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Login to post Forums » Off-topic discussion » Turbine question

Aug. 4, 2008 10:09 p.m. Wall-e SuperDork

We are supposed to be getting some new buses to test at work. They are going to be turbine powered hybrids. I had always thoughjt that one of the knocks on turbines was that they were dirty. If that's the case then this seems like a step backwards. The people that told me about it could only use ad-speak, like turbines are the engine of the future and they are compact. They were completely lacking any technical knowledge. There is some significant money to be spent so I'm not doubting it's viability, atleast on paper, but there has to be something I'm missing. Please enlighten me.

For what it's worth, the first one was "unattractive", but the next ones are supposed to be better
Aug. 5, 2008 8:56 a.m. Dr. Hess SuperDork

Modern gas turbines are not dirty. They are very efficient. NOX might be the only issue because of the temps they run at. A turbine hybrid, that's pretty cool. The problem with turbines is always acceleration. They take a while to spool up, unlike a piston motor. With a hybrid, if you are running the generator, you can bring it up to speed and leave it there.
Aug. 5, 2008 9:16 a.m. John Brown SuperDork

How much could that windshied cost? Christ!
Aug. 5, 2008 9:22 a.m. matt_fulghum New Reader

Is the turbine actually going to be driving the wheels, or is it going to be a turboalternator setup? Turboalternators are a fantastic idea because they can run at pretty much constant rpm, which turbines like, but put out a massive amount of power for their weight and are extremely efficient.
Aug. 5, 2008 9:37 a.m. Wall-e SuperDork

The turbine will be charging the batteries. Our hybrids all use electric motors to drive the wheels and the fuel powered engines to run the generator and pumps.

I would guess that we will get different windshields if it goes beyond the testing stage given the number we lose. It would at least be split in half so you could just replace the broken side.
Aug. 5, 2008 9:51 a.m. Jensenman SuperDork

I was under the impression that a natural gas fueled turbine was a very clean burning engine but if run on gasoline or diesel it was kinda dirty, much like a rotary.
Aug. 5, 2008 9:51 a.m. doitover New Reader

That's interesting. The French TGV was originally a turbine hybrid but switched to diesel due to fuel costs.

Trains don't have batteries though so if they aren't using all of their power it's just being lost.
Aug. 5, 2008 10:28 a.m. Dr. Hess SuperDork

Gas turbines are usually "multi-fuel." They'll burn anything you can push into them under pressure. They may prefer JP4, but gasoline, Diesel, kerosene, ground up coal, whatever, just push it in.
Aug. 5, 2008 11:55 a.m. wlkelley3 Reader

What the good Dr. said. Turbine are clean, especially if you run a cleaner fuel. They run on anything that burns, naturally the better, cleaner burn the engine is more effecient. The downfall to turbines are they are designed to run at a contant rpm, the don't accel/decel very well (think turbo lag - same theory). The plus side is they can be extremely compact for displacement. Running as a hybrid would make the turbine more useful. Turbine running at a constant rpm running an alternator/generator to run electric motors/charge batteries should be fairly effiecient. Might need a pretty good muffler as turbine make a lot of noise, especially in the upper frequencies. I've been working around turbines for over 30 years.
Aug. 5, 2008 12:24 p.m. Dr. Hess SuperDork

wlkelley3, question for ya: If I wanted an Organic Rankine Cycle turbine, say of around 5KW power, how could I come up with an efficient one cheap? Gas would likely be R134a because it's relatively cheap. We have a manual 6" lathe, a small 3 axis CNC mill, and a small oven good to about 1500F or so. I'm sure that the blade shape and other design parameters would be different for freon versus steam or other gasses, and I'm thinking multi-stage for efficiency. Really cool would be to gang several junkyard turbo centers together with a fabbed section between them to redirect the freon to the next blade, but I'm sure that the blade shape used in automotive turbos would be terrible for efficiency. I'd really like to get about 75% thermodynamic efficiency from the turbine section.

Just thinkin'.
Aug. 5, 2008 12:35 p.m. Nashco Dork

As pointed out, cleanliness isn't much of an issue with modern turbines and good fuel, but noise and heat are. Heat is the easier of the two to manage, noise will be a big problem IMO. Imagine a street full of busses howling along, talk about noise pollution!

Let us know when you check it out, I'm interested to hear more about it.

Bryce
Aug. 5, 2008 7:50 p.m. MadScientistMatt HalfDork

Dr. Hess wrote:

wlkelley3, question for ya: If I wanted an Organic Rankine Cycle turbine, say of around 5KW power, how could I come up with an efficient one cheap? Gas would likely be R134a because it's relatively cheap. We have a manual 6" lathe, a small 3 axis CNC mill, and a small oven good to about 1500F or so. I'm sure that the blade shape and other design parameters would be different for freon versus steam or other gasses, and I'm thinking multi-stage for efficiency. Really cool would be to gang several junkyard turbo centers together with a fabbed section between them to redirect the freon to the next blade, but I'm sure that the blade shape used in automotive turbos would be terrible for efficiency. I'd really like to get about 75% thermodynamic efficiency from the turbine section.

Just thinkin'.

Looks like you've got quite a cool shop to play with there. Most steam turbines are axial flow rather than the radial-inlet design you see on turbochargers. Axial turbines tend to work better for high volume / low pressure situations, while radial designs are more efficient when you have more pressure and less volume. For a small steam engine, turbo centers might not be that bad an idea. Particularly since they're already balanced to run at 100,000 RPM.
Aug. 5, 2008 9:05 p.m. ignorant SuperDork

MadScientistMatt wrote:

Dr. Hess wrote:

wlkelley3, question for ya: If I wanted an Organic Rankine Cycle turbine, say of around 5KW power, how could I come up with an efficient one cheap? Gas would likely be R134a because it's relatively cheap. We have a manual 6" lathe, a small 3 axis CNC mill, and a small oven good to about 1500F or so. I'm sure that the blade shape and other design parameters would be different for freon versus steam or other gasses, and I'm thinking multi-stage for efficiency. Really cool would be to gang several junkyard turbo centers together with a fabbed section between them to redirect the freon to the next blade, but I'm sure that the blade shape used in automotive turbos would be terrible for efficiency. I'd really like to get about 75% thermodynamic efficiency from the turbine section.

Just thinkin'.

Looks like you've got quite a cool shop to play with there. Most steam turbines are axial flow rather than the radial-inlet design you see on turbochargers. Axial turbines tend to work better for high volume / low pressure situations, while radial designs are more efficient when you have more pressure and less volume. For a small steam engine, turbo centers might not be that bad an idea. Particularly since they're already balanced to run at 100,000 RPM.

How to take off the power without throwing off balance is key... If you want a compressor you are ok. Except for the fact that comp covers are poorly sealed. ask me how I know.
Aug. 6, 2008 6:50 a.m. Dr. Hess SuperDork

Well, the Organic Rankine Cycle uses refridgerant as the gas, which has several advantages over steam. I was thinking of going steam, but getting the water up to the temps needed for a steam turbine with solar energy is a lot more work than getting water up to 150 degrees, then using a heat exchanger for the ORC freon based system. I think the blade shape is all wrong on the automotive turbine, radial v. axial et. al., and single stage v. multi stage for this application, but it might be usable with mods. Getting the power out, I think, from a small turbine like that: Small gear on the end of the turbine shaft, turns larger intermediate gear that turns the generator. Depending on how fast the turbine spins under a load, gear the final output down to about 3K RPM for the HF generator. Just thinkin...
Aug. 6, 2008 12:01 p.m. jeffmx5 New Reader

Grassroots turboshaft engine with construction photos: http://rcdon.com/html/gr-5_turboshaft_engine_project4.html
Aug. 6, 2008 12:11 p.m. Xceler8x Reader

Sounds like they're doing what a backyard engineer was doing a year or so ago. Using a turbine, at a constant speed, to recharge batteries. The good is that the turbine only comes on when needed and runs at it's most efficient RPM. The batteries and electric motor(s) do all the grunt work in the meantime.

The Article I mentioned:

Turbine Hybrid powered Hummer
Aug. 6, 2008 12:12 p.m. wlkelley3 Reader

Had a better reply last night but hit the wrong key and lost it. Had to google it to find out what it is, Wiki ftw. Neat technology but couldn't find one in the size your looking at, most seem to be for backup power for a building. I do agree, don't think the blade shape in turbos would be effecient enough. Also as you stated automotive turbos are single stage and multi-stage would be more effecient for this use. Can't think of anything grassroots that is multi-stage, though. You would be on your own for that. I think your right about the freon since it takes less heat to convert it to a gas than water. An inexpensive Organic Rankine Cycle Turbine the size to operate a house would be nice for backup power, or even main power at something like a cabin on the lake or mountains. I did find a website that makes these turbine (the huge ones - like 30KW & up) also make solar panels that works similiar and can be hooked in series for larger output, have the link at home not here at work.
Aug. 6, 2008 1:24 p.m. Dr. Hess SuperDork

My vision: A 5-ish KW ORC system fed by an inexpensive roof top based solar collector with 2/3rds H2O, 1/3rd Toyota Red antifreeze and a bottle of water wetter. Small pump. One rooftop, say, 3M x 10M, is 30KW of solar energy for 12 hours, or 360KWH. We only need about 5ish output, so efficiency doesn't have to be that great, but the more the better. Water goes through a heat exhanger, heats freon, freon spins 5-ish KW turbine that spins HF generator or two. Add a little here and there for losses to heat, pumping, etc. 5KW output runs the house during the day, charges Ultra Capacitors with excess. Ultra Capacitors run the house at night and also charge up the electric Truck.

Costs: The solar collector is just copper pipe, some wood, black paint, plexiglass and a small pump. Cheap and easily available at Home Depot. Freon: Not that much, wally world. Heat exchanger: Two copper pipes from Home Depot, using the counter current multiplier effect like God did when he invented the kidney. Turbine: Probably going to have to build it from scratch. The first multistage steam turbine ever made was 20HP and made like 130 years ago. We should have that level of thechnology now in my shop and my friend's garage (he has the mill and oven). Better tolerances and better materials today also. The key may be to sand cast the turbine blades and the inter-stage flow reversers from beer cans. Gotta think about it. Generators are at HF at a few hundred for like 3KW PTO units. If we could scale up production, I bet the whole thing could be built for $2K, not including the ultra capacitors, which are not comercially available today. For today, one could replace the UC's with a chemical battery and have lower overall efficiency on the stored portion.

That home built turbine was interesting. I don't know what he made his blades out of or how fast he plans on spinning them, but he has an interesting project going.
Aug. 6, 2008 2:26 p.m. amaff Reader

The video on the last page of his build site had him up near 15,000 RPMs. The 'turbine' was a hybrid T3/T4 turbo.
Aug. 6, 2008 10:16 p.m. wlkelley3 Reader

solar turbine and wasteheat turbineHere's the link's i mentioned.

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