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NASA NTRS2017

Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule

Propylene oxide was recently identified in the interstellar medium, but few laboratory results are available for this molecule to guide current and future investigations. To address this situation, here we report infrared spectra, absorption coefficients, and band strengths of solid propylene oxide along with the first measurement of its refractive index and a calculation of its density, all for the amorphous solid form of the compound. We present the first experimental results showing a low-temperature formation pathway for propylene oxide near 10 K in interstellar ice analogs. Connections are drawn between our new results and the interstellar molecules propanal and acetone, and predictions are made about several as yet unobserved vinyl alcohols and methylketene. Comparisons are given to earlier laboratory work and a few applications to interstellar and solar system astrochemistry are described.

molecular processes↗

NASA NTRS2016

Potential Precursor Compounds for Chlorohydrocarbons Detected in Gale Crater, Mars, by the SAM Instrument Suite on the Curiosity Rover

The detection of chlorinated organic compounds in near-surface sedimentary rocks by the Sample Analysis at Mars (SAM) instrument suite aboard the Mars Science Laboratory Curiosity rover represents an important step toward characterizing habitable environments on Mars. However, this discovery also raises questions about the identity and source of their precursor compounds and the processes by which they become chlorinated. Here we present the results of analog experiments, conducted under conditions similar to SAM gas chromatography-mass spectrometry analyses, in which we pyrolyzed potential precursor compounds in the presence of various Cl salts and Fe oxides that have been identified in Martian sediments. While chloromethanes could not be unambiguously identified, 1,2-dichloropropane (1,2-DCP), which is one of the chlorinated compounds identified in SAM data, is formed from the chlorination of aliphatic precursors. Additionally, propanol produced more 1,2-DCP than nonfunctionalized aliphatics such as propane or hexanes. Chlorinated benzenes ranging from chlorobenzene to hexachlorobenzene were identified in experiments with benzene carboxylic acids but not with benzene or toluene. Lastly, the distribution of chlorinated benzenes depended on both the substrate species and the nature and concentration of the Cl salt. Ca and Mg perchlorate, both of which release O2 in addition to Cl2 and HCl upon pyrolysis, formed less chlorobenzene relative to the sum of all chlorinated benzenes than in experiments with ferric chloride. FeCl3, a Lewis acid, catalyzes chlorination but does not aid combustion. Accordingly, both the precursor chemistry and sample mineralogy exert important controls on the distribution of chlorinated organics.

Miller, Kristen E.↗

NASA NTRS2013

Detection of Propene in Titan's Stratosphere

The Voyager 1 flyby of Titan in 1980 gave a first glimpse of the chemical complexity of Titan's atmosphere, detecting many new molecules with the infrared interferometer spectrometer (IRIS). These included propane (C3H8) and propyne (CH3C2H), while the intermediate-sized C3Hx hydrocarbon (C3H6) was curiously absent. Using spectra from the Composite Infrared Spectrometer on Cassini, we show the first positive detection of propene (C3H6) in Titan's stratosphere (5(sigma) significance), finally filling the three-decade gap in the chemical sequence. We retrieve a vertical abundance profile from 100-250 km, that varies slowly with altitude from 2.0 +/- 0.8 ppbv at 125 km, to4.6 +/- 1.5 ppbv at 200 km. The abundance of C3H6 is less than both C3H8 and CH3C2H, and we remark on an emerging paradigm in Titans hydrocarbon abundances whereby alkanes greater than alkynes greater than alkenes within the C2Hx and C3Hx chemical families in the lower stratosphere. More generally, there appears to be much greater ubiquity and relative abundance of triple-bonded species than double-bonded, likely due to the greater resistance of triple bondsto photolysis and chemical attack.

Titan↗

NASA NTRS2017

Mapping Vinyl Cyanide and Other Nitriles in Titan's Atmosphere Using ALMA

Vinyl cyanide (C2H3CN) is theorized to form in Titan's atmosphere via high-altitude photochemistry and is of interest regarding the astrobiology of cold planetary surfaces due to its predicted ability to form cell membrane-like structures (azotosomes) in liquid methane. In this work, we follow up on the initial spectroscopic detection of C2H3CN on Titan by Palmer et al. with the detection of three new C2H3CN rotational emission lines at submillimeter frequencies. These new, high-resolution detections have allowed for the first spatial distribution mapping of C2H3CN on Titan. We present simultaneous observations of C2H5CN, HC3N, and CH3CN emission, and obtain the first (tentative) detection of C3H8 (propane) at radio wavelengths. We present disk-averaged vertical abundance profiles, two-dimensional spatial maps, and latitudinal flux profiles for the observed nitriles. Similarly to HC3N and C2H5CN, which are theorized to be short-lived in Titan's atmosphere, C2H3CN is most abundant over the southern (winter) pole, whereas the longer-lived CH3CN is more concentrated in the north. This abundance pattern is consistent with the combined effects of high-altitude photochemical production, poleward advection, and the subsequent reversal of Titan's atmospheric circulation system following the recent transition from northern to southern winter. We confirm that C2H3CN and C2H5CN are most abundant at altitudes above 200 km. Using a 300 km step model, the average abundance of C2H3CN is found to be 3.03 +/- 0.29ppb, with a C2H5CN/C2H3CN abundance ratio of 2.43 +/- 0.26. Our HC3N and CH3CN spectra can be accurately modeled using abundance gradients above the tropopause, with fractional scale-heights of 2.05 +/- 0.16 and 1.63 +/- 0.02, respectively.

Lai, J. C.-Y.↗

NASA NTRS2015

The Quick Fire Emissions Dataset (QFED): Documentation of Versions 2.1, 2.2 and 2.4: Technical Report Series on Global Modeling and Data Assimilation - Volume 38

Biomass burning is an important source of particulates and trace gases and a major element of the terrestrial carbon cycle. Well constrained emissions from vegetation fires are needed to model direct and indirect effects of biomass burning aerosols, to model homogeneous and heterogeneous chemistry in the atmosphere, and to perform credible Earth system analysis, and climate and air pollution studies. To improve the performance of NASA Goddard Earth Observing System Model (GEOS) in the areas of atmospheric constituent modeling with a focus on biomass burning we developed the Quick Fire Emissions Dataset (QFED). The QFED emissions are based on the fire radiative power (top-down) approach and draw on the cloud correction method developed in the Global Fire Assimilation System (GFAS). Location and fire radiative power of fires are obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 fire products (MOD14 and MYD14) and the MODIS Geolocation products (MOD03 and MYD03). QFED strengths are high spatial and temporal resolutions and near-real time availability. Daily mean emissions are available at 0.3125 times 0.25 degrees and in recent versions also at 0.1 times 0.1 degrees. QFED provides emissions of black carbon, organic carbon, sulfur dioxide, carbon monoxide, carbon dioxide, PM2.5, ammonia, nitrogen oxides, methyl ethyl ketone, propylene, ethane, propane, n- and i-butane, acetaldehyde, formaldehyde, acetone and methane. Two QFED product systems are maintained by the NASA Global Modeling and Assimilation Office (GMAO): one that produces near real-time daily emissions used operationally in the GEOS-5 Data Assimilation System, and one that produces an extended historical dataset with daily emissions from March 2000 to the present. The historical dataset also provides monthly mean and monthly climatological emissions.

Koster, Randal D.↗

NASA NTRS2019

A Simple Transient Thermal Test Assembly for Insulation Materials

A simple transient thermal test was developed for evaluating the thermal performance of high-temperature flexible insulation materials in atmospheric pressure air. The test setup was inspired by the test assembly used for evaluating the performance of fire shelters and fire protective clothing. The heating source used was a burner supplied with propane gas that can generate relatively uniform heating over a wide area. The ratio of the in-plane width to thickness of the insulation test sample in the test assembly was selected to be greater than ten so that the heat transfer in the center of the test assembly was nearly one-dimensional. A rigid, thin Inconel plate was used as the septum plate directly exposed to the flame to provide a relatively uniform, known-temperature boundary condition for the test assembly, and to prevent convective heat transfer through the test insulation from the burner. The test sample, flexible alumina paper insulation, was placed between the Inconel plate and a thin titanium witness plate. The overall assembly was further insulated using a combination of rigid and flexible ceramic insulations to minimize heat losses from the periphery of the test assembly. Thermocouples installed on the septum and witness plates and inside the insulation test sample provided temperature measurements at various locations. For the evaluation tests, the Inconel septum plate reached temperatures between 780°C and 850°C for tests with flame exposure durations of 120 sec to 300 sec. The measured temperatures for various tests with similar flame exposure times were repeatable. A one-dimensional numerical heat transfer model of the test assembly was developed. The close agreement between measured and predicted temperatures on the titanium witness plate and inside the insulation test sample indicated that this test may provide a one-dimensional thermal testing capability for evaluation of thermal performance of similar insulations.

Daryabeigi, Kamran↗

NASA NTRS2019

Laboratory-Based Thermal Shock Investigation of Heat Flux Sensors for the Mars 2020 Backshell

In 2012 during the entry, descent, and landing of the Mars Science Laboratory (MSL), the MSL Entry, Descent, and Landing Instrumentation (MEDLI) sensor suite was collecting in-flight heatshield pressure and temperature data. The data collected by the MEDLI instruments has since been used for reconstruction of vehicle aerodynamics, atmospheric conditions, aerothermal heating, and Thermal Protection System (TPS) performance as well as material response model validation and refinement. The Mars Entry, Descent, and Landing Instrumentation 2 (MEDLI2) sensor suite for the Mars 2020 heatshield and backshell is being designed to expand on the measurements and knowledge gained from MEDLI. Similar to MEDLI, MEDLI2 will measure the pressure and temperature of the heatshield. MEDLI2 will additionally measure the temperature, pressure, total heat flux, and radiative heat flux on the backshell.Since the backshell instrumentation is new to MEDLI2, Do No Harm (DNH) testing was conducted on instrumented backshell TPS (SLA-561V) panels. The panels consisted of four pressure port holes, one Mars Entry Atmospheric Data System (MEADS) pressure port plug, one MEDLI2 Integrated Sensor Plug (MISP) thermal plug, and one heat flux sensor. DNH testing was conducted to ensure the performance of the TPS was not degraded due to sensor integration and to characterize any TPS performance changes. The testing consisted of environmental testingâ€” vibration, shock, thermal vacuum (TVAC) cyclingâ€” and bounding aerothermal (arc jet) testing. During arc jet testing, the heat flux sensors embedded in the SLA-561V panels exhibited an unexpected temporary reduction in the heat flux sensor temperature and response. After review of the test results, it was determined that this unexpected response was confined to the two heat flux sensors that experienced the greatest thermal shock condition. This condition consisted of a liquid nitrogen (LN2) bath that induced temperatures of approximately -190Â°C, and then a transition (thermal shock) to an arc jet test at a heat rate of approximately 21 W/cm2. Both heat flux sensors that were exposed to this thermal shock experienced a blister in the thermal coating during the arc jet test.Two heat flux sensor thermal shock test series were performed to investigate the cause of the blistering and subsequent energy release. In these tests, the heat flux sensor was first cold soaked in either a dry ice or LN2 bath to induce temperatures of approximately -78Â°C or -190Â°C, respectively. Then the sensors were thermally shocked using two propane torches with a heat rate of either approximately 8 W/cm2 or 21 W/cm2. The key findings indicated that there is a correlation between thermal shock and the blistering observed in the DNH test series, and that the cause appeared to be rooted in the heat flux sensor epoxy that encapsulates the sensor thermopile.Since the heat flux sensors are required to measure heat fluxes up to 15 W/cm2 during the Mars 2020 entry, a third test series was designed to determine if blistering is an issue at this maximum expected flight heat flux. Results from all three thermal shock test series and a discussion about whether or not blistering of the heat flux sensor thermal coating could be an issue for the Mars 2020 mission will be presented.

Miller, R. A.↗

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

pressure gain combustion↗

DOE OSTI2021

Intra-Molecular Isotope Study of Light Hydrocarbons

Light hydrocarbons (C 1 -C 10 ) are the largest fraction of petroleum hydrocarbons and some of the most ubiquitous and mobile fluids within sedimentary basins. It has been increasingly recognized that hydrocarbons of varying chain-lengths can be stable even under mantle conditions and that their fluxes may play a key role in the carbon dynamics of the Earth. Major formation mechanisms of these light hydrocarbons include microbial, thermogenic, and abiogenic origins. Despite their proven utility, conventional approaches using the bulk or global stable isotopes of light hydrocarbons are often not sufficient to distinguish their sources (particularly, biogenic vs. abiogenic), maturation stages/temperatures, and migration-degradation processes. Most natural compounds, including light hydrocarbons, are composed of a set of diverse isotopic molecules that differ in the number of isotopic substitutions and/or positions of isotopic substitution within a given molecules. Many of light hydrocarbon molecules contain hydrogen and carbon in energetically non-equivalent positions: isotopomers or position-specific (intra-molecular) isotope fractionation. Position-specific isotopic compositions can differ due either to equilibrium or to path-dependent kinetic or biological processes. Thus, the position-specific isotopic fractionation between different carbon and hydrogen positions within a single molecular compound could be used regardless of their reactants and other products. We hypothesize that the formation, transport and degradation processes of light hydrocarbons in the subsurface induce and control significant, perhaps unique position-specific 13 C/ 12 C and 2 H/ 1 H isotope fractionation. In this proposal, we propose to develop a new dimension in stable isotope geochemistry of light hydrocarbons: intra-molecular isotope study of light hydrocarbons. The specific objectives of our proposal include: (a) develop robust and routine quantitative nuclear magnetic resonance (NMR) methods for high-precision/high-accuracy isotopomer analysis of propane and other light hydrocarbons (C 3 -C 10 ), (b) gain a first clear picture on position-specific δ 2 H and δ 13 C values of select light hydrocarbons of both natural and industrial sources, including samples of natural gases (C 3 and possibly C 4 -C 5 ) collected from select sedimentary basins with conventional and unconventional reservoirs, (c) acquire information on position-specific 13 C/ 12 C and 2 H/ 1 H isotope fractionation of light hydrocarbons in key natural processes (thermogenic formation and oxidative degradation) based on well-controlled laboratory experiments, and (d) establish a general framework for interpreting/modeling position-specific 13 C/ 12 C and 2 H/ 1 H isotope compositions of light hydrocarbons. Intra-molecular isotope study of light hydrocarbons is expected to open up great potentials that the bulk and position-specific isotope fractionation of light hydrocarbons, in combination with mathematical/theoretical kinetic models, could provide unprecedented wealth of information on the sources, transport, and sinks of light hydrocarbons in sedimentary basins and deep Earth.

03 NATURAL GAS↗

DOE OSTI2021

Evaluation of Contact Resistance and Fin Effectiveness of Enhanced, Brazed "Dogbone" Fin and Serpentine Tube Heat Exchangers for Air Conditioning and Heat Pump Applications

The energy consumption due to air conditioning is projected to increase by 1.3 and 4.5 times by 2050 compared to 2010 for members and non-members of the Organization of Economic Coordination and Development (OECD), respectively. Greenhouse Gas (GHG) emissions must be carefully managed to minimize their hazardous contribution to climate change. Air conditioners (AC) and heat pumps (HP) contribute with direct GHG emissions through systemic refrigerant leakage, which consequently degrades the system’s performance and therefore increases its indirect GHG emissions as well. To address this issue, the goals of new systems include minimizing leakage risk, using low global warming potential (GWP) refrigerants such as natural refrigerants, and increasing system efficiency. This paper presents part of the efforts in the development of a brazed “dogbone” fin to continuous serpentine tube heat exchanger (HX) for AC/HP applications. The main advantages of such technology are: 1) The potential to reduce 90% or more of the tube return-bends brazed joints compared to conventional tube-fin heat exchangers, thus minimizing leakage vulnerability, enabling the use of natural refrigerants like Propane and Ammonia that carry other concerning risks of flammability and toxicity ; and 2) The brazed fin to the tube joints should yield very low contact resistance. In order to quantify and estimate the impacts of contact resistance and fin effectiveness, a numerical-experimental study is investigated. The novel enhanced brazed “dog-bone” fin is compared to an equivalent pressure expanded fin. The results showed that the expanded fin has consistently greater effective heat transfer but greater contact resistance as well. Furthermore, the brazed fins have up to 20% lower pressure drop. The trade-off comparison shows that the thermal-hydraulic ratio between the two fins is equivalent for air velocities below 2m/s; for greater velocities, however, the expanded fin is favored since it has less fin efficiency penalty. For HVAC&R applications, the air velocities are typically low which makes the proposed technology competitive and a viable option in the pursuit of refrigerant leakage reduction.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2022

The Impact of LPG Composition on Performance, Emissions, and Combustion Characteristics of a Pre-mixed Spark-Ignited CFR Engine

Research on alternative fuels has made significant progress as demands for cleaner and more efficient engine operation intensifies. Liquefied petroleum gas (LPG) can offer a potential alternative fuel route in the Diesel fuel dominated heavy-duty transportation sector due to its low cost, high anti-knock limit relative to gasoline, and reduced emission levels. In this work, experimental investigations are performed to study the effects of LPG compositions on performance, emissions, and combustion behavior of a spark-ignited (SI) cooperative fuel research (CFR) engine under stoichiometric conditions. Four LPG blends (chemically pure propane, a representative US blend, HD-5, and a representative European blend) representing the present LPG market are chosen. The impact of fuel composition is studied under different compression ratios (CR), ranging from 7:1 to 10:1 with one-unit increments, and at constant engine speed, intake manifold air pressure (IMAP) and 50% burn crank angle (CA50). The results show that fuel composition has minimal effect on engine efficiency over the CR range 7:1 to 10:1. Engine-out emissions are substantially affected by fuel compositions with the representative European blend indicating higher unburned hydrocarbon (UHC) emissions, particularly at higher CR. The representative US blend emits the lowest brake specific CO (bsCO) averaged over the tested CR range. With the increase of CR, end-gas autoignition intensifies for all blends and the representative European blend demonstrates the highest knock intensity of all tested blends, due to the presence of the more reactive fuel component, n-butane.

Fosudo, Toluwalase↗

DOE OSTI2022

Performance Assessment of High-Efficiency Refrigerated Display Cases with Low-GWP Refrigerants: Preprint

As California policy makers enforce new regulations such as SB 1383 to achieve state greenhouse gas (GHG) reduction goals, it will be critical to understand the energy efficiency implications of low global warming potential (GWP) refrigerants in commercial refrigeration applications. The goal of this research project, funded by Commonwealth Edison was to assess the energy performance of two high efficiency medium-temperature, self-contained, reach-in display cases that utilized natural refrigerant propane (R-290), and hydrofluorocarbon (HFC) drop-in hydrofluoroolefin R-513a, respectively. Performance of these display cases were compared to a baseline fixture using HFC (R-134a) under equal conditions in a controlled environment chamber. These display cases were selected due to their widespread use in convenience stores, and small supermarkets. The high efficiency cases were equipped with energy efficient lighting, improved panel insulation, high efficiency evaporator and condenser fan motors, and high effectiveness heat exchangers. The test method used in this project was foundationally inspired by the ANSI/ASHRAE 72-2018 standard method to evaluate each case under equivalent conditions. However, minor modifications to this methodology were implemented to better represent more realistic operation of the units. While maintaining target product temperature, the energy efficient fixtures containing R-290 and R-513a consumed 61.8% to 32.6% less energy, respectively, than a baseline case using R-134a refrigerant. The daily energy consumption of the R-290, R-513a, and baseline display cases at the upper limit of environmental conditions was 4.30, 7.59, and 11.26 kWh/day, respectively.

alternative refrigerants↗