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

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

A comparative density functional study on electrical properties of layered penta-graphene

We present a comparative study of the influence of the number of layers, the biaxial strain in the range of −3% to 3%, and the stacking misalignments on the electronic properties of a new 2D carbon allotrope, penta-graphene (PG), based on hybrid-functional method within the density functional theory (DFT). In comparison with local exchange-correlation approximation in the DFT, the hybrid-functional provides an accurate description on the degree of p{sub z} orbitals localization and bandgap. Importantly, the predicted bandgap of few-layer PG has a weak layer dependence. The bandgap of monolayer PG is 3.27 eV, approximately equal to those of GaN and ZnO; and the bandgap of few-layer PG decreases slowly with the number of layers (N) and converge to 2.57 eV when N ≥ 4. Our calculations using HSE06 functional on few-layer PG reveal that bandgap engineering by stacking misalignment can further tune the bandgap down to 1.37 eV. Importantly, there is no direct-to-indirect bandgap transition in PG by varying strain, layer number, and stacking misalignment. Owing to its tunable, robustly direct, and wide bandgap characteristics, few-layer PG is promising for optoelectronic and photovoltaic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Evolutionary analyses of non-family genes in plants

There are a large number of non-family (NF) genes that do not cluster into families with three or more members per genome. While gene families have been extensively studied, a systematic analysis of NF genes has not been reported. We performed comparative studies on NF genes in 14 plant species. Based on the clustering of protein sequences, we identified ~94,000 NF genes across these species that were divided into five evolutionary groups: Viridiplantae-wide, angiosperm-specific, monocot-specific, dicot-specific, and those that were species-specific. Our analysis revealed that the NF genes resulted largely from less frequent gene duplications and/or a higher rate of gene loss after segmental duplication relative to genes in both low-copy-number families (LF; 3 10 copies per genome) and high-copy-number families (HF; >10 copies). Furthermore, we identified functions enriched in the NF gene set as compared with the HF genes. We found that NF genes were involved in essential biological processes shared by all plant lineages (e.g., photosynthesis and translation), as well as gene regulation and stress responses associated with phylogenetic diversification. In particular, our analysis of an Arabidopsis protein-protein interaction network revealed that hub proteins with the top 10% most connections were over-represented in the NF set relative to the HF set. This research highlights the roles that NF genes may play in evolutionary and functional genomics research.

Ye, Chuyu↗
DOE OSTI2019

Conservation and diversity in the secondary forward photodynamics of red/green cyanobacteriochromes

Cyanobacteriochromes (CBCRs) are photosensitive proteins that are distantly related to the phytochrome family of photoreceptors and, like phytochromes, exhibit photoactivity initiated by the excited-state photoisomerization of a covalently bound bilin chromophore. The canonical red/green photoswitching sub-family is the most studied class of CBCRs studied to date. Recently, a comparative study of the ultrafast (100 fs–10 ns) forward photodynamics of nine red/green photoswitching CBCR domains isolated from Nostoc punctiforme were reported (S. M. Gottlieb, P. W. Kim, C.-W. Chang, S. J. Hanke, R. J. Hayer, N. C. Rockwell, S. S. Martin, J. C. Lagarias and D. S. Larsen, Conservation and Diversity in the Primary Forward Photodynamics of Red/Green Cyanobacteriochromes, Biochemistry, 2015, 54, 1028–1042). We extend this study by characterizing the secondary (10 ns–1 ms) forward photodynamics of eight red/green photoswitching CBCRs from N. punctiforme with broadband time-resolved absorption spectroscopy. We demonstrate that the dynamics of these representative red/green CBCRs can be separated into two coexisting pathways involving a photoactive pathway that is successful in generating the terminal light-adapted 15E P g population and an unsuccessful pathway that stalls after generating a meta-stable Lumi-O f intermediate. The photoactive pathway evolves through a similar mechanism from excitation of the dark-adapted 15Z P r state to generate a far-red absorbing Lumi-R f and then via a succession of blue-shifting photointermediates to ultimately generate the 15E P g state. This suggests a steady deviation from planarity of the bilin chromophore during the dynamics. While, the general mechanism for this evolution is conserved among these CBCBs, the timescales of these dynamics deviate significantly. Only half of the characterized CBCRs exhibit the unproductive pathways due to photoexcitation of dark-adapted 15Z P o sub-population that upon photoexcitation generates a meta-stable Lumi-O f intermediate, which eventually decays back to the 15Z P o subpopulation. 15Z P o is ascribed the horizontal Asp657 configuration that disrupts H-bonding with the chromophore in the dark-adapted state; its presence can be identified via enhanced absorption of high-energy tail of the electronic absorption spectrum.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Comparative ion insertion study into a nanostructured vanadium oxide in aqueous salt solutions

We present a comparative study for the electrochemical insertion of different cations into a nanostructured vanadium oxide material. The oxide is hydrothemally synthesized and electrically characterized by variable temperature measurements. The electrochemical reactions are performed in aqueous chloride solutions of lithium, sodium, potassium, and ammonium, and the electrochemical behavior of various cycles are correlated with visual changes in the vanadium oxide nanosheets as observed by scanning electron microscopy. We note an increase in the specific charge per cycle in the cases of sodium and ammonium ions only, correlated with minimal physical changes to the nanosheets. The differing behavior of the various ions has implications for their use in electrical energy storage applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

In Patients with Localized and Resectable Gastric Cancer, What is the Optimal Extent of Lymph Node Dissection—D1 Versus D2 Versus D3?

Background: Despite advances in the treatment of patients with gastric cancer, the debate over the optimal extent of lymphadenectomy continues. Method: A review of the classification, rationale for, and boundaries of lymphadenectomy is presented. A review of the available literature comparing D1 versus D2 versus D3 lymphadenectomy was performed and included randomized controlled trials, and prospective and retrospective comparative and non-comparative studies. Results: Earlier studies demonstrated increased morbidity with D2 compared with D1 lymphadenectomy, with no significant survival benefit. More recent studies have demonstrated survival benefit of a pancreas and spleen-sparing D2 lymphadenectomy in patients with advanced, node-positive tumors. Para-aortic/D3 dissections contribute to increased morbidity, with no survival benefit. Conclusions: In patients with resectable gastric adenocarcinoma, a D2 lymph node dissection preserving the pancreas and spleen should be considered standard for optimal staging and treatment, provided it is performed by surgeons with sufficient expertise. Extended lymph node dissections beyond D2 should not be routinely performed as it has been shown to have increased morbidity, with no improvement in outcomes. While systemic chemotherapy should be considered standard in patients undergoing D2 lymphadenectomy, the role of adjuvant radiation continues to evolve.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

A critical comparison of ten disposable cup LCAs

Disposable cups can be made from conventional petro-plastics, bioplastics, or paperboard (coated with petro-plastics or bioplastics). This study compared ten life cycle assessment (LCA) studies of disposable cups with the aim to evaluate the robustness of their results. The selected studies have only one impact category in common, namely climate change with global warming potential (GWP) as its category indicator. Quantitative GWP results of the studies were closer examined. GWPs within and across each study show none of the cup materials to be consistently better than the others. Comparison of the absolute GWPs (after correction for the cup volume) also shows no consistent better or worse cup material. An evaluation of the methodological choices and the data sets used in the studies revealed their influence on the GWP. The differences in GWP can be attributed to a multitude of factors, i.e., cup material and weight, production processes, waste processes, allocation options, and data used. These factors basically represent different types of uncertainty. Sensitivity and scenario analyses provided only the influence of one factor at once. A systematic and simultaneous use of sensitivity and scenario analyses could, in a next research, result in more robust outcomes. -- Highlights: • Conflicting results from life cycle assessment (LCA) on disposable cups • GWP results of LCAs did not point to a best or worst cup material. • Differences in GWP results are due to methodological choices and data sets used. • Standardized LCA: transparency of LCA studies, but still different in approaches.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Low-velocity repeated impact behaviors of Polymer Fiber Reinforced Plastics (PFRPs)

Modern fiber-reinforced composites have become ubiquitous across multiple industries due to their excellent weight-to-strength ratio. Typically glass or carbon fibers are widely used. While Glass or Carbon Fiber-Reinforced Plastics (GFPRs or CFPRs) have good stiffness, strength, and fatigue life, they are expensive and difficult to recycle. Researchers are exploring Polymer Fiber-Reinforced Plastics (PFRPs) as an alternative solution. PFRPs utilize polymer fibers and a polymer matrix. A wide range of materials options is available, including low-cost thermoplastics such as polyethylene or polypropylene. These thermoplastics are easy to handle and recyclable without special methods. Manufacturing parts using thermoplastics are well-established as well. However, their mechanical performances have not been extensively studied compared to GFRPs or CFRPs. This study examines the low-velocity impact resistance of PFRPs made of different thermoplastics. The low-velocity impacts are applied through a drop-weight tower. The experiment is divided into two cases: a single perforation impact and low-energy repeated impacts. Energy absorption and the number of impacts to failure are measured. The results are compared to traditional CFRPs which have a thermoset matrix. The PFRPs demonstrate energy absorption capabilities comparable to or greater than those of CFRPs with respect to specimen thickness and density. Additionally, the PFRPs show significantly higher impacts-to-failure than the CFRPs in low-energy repeated impact tests. This is particularly noteworthy considering that the PFRPs are much simpler and more economical to manufacture than CFRPs. To further

Ko, Seunghyun↗
DOE OSTI2021

Controlling MoO 2 and MoO 3 phases in MoO x /CNTs nanocomposites and their application to anode materials for lithium-ion batteries and capacitors

Molybdenum oxides (MoO 2 and MoO 3 ) are attractive anode materials for Li- and Na- ion batteries. Although there have been extensive studies on them individually, systematic and comparative studies are still lacking. Here, we demonstrate a facile and straightforward synthesis method to control the phase and oxidation state in the MoO x /CNTs nanocomposites via hydrothermal reaction followed by heat-treatment. By changing the gas atmosphere during the annealing process, well-dispersed MoO 2 /CNTs and MoO 3 /CNTs nanocomposites are formed without altering their overall morphology. This strategy enables us to investigate the true structure-property correlation of MoO x /CNTs nanocomposites by comparing the structure and electrochemical properties of MoO 2 /CNTs and MoO 3 /CNTs. When tested as anode materials for lithium-ion batteries, both HT-MoO 2&3 /CNTs electrodes show much-improved cycling stability and rate performance compared to the rod-shaped bulk MoO 3 electrode. In situ Mo K-edge x-ray absorption spectroscopy (XAS) has been further employed to compare and elucidate Li + storage mechanisms of both electrodes. When employed to the negative electrode of a high-power lithium-ion capacitor (LIC), the LIC full-cell composed of HT-MoO 3 /CNTs negative and activated carbon positive electrodes demonstrates impressive energy and power densities (~ 90 Wh kg –1 with 2000 W kg –1 ) and excellent cycling stability (96.8 % capacity retention after 300 cycles), revealing the versatility of the MoO x /CNTs electrodes in energy applications.

25 ENERGY STORAGE↗
DOE OSTI2022

Impurity leakage and radiative cooling in the first nitrogen and neon seeding study in the closed DIII-D SAS configuration

A comparative study of nitrogen versus neon has been carried out to analyze the impact of the two radiative species on power dissipation, SOL impurity distribution, divertor and pedestal characteristics. The experimental results show that N remains compressed in the divertor, thereby providing high radiative losses without affecting the pedestal profiles and displacing carbon as dominant radiator. Neon, instead, radiates more upstream than N thus reducing the power flux through the separatrix leading to a reduced ELM frequency and compression in the divertor. A significant amount of neon is measured in the plasma core leading to a steeper density gradient. The different behavior between the two impurities is confirmed by SOLPS-ITER modeling which for the first time at DIII-D includes multiple impurity species and a treatment of full drifts, currents and neutral–neutral collisions. The impurity transport in the SOL is studied in terms of the parallel momentum balance showing that N is mostly retained in the divertor whereas Ne leaks out consistent with its higher ionization potential and longer mean free path. This is also in agreement with the enrichment factor calculations which indicate lower divertor enrichment for neon. The strong ionization source characterizing the SAS divertor causes a reversal of the main ions and impurity flows. The flow reversal together with plasma drifts and the effect of the thermal force contribute significantly in the shift of the impurity stagnation point affecting impurity leakage. This work provides a demonstration of the impurity leakage mechanism in a closed divertor structure and the consequent impact on pedestal. Since carbon is an intrinsic radiator at DIII-D, in this paper we have also demonstrated the different role of carbon in the N vs Ne seeded cases both in the experiments and in the numerical modeling. Here, carbon contributes more when neon seeding is injected compared to when nitrogen is used. Finally, the results highlight the importance of accompanying experimental studies with numerical modeling of plasma flows, drifts and ionization profile to determine the details of the SOL impurity transport as the latter may vary with changes in divertor regime and geometry. In the cases presented here, plasma drifts and flow reversal caused by high level of closure in the slot upper divertor at DIII-D play an important role in the underlined mechanism.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Accuracy of surface registration compared to conventional volumetric registration in patient positioning for head-and-neck radiotherapy: A simulation study using patient data

Purpose: 3D optical surface imaging has been applied to patient positioning in radiation therapy (RT). The optical patient positioning system is advantageous over conventional method using cone-beam computed tomography (CBCT) in that it is radiation free, frameless, and is capable of real-time monitoring. While the conventional radiographic method uses volumetric registration, the optical system uses surface matching for patient alignment. The relative accuracy of these two methods has not yet been sufficiently investigated. This study aims to investigate the theoretical accuracy of the surface registration based on a simulation study using patient data. Methods: This study compares the relative accuracy of surface and volumetric registration in head-and-neck RT. The authors examined 26 patient data sets, each consisting of planning CT data acquired before treatment and patient setup CBCT data acquired at the time of treatment. As input data of surface registration, patient’s skin surfaces were created by contouring patient skin from planning CT and treatment CBCT. Surface registration was performed using the iterative closest points algorithm by point–plane closest, which minimizes the normal distance between source points and target surfaces. Six degrees of freedom (three translations and three rotations) were used in both surface and volumetric registrations and the results were compared. The accuracy of each method was estimated by digital phantom tests. Results: Based on the results of 26 patients, the authors found that the average and maximum root-mean-square translation deviation between the surface and volumetric registrations were 2.7 and 5.2 mm, respectively. The residual error of the surface registration was calculated to have an average of 0.9 mm and a maximum of 1.7 mm. Conclusions: Surface registration may lead to results different from those of the conventional volumetric registration. Only limited accuracy can be achieved for patient positioning with an approach based solely on surface information.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

System benefits of industrial battery storage: A comparison of grid and facility control and dispatch

Customer-owned, distributed battery installations are being incentivized by utilities to increase installed battery capacity. In many of these incentive agreements, the battery owner relinquishes battery control to the utility in exchange for incentive money. The industrial sector has lagged in storage installation when compared to the residential and commercial sectors. This study compares the economic advantages to utilities and industrial facilities in different dispatch control situations. The study presents a novel framework for the optimization of multiple systems using load profiles from the industrial, residential, and commercial sectors. Case studies are presented to illustrate different dispatch scenarios. Further, the simulations showed more fiscal benefit for the industrial facilities to dispatch the battery for electrical demand reduction than utility dispatch. In the case studies, facility dispatch control resulted in an increase of facility savings by a factor of about 8.7 when compared to utility dispatch. Battery size plays a significant factor on the impact of the grid’s generating costs, showing that larger batteries can provide significant benefit even if dispatched by the facility. Future policies concerning industrial battery installations should consider overall economic benefits to utility and facility in the form of rate structures and incentive participation based on battery size.

25 ENERGY STORAGE↗
DOE OSTI2015

A planning comparison of 7 irradiation options allowed in RTOG 1005 for early-stage breast cancer

This study compared the 7 treatment plan options in achieving the dose-volume criteria required by the Radiation Therapy Oncology Group (RTOG) 1005 protocol. Dosimetry plans were generated for 15 representative patients with early-stage breast cancer (ESBC) based on the protocol-required dose-volume criteria for each of the following 7 treatment options: 3D conformal radiotherapy (3DCRT), whole-breast irradiation (WBI) plus 3DCRT lumpectomy boost, 3DCRT WBI plus electron boost, 3DCRT WBI plus intensity-modulated radiation therapy (IMRT) boost, IMRT WBI plus 3DCRT boost, IMRT WBI plus electron boost, IMRT WBI plus IMRT boost, and simultaneous integrated boost (SIB) with IMRT. A variety of dose-volume parameters, including target dose conformity and uniformity and normal tissue sparing, were compared for these plans. For the patients studied, all plans met the required acceptable dose-volume criteria, with most of them meeting the ideal criteria. When averaged over patients, most dose-volume goals for all plan options can be achieved with a positive gap of at least a few tenths of standard deviations. The plans for all 7 options are generally comparable. The dose-volume goals required by the protocol can in general be easily achieved. IMRT WBI provides better whole-breast dose uniformity than 3DCRT WBI does, but it causes no significant difference for the dose conformity. All plan options are comparable for lumpectomy dose uniformity and conformity. Patient anatomy is always an important factor when whole-breast dose uniformity and conformity and lumpectomy dose conformity are considered.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2024

Evaluation of the Impact of Concentration and Extraction Methods on the Targeted Sequencing of Human Viruses from Wastewater

Sequencing human viruses in wastewater is challenging due to their low abundance compared to the total microbial background. This study compared the impact of four virus concentration/extraction methods (Innovaprep, Nanotrap, Promega, and Solids extraction) on probe-capture enrichment for human viruses followed by sequencing. Different concentration/extraction methods yielded distinct virus profiles. Innovaprep ultrafiltration (following solids removal) had the highest sequencing sensitivity and richness, resulting in the successful assembly of several near-complete human virus genomes. However, it was less sensitive in detecting SARS-CoV-2 by digital polymerase chain reaction (dPCR) compared to Promega and Nanotrap. Across all preparation methods, astroviruses and polyomaviruses were the most highly abundant human viruses, and SARS-CoV-2 was rare. These findings suggest that sequencing success can be increased using methods that reduce nontarget nucleic acids in the extract, though the absolute concentration of total extracted nucleic acid, as indicated by Qubit, and targeted viruses, as indicated by dPCR, may not be directly related to targeted sequencing performance. Further, using broadly targeted sequencing panels may capture viral diversity but risks losing signals for specific low-abundance viruses. Overall, this study highlights the importance of aligning wet lab and bioinformatic methods with specific goals when employing probe-capture enrichment for human virus sequencing from wastewater.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

A COMPARISON OF THE CLUSTERING PROPERTIES BETWEEN GALAXIES AND GROUPS OF GALAXIES

In this study, I apply cluster analysis and perform comparative studies of clustering properties between galaxies and groups of galaxies. It is found that the number of objects N{sub max} of the richest system and the maximal length D{sub max} of the largest system for groups in all samples are apparently larger than ones for galaxies, and that galaxies preferentially form isolated, paired, and small systems, while groups preferentially form grouped and clustered systems. These results show that groups are more strongly clustered than galaxies, which is consistent with statistical results of the correlation function.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Influence of microwave driver coupling design on plasma density at Testbench for Ion sources Plasma Studies, a 2.45 GHz Electron Cyclotron Resonance Plasma Reactor

A comparative study of two microwave driver systems (preliminary and optimized) for a 2.45 GHz hydrogen Electron Cyclotron Resonance plasma generator has been conducted. The influence on plasma behavior and parameters of stationary electric field distribution in vacuum, i.e., just before breakdown, along all the microwave excitation system is analyzed. 3D simulations of resonant stationary electric field distributions, 2D simulations of external magnetic field mapping, experimental measurements of incoming and reflected power, and electron temperature and density along the plasma chamber axis have been carried out. By using these tools, an optimized set of plasma chamber and microwave coupler has been designed paying special attention to the optimization of stationary electric field value in the center of the plasma chamber. This system shows a strong stability on plasma behavior allowing a wider range of operational parameters and even sustaining low density plasma formation without external magnetic field. In addition, the optimized system shows the capability to produce values of plasma density four times higher than the preliminary as a consequence of a deeper penetration of the magnetic resonance surface in relative high electric field zone by keeping plasma stability. The increment of the amount of resonance surface embedded in the plasma under high electric field is suggested as a key factor.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Effects of Dopant Metal Variation and Material Synthesis Method on the Material Properties of Mixed Metal Ferrites in Yttria Stabilized Zirconia for Solar Thermochemical Fuel Production

Mixed metal ferrites have shown much promise in two-step solar-thermochemical fuel production. Previous work has typically focused on evaluating a particular metal ferrite produced by a particular synthesis process, which makes comparisons between studies performed by independent researchers difficult. A comparative study was undertaken to explore the effects different synthesis methods have on the performance of a particular material during redox cycling using thermogravimetry. This study revealed that materials made via wet chemistry methods and extended periods of high temperature calcination yield better redox performance. Differences in redox performance between materials made via wet chemistry methods were minimal and these demonstrated much better performance than those synthesized via the solid state method. Subsequently, various metal ferrite samples (NiFe 2 O 4 , MgFe 2 O 4 , CoFe 2 O 4 , and MnFe 2 O 4 ) in yttria stabilized zirconia (8YSZ) were synthesized via coprecipitation and tested to determine the most promising metal ferrite combination. It was determined that 10 wt.% CoFe 2 O 4 in 8YSZ produced the highest and most consistent yields of O 2 and CO. By testing the effects of synthesis methods and dopants in a consistent fashion, those aspects of ferrite preparation which are most significant can be revealed. More importantly, these insights can guide future efforts in developing the next generation of thermochemical fuel production materials.

Leonard, Jeffrey↗
DOE OSTI2018

Radiofrequency and Microwave Ablation Compared to Systemic Chemotherapy and to Partial Hepatectomy in the Treatment of Colorectal Liver Metastases: A Systematic Review and Meta-Analysis

PurposeTo assess safety and outcome of radiofrequency ablation (RFA) and microwave ablation (MWA) as compared to systemic chemotherapy and partial hepatectomy (PH) in the treatment of colorectal liver metastases (CRLM).MethodsMEDLINE, Embase and the Cochrane Library were searched. Randomized trials and comparative observational studies with multivariate analysis and/or matching were included. Guidelines from National Guideline Clearinghouse and Guidelines International Network were assessed using the AGREE II instrument.ResultsThe search revealed 3530 records; 328 were selected for full-text review; 48 were included: 8 systematic reviews, 2 randomized studies, 26 comparative observational studies, 2 guideline-articles and 10 case series; in addition 13 guidelines were evaluated. Literature to assess the effectiveness of ablation was limited. RFA + systemic chemotherapy was superior to chemotherapy alone. PH was superior to RFA alone but not to RFA + PH or to MWA. Compared to PH, RFA showed fewer complications, MWA did not. Outcomes were subject to residual confounding since ablation was only employed for unresectable disease.ConclusionThe results from the EORTC-CLOCC trial, the comparable survival for ablation + PH versus PH alone, the potential to induce long-term disease control and the low complication rate argue in favour of ablation over chemotherapy alone. Further randomized comparisons of ablation to current-day chemotherapy alone should therefore be considered unethical. Hence, the highest achievable level of evidence for unresectable CRLM seems reached. The apparent selection bias from previous studies and the superior safety profile mandate the setup of randomized controlled trials comparing ablation to surgery.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

An equivalent dissipation rate model for capturing history effects in non-premixed flames

The effects of strain rate history on turbulent flames have been studied in the. past decades with 1D counter flow diffusion flame (CFDF) configurations subjected to oscillating strain rates. In this work, these unsteady effects are studied for complex hydrocarbon fuel surrogates at engine relevant conditions with unsteady strain rates experienced by flamelets in a typical spray flame. Tabulated combustion models are based on a steady scalar dissipation rate (SDR) assumption and hence cannot capture these unsteady strain effects; even though they can capture the unsteady chemistry. In this work, 1D CFDF with varying strain rates are simulated using two different modeling approaches: steady SDR assumption and unsteady flamelet model. Comparative studies show that the history effects due to unsteady SDR are directly proportional to the temporal gradient of the SDR. A new equivalent SDR model based on the history of a flamelet is proposed. An averaging procedure is constructed such that the most recent histories are given higher weights. This equivalent SDR is then used with the steady SDR assumption in 1D flamelets. Results show a good agreement between tabulated flamelet solution and the unsteady flamelet results. This equivalent SDR concept is further implemented and compared against 3D spray flames (Engine Combustion Network Spray A). Tabulated models based on steady SDR assumption under-predict autoignition and flame lift-off when compared with an unsteady Representative Interactive Flamelet (RIF) model. However, equivalent SDR model coupled with the tabulated model predicted autoignition and flame lift-off very close to those reported by the RIF model. This model is further validated for a range of injection pressures for Spray A flames. The new modeling framework now enables tabulated models with significantly lower computational cost to account for unsteady history effects. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Kundu, Prithwish↗