Wave disk engine
A wave disk engine or wave disk generator is a type of pistonless rotary engine being developed at Michigan State University and Warsaw Institute of Technology. The engine has a spinning disk with curved blades. Once fuel and air enter the engine, the rotation of the disk creates shockwaves that compress the mixture. When ignited, the burning mixture expands, pushing against the blades, causing them to spin. The spinning of the disk itself opens and closes intake and exhaust ports. The proposed concept was called a radial internal combustion wave rotor.
Wave rotors utilize shock waves to transfer energy between a high-energy fluid to a low-energy fluid, thereby increasing both temperature and pressure of the low-energy fluid (also called pressure wave machines or pressure exchangers).
As with all heat engines, the efficiency of a wave disk engine is governed by the temperature difference between the hot and cold sides (see Carnot's theorem). Compared to a conventional piston engine (reciprocating engine), a wave disk engine works at higher peak temperature, which theoretically makes it more efficient. The design also works without a cooling system, saving weight. Compared to turbine based systems, the rotational speed and the rotor-blade temperature of the wave disk engine is lower, which creates lower stress on materials, and consequently less demanding requirements for materials, leading to cheaper manufacturing and maintenance costs.
Earlier wave rotor implementations were mainly axial flow, where the scavenging process of returning hot compressed air back into the turbine is complex. The wave-disc engine uses a radial and circumferential flow, using centrifugal forces for scavenging. Curved channels provide greater length for the same disc diameter compared to straight channels, allowing the travel times of the waves to be tuned properly.
The wave-disk engine has the potential for better energy efficiency compared to conventional internal combustion engine designs and can potentially save weight. Possible applications include charging batteries in hybrid vehicles, which could reduce weight by about 1,000 pounds (450 kg). It promises to be up to 60% efficient, 30% lighter, and 30% cheaper to manufacture than an equivalent conventional piston engine, and to reduce emissions by 90%.
Michigan State University and Warsaw Institute of Technology researchers claim to have a prototype wave-disk engine and electricity generator that could replace current backup generator technology of plug-in electric hybrid vehicles. The research team is led by Associate Professor of Mechanical Engineering Norbert Müller and has been given $2.5 million funding from the United States Department of Energy's ARPA-E program. Müller's team hoped to have a vehicle-sized 25 kilowatt (33 hp) wave disc engine/generator ready by the end of 2011. As of January 2013, the project is looking into commercialization of the technology. 
About the current status and mystery about progress to date and the future,
The Wave Disk intake is in the center of the donut shaped disk. The seal would be pulled from the mating surface by centrifugal force. The power transmission from a donut shape is also a problem. To operate efficiently no mechanical torque could act to bind or distort the disk inside the housing. As the drawings made available so far show, the power take off would need to be at the exterior diameter of the disk and some kind of counter load would need to balance the disk inside the housing.— September 2013, newenergyandfuel.com
- Shock wave puts hybrid engines in a spin, Helen Knight, New Scientist, 15 March 2011, Accessed March 2011
- "Radial-flow wave rotro concepts, unconventional designs and applications" (PDF). egr.msu.edu. 2004-11-13. Retrieved 2011-03-20.
- Shockwave-Generating Wave Discs Could Replace Internal Combustion Engines Popular Science Magazine, 03.16.2011, Accessed March 2011
- "Wave Disk Engine". DOE ARPA-E. Retrieved 2011-04-25.
- "Wave disk engines to make hybrid vehicles cheaper, more efficient". ZDnet.com. 2009-11-01. Retrieved 2011-03-20.
- "Michigan State University Receives $2.5M ARPA-E Award to Build Wave Disc Engine/Generator for Series Hybrid Applications". greencarcongress.com. 2009-10-31. Retrieved 2011-03-20.
- "New engine sends shock waves through auto industry". MSNBC. 2011-04-06. Retrieved 2011-04-09.
- "ARPA-E Awardees Selected for NSF Innovation Corps Program". 2013-01-22.
- Numerical investigation of the Wave Disk Micro-Engine concept - International Journal of Gas Turbine, Propulsion and Power Systems December 2008, Volume 2, Number 1
- Shockwave Engine: Wave Disk Engine, ARPA-E site for Michigan State University, U.S. Department of Energy
- Directory:Wave Disk Engine, PESWiki
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- A Review of Wave Rotor Technology and Its Applications Akbari and Nalim, Department of Mechanical Engineering, Purdue School of Engineering and Technology, Indianapolis, IN, USA. Published in Journal of Engineering for Gas Turbines and Power OCTOBER 2006, Vol. 128 / 719. Accessed March 2012