September 6, 2013

Jay Lofstead is Sandia’s fourth R&D 100 winner

A WINNER — Jay Lofstead (1423) is Sandia’s fourth R&D 100 winner this year. His Sandia affiliation was inadvertently not listed in Oak Ridge’s winning entry for the ADIOS code. Jay was one of the initiators of the technology. (Photo by Randy Montoya)

by Neal Singer

Jay Lofstead (1423) is the fourth Sandia winner of an R&D100 award this year. His Sandia affiliation inadvertently was not listed in Oak Ridge’s winning ADIOS code entry. Jay was one of the initiators of that technology.

ADIOS, which stands for Adaptable Input/Output System, a high-performance input-output software that can access data from storage and from data streams. It was originally developed to help run fusion plasma codes, which typically must handle billions of particles in high-fidelity simulations. Since its inception, the code now has been used in supercomputer calculations involving combustion research, earthquake simulations, quantum physics, computational fluid dynamics, climate research, and weather forecasting.

It maintains adaptable, easy-to-use, and scalable I/O plug-ins across a variety of platforms. The software framework is designed to handle the input/output requirements of current and future “big data” applications, where efficiency and portability are a must.

Among its advantages are data staging methods that allow independent applications to run concurrently for memory-to-memory data exchange, thereby streamlining workflows. Potential applications lie in cloud computing and financial services.

R&D 100 awards focus attention on research ideas that have been put into use, in contrast with more typical science awards that honor pure research. Since 1976, Sandia has won 105 R&D 100 awards.

Sandia’s three other winners this year (see Lab News, July 26) are Bruce Burkel, for the Membrane Project Lithography team; Mike Heroux, the Mantevo project; Cliff Ho and Cianan Sims, the Solar Glare Hazard Analysis Tool.


-- Neal Singer

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Low-temperature combustion enables cleaner, more efficient engines

Using new optical diagnostic techniques, Mark Musculus (8362) and his colleagues identified the sources of key pollutants from LTC engines. Understanding how LTC works as a combustion technique may lead to broader use of cleaner diesel engines. (Photo by Dino Vournas)

by Mike Janes

As demand climbs for more fuel-efficient vehicles, knowledge compiled over several years about diesel engines and a new strategy known as “low-temperature combustion” (LTC) might soon lead auto manufacturers and consumers to broader use of cleaner diesel engines in the United States.

The journal Progress in Energy and Combustion Science published a summary of recent research on diesel LTC in a review article titled “Conceptual models for partially premixed low-temperature diesel combustion.” The article, prepared by Mark Musculus, Paul Miles, and Lyle Pickett (all 8362), provides what the authors say is a necessary science base for auto and engine manufacturers to build the next generation of cleaner, more fuel-efficient engines using LTC.

“Diesel engines are generally more efficient than gasoline engines,” says Mark. “When long-haul truck drivers are burning thousands of gallons per year for cross-country freight runs, or when consumers are faced with high fuel prices, a more efficient engine becomes very important.” The increased efficiency also translates into lower carbon dioxide (CO2) emissions, which are a major driver of global climate change.

Though diesel engines are more efficient, they still have serious pollutant emissions problems.

Gasoline-powered engines have become ever cleaner by inserting better and better catalytic converters between the engine and the tailpipe to clean up pollutants created by the engine.

But the same catalytic converter that works so well for gasoline engines will not work for diesel engines. Other more complicated exhaust aftertreatment systems are deployed in modern diesel engines, but engine designers and operators would like to avoid the cost and efficiency penalties imposed by those systems.

“It would be great to find some other way to clean up the diesel engine if we want to enjoy its full efficiency advantages,” explains Mark, “and LTC might just be the solution.”

Low-temperature combustion reduces NOx and smoke

Largely due to landmark work in the 1980s and 1990s at Sandia’s Combustion Research Facility (CRF) in California, researchers already understand how pollutants are created during conventional diesel combustion. Details of how conventional diesel combustion works — research that took advantage of special optical engines and diagnostics with lasers and scientific cameras to probe the combustion processes — were consolidated into a much-referenced conceptual model developed by Sandia’s John Dec in 1997.

The laser-based diagnostics showed that one pollutant, smoky particulate matter, or PM, was formed in regions where fuel concentrations were too high. Another serious pollutant, nitrogen oxides, or NOx, arose from a high-temperature flame inside the engine. NOx emissions are not only toxic, but once released into the atmosphere and exposed to sunlight, they react with other pollutants to create ground-level ozone, or smog.

LTC addresses the NOx emissions by recirculating some of the exhaust gases expelled by a diesel engine back inside the engine, where they absorb the heat from combustion. With this dilution effect, the combustion temperatures are lower so NOx formation is significantly reduced. The other part of the LTC strategy, Musculus said, is to spray in fuel earlier in the engine cycle to give the fuel more time to mix with air before it burns. LTC thereby avoids much of the fuel-rich regions that lead to PM as well as the high temperatures that lead to NOx.

Breakthrough measurement identifies sources of other pollutants

While LTC helps reduce PM and NOx pollution, it is not without its own problems. While NOx and PM are reduced, other pollutants go up, including carbon monoxide (CO) and unburned hydrocarbons (UHC) from the fuel. Both are not only toxic, but also result in a loss of fuel efficiency.

The CRF research team identified the sources of these emissions from LTC engines using new optical diagnostic techniques. In a breakthrough measurement, researchers used two-photon laser-induced fluorescence to map in-cylinder CO, a difficult measurement that had never been achieved inside a diesel engine.

Detecting UHC is also problematic because many different chemical species make up the overall UHC, and their composition evolves during combustion. So, instead of detecting UHC directly, researchers used laser-induced fluorescence of other markers of combustion, such as formaldehyde and hydroxyl, to observe and understand the chemical processes that lead to UHC. The combined measurements showed that the fuel that ended up near the fuel injector was “over-mixed” — there was too much air and not enough fuel, so the fuel couldn’t burn to completion, leading to the CO and UHC in the exhaust.

With this new understanding of UHC and CO emissions, Mark and former Sandia post-doctoral researcher Jacqueline O’Connor looked for a way to increase the fuel concentration in that area. One way, they discovered, is to add post-injections, which are smaller squirts of fuel after the main spray, which add more fuel in just the right area. With the post-injections, the zone of complete combustion extends over a larger region, leading to lower UHC and CO emissions while increasing efficiency by making sure that less fuel is wasted by not even burning it.

Mark and his colleagues, through their latest research paper, hope to communicate the details of how LTC works to the broader engine research community. “This is the kind of scientific research and data that engine designers, who help to guide our research, tell us they need so that they can build the kind of fuel-efficient diesel engines that consumers will want,” he says.

The Sandia work was completed for the US Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE).


-- Mike Janes

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Study could help improve nuclear waste repositories

YIFENG WANG (6222) examines a clay sample from South Dakota as student intern Jessica Kruichak (6222) prepares clay materials for iodide sorption experiments. A team of Sandia researchers is working to understand how fast iodine-129 released from spent nuclear fuel would move through a deep clay-based geological repository. (Photo by Randy Montoya)

by Sue Major Holmes

 Here’s the problem faced by a team of Sandia researchers: figuring out how fast iodine-129 released from spent nuclear fuel would move through a deep clay-based geological repository.

Understanding that process is crucial because countries worldwide are considering underground clay formations for nuclear waste disposal, since clay offers low permeability and high radionuclide retention. Even when a repository isn’t sited in clay, engineered barriers to improve waste isolation often include a compacted buffer of bentonite, a common type of clay.

Iodine-129, a radioactive isotope with a half-life of 15.7 million years, is an important fission product in spent nuclear fuel and a large contributor to the predicted total radiation dose from a deep geological repository. So even a small improvement in the ability of clay to retain iodine-129 can make a difference in total dose predictions.

Some evidence indicates weak interaction between clay and iodide, a negatively charged predominant chemical species of iodine in geologic repositories, says Yifeng Wang (6222), who leads the radionuclide-clay interaction study. Computer models haven’t been able to adequately explain clay’s chemical behavior with iodide, and the mechanism is difficult to study because the faint interaction is easily masked by measurement uncertainties.

 “It seems there’s some kind of previously unrecognized mechanism that accounts for that kind of interaction,” says Yifeng, co-principal investigator for the Laboratory Directed Research and Development project now in its third and final year.

His team concluded the interaction, often disregarded as experimental noise, is real and that there might be engineering ways to improve clay’s ability to retain iodide.

Sandia team focuses on clay structure

The team —Yifeng and former co-principal investigator Andy Miller, who recently left Sandia; lab technician Hernesto Tellez; and year-round interns Jessica Kruichak and Melissa Mills (all 6222) — developed experiments with different clays, focusing on their structural characteristics. Past studies of iodide retention in clay concentrated on bentonite. Yifeng’s team instead studied several different clays, five with the same type of layered structure as bentonite.

Although industries are accustomed to using the plentiful and oft-studied bentonite, the team’s experiments show other clays have higher radionuclide retention capability and might isolate spent fuel waste better. Kaolinite had the best iodide retention of the five clays with layering properties. “So we can say our work can help us select a better clay material or a combination of clay materials,” Yifeng says.

Team members believe they discovered a mechanism for iodide-clay interactions that allows more accurate prediction of iodine-129 movement in a geologic repository. The finding was presented in May to the International High Level Radioactive Waste Management Conference in Albuquerque and was published in the conference proceeding.

The experimental data indicate iodide directly interacts with clay interlayer sites. That raises the question of how negatively charged iodide gets into negatively charged interlayer sites, since like charges repel each other, similar to magnets of the same polarity.

“So that contradicts the conventional concept,” Yifeng says.

The team got clues about what was going on by studying the problem at the nanoscale, 100,000 times smaller than the diameter of a human hair. At that scale, Yifeng says, the property of water changes in a way that enhances the pairing of ions.

Conclusion: Ion pairing explains iodide reaction with clay

Ion pairing explains how iodide reacts with clay and moves into the pores despite the fact both iodide and clays are negatively charged.

The team postulates that iodide pairs with positively charged sodium to create a neutral ion pair. That occurs because of the enhanced ion association capability of water trapped in nanometer-scale clay interlayers, resulting in a pairing that helps iodide move into the interlayer by minimizing electric repulsion, Yifeng says.

Clay is densely compacted when it’s used as a barrier and can swell as it contacts with water. “That’s why people use clay materials and compact it,” Yifeng says. “It’s a good engineered barrier to isolate radionuclides.”

Retention properties increase with compaction, which makes the pores smaller, he says. “That’s another way to increase the effectiveness of clay materials,” he says.

But Sandia’s study also suggests measurements in labs have not been as accurate as they could be. Usually researchers break up samples before they measure the solvency of a specific material. “We show actually the nano-pore confinement makes a big difference,” Yifeng says. “That means what you measure in the lab most of the time is not representative of an actual compacted material. The compacted material may in fact give you better retention.”


-- Sue Major Holmes

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