The engine is like a jet engine in that it relies on continous isobaric combustion using compressed air delivered by a turboshaft. The only - though significant - difference is the gerotor mechanism of the compressor and turbine. This brings down the size at which the design is competitive, but you'd still need 10,000 RPM or more to get adequate specific power for a vehicle engine -> noisy.

In this setup, the turbine is continously exposed to high temperatures. In large jet engines, some of the compressed air is forced through the shaft and turbine vanes to create a shroud of relatively cool air such that the combustion can occur at very high temperatures for better thermodynamic efficiency.

Small (radial) turbines cannot be cooled this way due to manufacturing limitations. It's unclear if the inner and outer parts of a gerotor turbine design rated at e.g. 50kW could protected by air shrouds. If not, maximum process temperatures are limited by the turbine material and thermodynamic efficiency will be rather less than advertised above.

The other issue is that the outer part of the turbine gerotor is a hot drum spinning at high RPM. The entails non-trivial air friction and radiation losses.

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The fuel process may be more interesting. A 90% conversion rate for arbitrary biomass would be great. Higher energy density (i.e. longer hydrocarbon chains) are very desireable for increased range and the ability to blend in higher fractions into regular gasoline.

Kinda reminds me of a gang of MGB oil pumps plumbed together.

Barry -

the 100.000 RPM number referred to radial turbines such as are used in turbochargers. The gerotors proposed here would deliver similar power at 1/10 that speed but the components feature larger moments of inertia. Torque flux is moment of inertia (constant) times angular acceleration, i.e. transient response might be no better than a single-stage radial compressor-turbine combo.

On a related note: in a car, torque demand rises with speed, which is coupled to engine RPM via the transmission (incl. serial hybrids). A single-stage Brayton engine also feature a torque curve that rises with RPM. This is a recipe for poor RPM stability, even instability in certain scenarios. What you want is an engine with a negative torque-RPM slope for a given fuel flow. This can be achieved by adding a load turbine, at significant cost and reduced fuel efficiency.

The MixAlco link took too long to download on my slow internet service. However I'd bet the hydrogenation process reduces EROEI despite the high conversion of raw material. There must be a trade-off between the cost of hydrogen and the convenience of fuels that can be used in existing engines.

The StarRotor compressor and expander looks to operate pretty nice, even at lower rpm <=10,000. However, a big problem with this design is not only the noise, but thermal expansion of the housing and inner star rotor. This will result in thermal deformations that could result in wear, damage, and further increase the noise levels. This will also result in sealing losses on the axial rotor sides between the rotor and housing that will result in high pressure losses. Even with this thermal expansion you will still get some air flow that is under pressure. However, the pressure would be unstable and unpredictably degrading with use, resulting in A/F ratio control problems.

I'd still like to know how an inexpensive surface treatment is suppose to prevent pressurized gases from leaking past the "non-contacting" gerotors. Sealing issues were the bane of the Wankel's development and the challenge of balancing friction with losses continues to challenge all engine designers to this day.

I don't care how efficient this motor would be. If a rotar became free at 100,000 rpm, it would slice through several inches of steel like butter. Just ask the air force which has had experience with high speed gyros.

[email protected]

Countless attempts to invert compressor to work as combustion engine invariably failed, Wankel rotary being only one limited exception. This one does not seem to address any old problem of such designs. And 10 000 RPM engine for family sedan?!

P.S. John W.: I am fascinated with Razer too.

Andrey:
"And 10 000 RPM engine for family sedan?!"
With the reliability of a Formula-1 car, 300 miles and.... KABOOM!!
Roger Arnold:
Hell yea, now to find a cheap, high quality source of lime that uses little energy as possible, and is eco-conscious.
Adrian Akau:
Another analogy would be centrifuges used in concentration of substances (liquid, gases) due to different densities /atomic masses. The Iranians have found out spinning those tubes at ~50,000 rpm ain't so easy. Minor imperfections, and metal goes flying everywhere at high subsonic speeds.

My interest in any small engine is to act as a generator which continually recharges a bank of batteries in an electrically-driven vehicle. The batteries are the primary power source for the electric motor, capable of variable output based on demand. Is it possible to hook up a generator that provides some fixed power level to recharge the batteries? The battery bank essentially acts as a capacitor for those times when demand is higher than the gas/electric generator is putting out. If the batteries are fully charged (as during extended-idle traffic jams in a crowded urban environment), the generator is idled or shut down until charging is required again.

If you can wire/control this correctly, then having an engine with poor transient response is no longer a problem, because the motor runs at its peak efficiency all the time, and the transients are handled by the batteries. High power is only required of an automobile when accelerating. Cruise doesn't require much power at all (provided the aerodynamic traits of the vehicle are reasonable), so it wouldn't take much of a generator to meet the RMS power demand.

BTW, I agree the most intriguing aspect of this article is the high-power-density biomass-derived fuel. Let's turn our landfills into an energy source! Obviously they wouldn't provide anywhere near all of our energy demand, but they would be doing more good than just sitting there looking ugly. Any way to turn waste into energy is cool. ;-)

Well my own comment knocked my engine off the #1 spot on yahoo. Well it is still #2 which is real good. No big company wants to develop my engine because there is no money in it for them. People can collect their own biomass and won't have to pay gasoline tax. Ethanol is the big thing, but can you imagine there will have to be an ethanol plant in every county in the country to make enough ethanol. Total biomass is much more efficient, probably 10 times as much. Some people may be concerned that my Biomass Engine would not fire evenly. But the one hot combustion chamber could be designed to even that out. And using fine dust solids is done all the time in other industries. The patent link on my web site does not work due to a change at the patent office. However, the patent office search engine comes up and you can click on patent number and enter my patent 4949688 which is lapsed and free to anybody. My engine is perfectly balanced both in rotation and in intertia. So if you are a machinist or know one, build it and test it. We have to do something to stop the high price of gasoline and diesel. My email is on my web site.

John,

Steam is like any other heat engine. Carnot tells you what the efficiency is. Whether ICE, brayton, rankine, stirling or any other heat engine, the efficiency is based on the cold to hot difference. Fuel cells are not heat engines and go from chemical to electrical directly. They would be more efficient than steam.

Posted by: Cosmo | Apr 28, 2006 1:03:48 PM

The MixAlco link took too long to download on my slow internet service. However I'd bet the hydrogenation process reduces EROEI despite the high conversion of raw material. There must be a trade-off between the cost of hydrogen and the convenience of fuels that can be used in existing engines.

Cosmo, if you get your H2 from gasification of the undigested product, then the EROEI (defined as Energy return as liquid fuel product on energy invested from fossil fuels, thus ignoring any extra electricity produced) is actually INCREASED, because you are putting some of the energy of the undigested product into your liquid fuel product, which would otherwise be simply used to produce electricity, which more than likely would be in excess anyway and you would need to sell it to the grid.