Wave Disk Engine - New engine design from MSU and ARPA-E that sounds too good to be true

by | Mar 18, 2011 09:43 AM ET

We are all familiar with the internal combustion engines that we have in our cars. They are remarkably reliable but not very efficient, turning only 15% to 20% of the gasoline they burn into motion. The rest of the energy in the gasoline is lost as waste heat.

Many people have tried many things to improve the efficiency - some with more credibility than others:

Now there is a new engine design getting a lot of press this week because the U.S. government has decided to fund it:

- Wave Disk Engines could be 3.5 times More Fuel Efficient and should have 25 KW prototype by yearend

- Shock wave puts hybrid engines in a spin

- Shockwave-Generating Wave Discs Could Replace Internal Combustion Engines

ARPA-E is providing $2.5 million in funding to develop the engine designed by Dr. Norbert Mueller of Michigan State University and the claim is this:

Michigan State University: Wave Disk Engine

Michigan State University is developing a novel generator for use in hybrid automobile engines. Nearly 85 percent of automobile fuel is wasted. Only 15 percent of fuel is actually used for propulsion. The new generator will make better use of automobile fuel. It is projected that the generator will use 60 percent of fuel for propulsion, thus significantly reducing the percentage of fuel that is wasted. The generator is compact in size (about the size of a cooking pot), yet it will replace nearly 1,000 lbs. of engine, transmission, cooling system, emissions, and fluids. As a result, automobile companies will be able to produce lighter, more fuel-efficient hybrid vehicles. If successful, this project will significantly increase fuel consumption efficiency, reduce automobile emissions by up to 90 percent, substantially decrease U.S. imports of fossil fuels from foreign sources, and create new jobs.

Elsewhere the ARPA-E site claims that the wave disc engine will result in "a 'hyper efficient' serial hybrid vehicle that provides a 3.5 times improvement in fuel consumption efficiency."

Hear Dr. Mueller describe the engine here:

Why does this sound too good to be true? Because there are limits to how efficient a real-world gas turbine engine can be, and the claims here ("the generator will use 60 percent of fuel for propulsion") are beyond those limits. In addition, when looking at the image on this page...

  • The first thing that is uncomfortable is the fact that intake and exhaust happen simultaneously, and generally that opens the possibility for flow-through.
  • Second, there is no obvious compression step, and compression is important to efficiency. The image says, "Shock waves compress air and fuel". The only way for this to happen, since there is neither a mechanical volumetric change evident (as in the compression stroke of a piston engine) nor a ramming compression step (as in a ram jet or pulse jet engine), is for the "shock waves" to create some sort of stratified charge in the closed-off chamber. This would have to be a completely new technique, and there is no description or detail on this technique offered, so we are left to wonder what the technique is doing. Also note that if compression is happening through stratification, there would need to be a vacuum forming elsewhere in the chamber. (While it is possible for pulse jet engines to operate statically (without ram air), their efficiency is generally terrible because of lack of compression. So the wave disk engine, again, would be breaking new ground).
  • Keep in mind all of the problems that Rotary Engines have with sealing. A gas turbine engine (or a ram jet engine) does not need seals because the compression phase acts as a wall that forces all thrust out the open end. There appear to be no seals in the wave disk engine, so what keeps the compressed stratified charge in its chamber?

I would love to be proven wrong on this - the world could really benefit from a 60% efficient engine. However, these three problems lead me to believe that this engine will not be 60% efficient in the real world. We can revisit in a year and see if I am right or wrong.

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