turbine engine + CVT
turbine engine + CVT
(OP)
First post for me here (but have read hundreds) 
This idea has been rolling around in my head for several years now. I know that about 30-40 years ago, Chrysler (and perhaps others?) was experimenting with turbine engines in cars. I remember a Speed Channel (when it was Speedvision) epdisode enterviewing a guy who owned one of these. It idled at 20,000 rpm, redlined at around 40,000, had something like 125 hp and 425 lb-ft. (Depending on which model you look at, hp tended to be 100-140, and torque 375, 425, etc).
The obvious problem (beside gearing it way way down) is the fact that a turbine engine is best suited for constant use under load, rather than on-off acceleration. So you either have to make a big turbine, use a lotta gas the 90% of the time you don't need power, and have the performance, or put in a more efficient turbine, but have no power when you need to pass / pull away from a stop / hill climb.
Seems to me the solutions is turbine + CVT...the infinite gearing would allow you to stay at peak torque RPM nonstop (great mileage), and the super-wide gearing would let you multiply that torque into power when you needed it.
What do you guys think? I wonder why, with all the expensive hybrids being built, none of the manufacturers have tried this recently.
This idea has been rolling around in my head for several years now. I know that about 30-40 years ago, Chrysler (and perhaps others?) was experimenting with turbine engines in cars. I remember a Speed Channel (when it was Speedvision) epdisode enterviewing a guy who owned one of these. It idled at 20,000 rpm, redlined at around 40,000, had something like 125 hp and 425 lb-ft. (Depending on which model you look at, hp tended to be 100-140, and torque 375, 425, etc).
The obvious problem (beside gearing it way way down) is the fact that a turbine engine is best suited for constant use under load, rather than on-off acceleration. So you either have to make a big turbine, use a lotta gas the 90% of the time you don't need power, and have the performance, or put in a more efficient turbine, but have no power when you need to pass / pull away from a stop / hill climb.
Seems to me the solutions is turbine + CVT...the infinite gearing would allow you to stay at peak torque RPM nonstop (great mileage), and the super-wide gearing would let you multiply that torque into power when you needed it.
What do you guys think? I wonder why, with all the expensive hybrids being built, none of the manufacturers have tried this recently.
Northwestern University Engineer, class of 2007
Talk To Other Members
RE: turbine engine + CVT
Even the most efficient point for a turbine is nothing to write home about efficiency-wise - do a search and I bet you can't find any small pure turbine installations that are better than 240 g/kWh.
Typical performance from Capstone - 28% efficiency for a unit that weighs 3/4 ton and produces 80 hp.
Toyota Prius engine would weigh less than half that, is more efficient, and more powerful.
Cheers
Greg Locock
RE: turbine engine + CVT
Their 30 kW turbine with integral generator is 102 kg.
They make no claims about part throttle efficiency that I can find.
Cheers
Greg Locock
RE: turbine engine + CVT
The Chrysler cars, after a couple years of tinkering, went from 13 or 14 mpg up to 18 and 20 mpg. Figure the cars weighed 3600-3800 lbs, since they were big sedans. No CVTs, obviously.
So, if you built a CVT-trannied car, you wouldn't need 425 lb-ft. Let's make the car around 3000 lbs. Maybe 2800 (so 10-20% less). Also, it's not going to be a wall aerodynamically, as the original cars were. Scale down that turbine from 425 to, say, 250-300 lb-ft, use the gearing to make up for low power (dunno enough about turbines to guess how much fuel that'd save...would it be proportional to going from 425 to 250-300 lb-ft piston engine?).
Then take into consideration 30-40 years of turbine engine developments, better fuel, better overall automotive engineering (drivetrain power losses, etc)...performance will be better than the original cars easily. And we've gotta have the mileage from 20 into the mid-30s.
Or was I too liberal with my estimates?
Northwestern University Engineer, class of 2007
RE: turbine engine + CVT
I'll need a 3d map showing sfc vs speed vs torque, or a 2d line showing demand power and optimum sfc for that power.
Frankly, gas turbines only make sense if you can do something useful with the waste heat, and even then, you'd be better off with a diesel if you are primarily interested in power rather than heat, and you need (as I have tried to emphasise) good sfc at low power outputs.
Cheers
Greg Locock
RE: turbine engine + CVT
The mind boggles as to why the engineers never put two and two together, by implementing a high pressure stage at the turbine core. The best solution would be a 3-cylinder 2-stroke engine, but any piston arrangement would work. Imagine if high pressure ratio turbo supplemented systems had had the benefit of 40 years of developement! We wouldn't be arguing about CO2 emissions now.
Rover also invented the Torrotrack type CVT. Why they came up with the Metro is anyones guess...
Mart
RE: turbine engine + CVT
1. The bigger the engine, the better the efficiency. Small engines are much less efficient.
2. Very sluggish power response. Pilots who learn to fly in piston aircraft are amazed when they transition to turbine aircraft and see how much time it takes a turbine engine to respond to a power adjustment -- on the order of ten seconds or so.
3. Very narrow power range. At 80% power a turbine is essentially idleing.
4. Takes a long time to start (five-ten minutes, at least in aircraft) -- unless you have some special Israeli type instant response starting device.
5. To be as efficient as a diesel, you need some type of waste heat energy retrieval system. In power plants a Rankine "bottoming cycle" is typically used to increase efficiency from 35-40% to 50-55%. This would significantly add to complexity of the system.
It is interesting to note that any engine that has a turbocharger is essentially a type of turbine engine.
RE: turbine engine + CVT
Also, there is a turbine powered motorcycle for sale right now, Jay Leno has one. It too is totally impractical but way cool.