High Voltage Electromachinery: The Key to Absurdly High Power-to-Weight Ratios?

Gas turbine engines have a very high power-to-weight ratio, small size for a given power output, and less complexity than piston engines. Most of their other characteristics are negatives in an automotive application, viz. high exhaust temperature, low torque outside their optimum power range, noise, and a large appetite for fuel.

Many of the problems associated with automotive gas turbine power plants have been solved, largely by the Chrysler Corporation. The one remaining intractable is high fuel consumption.

Gas turbine powered locomotives were used by Union Pacific for several years, but went away when the market for their cheap residual fuel improved due to an expanding plastics industry. When they became uneconomic, they were retired from service.

Of course, this shouldn't discourage you from trying to improve other elements of hybrid vehicles. But unless you intend to develop a gas turbine with better fuel efficiency, you should probably investigate a different prime mover.

One option for your prime mover is the Starrotor, developed by a colleague of mine.

It has the thermodynamic efficient you seek, runs at higher shaft speeds than otto or diesel cycle engines, runs at slower shaft speeds than centrifugal or axial brayton cycle turbo machines. It is not quite ready for manufacturing but is getting close.

See www.starrotor.com

Higher speed is only going to serve to give you a higher frequency of whatever voltage you are designed for. The design of rotor and stator windings, excitation methods and levels, etc. will determine your voltage output. You may find yourself limited by design factors of other components between your turbine and the batteries regarding high speed and/or high voltage.

Try seeing what information is available through IEEE or its members.

Hello,

when seeking superhigh power to weight ratios, once beyond the prime mover(s), you might want to look at Hydraulics. You will find some extraordiary power/weight ratios in fluid Power. Naturally, there are some potential negatives, but I suspect that you will need to employ fluid power to accomplish the optimum sizie objectives.

best wishes in your quest. One note: PLEASE advocate accessing OUR oil resources!

I will gladly provide additional information on request. If possible, please state desired output torques, speeds, size and weight objectives. The prime mover statistics would also be helpful.

regards,

John conwillow@aol.com

I was always under the impression that gas turbines offered higher thermal efficiencies than reciprocating power cycles (I think the atkinson is the most efficient)

http://en.wikipedia.org/wiki/Atkinson_cycle

My reasoning was that gas turbines offer much higher compression ratios (pinging/knocking/predetonation is not an issue). I also thought gas turbine engines have less friction than reciprocating engines. They're also much more tolerant to poor quality fuels, and so there are upstream energy gains in the crude refinement process, since gas turbine vehicles could run off low grade (low energy cost) hydrocarbons.

This is all speculation though, and I could be entirely incorrect.

As far as I know, shaft speed is related to frequency in synchronous machines, but it also could facilitate high voltages with less windings because field lines are cut quicker/at higher rates.

the efficiency of gas turbines drops as the shrink in size because of tip clearance losses and non-scalability of viscous effects. The advantage of fuel flexibility is nice though and I think is even more flexible than a diesel.

I believe that some european companies are going to voltages over 12v for cars in order to get higher energy density. It is just like cranking hydraulic pressure from 3000psi to six or 8 thousand PSI. I think what may limit this is safety concerns. Even for DC anything over 40 volts (42 volts?) needs covers and shield for safety reasons. and there would need tobe interlock and such to keep people from frying themselves, or cops and firemen at the scene of a crash, or the tow truck guy, or whatever.

In theory though the idea is sound. power is effort(voltage, pressure, force, torque) times flow (electrical current, fluid volumetric flow, velocity, rotational velocity)

cranking one up allows you to reduce the other and keep power constant.