The wave disc engine, a new implementation of wave rotor technology, was earlier developed by the Michigan State group in collaboration with researchers from the Warsaw Institute of Technology. About the size of a large cooking pot, the novel, hyper-efficient engine could replace current engine/generator technologies for plug-in hybrid electric vehicles.

Researchers from Michigan State University have been awarded $2.5 million from the Department of Energy’s ARPA-E program ( earlier post ) to complete its prototype development of a new gasoline-fueled wave disc engine and electricity generator that promises to be five times more efficient than traditional auto engines in electricity production, 20% lighter, and 30% cheaper to manufacture.

The award will allow a team of MSU engineers and scientists, led by Norbert Müller, an associate professor of mechanical engineering, to begin working toward producing a vehicle-size wave disc engine/generator during the next two years, building on existing modeling, analysis and lab experimentation they have already completed.

Our goal is to enable hyper-efficient hybrid vehicles to meet consumer needs for a 500-mile driving range, lower vehicle prices, full-size utility, improved highway performance and very low operating costs. The WDG also can reduce carbon dioxide emissions by as much as 95 percent in comparison to modern internal combustion vehicle engines. —Norbert Müller

The Wave Disc Engine. The wave disc engine is a new implementation of wave rotor technology (also called Pressure Wave Machines or Pressure Exchangers). Wave rotors are unsteady-flow devices that utilize shock waves to transfer energy directly between a high-energy fluid to a low-energy fluid, thereby increasing both temperature and pressure of the low-energy fluid. Wave rotor technology has shown a significant potential for performance improvement of thermodynamic cycles.

Hyprex pressure wave charger. Source: Swissauto Wenko. Click to enlarge.

Wave rotor technology has been explored since 1906, although its first significant application was in 1940 by Brown Boveri Company (BBC, today ABB) which used it as a high pressure stage for a gas turbine locomotive engine. In 1986, Mazda introduced the Mazda 626 Cappela model, which had a 2-liter diesel engine equipped with a Comprex wave rotor (from BBC) used as a supercharger. Mazda produced 150,000 Comprex diesel cars. Other car manufacturers including Opel, Mercedes, Peugeot and Ferrari used the Comprex. Swissauto Wenko AG of Switzerland produces a modern version of the Comprex—the Hyprex—designed for small gasoline engines.

Earlier wave rotor implementation were mainly axial flow. In axial-flow configurations, noted Müller and co-authors in a 2004 paper, pure scavenging is a challenging task. Although it is possible to achieve a full scavenging process for both through and reverse- flow configurations, the solutions lead to more complex configurations. The wave disc technology, however, uses a radial and circumferential flow.

This can substantially improve the scavenging process by using centrifugal forces...Compared with straight channels, curved channels provide a greater length for the same disc diameter, which can be important to obtain certain wave travel times for tuning. With curved channels also the angle against the radius can be changed freely. This allows modulating of the inflow direction acting accelerating component of the centrifugal force and also to choose the inlet and outlet angle independently.

The latter enables independent matching with the flow direction through the stationary inlet and outlet ports or the use of a freely chosen incidence angle for a self-driving configuration. Furthermore, curved channels may be more effective for self-propelling and work extraction in the case of a wave turbine or work input for additional compression, analogous to the principle of turbomachines. —Piechna et al. (2004)

The earlier MSU investigations of wave rotor and radial wave rotor technology were exploring gas turbine applications in addition to supercharging or refrigeration. In a gas turbine application, the team noted, positioning the combustion process internally in the wave rotor could simplify porting between the turbo-compressor and the wave disc “enormously”. This led to a proposed concept of a Radial Internal Combustion Wave Rotor—the precursor to the wave disc engine.

Early concept of an internal combustion wave disc engine. The fuel supplies (green) are located at the inner inlet port. The mixture in the channel is ignited either by a stationary igniter acting through holes in the channel (yellow) or by rotating electrical igniters activated only in a certain angular position of the mixture-filled channel.



The air-fuel mixture can be radially stratified. Combustion starts in the central part of the channel, where the fuel/air mixture is rich and flame propagates to inner and outer end of the cell. Since heat release increases pressure inside the channel, opening the outer channel end generates an outflow of the exhaust gases. For curved channels, torque is given to the disc during the flow scavenging.



This can be used for self-driven rotation or for external work extraction through a shaft or a generator. The outflow of the burned gases can induce an inflow of air and air-fuel mixture into the channels, refilling and cooling the cell before the cycle starts again.



Source: Piechna, 2004. Click to enlarge.

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