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NASA NTRS2020

Emission Characteristics of an Axially Staged Sector Combustor for a Small Core High OPR Subsonic Aircraft Engine

This paper presents the nitrogen oxides, carbon monoxide, and particulate matter emissions of a single sector axially staged combustor sector designed and fabricated by United Technologies Research Center (UTRC) in partnership with NASA under a compact low-emissions combustor contract supported by the NASA Advanced Air Transport Technology (AATT) N+3 project. The test was conducted at NASA Glenn Research Center's CE-5 combustion test facility. The facility provided inlet air temperatures up to 922 K and pressures up to 19.0 bar. The combustor design concept, called Axially Controlled Stoichiometry (ACS), was developed by Pratt & Whitney (P&W) under NASA's Environmentally Responsible Aviation (ERA) program for an N+2 combustor for use in twin-aisle subsonic aircraft engines. Under the N+3 project the ACS combustor was scaled-down for application to small-core N+3 engines for use in single-aisle aircraft. The results show that the NOx and CO emissions characteristics are similar in both the N+2 and N+3 applications. The non-volatile particulate matter (nvPM) emissions trends are similar to CO emissions with an exception at high fuel-air ratio, as inlet air temperature and pressure conditions change from taxi to approach. Three NOx correlation equations are generated to describe theNOx emissions of this combustor. The percentage landing and takeoff (LTO) NOx reduction of the N+3 ACS combustor is between 82% and 89% relative to the ICAO CAEP/6 standard, which meets the NASA N+3 goal of exceeding 80% LTO NOx reduction.

He, Zhuohui J.↗
NASA NTRS2020

Advancing Development of Environmental Barrier Coatings Resistant to Attack by Molten Calcium-Magnesium-Aluminosilicate (CMAS)

Ceramic matrix composites (CMCs) are a leading material system to replace metal-based parts in the hot-section of air-breathing turbine engines to improve fuel efficiency in aircraft engines. CMCs have higher temperature capabilities and lower density compared with traditional metallic structural materials. However, silicon-based CMCs are susceptible to oxidation in the harsh combustion environment encountered in turbine engines. Consequently, environmental barrier coatings (EBCs) are being developed to protect CMC components to improve durability and extend service life of CMCs. Sand, volcanic ash and other particulate debris, which are generally comprised of calcium-magnesium-aluminosilicate (CMAS) and other trace oxides, are routinely ingested by aircraft engines. At temperatures above 1200°C, CMAS particulates melt. Near target operating temperatures (~1500°C) of future CMC-based aircraft engines, molten CMAS behaves like a viscous melt that can infiltrate and chemically interact with protective coatings. These interactions can cause premature failure of the EBC system and ultimately the overall CMC engine component. Degradation of candidate EBC materials by molten CMAS will be presented with a focus on recent work, as well as methods of evaluating the complex high-temperature materials interactions, underway at NASA Glenn Research Center.

Wiesner, Valerie L.↗
NASA NTRS2020

Remote Sensing of Diatom Bloom Succession

Marine diatoms are major biogeochemical and ecological “influencers” that contribute to a large fraction of the carbon export and supplying fisheries (Falkowski 2015). The fluxes of carbon transfer to the food web or to the deep ocean vary according to the stage of a diatom bloom (Du Toit 2018). Stages can be determined using inherent optical properties that reflect their physiological state, such as the chlorophyll fluorescence to particulate backscattering ratio (ChlF/b(sub bp), Cetinic et al. 2015). Identifying the bloom stage can potentially improve biogeochemical models of carbon export and fishery management. However, it is not yet possible to adequately determine the stage of phytoplankton blooms using satellites. Satellite-derived remote sensing reflectance R(sub rs)(𝜆) allow for remote identification of diatom blooms in the open ocean (Sathyendranath et al. 2004), and there are techniques to estimate the fluorescence quantum yield (𝜑) that, when high, can indicate the nutrient limitation that often takes place when blooms start to senesce (Behrenfeld et al. 2009). The goal of this study is to use the ratio between the normalized fluorescence line height from R(sub rs)(𝜆) (nFLH) and the particulate backscattering (b(sub bp)(443)) provided by satellites to identify exponentially growing and senescent diatom blooms from space.

Lange, Priscila K.↗
NASA NTRS2013

TPSAS-NF1676L-16299-DND

As part of the American Recovery and Reinvestment Act (ARRA) of 2009, the DOE ARM program deployed a new ground-­‐based Arctic High Spectral Resolution Lidar (AHSRL) at the North Slope of Alaska (NSA) site. This lidar, which is based on the AHSRL that was part of the NOAA’s SEARCH (Study of Environmental Arctic Change) contribution to the Canadian Network for the Detection of Atmospheric Change (CANDAC) facility at Eureka, Nunavut Territory, is an autonomous lidar that provides calibrated profiles of particulate (i.e. aerosol and cloud) backscatter cross section, optical thickness and circular depolarization at 532 nm. The AHSRL provides measurements of both intensive and extensive particulate properties. The intensive parameters depend only on the nature of the particles (size, composition, shape), not on the quantity or concentration. Here we show examples of the AHSRL data during both clear and cloudy conditions to show how these measurements can be used to depict aerosols and clouds over the NSA.

Marian Clayton↗
NASA NTRSDate not supplied

TPSAS-NF1676L-20108-DND

This presentation describes several enhancements planned for the version 4 aerosol subtyping and lidar ratio selection algorithms of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument. The CALIOP subtyping algorithm determines the most likely aerosol type from CALIOP measurements (attenuated backscatter, estimated particulate depolarization ratios de, layer altitude), and surface type. The aerosol type, so determined, is associated with a lidar ratio (LR) from a discrete set of values. In the version 3 algorithms, there are 6 pairs of 532 and 1064 nm lidar ratios. Some of these lidar ratios will be updated in the version 4 algorithms. In particular, the dust and polluted dust will be adjusted to reflect the latest measurements and model studies of these types. The algorithms are being updated to eliminate the occasional confusion between smoke and clean marine aerosols seen in version 3 by modifications to the elevated layer flag definitions that are used to determine the presence of smoke aerosols over the ocean. In the subtyping algorithms pure dust is determined by high estimated particulate depolarization ratios [de > 0.20]. Mixtures of dust and other aerosol types are determined by intermediate values of the estimated depolarization ratio [0.075< de <0.2]. The version 3 algorithms are limited to mixtures of dust and smoke, the so-called polluted dust aerosol type. To differentiate between mixtures of dust and smoke, and dust and marine aerosols, a new aerosol type will be added in the version 4 data products. In the revised classification algorithms, polluted dust will still defined as dust + smoke/pollution but in the marine boundary layer instances of moderate depolarization will be typed as dusty marine aerosols with a lower lidar ratio [LR = 35 sr] than polluted dust [currently LR = 55 sr]. The dusty marine type introduced in version 4 is modeled as a mixture of dust + marine aerosol. In the v3 algorithms the frequency of dust and polluted dust aerosols at daytime is higher than at nighttime. We present possible reasons for this and present the v4 distributions resulting from both improved background slope corrections of the daytime depolarization ratios and changes to the daytime thresholds for the polluted dust and dusty marine types of version 4. To gauge the impact of the enhancements, we contrast the following between versions 3 and 4: aerosol type, parameter distributions of each type, layer heights of maximum frequency, and distributions of smoke in biomass burning regions. To illustrate specific impacts the presentation shows case studies of version 3 and version 4 vertical feature masks of the aerosol subtypes, where appropriate, for the above enhancements.

A Omar↗
NASA NTRS2017

TPSAS-NF1676L-28148-DND

Currently, ocean carbon biomass is estimated from ocean color measurements primarily through particulate backscatter coefficients (bbp). Small non-algal particles contribute significantly to bbp due to the fact that small particles scatter more isotropically while bigger particles scatter mostly in the forward direction. CALIPSO’s ocean subsurface cross polarization measurements (Figure 1) are not sensitive to small particles far less than 2 microns in size since these particles rarely cause depolarization. Thus, cross polarization backscatter is contributed mostly by larger, depolarizing phytoplankton particles. This is why CALIPSO’s cross polarization has much larger contrasts comparing with MODIS reflectance (CALIPSO cross polarization is very weak in Gyres and much stronger in high latitudes, See Figure 1). CALIPSO cross-polarization measurements in the Southern Oceans also suggest that water cloud droplet number concentration covaries with phytoplankton carbon biomass (Figure 2), but it has less correlation with particulate organic carbon (POC) (Figure 2) and chlorophyll concentration. The study also agrees with water cloud droplet size retrieved from Parasol’s polarization measurements.

Yongxiang Hu↗
NASA NTRSDate not supplied

CONTAMINATION CONTROL FOR ULTRA-SENSITIVE LIFE DETECTION SCIENCE MISSIONS

"This study report summarizes technological developments in science-required contamination control for cost-capped, life-detection missions in the Solar System. Technology advances focus on developing implementable strategies to restrict contamination of the spacecraft and instruments by the launch vehicle hardware. Secondary bake out operations during cruise further reduce molecular contaminants down to femtomolar levels in the sample path. The study validated a full-spacecraft, deployable barrier design as an effective strategy to isolate the spacecraft from the pre-launch processing and launch environment (e.g., fairing acoustic materials). It accommodates late mounting of RTGs and other required prelaunch activities. A new, high-fidelity physics, contamination-transport model for particles (including cells and their parts) and science-relevant molecules (e.g., possible biomolecules) was developed to validate the barrier concept. Importantly, this model takes into account the physics of extremely clean surfaces achieved by the best traditional contamination engineering. The ability to deal with very low levels of particulate and molecular contamination makes this model unique among standard contamination modeling approaches. Modeling also demonstrated that a high-temperature bake out during interplanetary cruise of the sample collector that comprises the largest surface area in the sample path for an Enceladus orbiter reference mission, was extremely effective. This study included the evaluation of other details necessary for an effective contamination control strategy for life detection missions including feasibility of achieving parts per trillion level cleanliness for semi-volatile hydrocarbons in nitrogen purge gas, identification of launch vehicle services required for the baseline contamination control, and defining additional contamination control measures to be taken during launch operations. Key results of the study are: • New spacecraft barrier design that accommodates RTGs is readily cleanable and repairable. Deployment of a 1/3 scale model was successfully demonstrated. • The barrier reduces particle contamination (likely biological) from fairing to spacecraft by 1e-2 to 1e-3. • On-cruise bake-out of critical surfaces significantly reduced molecular contamination (by as much as 1e-12). Subsequently, the probability of a surface contamination particle being transported to an instrument by an ice particle is less than 5.1e-5 (for microbes specifically, 4.39e-10). The report concludes that a full-spacecraft barrier designed specifically for life-detection missions that require stringent control of particulate and molecular contaminates is an effective means of mitigating risks of false positive and negative results for life signature investigations. Further, secondary cleaning steps for critical sections of the sample path can be highly effective at reducing molecular contaminants to low femtomolar levels."

Contamination↗
NASA NTRS2018

Multi-Angle Imager for Aerosols Thermal Control System

The Multi-Angle Imager for Aerosols (MAIA) Thermal Control System is a NASA funded instrument that will collect data to help characterize airborne particulate matter over a number of population centers across the globe using multi-angle spectropolarimetric imagery. The data collected by MAIA will facilitate assessments of the impacts of different types of particulate matter on adverse health outcomes. MAIA is a hosted payload meant to operate in a near-circular sun-synchronous polar orbit, with a mean altitude between 600 km and 850 km. The nominal on-orbit mission design lifetime is three years. Temperature control of the MAIA instrument is accomplished with a combination of passive radiators and heaters. The focal plane module (FPM) is cooled to ≤ 235K with a disc shaped radiator that faces the anti-sun side of the sun-synchronous orbit. The temperature of the MAIA cameras and associated electronics is controlled with a cylindrical shaped radiator that projects a near constant area in the nadir direction as the cameras rotate. A noteworthy feature of the MAIA thermal control system design is the novel, low cost, rotationally articulating thermal strap used to transfer heat from the FPMs to their associated FPM Radiator. The strap spans one of the axes of rotation, sweeping out an arc of approximately 60° as the instrument operates. A prototype of the articulating thermal strap was life tested to 260,000 cycles with no signs of significant degradation. An overview of the MAIA thermal control system baseline design is presented, with focus on its novel aspects, including life testing of the prototype articulating thermal strap. In addition, a discussion of the considerations involved in designing a thermal control system for a hosted instrument is provided.

Rosas, Rogelio↗
NASA NTRSDate not supplied

Contamination Control for Ultra-Sensitive Life-Detection Missions

"This study report summarizes technological developments in science-required contamination control for cost-capped, life-detection missions in the Solar System. Technology advances focus on developing implementable strategies to restrict contamination of the spacecraft and instruments by the launch vehicle hardware. Secondary bake out operations during cruise further reduce molecular contaminants down to femtomolar levels in the sample path. The study validated a full-spacecraft, deployable barrier design as an effective strategy to isolate the spacecraft from the pre-launch processing and launch environment (e.g., fairing acoustic materials). It accommodates late mounting of RTGs and other required prelaunch activities. A new, high-fidelity physics, contamination-transport model for particles (including cells and their parts) and science-relevant molecules (e.g., possible biomolecules) was developed to validate the barrier concept. Importantly, this model takes into account the physics of extremely clean surfaces achieved by the best traditional contamination engineering. The ability to deal with very low levels of particulate and molecular contamination makes this model unique among standard contamination modeling approaches. Modeling also demonstrated that a high-temperature bake out during interplanetary cruise of the sample collector that comprises the largest surface area in the sample path for an Enceladus orbiter reference mission, was extremely effective. This study included the evaluation of other details necessary for an effective contamination control strategy for life detection missions including feasibility of achieving parts per trillion level cleanliness for semi-volatile hydrocarbons in nitrogen purge gas, identification of launch vehicle services required for the baseline contamination control, and defining additional contamination control measures to be taken during launch operations. Key results of the study are: • New spacecraft barrier design that accommodates RTGs is readily cleanable and repairable. Deployment of a 1/3 scale model was successfully demonstrated. • The barrier reduces particle contamination (likely biological) from fairing to spacecraft by 1e-2 to 1e-3. • On-cruise bake-out of critical surfaces significantly reduced molecular contamination (by as much as 1e-12). Subsequently, the probability of a surface contamination particle being transported to an instrument by an ice particle is less than 5.1e-5 (for microbes specifically, 4.39e-10). The report concludes that a full-spacecraft barrier designed specifically for life-detection missions that require stringent control of particulate and molecular contaminates is an effective means of mitigating risks of false positive and negative results for life signature investigations. Further, secondary cleaning steps for critical sections of the sample path can be highly effective at reducing molecular contaminants to low femtomolar levels."

contamination, life detection, barrier, modeling↗
NASA NTRS2020

Modeling the smoky troposphere of the southeast Atlantic: a comparison to ORACLES airborne observations from September of 2016

In the southeast Atlantic, well-defined smoke plumes from Africa advect over marine boundary layer cloud decks; both are most extensive around September, when most of the smoke resides in the free troposphere. A framework is put forth for evaluating the performance of a range of global and regional atmospheric composition models against observations made during the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) airborne mission in September 2016. A strength of the comparison is a focus on the spatial distribution of a wider range of aerosol composition and optical properties than has been done previously. The sparse airborne observations are aggregated into approximately 2° grid boxes and into three vertical layers: 3–6 km, the layer from cloud top to 3 km, and the cloud-topped marine boundary layer. Simulated aerosol extensive properties suggest that the flight-day observations are reasonably representative of the regional monthly average, with systematic deviations of 30 % or less. Evaluation against observations indicates that all models have strengths and weaknesses, and there is no single model that is superior to all the others in all metrics evaluated. Whereas all six models typically place the top of the smoke layer within 0–500 m of the airborne lidar observations, the models tend to place the smoke layer bottom 300–1400 m lower than the observations. A spatial pattern emerges, in which most models underestimate the mean of most smoke quantities (black carbon, extinction, carbon monoxide) on the diagonal corridor between 16° S, 6° E, and 10° S, 0° E, in the 3–6 km layer, and overestimate them further south, closer to the coast, where less aerosol is present. Model representations of the above-cloud aerosol optical depth differ more widely. Most models overestimate the organic aerosol mass concentrations relative to those of black carbon, and with less skill, indicating model uncertainties in secondary organic aerosol processes. Regional-mean free-tropospheric model ambient single scattering albedos vary widely, between 0.83 and 0.93 compared with in situ dry measurements centered at 0.86, despite minimal impact of humidification on particulate scattering. The modeled ratios of the particulate extinction to the sum of the black carbon and organic aerosol mass concentrations (a mass extinction efficiency proxy) are typically too low and vary too little spatially, with significant inter-model differences. Most models overestimate the carbonaceous mass within the offshore boundary layer. Overall, the diversity in the model biases suggests that different model processes are responsible. The wide range of model optical properties requires further scrutiny because of their importance for radiative effect estimates.

Yohei Shinozuka↗
NASA NTRS2021

On the Cycling of 231 Pa and 230 Th in Benthic Nepheloid Layers

The naturally-occurring radionuclides protactinium-231 ( 231 Pa) and thorium-230 ( 230 Th) are produced at approximately uniform rates in the ocean and thought to be removed from the water column through a reversible exchange with settling particles. Recent measurements along the U.S. GEOTRACES North Atlantic transect (GA03) revealed two features which are at odds with current understanding about 231 Pa and 230 Th cycling in the ocean: (i) a sharp decrease in dissolved 231 Pa ( 231 Pa d ) and 230 Th ( 230 Th d ) activities with depth below 2000-4000 m and (ii) very high particulate 231 Pa ( 231 Pa p ) and 230 Th ( 230 Th p ) activities near the bottom, at a number of stations between the New England continental shelf and Bermuda. Concomitant measurements of light attenuation from beam transmissometry showed that both features occur in benthic nepheloid layers (BNLs), which suggests that these features may stem, at least partly, from the presence of resuspended sediment in the deep water column. Here we explore the behaviour of 231 Pa and 230 Th in BNLs by using (i) radionuclide, optical, and hydrographic data from the western segment of GA03 (west of Bermuda) and (ii) a simplified model of particle and radionuclide cycling that includes a lateral particle source. First, the BNLs observed at GA03 stations are characterized from measurements of the beam attenuation coefficient converted to particle concentrations. At all stations, particle concentrations below the clear water minimum were the highest in the bottom mixed layer, whose thickness ranged from 95 to 320 m, and decreased generally with height above the bottom. The thickness of strong BNLs varied from 482 to 1358 m and the vertical integral of particle concentration in excess to that at the clear water minimum varied from 1 x 10 4 to 2 x 10 6 mg m −2 , among different stations. Second, the particle-radionuclide model is fitted to data from stations GT11-04 (New England continental rise) and GT11-08 (Hatteras abyssal plain), where samples for radionuclide analyses were collected in the BNL. The model can reproduce simultaneously the increase of particle concentration with depth, the low 231 Pa d and 230 Th d in the BNLs, and the high 231 Pa p and 230 Th p near the bottom. According to the model, at heights less than about 300 m above the seafloor, the dissolved phase was set primarily by a balance between adsorption and desorption, with vertical turbulent mixing playing a secondary role, whilst the particulate phase behaved largely as a non-reactive constituent supplied laterally and transported vertically by particle settling and turbulent mixing. Sensitivity tests with the model suggest that lateral particle sources near continental slopes and similar reliefs can produce significant biases both in the 230 Th normalization method and in the interpretation of sediment 231 Pa/ 230 Th records. Our findings yield insights into the influence of sediment resuspension and transport on 231 Pa and 230 Th in the deep ocean and highlight the need for considering these processes in paleoceanographic applications.

Nepheloid layer↗
NASA NTRS2021

Interpretation of Spectral LiDAR Backscattering off the Florida Coast

A multispectral backscattering LiDAR (Light detection and range) system (hereafter Oculus) was integrated into a wave glider and used to estimate the scattering order (i.e., single vs multiple collisions), inherent optical properties (IOPs) and characteristics of particulate scatterers (i.e., relative size, composition and motion) on shelf waters of South East Florida. Oculus has a dual-wavelength configuration (473 and 532 nm) and two detection geometries (off- and on-axis). Characteristics of scatterers were investigated based on two complementary LiDAR-derived proxies (the Structural Dissimilarity Index and the spectral slope of LiDAR backscattering). In March 2017, field measurements showed a covariation between direct and diffuse backscattering contributions during morning hours and away from shore. LiDAR attenuation coefficients explained up to 57% of IOPs variability. The analysis of LiDAR-derived proxies suggested higher turbidity and larger particulates near the coast.

LiDAR↗
NASA NTRS2022

Controlling Triboelectrification Effects on Spacecraft Ethernet Cabling

Triboelectric charging of a spacecraft and launch vehicles on ascent may occur due to the process of contact and separation between the vehicle skin and aerosols, dust, ice, water droplets, smoke, and other particulates encountered in the flight path. Depending on characteristics at the atomic and molecular levels of the vehicle skin’s surface and the substances and particulates encountered, electrical charge will transfer between the vehicle and the encountered substances, resulting in an accumulation of electrical charge on the vehicle skin. If the vehicle skin is conductive and electrically bonded such that in its entirety it presents an equipotential surface, then the accumulated electrical charge will spread in a nearly uniform manner leaving all regions with a nearly equal potential with respect to each other and the surrounding environment. Regions that are not electrically bonded as described, or surfaces that have resistivity values, can reach different potentials than the surrounding surfaces. When this happens, the differing potentials may grow to very large magnitudes, leading to electrostatic discharge events between the regions. As the vehicle rises in altitude, the breakdown potential between these regions of differing potential decreases commensurate with decreases in atmospheric density and pressure. If the potential differences between surfaces of the vehicle become equal to or exceed the breakdown potential, one or more discharge events may occur, each of them generating voltage and current transients that can easily damage or interfere with the designed operation of on-board electrical, avionic, and communications and navigation systems. This lesson learned discusses an in-flight anomaly caused by triboelectric discharge events and exacerbated by the lack of adequate cable shielding that affected flight computer communication links. Also discussed are mitigations to prevent this occurrence.

Ethernet↗
NASA NTRSDate not supplied

Thermochemical/Thermomechanical Synergies in High Temperature Solid Particle Erosion of CMAS-Exposed EBCs

Environmental barrier coatings (EBCs) are an enabling technology for the use of SiC-based ceramic matrix composites in next generation gas turbine engines. In the extreme engine environment, EBCs must be able to withstand a variety of individual damage mechanisms and their interactions with each other. Ingested particulates/debris can cause both thermochemical and thermomechanical degradation of EBCs. Siliceous debris primarily based on calcium magnesium aluminosilicates (CMAS) can melt and infiltrate and/or react with EBCs above >1200°C. Similarly, ingested debris can lead to mechanical damage and recession of coatings due to particulate erosion. Both modes of degradation can occur simultaneously during engine operation, and it is crucial to comprehensively understand the mechanisms of coating failure due to high-temperature particulate interactions. This study assesses the erosion durability of Yb2Si2O7-based EBCs exposed to CMAS of various loads in NASA Glenn’s Erosion Burner Rig Facility. CMAS exposures and erosion testing were carried out at 1316°C. The effects of CMAS loading and exposure time on EBC erosion durability were evaluated using Al2O3 as an erodent material.

EBC↗
NASA NTRS2023

Broader Impacts and Outreach Videos on Ocean Physics and Biogeochemistry

This is just a preliminary NF1676 in advance of filming for a project....A convergent team of experts in biology, chemistry, physics, engineering, mathematics, and computational modeling examine how dynamic and coupled phytoplankton-pathogen-particle-predator linkages coalesce to explain the observed high spatial variability in the efficiency of the export of particulate organic carbon (POC) to the deep ocean. They elucidate and quantify the linkages between viruses and ballast minerals to increase understanding of carbon cycling in the oceanic biological carbon pump and the impact of viruses within it. By providing knowledge than can be used to improve the parameterization of carbon export in Earth system models, the project will help reduce uncertainty in regional marine biogeochemical projections, potentially improving marine ecosystem and fisheries management on timescales from seasons to decades. The project includes activities that provide teaching resources and hands-on training to educators within a ‘Tools of Science’ program that provides a simple and succinct way to communicate the process of scientific research to students in a way that is useful to teachers. The project couples laboratory-based experiments on model host-virus-grazer systems with extensive field based observational and manipulative studies on natural populations of diatoms and coccolithophores, the two phytoplankton groups that account for most of the estimated particulate organic matter flux to the deep ocean. Experiments and measurements integrate diagnostic biological and chemical controls on infection and particle coagulation theory with microscale physics and grazing to quantify links to each hypothesized export mechanism under field-relevant turbulent conditions. Cutting-edge engineering and analytical tools are used to diagnose and track infection dynamics while characterizing and quantifying particle aggregation and disaggregation, mineral dissolution, sinking dynamics, grazing rates, and fecal pellet production at unprecedented resolution and under well-defined, microscale physical regimes. Field campaigns elucidate the relative efficiency of hypothesized mechanisms in stimulating POC export in natural blooms, while providing bulk and size-resolved estimates of POC flux.

Daniel B Whitt↗
NASA NTRS2023

The Projected Future Degradation in Air Quality is Caused by More Abundant Natural Aerosols in a Warmer World

Previous studies suggest that greenhouse gas-induced warming can lead to increased fine particulate matter concentrations and degraded air quality. However, significant uncertainties remain regarding the sign and magnitude of the response to warming and the underlying mechanisms. Here, we show that thirteen models from the Coupled Model Intercomparison Project Phase 6 all project an increase in global average concentrations of fine particulate matter in response to rising carbon dioxide concentrations, but the range of increase across models is wide. The two main contributors to this increase are increased abundance of dust and secondary organic aerosols via intensified West African monsoon and enhanced emissions of biogenic volatile organic compounds, respectively. Much of the inter-model spread is related to different treatment of biogenic volatile organic compounds. Our results highlight the importance of natural aerosols in degrading air quality under current warming, while also emphasizing that improved understanding of biogenic volatile organic compounds emissions due to climate change is essential for numerically assessing future air quality.

Climate and Earth system modelling↗
NASA NTRSDate not supplied

Thermochemical/Thermomechanical Synergies in High-Temperature Solid Particle Erosion of CMAS-Exposed EBCs

Environmental barrier coatings (EBCs) are an enabling technology for the use of SiC-based ceramic matrix composites in next generation gas turbine engines. In the extreme engine environment, EBCs must be able to withstand a variety of individual damage mechanisms and their interactions with each other. Ingested particulates/debris can cause both thermochemical and thermomechanical degradation of EBCs. Siliceous debris primarily based on calcium magnesium aluminosilicates (CMAS) can melt and infiltrate and/or react with EBCs above 1200°C. Similarly, ingested debris can lead to mechanical damage and recession of coatings due to particulate erosion. Both modes of degradation can occur simultaneously during engine operation, and it is crucial to comprehensively understand the mechanisms of coating failure due to high-temperature particulate interactions. This study assesses the erosion durability of Yb 2 Si 2 O 7 -based EBCs exposed to CMAS of various loads in NASA Glenn’s Erosion Burner Rig Facility. CMAS exposures and erosion testing were carried out at 1316°C. The effects of CMAS loading and exposure time on EBC erosion durability were evaluated using Al 2 O 3 as an erodent material.

CMAS↗
NASA NTRSDate not supplied

Thermochemical/Thermomechanical Synergies in High Temperature Solid Particle Erosion of CMAS Exposed EBCs

Environmental barrier coatings (EBCs) are an enabling technology for the use of SiC-based ceramic matrix composites in next generation gas turbine engines. In the extreme engine environment, EBCs must be able to withstand a variety of individual damage mechanisms and their interactions with each other. Ingested particulates/debris can cause both thermochemical and thermomechanical degradation of EBCs. Siliceous debris primarily based on calcium magnesium aluminosilicates (CMAS) can melt and infiltrate and/or react with EBCs above >1200°C. Similarly, ingested debris can lead to mechanical damage and recession of coatings due to particulate erosion. Both modes of degradation can occur simultaneously during engine operation, and it is crucial to comprehensively understand the mechanisms of coating failure due to high-temperature particulate interactions. This study assesses the erosion durability of Yb 2 Si 2 O 7 -based EBCs exposed to CMAS of various loads in NASA Glenn’s Erosion Burner Rig Facility. CMAS exposures and erosion testing were carried out at 1316°C. The effects of CMAS loading and exposure time on EBC erosion durability were evaluated using Al2O3 as an erodent material.

EBC↗