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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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At least 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Assessment of Enthalpy-Based Conditional Moment Closure Models in Predicting Ignition of Lean and Stoichiometric PRF-Air Mixtures with Temperature Inhomogeneity

Accurate prediction of the ignition delay in turbulent flows is important in developing advanced combustion technology for internal combustion engines. Enthalpy-based conditional moment closure (CMC) models are assessed with 2-D direct numerical simulation (DNS) data for ignition of homogeneous PRF-air mixtures with temperature inhomogeneity in homogeneous isotropic turbulence. The sensible-enthalpy-based CMC model is compared with the total-enthalpy-based formulation, with the focus being placed on assessing the capability of the CMC models in predicting ignition processes under different engine conditions. A priori analysis shows that the total-enthalpy-based CMC gives good predictions of the heat release rates in the lean mixtures when the temperature inhomogeneity level is low, but leads to significant overprediction under the stoichiometric condition regardless of the thermal stratification levels. On the other hand, the sensible enthalpy formulation performs well for all conditions considered in this study due to the suppressed conditional temperature fluctuations. A mapping method to model conditional scalar dissipation rates and probability density function of sensible enthalpy is also assessed.

Wang, Wei↗
DOE OSTI2019

Results of the Phenix Dissymmetric Test Benchmark Exercise

In the context of the European H2020 project SESAME, a work package was dedicated to the validation of code coupling for the thermal-hydraulics of pool type reactors. To this end, CEA proposed a benchmark exercise of the so-called dissymmetric test performed at the end of life of the PHENIX reactor. The PHENIX reactor was an experimental reactor operated by CEA in France from 1974 until 2009. The knowledge and data acquired over the lifetime of this reactor are of paramount importance for the development of future sodium-cooled generation IV reactors. At the beginning of this test, the reactor is operated at nominal power (350 MWth) with 3 primary pumps and 4 intermediate heat exchangers. During this test, a pump trip occurs at the secondary side of one of the two loops (one loop provides coolant to two intermediate heat exchangers). The chain reaction is then stopped while the pumps remain operating at nominal speed. Dissymmetric flow patterns are then observed in the cold pool as hot sodium leaves the intermediate heat exchangers that are no longer cooled. The failed secondary pump is then restarted while the rotational speed of the other is reduced. Eventually, a stable homogeneous state is reached. This transient is challenging for both modelers and codes since this exercise tackles an industrial scale reactor featuring complex flows and interactions between different scales. The physical phenomena observed include thermal stratification, flow mixing and buoyancy effects. In order to accurately model these phenomena for a reasonable computational costs, the partners used System Thermal Hydraulics codes coupled with Computational Fluid Dynamics codes and one even included a subchannel code. In this paper, the PHENIX reactor and its behavior during the dissymmetric test are described. Then, a comparison of the different modeling options selected by the partners is offered. Finally, the results are compared to the experimental data and discussed and modelling recommendations are proposed.

code coupling↗
DOE OSTI2014

Method for operating homogeneous charge compression ignition engines using conventional gasoline

A method for the operation of homogeneous charge compression ignition engines (HCCI) using gasoline or similar single-stage ignition fuels. Partial fuel stratification (PFS), intake pressure boosting and controlled BDC-intake temperatures, typically in the range of 95° C. to about 125° C., are used to reduce combustion pressure rise rates (PRR), and therefore, the knocking propensity of homogeneous charge compression ignition engines operating on gasoline or similar fuels.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2019

Hydrocarbons as natural refrigerants for heat pump water heating applications

Growing awareness of the potential environmental impacts of conventional refrigerants (CFCs and HFCs) has led to efforts to identify suitable refrigerants for various heat pump applications with minimum environmental impact. This study is focused on the performance evaluation of pure propane and isobutane as drop-in-replacement for R134a for heat pump water heating (HPWH). A component-based model is used to predict the performance. Key performance parameters such as unified energy factor, first hour rating and thermal stratification in the water tank are investigated. Appropriate experiments are conducted to validate the finding from model. Simulation and experimental findings suggest that both alternative refrigerants could provide comparable system performance to that of the baseline system containing R134a. System refrigerant charge and the condenser discharge temperature are established to investigate the potential of hydrocarbon refrigerants to substitute R134a without significant system modifications.

Nawaz, Kashif↗
DOE OSTI2019

Electric Field Intensity Modulated Scattering as a Thin-Film Depth Probe

Grazing incidence x-ray scattering provides nanostructural information for thin film samples, but single images generally do not provide information on film thickness or the full complex index of refraction. Additionally, for thin films that possess stratification of scatterers vertically within a sample, it can be difficult to determine where those scatterers are positioned. We present an in-situ method to extract film thickness, the index of refraction, and depth information using scattering images taken across a range of incident angles. The underlying theory is presented, and we validate the technique using two sets of polymer thin films. Finally, we discuss how it can be implemented as a general beamline procedure. This technique is applicable to any thin-film material and has potentially far-reaching impact by enabling depth-sensitive information in situ at any grazing incidence-capable beamline.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Direct numerical simulation of an auto-ignitive turbulent flame in a stratified dimethyl-ether (DME)/air mixture

Direct numerical simulations (DNS) of a turbulent premixed flame in an auto-ignitive dimethyl-ether (DME)/air mixture exhibiting two-staged ignition were conducted at elevated pressure and temperature using a statistically stationary planar configuration. Three sets of conditions with an identical turbulence intensity, but different stratification/turbulence length scales and correlations between temperature (T) and equivalence ratio (f) fields were simulated to study the dynamics of turbulent premixed flame propagation at auto-ignitive conditions. The influence of different stratification length scales and T-f correlations on turbulent flame speed was examined by comparing the flame statistics obtained from 2D simulations against laminar 1D solution. A global analysis of the front propagation speed was carried out for determining the effect of turbulent wrinkling and the role of upstream auto-ignition on the overall burning rate.

Desai, Swapnil S.↗
DOE OSTI2017

Shock propagation and mixing through a stratified gas

In this work, we investigate the characteristics of a shock wave propagating through a stratified gas. The objective is to understand the formation and evolution of the system of waves that results from the interaction, as well as the induced mixing. This work is motivated by understanding the shock-induced mixing and system of waves that arise by the interaction of a detonation wave with the fuel/air injection system in a rotating detonation engine. In these devices, one of the key limiting factors in achieving stable detonation and pressure gain is associated with the stratification induced by a non-uniform and incom- plete mixing process. To investigate some of the fundamental aspects of the rapid distortion induced by a detonation wave on the non-uniform flow, we conduct a combined analytical and experimental analysis on a simplified and reduced problem. Experimentally, we consider a single row of injectors of regular spacing that generate a non-reacting turbulent non-uniform flow and are subject to an incident transverse normal shock. Different gasses and shock strengths are used to generate a range of den- sity and velocity ratios that are comparable to what could be experienced through a detonation. Using Schlieren and PLIF imaging, the evolution of mixture fraction throughout the flowfield is investigated. The pres- ence of instabilities and the formation of a system of reflected waves is observed and investigated. A variable property, 1-D, multi-isentropic method of characteristics model is constructed to theoretically investi- gate the shock propagation and interaction with the stratified flow.

Chacon, Fabian↗
DOE OSTI2023

High-fidelity Experiments of Turbulent Buoyant Jets from Simultaneous Particle Image Velocimetry and Laser Induced Fluorescence

Accurate models of turbulent buoyant flows are essential for the design of nuclear reactors thermal hydraulics and passive safety systems. However, available models fail to fully capture the physics of turbulent mixing when buoyancy becomes predominant with respect to momentum. Therefore, high-fidelity experiments of well-controlled fundamental flows are needed to develop and validate more accurate models. We performed experiments of positive and negative turbulent buoyant jets, both in uniform and stratified environments, with the aim of understanding the thermal hydraulics of turbulent mixing with variable density and providing high-fidelity data for the development and validation of turbulence models. Non-intrusive, simultaneous Particle Image Velocimetry and Laser Induced Fluorescence measurements were carried out to acquire instantaneous velocity and concentration fields on a vertical section parallel to the axis of a jet in the self-similar region. The Refractive Index Matching method was applied to measure high-resolution buoyant jets with up to 8.6% density difference. These data are free of the typical errors that characterize optical measurements of buoyancy driven flows (e.g., natural and mixed convection) where the refractive index of the fluid is inhomogeneous throughout the measurement domain. Turbulent statistics and entrainment of buoyant jets in uniform and stratified environments are presented. These data are compared with non-buoyant jets in uniform environment, as a reference to investigate the effects of buoyancy and stratification on turbulent mixing. The results will be used for the assessment of current turbulence models and as basis for the development of a new one that captures turbulent mixing.

42 ENGINEERING↗
DOE OSTI2017

Determining Salinity Recharge Time for Deep Borehole Disposal - 17480

It is generally accepted that the borehole above the disposal zone of a deep borehole disposal must be sealed 'completely' and 'permanently'. By completely it is meant that the seal zone overall must not allow fluids to flow up through it more readily than they could through the surrounding geological barrier. By permanently it is meant that the seal(s) must maintain their function(s) for long enough to satisfy the safety case which could be in excess of 100,000 years. However, designing seals to meet these exacting requirements may be a case of over-engineering because the perturbations in the salinity gradients and density stratification of the groundwater created in and around the borehole during the drilling and operational phases of the borehole would be transient. Darcy flow of groundwater and diffusional flows will re-establish the salinity gradient which is one of the main barriers to the upward flow of fluid through the borehole and surrounding rock, restoring the natural barrier and making the engineered seals redundant. In this paper we address the question of the timescale over which this recharge can be expected to take place. Our methodology involves establishing a mathematical model whose solution gives the time taken for an initial pressure disturbance to reach a steady state and the migration rates of brines resulting from this pressure field. We discuss the model, its assumptions and the solutions, both analytical and numerical. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Molten Salt Sampling Techniques and Analytical Approaches

Recent global interest in pyroprocessing and molten salt reactors has brought salt sampling methods and techniques back to the forefront of nuclear safeguards concerns. Issues with uranium supplies have also encouraged various countries to pursue advanced nuclear fuel cycles. Tracking nuclear material in molten salt has proven to be a challenge and updating molten salt sampling will greatly help in this endeavor. Molten salt is problematic to sample due to salt stratification, lack of homogeneity, solids, and difficulty with hot cell adaptations. Various salt sampling techniques have been used since before the 1960s including surface, spoon/spatula, and bar solidification. Since then, new types of sampling techniques have been developed to improve sampling results. These include rod/dip, pipet, suction, filtered sampling along with devices such as the Valve Core Sampler and the Multi-Level Sampler. These different approaches are being analyzed and improved upon along with developing requirements for an improved salt sampling device. Work continues to develop salt samplers that are more robust, easier to segment, collect at a specific depth, can work with filters, and can collect fines. Sampling parameters are also being narrowed in terms of stirring, settling time, filtration, depth, etc. In the future, we hope to address deficiencies for process control and nuclear material accountancy control by determining the best way to collect samples that minimizes contaminants and is representative. A compilation of salt sampling approaches, analyses techniques, and an evaluation of findings will be presented.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Particle transport in Markov stochastic mixtures with spatial gradients

Markov geometries are a prototype class of stochastic media that are widely used to model complex disordered systems. In a series of recent works, we have shown that spatially homogeneous (but possibly non-isotropic) Poisson tessellations can be conveniently used in order to generate three-dimensional realizations of Markov media and thus characterize the features of particle transport e.g. in fragmented fuel elements following severe nuclear accidents or Rayleigh-Taylor turbulent mixing for inertial confinement fusion. In this paper we show that Poisson tessellations can be extended to take into account the presence of spatial gradients, which commonly occur in real-world applications due to material stratification. For this purpose, we will provide an explicit construction of spatially-non-homogeneous Poisson tessellations, fully characterize their statistical properties, and finally illustrate the behaviour of particle transport in such random media. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

“Max-tech FHR”: What is the maximum technically achievable water delivery capacity from a single 120 V plug?

Electrifying water heating will require affordable, direct drop-in replacements for existing gas water heaters that meet consumer expectations for hot water delivery. For many replacement scenarios, affordability requires a replacement option with like-for-like physical product dimensions, and existing consumer expectations presume a large delivery capacity from a small water heater. This work explores the technical potential for hot water delivery capacity for a heat pump water heater (HPWH) powered from a common 120 V plug. Delivery capability in this work is quantified by two metrics: the First Hour Rating (FHR) defined in the Code of Federal Regulations, and a real-world draw profile that resulted in hot water runout during field studies of 120 V HPWHs. The work focuses on the common “tall-and-slim” gas water heater product category, with external product dimensions of 20 inch diameter and 60 inch height. Using a simulation model in DOE/ORNL Heat Pump Design Model, validated by experimental baseline testing of a commercially available 120 V HPWH model, several measures were evaluated to maximize the delivery capacity of a 120 V HPWH. The 120 V HPWH was constrained by 1) external product dimensions of 20 in diameter and 60 inch height, 2) electrical power of 1.5 kW (85% of the available power from a dedicated 120 V, 15 A circuit), and 3) commercially-available components. The measures implemented included a large compressor, a pumped loop with plate heat exchanger to maximize tank stratification, enlarged heat exchangers, and relatively thin insulation to maximize the water storage volume.

Gluesenkamp, Kyle↗
DOE OSTI2025

Evaluating Chemical Kinetics Predictions for Propane Using 3-D and 0-D Models in a Boosted Spark-Ignited Engine

Propane has been shown to be a promising alternative fuel to reduce emissions while simultaneously achieving high efficiencies in medium- and heavy-duty engines. These high-power density applications require boosted engines which, combined with high compression ratio, can lead to auto-ignition and knock. While three-dimensional (3-D) computational fluid dynamics (CFD) models are often used for resolving the complex fluid flow in engines, these models can become computationally expensive when simulating detailed chemical kinetics. Likewise, zero-dimensional (0-D) models are computationally concise enough for kinetics development, but lack any flow-field information which governs the flame propagation processes in spark ignition (SI) engines. This work presents a comprehensive comparison between 3-D and 0-D closed cycle simulations at knocking conditions in a high compression ratio high stroke-to-bore ratio propane engine. In order to initialize the flow-field for the 3-D closed cycle (intake valve closing, (IVC) to exhaust valve opening, (EVO)) simulation, a motored multi-cycle 3-D model was run using Converge to create a map at IVC, reducing the computational time. The map allowed a non-homogeneous 3-D closed cycle simulation to be satisfactorily validated against experiments, while a homogeneous case using only the turbulence field mapping was also simulated, mimicking 0-D modeling. The 3-D simulations were used to prescribe the initial conditions (e.g., IVC thermodynamics, speciation, burn-rate profile) for a 2-zone 0-D SI engine model in Chemkin Pro for both cases. It was found that 2-zone 0-D modeling underpredicted the knock onset timing, likely due to the lack of thermal stratification in the unburned gas region. Future work will carry multi-zone 0-D modeling to capture the fuel auto-ignition in the unburned region.

Douvry-Rabjeau, Julien [Oakland University, Roches↗
DOE OSTI2025

Validation of Pronghorn for Natural-Circulation Molten Salt Loops

This paper presents the development and validation of a high-fidelity thermal-hydraulic model of a molten salt natural circulation flow loop, designed for integration within a digital twin framework. The study evaluates the performance of Idaho National Laboratory’s Pronghorn against experimental data from Texas A&M University Molten Salt Flow Loop (MSFL) four Hitec-salt test benchmark data. Natural circulation of high-Prandtl-number fluids exhibits complex, counter-intuitive flow patterns that make pointwise thermocouple readings unreliable. Experimental work at TAMU’s MSFL provides benchmark data, including flow visualization at a test-section and centerline steady-state temperature measurements along the loop. Validation includes four single-phase natural circulation test cases with Hitec salt. Key metrics include flow profile agreement and steady-state temperature accuracy. Pronghorn results for two-dimensional single-phase agree qualitatively with the experimental flow profile. This paper illustrates the importance of Computational Fluid Dynamics (CFD) in elucidating the behavior of high-Prandtl-number thermal-hydraulics, along with how misleading centerline temperature measurements can be. Pronghorn reproduces the axial and radial stratification that makes single thermocouple readings unreliable. Future research will focus on reduced-order modeling techniques to enable rapid simulation suitable for real-time digital twin applications. The validated cases provide a basis for developing reduced-order surrogates aimed at real-time digital-twin applications.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Impact of data assimilation on Eulerian versus Lagrangian estimates of upper ocean transport

Using four-dimensional variational analysis, we produce an estimate of the state of a coastalregion in Northern Norway during the late winter and spring in 1984. We use satellite sea surface tempera-ture and in situ observations from a series of intensive field campaigns, and obtain a more realistic distribu-tion of water masses both in the horizontal and the vertical than a pure downscaling approach can achieve.Although the distribution of Eulerian surface current speeds are similar, we find that they are more variableand less dependent on model bathymetry in our reanalysis compared to a hindcast produced using thesame modeling system. Furthermore, Lagrangian drift currents on the other hand are significantly changed, with overallhigher kinetic energy levels in the reanalysis than in the hindcast, particularly in the superinertial frequencyband.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Direct Numerical Simulations of Autoignition in Stratified Dimethyl-ether (DME)/Air Turbulent Mixtures

In our paper, two- and three-dimensional direct numerical simulations (DNS) of autoignition phenomena in stratified dimethyl-ether (DME)/air turbulent mixtures are performed. A reduced DME oxidation mechanism, which was obtained using rigorous mathematical reduction and stiffness removal procedure from a detailed DME mechanism with 55 species, is used in the present DNS. The reduced DME mechanism consists of 30 chemical species. This study investigates the fundamental aspects of turbulence-mixing-autoignition interaction occurring in homogeneous charge compression ignition (HCCI) engine environments. A homogeneous isotropic turbulence spectrum is used to initialize the velocity field in the domain. Moreover, the computational configuration corresponds to a constant volume combustion vessel with inert mass source terms added to the governing equations to mimic the pressure rise due to piston motion, as present in practical engines. DME autoignition is found to be a complex three-staged process; each stage corresponds to a distinct chemical kinetic pathway. The distinct role of turbulence and reaction in generating scalar gradients and hence promoting molecular transport processes are investigated. Then, by applying numerical diagnostic techniques, the different heat release modes present in the igniting mixture are identified. In particular, the contribution of homogeneous autoignition, spontaneous ignition front propagation, and premixed deflagration towards the total heat release are quantified.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2022

Numerical analysis of soot emissions from gasoline-ethanol and gasoline-butanol blends under gasoline compression ignition conditions

In the present work, computational fluid dynamics (CFD) simulations of a single-cylinder gasoline compression ignition (GCI) engine were performed to investigate the impact of blending two biofuels, ethanol and n-butanol, with gasoline on the trade-off between combustion phasing and soot emissions under low load conditions. Here, in order to represent market gasoline (RD5-87), a four-component toluene primary reference fuel (TPRF) + ethanol (ETPRF) surrogate (with 20% ethanol by mole; E20) was formulated using a neural network based octane predictor such that the surrogate had the same ethanol content, Research Octane Number (RON) and Octane Sensitivity (S). In addition, a novel skeletal kinetic mechanism for ETPRF and TPRF + n-butanol (BTPRF) blends, incorporating polycyclic aromatic hydrocarbon (PAH) chemistry, was developed. A three-dimensional (3D) engine CFD formulation employing the skeletal mechanism, adaptive mesh refinement (AMR), finite-rate chemistry approach, and hybrid method of moments (HMOM) was adopted to capture the in-cylinder combustion phenomena and soot emissions. The engine CFD model was validated against RD5-87 experimental data for a broad range of start-of-injection (SOI) timings (-21/-27/-36/-45 crank angle degrees (CAD) after top-dead center (aTDC)), with respect to in-cylinder pressure, heat release rate, combustion phasing, and soot emissions. The closed-cycle simulation results were analyzed to elucidate the non-monotonic trend of soot emissions versus SOI timing: SOI-36 > SOI-45 > SOI-21 > SOI-27. Thereafter, the validated CFD model was employed to simulate the combustion of a gasoline-ethanol blend with 45% (by mole) ethanol (E45) and a gasoline-butanol blend with 45% (by mole) n-butanol (B45) under the same operating conditions to study the effects of fuel composition and SOI timing on combustion phasing and soot emissions. The sooting propensity followed the trend: B45 > E20 > E45 at all SOI timings. Overall, it was observed that the autoignition propensity was primarily related to fuel chemistry. On the other hand, sooting propensity showed strong coupling with both fuel chemistry and physical properties, with greater impact of fuel physical properties at advanced SOI timings.

30 DIRECT ENERGY CONVERSION↗