Feature: The Wave of the Future

An MSU researcher is working on a promising new engine that could reinvent how engines are powered to transform the entire industry.

“My design principle has always been to take a challenge that you have to overcome and turn that challenge into a benefit.”

So explains Norbert Müller, associate professor of mechanical engineering at Michigan State University, as he describes his path toward developing a new engine design that could revolutionize auto fuel efficiency.

His concept for a wave disk engine, using shock wave compression together with internal combustion and turbine propulsion, has recently caught the interest of a broad range of scientific publications and blogs. It also caught the interest of U. S. Secretary of Energy Steven Chu during a VIP tour of the 2011 ARPA-E Energy Innovation Summit at which Müller had been invited to showcase his work.

AN OLD IDEA, REVISITED

Early in his career Müller considered the potential for wave energy in turbomachinery. While developing his doctoral thesis he toyed with the concept of using shock waves to build a compressor. He put that idea on hold, aft er a professor advised him that such a compressor could not work using only shock waves.

“He was an excellent old-school turbomachinery person,” Müller explains. “By trade, I’m also a turbomachinery person. Turbomachinery people typically don’t like shock waves—as they mostly cause problems.”

Problems, Müller later decided, were just opportunities in work clothes.

After completing his PhD in mechanical engineering in 1999 at Technische Universita"t in Dresden, Germany (where he also earned BS and MS degrees), conducting post-doctorate work and establishing the teaching of turbomachinery at Columbia University, Müller joined the MSU College of Engineering faculty in 2001.

He took a second look at shock waves when his first graduate student, Pejman Akbari, reintroduced him to the concept of wave machines. Müller was excited to initiate research using principles of unsteady waves. Fully supported by Müller, Akbari’s doctoral work focused on a preliminary design for wave rotors to improve the performance of a variety of engines and machinery using new thermodynamic cycles. A wave rotor using compression and expansion waves to exchange energy between fluids with different pressures held promise for improving efficiency compared to existing internal combustion and turbine engines.

Müller began considering the potential for shock waves as a means to overcome general limitations in turbomachinery and to achieve very fast localized compression. Fast shock compression can result in greater energy efficiency than that typically utilized in various machines such as aircraft engines, power plant turbines or piston engines, such as those used in automobiles, lawn mowers and chain saws. Müller’s lab began working with pressure-exchange wave rotors capable of enhancing the power of a broad array of turbomachinery.

In the ensuing years, many graduate students have worked with Müller, both learning from and contributing to the design process. Müller recognizes the importance of his students to the work of his lab and encourages their contributions.

Current doctoral student Pablo- Francisco Parraga was drawn to work with Müller through his interest in green energy and engine mechanics.

“I was used to working with fewer resources,” Parraga notes. “Dr. Müller makes sure that everything is there to help you do your job properly. He allows me do what I feel necessary for my research, encouraging independent thinking.”

Müller’s former graduate student Pejman Akbari (who later joined the faculty of Columbia University) continues to visit MSU and works on the device in support of the ongoing research. Müller is also quick to note the contributions of Janusz R. Piechna of the Warsaw University of Technology as the co-inventor of the wave disk engine. Piechna spends as much time working with the MSU lab as his time allows.

PISTONS, SUPERCHARGERS AND WAVE DISKS

In the past, wave rotors have been used in automobiles as pressurewave superchargers for internal combustion (IC) engines. Such supercharged engines were available as early as the 1950s from auto companies such as Opel, Volkswagen and Mazda. The Mazda 626 diesel 2-litre engine continued to be available into the 1990s. By the turn of the century, however, turbochargers had become dirt cheap and wave rotor superchargers fell out of favor as fewer resources were invested in their development.

Müller conceived of a design that incorporated internal combustion (like that of a piston engine) with the extraction of energy as is done in turbomachinery where high-pressure, high-velocity gas turns the turbine blades.

In Müller’s view, IC engines and gas turbine engines each have their advantages and limitations. The confined combustion of the IC engine is more efficient than the steady state, theoretically constant-pressure combustion turbine engine. In the turbine, the combustor remains open to both intake and exhaust, so the flow goes through continuously and there is actually a pressure loss in the combustor.

The IC engine is a pressure gain combustor, providing higher efficiency for the cycle. However, the IC engine is limited by the piston traveling length and the work cycle is truncated. That means not all of the work available from the burnt hot gases is utilized in the engine as the gasses are not completely expanded. In fact, a car equipped with an IC engine typically uses only 15 percent of its fuel for propulsion. The gas turbine allows for complete expansion, but does not achieve a pressure gain in the combustor.

“We combine both the confined combustion of the internal combustion Otto Cycle engine with the complete expansion of the Brayton Cycle in a turbomachinery engine,” Müller explains. “To that, we added shock waves for internal energy transferral. The result is this so-called Humphrey Cycle, where we have the combination of confined Combustion and complete expansion— which leads us to higher efficiencies from the get-go.”

The resulting wave disk engine Can be a more efficient engine. When used in a serial electric hybrid car with regenerative braking, there is a potential that 60 percent of the fuel would actually be used for propulsion. With only one moving part, it would also be much smaller and lighter than currently available engines.

The wave disk engine has a rotor with curved channels that house a mixture of air and fuel as the rotor spins. The mixture can enter through central inlets; as the rotor spins, it blocks their exit through an outlet port. Th e sudden buildup of pressure produced by closing the exit end causes a shock wave to form, compressing the mixture. It is then ignited, the rotor continues spinning, and the hot gases leave at high speed through the outlet port; then the process repeats. The exhaust gas pushes against the curved channels, keeping the rotor spinning and producing torque.

In application, this engine wouldn’t directly power the wheels of an automobile; instead it would drive an electric generator, which in turn charges the battery in a hybrid car or other device.

THE WAVE DISK ADVANTAGE

As Müller sees it, there is much to like about this engine design: “Th e wave disk engine has a very simple geometry, it’s easy to manufacture, lower cost and lighter weight, and on top of this it actually has the potential of higher efficiency.”

The wave disk design eliminates many of the components of a conventional IC engine; there are no valves, pistons or crankshaft . The engine also requires no cooling system, transmission or fluids, meaning that maintenance costs are greatly reduced. The engine is about the size of a large cooking pot. With fewer parts, the wave disk engine would be much less expensive to produce than a traditional internal combustion engine, and it could be made to run on a variety of fuels.

Fuel economy comes from both the improved efficiency of the engine and the reduced weight of the automobile. Müller’s team estimated that a car fitted with the wave disk engine could be up to 20 percent lighter overall. Environmental advantages would be available both from the reduced fuel consumption and up to a 90 percent reduction in emissions in comparison to typical internal combustion engines currently on the road.

FEDERAL FUNDING AND A LARGER STAGE

The shockwave concept has gotten attention from the U.S. Department of Energy (DOE). In 2009, Müller’s team received a $2.5 million federal stimulus grant to build a prototype wave disk engine. It was among 37 energy research projects chosen in the first round of Advanced Research Projects Agency-Energy (ARPA-E) funding by the DOE.

More than 3,600 initial concept papers had been submitted to the DOE’s rigorous review process, which included input from multiple review panels composed of leading U.S. energy science and technology Experts, and ARPA-E’s program managers. The chosen projects were selected for their potential to accelerate innovation in clean energy technologies, increase America’s competitiveness and create jobs.

“We are one of the few universities receiving  first-round funding that got such a project granted without any industry partnership—just one single university,” Müller says. “That was not common in the  first round. It was said that this has been the most innovative project in automotive applications they Have found in a long time."

Miiller was also invited to participate in both the 2010 and 2011 ARPA-E Energy Innovation Summit in Washington, DC. He presented a prototype of his engine at the 2011 ARPA-E Energy Innovation Summit Technology Showcase in late February.

"There were more than 250 exhibitors at the energy summit, all chosen by ARPA-E to be the most significant energy projects in the country to be funded (by DOE) as high-risk/ high-payorfprojects," Miiller notes. "At the ARPA-E Summit, U.S. Secretary of Energy Steven Chu decided to have a special tour before the general opening and he asked to see a showcase of about 10 exhibitors. MSU was chosen to be included in this VIP tour and 1 had the pleasure to talk with Secretary Chu and his advisors about the prospects of this program."

Miiller's connection to ARPA-E has gatnered a fair amount of attention in national science media. His work featured prominently in an article in the February 2011 edition of Popular Science profiling the director of ARPA-E, Arun Majumdar. Since then, Miiller's wave disk engine project has been the subject of popular publications in print such as Scientific American, New Scientist and the New York Times, on TV {CNN, Discovery, PNR), radio (WJR, WKAR), and online {www.physorg. com), Ir is among the nominees for the 2011 Katerva Awards for the very best sustainability initiatives on the planet {www.katerva.org}, A Google search brings up several hundred mentions of Miiller s work.

THE FUTURE

While this research is very promising, it may be a while before you sec a wave disk engine automobile in your garage. A lab bench model is still a long way from a production-ready design. A lot more research is needed to develop a device that will work reliably under a broad variety of field conditions.

"The theory has been tested," Miiller says. "We have tested our model; it fired; it rotates. We have combustion within narrow, high-speed rotating channels. That is the first, most important thing."

Next, Miiller s team will be working on increasing power and efficiency. Having built a small prototype, he works toward a 25-kiIowatt version by the end of this year.

"If we are lucky, and have all or the support that we need, we could think that it is feasible to have a device that goes into a first test application within a year or two," Muller says. "But 1 have to emphasize that that is very optimistic and that is counting on continued support moving forward."

Ultimately, Muller sees a future in which the wave disk engine could be put to many uses. As a power generator, it could be used in any application in which engines are used today. Hie possibilities, it seems, are almost limitless.

"One of the easiest market entries seems to be stationary power generation," Muller notes. "The wave disk engine could be used for back-up power, mobile power or to power small households."

"We haven't seen limits in scaling, yet," he says. "Originally, this concept envisioned a micro scale—manufacturing gas turbine/wave disk engine on a chip to power a laptop battery. Today, for lab convenience, and for educational and existing applications, we are looking at a range between 1- 30 kilowatts power generation because this seems to be the highest demand."

A1- 30 kilowatt generator would be sufficient to supply energy to the battery of hybrid vehicles ranging from motor scooters, to SUVs, to boats and light aircraft. Muller foresees wave disk engines used in everything from electronics to power plants once design challenges resolve.

From where he sits, Norbert Muller sees die wave disk engine as a challenge with endless benefits.

Erancie I odd, '80, is director of marketing/or AlSU's College of Engineering. She and her husband Jay are members of the MSU Presidents Club and live in East Lansing with their two teenage sons.

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