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Mechanical Engineering

From left: David Rothamer, Jaal Ghandhi and Scott Sanders

From left: Assistant Professor David Rothamer, Grainger Professor of Sustainable Energy Jaal Ghandhi and Associate Professor Scott Sanders (large image)

A new view of internal combustion

A leader in spark ignition and diesel engine research, the renowned UW-Madison Engine Research Center (ERC) includes seven faculty and almost 60 students whose research ranges from in-cylinder combustion, fluid mechanics and heat transfer to engine aftertreatment systems.

One major area of research in the ERC is optical diagnostics, and three ERC faculty members are using lasers to “view” internal combustion — a traditionally invisible process that is, in many ways, not well understood. Essentially, fuel enters the engine cylinder and burns, producing work and some unintended gaseous emissions. However, researchers don’t know exactly what happens to the fuel during this process since it’s difficult to see inside a cylinder during combustion.

A better understanding of the combustion process could make it possible to design more efficient, low-emission engines. Using advanced laser diagnostics and optical engines — which include parts made from sapphire and fused silica — Grainger Professor of Sustainable Energy Jaal Ghandhi, Associate Professor Scott Sanders and Assistant Professor David Rothamer are obtaining detailed measurements that offer new insights into the combustion process.

One of their approaches is planar laser-sheet imaging, in which they “stretch” a laser beam into a sheet and pass it through a quartz ring that forms part of the engine cylinder. A camera fixed outside the engine images via a mirror and window in the piston as the combustion happens.

They also apply tomographic imaging, a technique widely used in medical imaging. Numerous beams from a custom-built laser (above) form a grid within the engine cylinder, and advanced computers subsequently reconstruct images from the multi-beam data. In addition, the group uses high-speed visualization techniques to view the natural light from the combustion process and understand its macroscopic properties.

Using these approaches, the group investigates engine processes by measuring gas composition, velocity and temperature, as well as liquid fuel and solid soot properties within the engine cylinder. Currently, their focus areas include ultra-high-resolution imaging and developing novel approaches for temperature imaging using ceramic phosphorescent nanoparticles.

The professors say their work benefits from collaboration with the entire ERC. “We can compare our optical measurements to computations by other ERC faculty and increase the fidelity of available computational models,” says Rothamer.

Sanders agrees. “Our optical work, coupled with the capabilities of the entire ERC, makes us a unique package unlike any other American university,” he says.

Multi-university alliance helps STEM students with disabilities

Enabling choice for people with disabilities is at the core of Professor Jay Martin ’s work with the Midwest Alliance. People with disabilities are severely underrepresented in science, technology, engineering and math (STEM) fields due to perceptions that STEM work is not accessible. To address this issue, three universities are working together to brainstorm system changes that will enable students with disabilities to make informed choices about careers in STEM fields.

The collaboration among UW-Madison, University of Illinois at Urbana-Champaign and University of Northern Iowa is known as the Midwest Alliance. Funded by the National Science Foundation, the collaboration began in 2005 and is the fourth project of its kind in the country. Since the alliance formed, it has offered mentoring, internship and placement support, and enrichment camps to students with disabilities in Wisconsin, Iowa and Illinois. Martin originally joined the collaboration to provide a technological perspective. Martin, who is also the director of the UW Center for Rehabilitation Engineering and Assistive Technology, has been the principal investigator for the Midwest Alliance since 2007.

His extensive experience in designing devices for people with disabilities complements the accessible systems and services expertise of the other alliance partners. One recent project he and his students developed is a reading device that uses a Nintendo Wii remote as an infrared camera to project text onto any surface, enabling people in wheelchairs to more easily read.

In addition to devices that improve daily life for people with disabilities, Martin and his students also design recreational technologies to enhance quality of life. Their projects include an advanced lightweight, modular wheelchair with a hybrid power system and airbags that could go as fast as 18 miles per hour and a sit-ski used in the 2009 American Birkebeiner national cross-country ski race.

“The objective of our work at UW-Madison is to enhance the interaction between the person and the technology so that the technology will in fact allow a person more choice than they’d have without it,” Martin says.

‘Laser tweezer’ could assemble the semiconductors of the future

Nanomembranes are thin, tiny building blocks that can be moved and assembled by a laser beam that acts like a tiny construction crane — a process called optical trapping or “laser tweezing.” Assistant Professor Ryan Kershner is developing innovative optical trapping techniques to manipulate large-area planar objects with sub-nanometer precision. These techniques could pave the way for a variety of new devices.

Kershner is experimenting with tiny glass beads that he can move and attach by an infrared beam to a nanomembrane suspended in fluid. The attached bead is easier to manipulate than directly moving the nanomembranes because the silicon membrane scatters the beam of light — a phenomenon that has not yet been explained by optical trapping research.

Kershner is currently working with a silicon nanomembrane developed by Erwin W. Mueller Professor and Bascom Professor of Materials Science & Engineering Max Lagally and his team. Once the bead is attached, Kershner can move the nanomembrane via two techniques: He can fix the bead at the focus of one laser beam and use a second holographically generated beam to move the membrane around it, or he can produce a hologram that makes and controls an array of laser beams that manipulate the membrane in multiple ways.

Kershner’s team uses the array technique to control and manipulate the membranes in three dimensions. To control the laser, Kershner and his students designed an optics system that directs a fiber laser to a spatial light modulator (SLM) and generates a hologram, which controls how the light is propagated in three dimensions. The light is then reflected off the SLM into the microscope where Kershner guides it to the nanomembranes.

Traditionally, laser tweezers are used as a sensitive measurement tool, but Kershner has expanded their use to assembling objects for a variety of potential applications, including nanostructured films, semiconductors, electronics and biological sensors.

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