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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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387 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Intercomparison of the representations of the atmospheric chemistry of pre-industrial methane and ozone in earth system and other global chemistry-transport models

An intercomparison has been set up to study the representation of the atmospheric chemistry of the pre-industrial troposphere in earth system and other global tropospheric chemistry-transport models. The intercomparison employed a constrained box model and utilised tropospheric trace gas composition data for the pre-industrial times at ninety mid-latitude surface locations. Incremental additions of four organic compounds: methane, ethane, acetone and propane, were used to perturb the constrained box model and generate responses in hydroxyl radicals and tropospheric ozone at each location and with each chemical mechanism. Although the responses agreed well across the chemical mechanisms from the selected earth system and other global tropospheric chemistry-transport models, there were differences in the detailed responses between the chemical mechanisms that could be tracked down by sensitivity analysis to differences in the representation of C1–C3 chemistry. Inter-mechanism ranges in NOx compensation points were about 0.17 ± 0.12 when expressed relative to the inter-mechanism average. Monte Carlo uncertainty analysis carried out with a single chemical mechanism put the intra-mechanism range a factor of three higher at 0.50 ± 0.12. Similar differences between inter-mechanism and intra-mechanism ranges were found for hydroxyl radical depletion but were up to a factor of six wider for ozone formation from incremental additions of organic compounds. The cause of the discrepancies between the inter- and intra-mechanism ranges was found to be the large uncertainties that are present in the laboratory determinations of the rate coefficients and product channel branching ratios of some key chemical reactions involving organic peroxy radicals and hydroperoxides. Whilst these large uncertainties are present in the laboratory determinations, there will be irreducible uncertainties in the predictions from the earth system and other chemistry-transport models of methane and tropospheric ozone trends since pre-industrial times and hence their contributions to the radiative forcing of climate change. Further definitive laboratory studies of the reaction rates and product yields of the reactions of the simple organic peroxy radicals and hydroperoxides are required to resolve and reduce current uncertainties in earth system and chemistry-transport model predictions.

atmospheric chemistry↗
NASA NTRS2021

Effect of Urea Links in the Backbone of Polyimide Aerogels

Flexible, conformal polyimide aerogels with low density, good mechanical properties and high surface areas have attracted much attention for many potential applications such as lightweight antenna substrates, insulating materials for launch vehicles, inflatable structures, aircraft or space suits. Development and improvements to fabrication of polyimide aerogel thin films have been reported over the last decade to meet the needs of many of these applications. However, most starting materials are expensive. In this research, we utilized commercially available, low cost monomers including 4,4’-bis(4-aminophenoxy)propane (BAPP) and 3,3’,4,4’-benzophenone tetracarboxylic dianhydride (BTDA), and 4,4-methylene diphenyl di-isocyanate (MDI) in fabricating polyimide (PI) and polyimide-urea (PIU), which were then cross-linked with 1,3,5-tris(4-aminophenoxy)benzene (TAB). It was found that the addition of MDI into the PI chains not only maintained the flexibility of the aerogel films, but also enhanced the film casting, allowing the production on pilot scale. With the capability in producing robust films at affordable cost, application of the PIU aerogel films can be expanded to terrestrial goods such as winter clothing, or pipe wrapping, etc. In addition, the presence of only a small addition of the urea links in the polyimide chains in PIU aerogels led to lower shrinkage when compared to the corresponding PI aerogels, leading to lower density

Baochau N. Nguyen↗
NASA NTRSDate not supplied

P52D-1583 - Further Improvements to Constraints on Titan’s Atmospheric n-Butane, via Ground-Based Observations

We have acquired high spectral resolution ground-based observations of Titan in the mid-infrared from NASA Infrared Telescope Facility’s Texas Echelon Cross Echelle Spectrograph instrument , designed to constrain the abundances of new molecules within Titan’s atmosphere. The target molecule for this work, n-butane (n-C H ), though predicted by photochemical models of Titan’s atmosphere , has never been detected. Using the NEMESIS radiative transfer code , we retrieved a disk-averaged temperature profile for Titan by modeling CH emission in the 1248 cm region. Using this temperature profile, we then retrieved disk-averaged profiles of ethene (C H ), propane (C H ), and propene (C H ) in the 956 and 965 cm regions, which are also home to the strong and vibrational features of n-butane. We used an n-butane pseudoline list from JPL in order to systematically introduce a range of n-butane mixing ratios into the model, to constrain the molecule’s abundance based on the model’s changing fit to the data. We derive 3-confidence upper limits at an altitude of 150 km of 48 and 31 ppb for n-butane, via the and bands in the 956 and 965 cm regions, respectively. These are significantly tighter upper limits when compared to the ~300 ppb upper limit found in our recent work which used the same methodology but on much lower resolution limb data collected by the Cassini spacecraft. Upper limits on gas abundances are important for continued improvement of photochemical models of Titan’s atmosphere, which is understood to be an important analog for the prebiotic Earth atmosphere . They are also important for understanding the composition of Titan’s lakes and seas, which are likely to contain these larger hydrocarbons . Finally, as larger molecules like C ’s are thought to be able to serve as formation sites for building haze particles, constraining their abundances is important for understanding the process of haze formation at Titan and at Earth Ref: [1] J. H. Lacy, et al., PASP, 2002. [2] Y.L. Yung, et al., ApJS, 1984. [3] M. Dobrijevic, et al., Icarus, 2021. [4] P. G. J. Irwin et al., JQSRT, 2008. [5] K. Sung, et al., JQSRT, 2020. [6] B. L. Steffens, et al., PSJ, 2022. [7] Clarke & Ferris, Origins Life Evol. Biosphere, 1997. [8] D. Cordier, et al., ApJ, 2008. [9] D. B. Curtis, et al., JPCA, 2005.

Brendan Steffens↗
NASA NTRSDate not supplied

Centrifugal Nuclear Thermal Rocket Challenges and Potential

The Centrifugal Nuclear Thermal Rocket (CNTR) is a liquid fueled fission propulsion concept designed to heat propellant to 5000 K prior to expansion through a nozzle. A specific impulse up to 1800 s may be achieved using hydrogen propellant, and a specific impulse up to 1000 s may be achieved using more storable propellants such as methane, ammonia, or propane. The high uranium density of the liquid metallic uranium or liquid uranium carbide fuel will help enable compact engines suitable for missions such as fast (<15 month) round trip human Mars missions or high delta-V missions in cislunar space. Long term applications of the CNTR could include the advanced exploration and utilization of the solar system through direct use of in-situ volatiles as propellant. Challenges associated with the CNTR are numerous. Centrifugal force is used to retain the liquid fuel in rotating fuel cylinders, and rotational velocities up to 5000 rpm may be required. Propellant flow must be directed such that all structures and moderators in the core are adequately cooled prior to the propellant entering the liquid fuel and being heated to 5000 K. The rotating fuel cylinder wall (RFCW) must have an inner surface designed to be compatible with liquid uranium metal or uranium carbide fuel up to at least 1500 K, and that inner surface may also need to be textured to help maintain acceptable wall temperatures. Propellant must flow radially inward through the RFCW while fuel is simultaneously contained. The RFCW should ideal-ly be made from a material with low neutron absorption to help minimize engine mass and facilitate the use of High Assay Low Enriched Uranium (HALEU) fuel in the system. The drive system for the rotating fuel cylinders must support all phases of operation. This paper will discuss computational and experimental research being conducted to address some of the challenges associated with the CNTR, and will also note potential mission benefits from the CNTR.

Michael G. Houts↗
NASA NTRSDate not supplied

Preliminary Study of Alternative Propellant Performance for a CNTR

Centrifugal Nuclear Thermal Propulsion is an advanced propulsion concept engine which utilizes a bubble through nuclear reactor to directly heat the propellent, containing the liquid fuel in rotating cylinders using centrifugal force. Past studies have almost exclusively focused on hydrogen propellant configurations of the engine with a theoretical performance of 1800 seconds specific impulse. Recent interest in alternative propellants has created a use case for using storable propellants at the cost of lower performance. Most notably ammonia, methane, and propane. The object of this work is to down select viable alternative propellants for use in a CNTR.

Mitchell Schroll↗
NASA NTRSDate not supplied

Computational Optimization of a Rotary Valved Pulse Combustor Concept

A resonant pulse combustor valve concept is introduced that utilizes two slotted, coaxial counterrotating discs for mechanical actuation at the combustor inlet. The intended test article for prototype demonstration is a small, 22 in. long, propane fueled laboratory combustor, flowing approximately 0.006 lbm/s of air. The objective is to develop an externally actuated (i.e., active) valve that yields better performance and longer life than the traditional internally actuated (i.e., passive), reed-type valve found on most pulse combustors. The rotary valve motion is optimized using an axisymmetric, two-dimensional computational fluid dynamic simulation with a domain that includes the valve as a moveable interior wall. Parameters such as slew rate, dwell period in the open position, and total closed period are varied using fuel specific impulse as the figure of merit. Variations in fuel injector location and air fuel ratio are also examined. Additionally, the performance impact of leakage from the rotary valve is quantified since leakage is endemic to the design. The optimized simulation results indicate that the rotary valve concept can deliver the desired performance attributes using disc rotational speeds and stresses that are well within the realm of modern materials. A preliminary mechanical valve design is included in the report.

pressure gain combustion↗
NASA NTRSDate not supplied

Computational Optimization of a Rotary Valved Pulse Combustor Concept

A resonant pulse combustor valve concept is introduced that utilizes two slotted, coaxial counterrotating discs for mechanical actuation at the combustor inlet. The intended test article for prototype demonstration is a small, 22 in. long, propane fueled laboratory combustor, flowing approximately 0.006 lbm/s of air. The objective is to develop an externally actuated (i.e., active) valve that yields better performance and longer life than the traditional internally actuated (i.e., passive), reed-type valve found on most pulse combustors. The rotary valve motion is optimized using an axisymmetric, two-dimensional computational fluid dynamic simulation with a domain that includes the valve as a moveable interior wall. Parameters such as slew rate, dwell period in the open position, and total closed period are varied using fuel specific impulse as the figure of merit. Variations in fuel injector location and air fuel ratio are also examined. Additionally, the performance impact of leakage from the rotary valve is quantified since leakage is endemic to the design. The optimized simulation results indicate that the rotary valve concept can deliver the desired performance attributes using disc rotational speeds and stresses that are well within the realm of modern materials. A preliminary mechanical valve design is included in the report.

pressure gain combustion↗