Supporting the Scientific Base for Competencies Essential to Sandia Missions
The DOE Office of Science (SC) is the single largest supporter of basic research in the physical sciences in the U.S., providing more than 40 percent of total funding in this area. Sandia has active research programs funded by:
Advances environmental and biomedical knowledge that promotes national security through improved energy production, development, and use; international scientific leadership that underpins the nation’s technological advances; and research that improves the quality of life for all Americans.
Supports world-class, high-performance computing and networking infrastructures as well as supporting fundamental research in mathematical and computational sciences to enable researchers in DOE scientific disciplines to analyze and predict complex phenomena for scientific discovery.
ARPA-E is an innovative and collaborative government agency that brings together America’s best and brightest scientists, engineers, and entrepreneurs.
The focus of Sandia’s ARPA-E program is to establish partnerships with universities, industry and other National Labs to create innovative energy solutions for the Nation through both maturation of industry capabilities and commercialization of our technologies.
Address Stationary and Transportation Energy pillars
Leverage differentiating facilities/capabilities and Research Foundations of Sandia Labs
Researchers Joe Oefelein and Guilhem Lacaze (both in Sandia’s Reacting Flow Research Dept.) won the American Institute of Aeronautics and Astronautics’ (AIAA’s) best paper award for their work on scramjet engine simulations. The paper, “A Priori Analysis of Flamelet-Based Modeling for a Dual-Mode Scramjet Combustor,” was a collaboration with Jesse Quinlan and James McDaniel (Univ. of Virginia) and Tomasz Drozda (NASA Langley Research Center).
AIAA is the largest aerospace professional society in the world, serving a diverse range of more than 30,000 individual members from 88 countries and 95 corporate members. AIAA’s mission is to inspire and advance the future of aerospace for the benefit of humanity. Their award was presented by the AIAA High-Speed Air-Breathing Propulsion Technical Committee for accomplishment in the arts, sciences, and technology of air-breathing propulsion systems.
Sandia researchers Joe Oefelein (left) and Guilhem Lacaze, recently recognized for their combustion-simulation work with a best paper award, discuss their work on scramjet engine simulations. (Photo by Loren Stacks)
Their paper presents a detailed analysis of combustion regimes in a scramjet, an engine that operates at super- to hypersonic speed and will be used in the future for military, point-to-point transport, and access-to-space applications. “The results presented in the paper are an excellent example of how collaborative teams across institutions can combine their expertise to provide new knowledge supporting the development of predictive combustion models for these systems,” Oefelein said.
The transition of a scramjet engine from dual-mode operation to scram-mode operation occurs in flight as a vehicle accelerates along its flight trajectory. During this transition, the combustion changes from primarily subsonic to largely supersonic. Understanding and predicting the physics of this transition is important to maintaining robust engine operation. Experimental investigations of dual-mode transition are typically limited by the inability of current hypersonic test facilities to vary the flow Mach number in real time through the transition process.
In their research, they modeled JP-7 fuel combustion chemistry using a 22 species, 18-step chemical reaction mechanism. They compared simulation results to experimentally obtained, time-averaged, wall-pressure measurements to validate their simulation solutions. Their analysis of the flowpath’s dual-mode operation showed regions of predominately nonpremixed, high-Damköhler number*, combustion. Regions of premixed combustion were also present, but associated with only a small fraction of the flow’s total heat-release. Their results also suggest that for scram-mode flowpath operation, the primary injector flames exhibit mixed combustion modes, in which significant heat release was found in regions of both nonpremixed and premixed conditions and at both moderate (Da = 1) and high (Da >>1) Damköhler numbers. Detailed analysis of the premixed combustion data suggest thin and broken reaction zones.
The research team found the effects of compressibility and heat losses have a significant effect on combustion—suggesting that a suitable flamelet manifold’s defining parameters should be pressure and enthalpy. Their analysis of the temperature and pressure at theoretical flamelet boundaries further supported the necessity of including pressure and enthalpy as manifold dimensions and suggested that the standard practice of using a single set of flamelet boundary conditions is an approximation.
The methodology’s critical component, apart from the details of the model itself, is the use of the a priori data in building a suitable flamelet table. After determining the applicability of flamelet models for a given flow field, a priori data regarding the flames must be elicited from a prior simulation or available experimental data. These data plots show the PDFs of static temperature and pressure (f[sub]T and f[sub]P, respectively) for fuel (Z > 0.99) and oxidizer (Z < 0.01) conditions for cases D584A (top) and S800A (bottom). Regions from which the data are sampled are shown above the respective plots, with the leftmost representing the primary injector flames and the rightmost representing the secondary injector flames.
This work fits into the philosophy of Sandia’s Combustion Research Facility where simulations complement experiments and bring key insights to improve real engines. “Because of the extreme velocities, experiments are rare and limited. That’s why we simulate those systems, to better understand how to optimize them,” Lacaze said. “To perform those simulations, we need to use models that accurately represent the flame, and our paper shows which approach is the most relevant and why.”
The study will help define the best simulation techniques needed to optimize future scramjets. Improved numerical accuracy at lower cost should help designers explore the key design attributes required for supersonic engine breakthroughs. The work has also helped establish new funding for Sandia through an award from the Defense Advanced Research Projects Agency (DARPA) involving uncertainty quantification of scramjet combustion.
The theme of the Nanomechanics and Nanometallurgy of Boundaries project at Sandia National Labs is to understand the connection between mechanical deformation and grain boundary instability in nanocrystalline metals. Our prior observations have led to the hypothesis that fatigue-induced abnormal grain growth is a precursor to crack initiation in nanocrystalline metals
[Padilla et al, Metall. Mater. Trans. A, 2011]. The development of this new technique is an instrumental step forward in connecting mechanical performance to rare microstructural events. Capturing the abnormal grain growth process associated with nanocrystalline fatigue was particularly problematic because it had only ever been observed by post-mortem fractography where the final fracture was needed to locate a ‘needle in the haystack’. While we have been developing a parallel effort to observe grain boundary mechanisms during high-cycle fatigue in the TEM, that effort will always be impeded somewhat by the limited interrogation volume of the TEM and hence will require a pre-existing starter notch/crack to localize the failure process.
While the experiments described in this paper were performed as a user at SSRL with a beamline limited to a ~100 μm monochromatic beam, we are currently exploring the extension of this technique to white beam experiments at the ALS or CHESS with either a microbeam or a broad ~1 mm scale beam, respectively. Both new sources also offer much faster area detectors that could greatly improve the techniques temporal ability to capture fatigue-induced (or otherwise thermomechancially induced) grain boundary instability. The technique could also be extended to cryogenic experiments where the kinetics for conventional boundary motion mechanisms are glacial. Finally, it is worth noting that this technique could apply to other materials science studies where there is a strongly bimodal grain size distribution, such as electrical steels (so-called Goss texture) or heterogeneous recrystallization phenomena.
In parallel with these in-situ characterization techniques, we are also exploring various metallurgical schemes to control grain boundary instability. While the current study is focused on a nanocrystalline Ni-based alloy, this technique could also be applied to emerging ‘thermodynamically stabilized’ alloys where grain boundary segregation is thought to eliminate the driving force for boundary motion [Abdeljawad and Foiles, Acta Materialia, 2015]. Such a stabilization scheme may one day offer nanocrystalline metals that are impervious or highly resistant to fatigue crack initation.
Recent experimental and theoretical results suggest that nanocrystalline metals can be thermodynamically stabilized by the free energy gain associated with the segregation of solute atoms to the grain boundary which will reduce grain boundary energy and so the driving force for nanocrystalline coarsening. A detail understanding of this proposed mechanism requires detangling the thermodynamics of the coupled bulk and interfacial regions of the metal. We have developed a novel diffuse-interface model of grain boundary segregation in binary metallic alloys that is capable of accounting for both bulk and interfacial energetics and the interaction of alloying elements with the grain boundary. The model presented here extends prior treatments by independently treating solute-solute interactions within both the bulk grains and the grain boundary regions. This alloys for the simultaneous treatment of both grain boundary segregation and phase separation processes.
Through analytic analysis of 1-D systems, the dependence of grain boundary energy on the alloy segregation energy parameters is examined and the results demonstrate that in order to obtain substantial reduction in the grain boundary energy and so thermodynamic stabilization of nanocrystalline metals that high concentrations of solute atoms is required. These analysis also show that this model can recover classic segregation isotherms such as the McLean isotherm and the Fowler-Guggenheim isotherm. Simulation of 2-D polycrystalline systems demonstrate that substantial retardation of grain growth can be obtained for appropriate alloy and segregation energetics.
In broader terms, this modeling approach provides an avenue to explore gran boundary solute segregation and its competition with phase separation in the understanding and design of hopefully stable nanocrystalline metals.
Future work will extend this model in three critical ways: (1) the influence of solute segregation on the grain boundary mobility, (2) a system with heterogeneous grain boundary properties will be incorporated, (3) the addition of a stress term in the energy functional to account for mechanically-induced instability. These model predictions could help guide alloy development for the purpose of boundary stabilization and aid in the mechanistic interpretation of binary alloy boundary evolution observations.
Pete Devlin, of the Department of Energy’s Fuel Cell Technology Office, cut the ribbon to initiate the Maritime Hydrogen Fuel Cell project to test a hydrogen-fuel-cell-powered generator at Young Brothers Ltd.’s Port of Honolulu facility. Left to right: Mark Glick, Hawaii State Energy Office, Glenn Hong, Young Brothers Ltd., Pete Devlin, John Quinn, US Dept. of Transportation Maritime Administration, and Marianne Walck, Sandia National Laboratories.
At Young Brothers Ltd.’s Port of Honolulu facility, Sandia is leading the Maritime Hydrogen Fuel Cell project to test a hydrogen-fuel-cell-powered generator as an alternative to conventional diesel generators. Last Friday’s project kickoff was attended by US Senator Brian Schatz (D-HI), Young Brothers President Glenn Hong, & Sandia-California VP Marianne Walck. “Today, we take another big step in transforming our nation to a clean energy economy,” said Schatz. “The fuel cell technology being deployed today will one day mean less carbon pollution in our ports and on the high seas. The great work from all the partners involved, especially Young Brothers, is helping lead the way to a cleaner, more energy-efficient future.”
Planning for the Maritime Hydrogen Fuel Cell project began in late 2012 with a study that determined that hydrogen fuel cells could replace diesel generators in providing auxiliary power on board and to ships at berth. The US Department of Energy’s (DOE) Fuel Cell Technologies Office and the US Department of Transportation’s Maritime Administration (MARAD) are funding the six-month deployment of the hydrogen-fuel-cell-powered generator.
“We are pleased to help expand this clean energy technology to new applications,” said Young Brothers, Ltd., President Glenn Hong. Young Brothers is hosting a project led by Sandia National Laboratories to test a hydrogen-fuel-cell-powered generator as an alternative to diesel in powering refrigerated containers. (Photo by David Murphy)
“At the point of use, hydrogen fuel cells produce nothing but water—zero pollutant emissions and no greenhouse gases,” said Joe Pratt, Sandia’s project lead. “This technology could enable major commercial ports and marine vessels to lessen their environmental impacts.”
An analysis by Sandia and DOE showed that due to fluctuating loads in maritime auxiliary power applications, a hydrogen fuel cell, which only supplies power when it is needed, is more energy efficient than a diesel engine.
Hydrogenics Corp. designed and built the hydrogen fuel-cell generator unit, comprised of four 30 kW fuel cells, a hydrogen storage system and power-conversion equipment, all packaged in a 20 ft shipping container. With 75 kg of on-board hydrogen storage, the generator has enough energy to power 10 refrigerated containers for 20 continuous hours of operation.
“Young Brothers will be testing and demonstrating this technology on our on-shore and ocean environments over the next six months,” said Hong. “We are very pleased to have been selected to participate in this project with our many national and international partners in expanding this clean technology into new applications.”
Hickam Air Force Base in Honolulu is supplying the hydrogen to power the fuel cell. The hydrogen is produced by electrolysis, the process of splitting water into hydrogen and oxygen—using electricity supplied by Hickam’s solar-powered electric grid.
The synthesis of well-defined nanoparticle materials has been an area of intense investigation, but size control in nanoparticle syntheses is largely empirical. Here, we introduce a general method for fine size control in the synthesis of nanoparticles by establishing steady state growth conditions through the continuous, controlled addition of precursor, leading to a uniform rate of particle growth. This approach, which we term the “extended LaMer mechanism” allows for reproducibility in particle size from batch to batch as well as the ability to predict nanoparticle size by monitoring
the early stages of growth. We have demonstrated this method by applying it to a challenging synthetic system: magnetite nanoparticles. To facilitate this reaction, we have developed a reproducible method for synthesizing an iron oleate precursor that can be used without purification. We then show how such fine size control affects the performance of magnetite nanoparticles in magnetic hyperthermia.