QUIKAG

My dad sells fractional ownerships in oil/gas wells through different partnerships. Anyway, a rich lady called him yesterday and her and her husband own a start-up out in San Francisco. Guess what they do?

They are building small turbines whose sole purpose will be to power a generator to keep the batteries charged on electric cars. Think about that for a minute. Turbines are horrible on cars when they are attached to a drivetrain, but when the turbines sole purpose is to spin a generator shaft to keep the batteries charged, it's ingenious.

Right now a plug-in hybrid (like the Volt) will have a small gas engine to recharge the batteries when they get low. I've heard of other derivatives that will use diesel engines which is a bit more efficient. But, imagine how efficient a small gas turbine would be that fires up, spins at 10,000rpm for 5 minutes to recharge a battery...

CG

Very interesting. This could work.

cravnpup

Already being done... But yes, not a bad idea..

Elistan

I'd love to see their numbers comparing a gas turbine to a diesel motor. I also wonder what fuel the turbines run on, and what EPA regulations they're subject to.

(Note I'm not bashing anything, I'm honestly curious about the merits of their system.)

Elistan

Oh, and by the way - turbines spin upwards of 100,000 rpm, not 10k.

QUIKAG

I'm an accountant, not an engineer. Anyway, all good points on the type of fuel, EPA, etc. Obviously, it's not market ready, but I would have to imagine that a very small gas turbine (maybe running on high octane av gas) that was specifically designed to spin a generator shaft would be pretty darn efficient compared to piston/diesel engines.

cravnpup, I have little doubt it's used in other commercial applications, but I have not yet heard of it being designed specifically for electric automotive platforms? Any links?

rockville

From what I recall turbines have large efficiency issues. A large gas turbine is more efficient than a diesel engine. The turbine's thermal cycle is also more efficient. The problem is the small gas turbines often have bad leakage issues. It's much harder to make a small, low cost, efficient compressor and turbine as compared to a large aircraft turbine. Little gas turbines are still great for HP/L (and given their 0 displacement they have infinite hp/L ).

A small gas turbine could have packing and other advantages (no cooling system for one) but I don't think it would be more efficient than a small diesel or even than a small gasoline engine.

Elistan

Actually, avgas is for piston driven engines. I did a quick search on model airplane gas turbines - they run on jet fuel/Jet A-1/kerosene/paraffin (pretty much different names for the same thing, actually.) With 5% oil mixed in for lubrication so the EPA might not care widespread use in cars. (Obviously it's okay for model jet hobbiests, but how many people do you know with a jet engine plane in their garage? )

Finding fuel would be interesting - you can't just find Jet A-1 at your local megamart. (Actually, looks like jet fuel and diesel are actually pretty similar... Hmm...)

Looks like a few grand will get you a turbine good for 10 hp or so. That'll certainly be good for a steady charge into a battery bank.

One problem is they like to run hot. 500 degrees appears to be a common minimum operating temperature, so running them for 5 minutes here or there wouldn't be good. You're better off running them for long periods, which would preclude quick 10 minute drives to the grocery store. Oh, wait, I got an idea - run 100% off the batteries until they're 90% drained, then run the turbine for however long it takes to get a full charge.

Railways, by the way, use deisel engines to power the generators in their locomotives. I suspect they've already looked at using turbines. No telling what their reasons are for sticking/going with diesel, but I'd be interesting to know those reasons.

QUIKAG

Interesting comments, Mark. I guess at second glance, it might not be quite as ingenious, but it certainly merits further research on the idea. which, I guess, is why this start-up is in existance and has venture capital funding.

rockville

That does depend on the turbine. The ones I was working with, Allison 501, were more like 15,000 RPM for the core (the second stage compressor/ first stage turbine). The output shaft speed was several thousand RPM.