combustion temperature of hydroxyl ammonium nitrate (HAN)-based monopropellants is higher than hydrazine, so the catalyst bed heater must be able to withstand repeated soak-back temperatures.
Thin film gas sensors are small, lightweight, and relatively easy to operate; however, the testing of these thin film gas sensors is difficult in harsh environments due to the exposure of critical components to the harsh environment. A need exists for the ability to test thin film gas sensor materials for their response to analytes of interest in a variety of environments, including harsh environments. Currently, a sample holder does not exist that will allow the testing of thin film gas sensor materials in harsh environments. Many of the thin film gas sensors require electrical and mechanical connections in order to operate. Harsh environments tend to degrade many of these connections, compromising sensor performance and shortening sensor lifetime. A sensor holder that provides exposure of the thin film sensor material to the harsh environment, while protecting the electrical and mechanical connections, is needed. The advantages of such a sample holder are that the sensors can be used in a wider range of environments (temperature, humidity, etc.), and a wider range of analytes can be evaluated (hydrazine, ammonia, hydrogen, etc.).
A new chemistry was developed for existing hydrazine absorbent/detoxification pads. Enhancements include faster reaction rates, weight reduction, a color change that indicates spill occurrence, and another color change that indicates successful hydrazine degradation. The previous spill control pad, using copper oxide on the silica gel substrate as the reactant, affected only 50 percent degradation of hydrazine after 9 hours. The new prototypes have been found to degrade hydrazine from 95 to 99.9 percent in only 5 minutes, and to below detection limits within 90 minutes.
A concept was evaluated of using nitrous oxide as (1) a monopropellant in thrusters for space suits and spacecraft and (2) a source of breathable gas inside space suits and spacecraft, both by exploiting the controlled decomposition of N2O into N2 and O2. Relative to one prior monopropellant hydrazine, N2O is much less toxic, yet offers comparable performance. N2O can be stored safely as a liquid at room temperature and unlike another prior monopropellant hydrogen peroxide does not decompose spontaneously. A prototype N2O-based thruster has been demonstrated. It has also been proposed to harness N2O-based thrusters for generating electric power and to use the N2 + O2 decomposition product as a breathable gas. Because of the high performance, safety, and ease of handling of N2O, it can be expected to be economically attractive to equip future spacecraft and space suits with N2O-based thrusters and breathable-gas systems.
Alternative-fuelled vehicles are a growing market, and emission performance of these vehicles should be thoroughly investigated. The emission legislation is however very diversified in different countries; a short summary of the legislation in the EU, the USA and Brazil is presented in this study. In the EU regulations, everything measured with the FID (Flame Ionization Detector) is treated as hydrocarbon emissions. In the USA the alcohols and aldehydes are measured and reported separately from hydrocarbons. In Brazil, the alcohol part can be measured separately on voluntary basis. The influence of some of these differences has been further investigated in this report. Results from two related studies are presented. The FID response for ethanol was investigated and emission testing of an E85-fuelled FFV (Flex Fuel Vehicle) was performed. The FID sensitivity at two different detector temperatures - 113°C (as stated by the US EPA when testing alcohol-fuelled vehicles) and 190°C (often used as default setting in the EU) - were investigated showing a higher FID response at 113°C. The response curve shows a slow response due to adsorption of ethanol in the measurement system. One FFV fuelled with E85 was tested on chassis dynamometer at two ambient temperatures: +22°C and -7°C. The ethanol emissions were analyzed with FTIR and sampled in impingers (standardized method approved in the USA). The acetaldehyde emissions were analyzed with FTIR and sampled in DNPH(2,4-dinitrophenyl hydrazine)-cartridges (standardized method approved in the USA). The FTIR provides second-by-second data which showed that high levels of unburned ethanol were emitted during the cold start phase. Comparison between the FTIR results and methods standardized in the USA were performed. The percentage distribution of some of the components included in the total hydrocarbons measured by the FID was investigated, and comparison between tests performed at the two different ambient temperatures can be made. The proportion of unburned ethanol increased at cold climate testing - from 24% at +22°C up to 53% at -7°C.
Three proposed methods for measuring trace quantities of hydrazines involve ionization and detection of hydrazine derivatives. These methods are intended to overcome the limitations of prior hydrazine-detection methods.
An electrochemical method of disposal of hydrazines dissolved in water has been devised. The method is applicable to hydrazine (N2H4), to monomethyl hydrazine [also denoted by MMH or by its chemical formula, (CH3)HNNH2], and to unsymmetrical dimethyl hydrazine [also denoted UDMH or by its chemical formula, (CH3)2NNH2]. The method involves a room-temperature process that converts the hydrazine to the harmless products N2, H2O, and, in some cases, CO2. In comparison with prior methods of disposing of hydrazines, the present method is safer and less expensive.
Substrates coated with a precious metal salt KAuCl4 have been found to be useful for detecting hydrazine vapors in air at and above a concentration of the order of 0.01 parts per million (ppm). Upon exposure to air containing a sufficient amount of hydrazine for a sufficient time, the coating material undergoes a visible change in color. Although the color change is only a qualitative indication, it can serve as an alarm of a hazardous concentration of hydrazine or as advice of the need for a quantitative measurement of concentration. Detection of hydrazine vapors by this technique costs much less and takes less time than does laboratory analysis of sorbent tubes using high-performance liquid chromatography, which is the technique used heretofore to detect hydrazines at concentrations down to 0.01 ppm.
A brief report summarizes an investigation of less-toxic alternatives to toxic monopropellant fluids used in launch vehicles, upper stages, and spacecraft propulsion. The toxic fluids in question are (1) hydrazine and its derivatives, used, variously, as fuels or by themselves as catalytically decomposable monopropellants; and (2) nitrogen dioxide, used as an oxidizer for such fuels.
A report proposes a system that would supply gas for inflating one or more inflatable structure(s) in outer space. The system would include a small tank of helium for initial inflation, plus a catalytic hydrazine gas generator that would supply makeup gas over the long term. After initial inflation, when makeup gas was needed, liquid hydrazine from a tank would be made to pass through a catalytic bed, where it would become decomposed into a mixture of N2, H2, and a small amount of NH3. This gaseous mixture would constitute the makeup gas and would be stored in the tank that previously contained the helium. The makeup gas would be released from the tank to the structure(s) as needed. In comparison with an inflation system based only on compressed gas stored in tanks, the proposed inflation system would offer the advantage of lower mass: About 25 percent of the masses of representative previously contemplated large inflatable outer-space structures would have been contained in their inflation systems. In contrast, the mass of the proposed inflation system has been estimated to be only about 13 percent of the total mass of a representative structure.
A report proposes a liquid/vapor-hydrazine thruster for use in controlling the attitude of a small spacecraft. From the upstream to the downstream end, the thruster would include a tank containing liquid hydrazine, a fast liquid valve, a heated prevaporizing plenum, a fast gas valve, and a heated catalytic bed. In one mode of operation (the conventional mode), heat would not be supplied to the prevaporizing plenum; instead, liquid hydrazine would be fed directly to the heated catalytic bed. In another mode of operation, heat would be supplied to the prevaporizing plenum, and the gas valve would be opened in brief pulses to pass the hydrazine vapor to the heated catalytic bed to produce small pulses of thrust. The use of vapor (as compared with liquid) feed in the pulse mode would make it possible to generate smaller impulses, which are better suited for highly precise spacecraft maneuvers.
A report proposes a small spacecraft attitude-control thruster in which the propellant material would be hydrazine that would be stored frozen until sublimed at the instant of use. From the upstream to the downstream end, the main components of the thruster would include a plug of solid hydrazine in a container, a rapid source of radiant heat (e.g., a laser diode or a flash lamp), and a heated-catalyst-and-nozzle assembly like that of a conventional hydrazine thruster. In operation, each pulse of radiant heat would cause a small amount of frozen hydrazine to sublime. The puff of hydrazine vapor thus generated would become chemically decomposed in the heated catalyst, and an impulse would be generated by the expansion of the puff of decomposition products in the nozzle. This thruster would be attractive for generating small impulses (impulse "bits") on command for precise maneuvering of a spacecraft that either remains below the freezing temperature of hydrazine (≈274 K) or that contains equipment to keep the hydrazine refrigerated.
A combination of procedure and equipment for loading liquid hydrazine into a spacecraft fuel tank that contains a diaphragm or bladder would be modified, according to a proposal. The purpose of the modifications is to enable fueling technicians to work safely, during all but a small part of the loading process, in less-restrictive protective attire.
In a proposed method for rapidly detecting hydrazine in air at concentrations at or above 10 parts per billion by volume (ppbv), tunable diode lasers (TDLs) and photodetectors would be used to measure infrared absorption spectra of both ammonia and hydrazine simultaneously. In this method, one would take advantage of the fact that (1) ammonia is formed in the decomposition of hydrazine and is always present when hydrazine is present and (2) the spectral features attributable to ammonia are much stronger than those attributable to hydrazine, and thus ammonia can be detected more easily. In a typical situation in which hydrazine is suspected of leaking and in which one could rule out an alternative source of ammonia (e.g., an open bottle of household ammonia solution or window cleaner), an ammonia spectrum could thus be taken as an indication of hydrazine.
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