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Results for “conversion efficiency”

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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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A continuum model for heat and mass transfer in moving-bed reactors for thermochemical energy storage

In this work, a continuum heat and mass transfer model coupling transport phenomena and high-temperature thermochemical reactions is developed for stationary packed-bed and counter-flow moving-bed reactors. After presenting the general modeling framework, we focus on the 2D axisymmetric version of the model for which validation is conducted with experimental results for a packed-bed reactor in the literature for manganese-iron oxide reduction/oxidation and an in-house counter-flow moving-bed reactor for magnesium-manganese oxide reduction up to 1450 °C. Transient simulation results including the local distributions of gas/solid temperatures, oxygen concentration and the extent of reaction, as well as the various energy flow components and energy conversion efficiencies are reported. The results based on the 2D axisymmetric model are also compared with those obtained from a previous 1D model. The comparison shows that capturing the radial variation is critical in reactor modeling and the 2D results demonstrate improved agreement with experiments. Specifically, large temperature variations along the radial direction are observed especially in the reaction zone; this non-uniform radial temperature distribution has a significant effect on the chemical reaction extent due to its strong dependence on temperature; and the overall oxygen concentration at the reactor exit and the predicted system efficiency are slightly lower in the 2D model compared to the 1D model. Finally, the present heat and mass transfer model can provide valuable insights into reactor design, scale-up, and operating conditions selection to maximize system energy storage efficiency.

25 ENERGY STORAGE↗
DOE OSTI2020

Time-Sequenced Flow Field Prediction in an Optima Spark-Ignition Direct-Injection Engine Using Bidirectional Recurrent Neural Network (bi-RNN) with Long Short-Term Memory

To further improve the energy conversion efficiency of internal combustion engine, the transient and complex air flow movement inside the cylinder needs to be better understood and controlled. Although the in-cylinder flow fields are highly stochastic with strong cycle-to-cycle fluctuations, machine learning can still provide an efficient way to learn and regress the complex flow movement process inside the cylinder. In this work, a bidirectional recurrent neural network (bi-RNN) model with long short-term memory was applied to predict the in-cylinder flow fields at different time steps using training data from mull-cycle particle image velocimetry (PIV) measurements. To evaluate the agreement between the true and predicted flow fields, structure and magnitude comparison indices are calculated both globally and locally. The comparison results show that the bi-RNN model can accurately predict the bulk flow and vortex motions from early intake stroke to compression stroke. This work demonstrates that the machine learning model has the potential to predict the underlying dynamics of the interaction between in-cylinder flows and provides a reliable way to improve temporal resolution in PIV flow data to better reveal transient in-cylinder flow features.

Bi-RNN model↗
DOE OSTI2022

Evaluation of PbTe and SnTe as Ohmic Contact Layers in CdTe Solar Cell Devices

For solar cells based on CdTe, the choice of a suitable back contact material is limited by CdTe's deep work function. Here, we explored p-type PbTe and SnTe as ohmic contacts to CdTe. These contact layers were grown on single crystal CdTe substrates by molecular beam epitaxy, and the valence band offset between film and substrate was measured using X-ray photoemission spectroscopy. Polycrystalline device structures were also grown by sublimation to assess performance improvements. Doping was achieved in PbTe by thallium incorporation. Only the highest Tl doped PbTe resulted in a desirable band alignment with the CdTe, forming an electron reflector and no hole barrier. Time-resolved photoluminescence measurements also revealed significant photocarrier lifetime improvements for only the highest doped PbTe. Consequentially, devices incorporating the highest doped PbTe layers showed increased power conversion efficiency, primarily from increased fill factor. Doping of the PbTe was measured via Hall effect with variable magnetic field, which was required due to the formation of an n-type parasitic interface layer. To properly interpret the variable field Hall measurements, we derived an expression for the magnetic field-dependent conductivity tensor of an L-valley semiconductor.

anisotropic band valley↗
DOE OSTI2025

Predicting the evolution of biomass bulk density through feedstock preprocessing: Discrete element modeling, regression analysis, and pilot-scale validation

Bulk density is an important material property of biomass feedstocks, influencing handling, storage, transport costs, and conversion efficiency. In this study, predictive regression models for loose and tapped bulk densities of Alamo and Cave-in-Rock switchgrass are developed using a comprehensive dataset generated via calibrated bonded-sphere discrete element method (DEM) simulations. Here, a key contribution of this study is the use of a DEM-based approach, which correlates density with moisture content and particle size distribution parameters and enables analysis across a continuous particle size range, overcoming limitations of purely experimental data. For comparison, regression models are also developed using only experimental data from pilot-scale runs at the Biomass Feedstock National User Facility at Idaho National Laboratory. Validation against pilot-scale data showed reasonable prediction accuracy for both model types, particularly for smaller particle sizes (post-secondary grinding). While the experimental model showed slightly better performance matching the validation data in some cases, the DEM-based model benefits from a much larger dataset, reduced predictor multicollinearity, and continuous parameter coverage, highlighting the utility of validated simulation models for developing robust predictive tools for biomass preprocessing applications.

09 - BIOMASS FUELS↗
DOE OSTI2023

Applications of biomass-derived solvents in biomass pretreatment – Strategies, challenges, and prospects

We report biomass pretreatment is considered a key step in the 2nd generation biofuel production from lignocellulosic biomass. Research on conventional biomass pretreatment solvents has mainly been focused on carbohydrate conversion efficiency, while their hazardousness and/or carbon intensity were not comprehensively considered. Recent sustainability issues request further consideration for eco-friendly and sustainable alternatives like biomass-derived solvents. Carbohydrate and lignin-derived solvents have been proposed and investigated as green alternatives in many biomass processes. In this review, the applications of different types of biomass pretreatment solvents, including organic, ionic liquid, and deep eutectic solvents, are thoroughly discussed. The role of water as a co-solvent in these pretreatment processes is also reviewed. Finally, current research challenges and prospects of utilizing biomass-derived pretreatment solvents for pretreatment are discussed. Given bioethanol's market potential and increasing public awareness about environmental concerns, it will be a priority adopting sustainable and green biomass pretreatment solvents in biorefinery.

09 BIOMASS FUELS↗
DOE OSTI2026

Xylose metabolic engineering of Issatchenkia orientalis for 3-hydroxypropionic acid production from cellulosic hydrolysate without nutrient supplementation

Bioconversion of lignocellulosic biomass offers a promising alternative to petroleum-based chemical production. However, inefficient xylose utilization and toxic compounds in cellulosic hydrolysate limit microbial fermentation, as the hydrolysate contains substantial amounts of xylose in addition to glucose. To address these challenges, we engineered Issatchenkia orientalis to produce 3-hydroxypropionic acid (3-HP) directly from sorghum hydrolysate under low-pH conditions. A heterologous xylose utilization pathway consisting of XYL1, XYL2, and XYL3 from Scheffersomyces stipitis was introduced into an engineered 3-HP producing strain, enabling efficient conversion of xylose to 3-HP. The engineered strain produced 46.8 g/L 3-HP from sorghum hydrolysate without nutrient supplementation. To eliminate the lag phase under low-pH conditions, fermentation was conducted at pH 6.0 for the first three days, after which pH control was discontinued and in situ 3-HP accumulation buffered the culture. This partial pH control strategy increased 3-HP productivity by 55% from 0.20 to 0.31 g/L∙h, while maintaining low-pH conditions. Introducing an additional copy of XYL2 further increased 3-HP titer to 53.5 g/L and the yield by 33%, from 0.30 to 0.40 g/g sugars, with pH reaching 4.5 at the end of fermentation. This represents one of the highest reported 3-HP titers and yields from cellulosic hydrolysate without additional nutrient supplementation. This work demonstrates a nutrient-independent and low-pH bioprocess for upgrading lignocellulosic hydrolysate into 3-HP, highlighting the industrial potential of engineered xylose-utilizing I. orientalis for sustainable production of platform chemicals from renewable feedstocks.

3-Hydroxypropionic acid↗
DOE OSTI2026

Closing the loop on plastics: Biological and hybrid routes for converting plastic waste to polyhydroxyalkanoates

Polyhydroxyalkanoate (PHA) production from plastic-derived substrates offers a promising route to mitigate plastic pollution while reducing dependence on conventional PHA feedstocks. Plastic waste represents an abundant carbon source for microbial fermentation, but efficient conversion remains limited by incomplete deconstruction, inhibitory intermediates, low carbon recovery, and challenges in process integration. Plastic-derived streams contain diverse compounds, including fatty acids, hydrocarbons, fatty alcohols, aldehydes, esters, and aromatic compounds generated during depolymerization. These intermediates can be metabolized by selected microorganisms, particularly Pseudomonas species with versatile fatty-acid and hydrocarbon pathways, as well as Cupriavidus necator and mixed microbial cultures. Unlike reviews that address plastic upcycling or PHA biosynthesis separately, this review focuses on the deconstruction–fermentation interface that governs plastic-to-PHA conversion. It consolidates current progress in plastic deconstruction, substrate conditioning, microbial metabolism, fermentation control, polymer recovery, and techno-economic and life-cycle considerations. Here, by emphasizing substrate composition, biological compatibility, plastic‑carbon recovery, and final polymer quality, the review identifies priorities for scalable and environmentally sustainable PHA production from plastic-derived substrates.

42 ENGINEERING↗
DOE OSTI2020

High-yield growth kinetics and spatial mapping of single-walled carbon nanotube forests at wafer scale

Emerging commercial applications of vertically aligned, single-walled carbon nanotube (SWCNT) “forests” require synthesis that minimizes nanotube diameter while maximizing number density across substrate areas exceeding centimeter scale. To address this need, we synthesized SWCNT forests on full silicon wafers with notable reproducibility and uniformity, and co-optimized growth for small diameters and high densities across large areas to access new territory in this 3D parameter space. We mapped the spatial uniformity of key structural features using Raman microscopy, synchrotron X-ray scattering, and Rutherford backscattering spectrometry. Low C 2 H 2 flux over sub-nm Fe/Mo catalysts produced small-diameter SWCNTs (2.1 nm) at high number densities (2.26 × 10 12 cm -2 ) on wafers up to 6 in. Although removing Mo resulted in larger SWCNT diameters and lower densities (<0.7 × 10 12 cm -2 ), mass conversion rates from C 2 H 2 to SWCNT product were high and remarkably invariant for catalyst compositions and densities (i.e., 47.7% or 1.30 × 10 6 % g-catalyst -1 on 4-in. wafers). These carbon conversion efficiencies far exceed typical benchtop reactors and are on par with the best reported literature values. Our detailed elucidation of correlations among structural characteristics within this resource-efficient process is expected to guide future scale-up efforts of SWCNT forest growth beyond wafer scale.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Synthesis of wafer-scale SWCNT forests with remarkably invariant structural properties in a bulk-diffusion-controlled kinetic regime

Robust synthesis of vertically aligned carbon nanotubes (VACNT) at large scale is required to accelerate deployment of numerous cutting-edge devices to emerging commercial applications. To address this need, this work demonstrates that the structural characteristics of single-walled CNTs (SWCNTs) produced in a growth regime dominated by bulk diffusion of the gaseous carbon precursor are remarkably invariant over a broad range of process conditions (precursor concentration increased up to 30-fold, catalyst substrate area from 1 cm 2 to 180 cm 2 , growth pressure from 20 to 790 mbar, and gas flowrates up to 8-fold). A simple growth kinetics model is derived that accounts for both reactant bulk diffusion and competing byproduct formation in the presence of excess hydrogen, which quantitatively reproduces the experimental data in the entire isothermal parameter space. The model enables critical predictions for process scale-up optimization including a potential 6-fold increase in CNT production rate, a ~90% carbon conversion efficiency in select conditions, and elimination of reaction rate decay observed at high pressures by using a hydrogen-free growth environment. This model-guided opportunity to substantially improve synthesis throughput and efficiency, in conjunction with the remarkably invariant CNT properties, is appealing for reliable VACNT device fabrication at both small and industrial scales.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Amorphous Ag 2-x Cu x S quantum dots: “all-in-one” theranostic nanomedicines for near-infrared fluorescence/photoacoustics dual-modal-imaging-guided photothermal therapy

Integrating dual-modal imaging and photothermal effect within a single nanosystem is an enormous challenge for current nanomedicine application. In this study, non-toxic amorphous Ag 2-x Cu x S quantum dots (QDs) possessing near-infrared fluorescence (NIRF), enhanced photothermal and photoacoustic (PA) performance, as “one-in-all” nanomedicines, are designed and obtained. Cu doping in amorphous Ag 2 S QDs causes red-shift of NIRF to the lowest tissue absorption wavelength in so called “first biowindow” (~820 nm) and improves photothermal conversion efficiency to 44.0% simultaneously. Density functional theory simulation results suggest the fluorescence red-shift and enhanced photothermal/photoacoustics properties can be attributed to the generation of intragap states introduced by Cu doping. The amorphous Ag 2-x Cu x S QDs exhibit high long-term biocompatibility. Under a single laser irradiation with relatively low power density, an effective tumor ablation induced by high photothermal effect of amorphous Ag 2-x Cu x S QDs is achieved in vivo. Simultaneously, the PTT process can be guided by high quality NIRF/PA dual-modal-imaging.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Unique W-Shape Y6 isomer as effective solid additive for High-Performance PM6:Y6 polymer solar cells

The current top-performing polymer solar cell (PSC) systems are mostly based on PM6:Y6 host blend. To date, numerous materials have been explored as the third component for these systems to form ternary blends or as additives. Vitrification agents are a group of additives proved to be useful in affecting the morphology of organic semiconductors. Here to design a suitable vitrification agent for non-fullerene electron acceptor Y6, an isomer strategy was explored where the thienothiophene wings of the Y6 molecule were inversed to form a W-shaped Y6 isomer of i-Y6. It was found that i-Y6 crystallized poorly with a different packing style than Y6 and could blend well in amorphous phase of Y6. These properties enabled i-Y6 to finely tune the morphology of PM6:Y6 blend at low additive dosages. The power conversion efficiency (PCE) of PM6:Y6 based PSC was raised from 16.827% to 17.433% at a dosage of Y6:i-Y6 ratio of 24:1. This work demonstrated isomerization as a viable strategy for developing solid additives for high performance PSC blends and vitrification agents as effective additives for tuning morphology and improving performances of PSCs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Verifying the structure-property-performance relationship of Y6-based small molecule acceptors by alkoxy-side chain isomerization and conjugated skeleton asymmetry

Non-fullerene small molecule acceptors (NF-SMAs) such as Y6 derivatives were the current working horse for the top performing polymer solar cells (PSCs). For this reason, numerous chemical modifications have been explored for establishing structure–property-performance relationship for Y6-based NF-SMAs. In this work, we explored the isomerization on asymmetrical Y6 derivatives by varying the position of alkoxy side chain on the thiophene linkage between the core and one of the end groups of Y6. The isomers with differences in conformational restriction raised by noncovalent interactions as well as steric hindrance revealed distinctive behavior in crystallization and polymorphism, which led to a significant contrast in PSC performances. Here the X-TO1 molecule with alkoxy side chain facing the end group (outward) displayed preferred molecular configuration and polymorph, delivering power conversion efficiency (PCE) of 15.63%, while its isomer X-TO2 showed coexisted polymorphs significantly increased the charge recombination in the PSC devices led to a low PCE around 3%. This structure–property-performance relationship not only highlighted the elegancy of isomerization in tuning the photovoltaic performances but also identified polymorphism as one of the causes for impairing photovoltaic performances of PSCs.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Biomass pretreatment with distillable ionic liquids for an effective recycling and recovery approach

Ionic liquid (IL) pretreatment methods show incredible promise for the efficient conversion of lignocellulosic feedstocks to fuels and chemicals. Given their low vapor pressures, distillation-based methods of extracting ionic liquids out of biomass post-pretreatment have historically been ignored in favor of alternative methods. We demonstrate a process to distill four acetate-based ionic liquids ([EthA][OAc], [PropA][OAc], [MAEthA][OAc], and [DMAEthA][OAc]) at low pressure and high purity that overcome some disadvantages of “water washing” and “one pot” recovery methods. Out of four tested ILs, ethanolamine acetate ([EthA][OAc]) is shown to have the most agreeable conversion metrics for commercial bioconversion processes achieving 73.6% and 51.4% of theoretical glucose and xylose yields respectively and >85 % recovery rates. Our process metrics are factored into a techno-economic analysis where [EthA][OAc] distillation is compared to other recovery methods as well as ethanolamine pretreatment at both milliliter and liter scales. In conclusion, although our TEA shows [EthA][OAc] distillation underperforming against other processes, we show a step-by-step avenue to reduce sugar production cost below the wholesale dextrose price at scale.

09 BIOMASS FUELS↗
DOE OSTI2024

Intensified biogas to liquid (IBGTL) Process: Experimental validation and modeling analysis

The Intensified Biogas to Liquid (IBGTL) process aims to overcome traditional economy-of-scale barriers in biogas-to-liquid fuel production by integrating bi-reforming and Fischer-Tropsch synthesis (FTS) in a single IBGTL reactor. This reactor operates at uniform pressure with different optimized temperatures across two zones for efficient conversion, utilizing multifunctional bi-reforming catalysts and high-temperature FTS catalysts. Bench scale experiments were carried out using landfill gas (LFG) in a single pass process, and the yield data from these experiments were fed into process scale-up design and techno-economic analysis (TEA) across four scenarios: (1) a single pass process, (2) a process with material recycling, (3) a process with liquefied petroleum gas (LPG) co-product recovery, and (4) a process with electricity generation from the fuel gas produced. TEA identified Scenario 2 as the most cost-effective, achieving a Minimum Fuel Selling Price (MFSP) of $\$4.59$ per gallon, competitive with the current national diesel price of $\$4.7$ per gallon. However, comparison with the conventional two-reactor system highlights the need for catalyst performance improvements. Sensitivity analysis emphasized the importance of manufacturing cost, liquid fuel yield, and biogas flow rate. Further analysis determined that the IBGTL process must achieve a diesel mass yield beyond 11.7% to surpass the economic viability of the conventional TriFTS (Tri-reforming followed by Fischer-Tropsch Synthesis) process. If the IBGTL process attains the TriFTS yield of up to 17%, the resulting MFSP could be approximately 31% lower than the current TriFTS MFSP. Furthermore, renewable energy credits and carbon credits can further enhance the economic viability of BGTL processes.

09 BIOMASS FUELS↗
DOE OSTI2026

Improving anaerobic digestion of sewage sludge to renewable natural gas by the Advanced Pretreatment & Anaerobic Digestion technology (APAD): Pilot testing

Conventional anaerobic digestion (AD) of sewage sludge in wastewater treatment facilities suffers from low carbon conversion efficiency (CCE = 40%) and requires costly CO2 removal for injection of the produced CH4 into the natural gas grid. To address these limitations, we developed the Advanced Pretreatment and Anaerobic Digestion (APAD) process. This integrates Advanced Wet Oxidation & Steam Explosion (AWOEx) pretreatment of residual sludge after conventional AD, followed by biogas upgradation using a novel methanogenic strain, Methanothermobacter wolfeii BSEL, converting CO2 with H2 into CH4 or RNG (renewable natural gas). Pilot-scale results demonstrated that AWOEx pretreatment achieved a CCE of 62% for the residual sludge, 68% higher than the conventional AD process. The CH4 production was further increased by 79%. Subsequent biogas upgrading in a trickling bed reactor with H2 further enhanced total methane output by 100% and resulted in a final CO2 concentration of =3%. The integrated APAD process achieved a remarkable overall CCE of 83%, resulting in a 200% increase in RNG output when compared to conventional AD. Techno-economic analysis revealed that AWOEx pretreatment alone reduced sludge treatment costs from $494 to $253 per ton of dry solids. The complete APAD process incurred a higher cost of treatment of $530 per ton, driven by prices for bottled H2. The process did, however, show gains in energy recovery and decarbonization. Renewable H2, which may reduce in price in the near future, can positively improve the economics of biogas upgrading for the APAD process.

Life Cycle Assessment (LCA)↗
DOE OSTI2026

Functionalized benzylamines from commercial kraft lignin

Benzylamines are key intermediates in pharmaceuticals, agrochemicals, and polymers, but their conventional production relies on benzyl chloride - a petroleum-derived compound with high toxicity and energy demands. Lignin, accounting for up to 30% of plant biomass, is the largest renewable source of aromatic carbon on Earth. However, its highly complex and recalcitrant structure poses a major barrier to efficient conversion into high-value chemicals. Here, in this study, we developed a catalytic approach to convert commercial kraft lignin into phenolic benzylamines through selective depolymerization and subsequent functionalization. We systematically evaluated the effects of three alcohol solvents, formic acid (FA), and a ruthenium-on‑carbon (Ru/C) catalyst on monophenol yield and selectivity. Up to 6.5 wt% monophenol yield was achieved using methanol (MeOH), FA, and Ru/C at 300 °C for 2 h. Quantum thermodynamic simulations based on the COSMO-RS model confirmed the superior solvation and reactivity of the MeOH + FA system, rationalizing observed product yield. The purified monophenolic products, primarily guaiacol and alkyl guaiacols, were then converted into functionalized benzylamines with >90% yield via a multicomponent Mannich reaction under mild conditions. Techno economic analysis (TEA) and life cycle assessment (LCA) underscore the importance of improving lignin depolymerization yields and expanding biorefinery scale. Solvent-only configurations outperform other options in both cost and emissions, with the methanol-only case performing the best ($\$$105 /kg and 26 kg CO 2e /kg) at a large-scale facility. This study establishes a scalable, bio-based pathway for producing benzylamines from commercial kraft lignin, advancing lignin valorization and offering a sustainable alternative to produce petrochemical-based benzylamines.

Catalytic reduction↗
DOE OSTI2022

Recent progress in in-situ visualization of electrochemical reactions in electrochemical energy devices

A growing body of evidence indicates that bubble dynamics are crucial performance-limiting factors on electrochemical reactions and energy conversion efficiencies in both half-cell and full cell device levels. This review aims to summarize the recent progress in in-situ visualization characterizations of electrochemical reactions and reactant/product transport in electrochemical energy systems. The latest achievements of various new electrodes, transparent cell designs, and development for simultaneous visualization of reactions at both electrodes and electrolyte/electrode interface are highlighted. The new insights into the influence of bubbles on reaction sites and associated electrochemical performances are discussed. Lastly, some perspectives on potential strategies for mitigating the bubble-induced energy losses are proposed for future research directions and opportunities in water electrolysis and other electrochemical energy systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Effect of heterostructure engineering on electronic structure and transport properties of two-dimensional halide perovskites

Organic-inorganic halide perovskite solar cells have attracted much attention due to their low-cost fabrication, flexibility, and high-power conversion efficiency. More recent efforts show that the reduction from three- to two-dimensions (2D) of organic–inorganic halide perovskites promises an exciting opportunity to tune their electronic properties. Here, we explore the effect of reduced dimensionality and heterostructure engineering on the intrinsic material properties, such as energy stability, bandgap and transport properties of 2D hybrid organic–inorganic halide perovskites using first-principles density functional theory. We show that the energy stability of engineered perovskite heterostructures is significantly enhanced. The heterostructures with improved stability also show excellent transport properties similar to their bulk counterparts. Furthermore, these layered chemistries demonstrate the advantage of a broad range of tunable bandgaps and high-absorption coefficient in the visible spectrum. The proposed 2D heterostructured material holds potential for nano-optoelectronic devices as well as for effective photovoltaics.

36 MATERIALS SCIENCE↗