[Aedo]

Turbines are often touted as more efficient than reciprocating engines... until you try to buy one. Does ayone know if there any turbines that are as efficient as IC engines in the 1-3MW range?

[Googolplex]

I know their are, but I don't know of any that are actually available to the consumer for purchase, or even any that are mass produced at all.

I also would be very interested in such a thing.

[ubercynicmeister]

Are you talking about Steam Turbnines?

Or gas turbines?

Or combined cycle turbines?

Steam ENGINES can be made quickly and easily and cost a whole lot less than turbines (no blade balancing problems) and can be as efficient, undeer the right circumstances.

No doubt someone will point out that steam engines need balancing, as well, yes I know...

For a small steam engine, please visit:

http://www.pritchardpower.com/

[Googolplex]

I assumed he meant gas turbines, since he compared to an IC engine. Thats certainly where my interest lies anyway.

[Aedo]

I assumed he meant gas turbines, since he compared to an IC engine. Thats certainly where my interest lies anyway.

Thanks - you are right in that I meant gas turbines. But if there are combined cycle ones of this size also interested.

[sol]

Adeo,

this will tickle your fancy

if you could use it to maybe recharge a battery and run the car electrically the gas turbine only needs to be on when the battery is x% of charge or you need the extra acceleration.

If they could be run on biodiesel, ethanol, jet or kerosene interchangeably this would give great flexibility in fuels.

But the trick would be to use a gas turbine & regen braking to help the km/L ratio.

[ChumpusRex]

The efficiency of such a small turbine is likely to be a lot worse than a reciprocating engine. Indeed, a reciprocating engine is likely to provide better efficiency at any size. (There is a reason why LNG tankers use diesel engines - they tried NG gas turbines, but the fuel costs were unacceptable).

Caterpillar do a small turbine - one which has been on sale since the 60s - called the Saturn 20 which has a 1 MW electrical output. It may be worth asking around their dealers.

A lot depends, though, on what you want to do with it. A diesel, or modified diesel, has the potential to be a lot more efficient. E.g. Caterpillar's 1MW spark-assisted NG fueled diesels get overall efficiency of about 35-38% compared to 22-24% for their turbine.

I'm not aware than CCGTs are available in the size desired, and even if they were, it's unlikely that their efficiency would exceed that of a reciprocating engine

[Aedo]

Adeo,

this will tickle your fancy

It did! Thanks Sol!

The efficiency of such a small turbine is likely to be a lot worse than a reciprocating engine. Indeed, a reciprocating engine is likely to provide better efficiency at any size.

This is what I have discovered but was hoping to be proved wrong.

Is it only in aero applications that turbines are more efficient than reciprocating engines? Where does the assertion that turbines are efficient come from?

[Dezakin]

Turbines can be more efficient that reciprocating engines, at least for a given size, and can be more reliable... but they have a fault in providing a fairly constant power out. This means that you cant stick one in a car and throttle the gas. At idle you'll be using way too much fuel and during accelleration you wont have enough.

This didnt stop carmakers in the early 60's from capitalizing on the 'jet age' hype and sticking turbines in cars and selling poor performers for novelty value.

A big advantage of turbines is that they'll burn anything, and you can hook up a steam or kalina cycle on the bottoming end for increased efficency, as in the gas turbine combined cycle plants that are all the rage now.

[Caoimhan]

I'm still hoping that the StarRotor turbine will pan out:

StarRotor

[Googolplex]

Turbines can be more efficient that reciprocating engines, at least for a given size, and can be more reliable... but they have a fault in providing a fairly constant power out. This means that you cant stick one in a car and throttle the gas. At idle you'll be using way too much fuel and during accelleration you wont have enough.

And thats what hybrids are for! My interest lies in using one, not to turn the wheels, but just to generate electricity when the batteries get low. Combine that with batteries, electric motors at the drive wheels, and regenerative breaking, and you have the ultimate hybrid car. No huge ICE, no transmission, no drive train, super light and super efficient. Also, no vibrations!

A big advantage of turbines is that they'll burn anything, and you can hook up a steam or kalina cycle on the bottoming end for increased efficency, as in the gas turbine combined cycle plants that are all the rage now.

Meaning a car that can run on gas, diesel, or even a really strong whiskey! Im still at a loss as to why such a car isn't availble yet.

[Dezakin]

Its an interesting idea, but I suspect a novelty item. To run a turbine engine outside of the aircraft environment, you need compressors. To get the amazing efficiency that power plant turbines burning natural gas get, you need a bottoming cycle. This doesnt speak well of a good power to weight ratio.

And really, constant power out diesel engines can allready reach rather amazing efficiencies. I suspect the future of hybrid cars is diesel rather than turbines.

[Aedo]

To get the amazing efficiency that power plant turbines burning natural gas get, you need a bottoming cycle. This doesnt speak well of a good power to weight ratio.

So are such generators available in the 1-3MW range? Power to weight is irrelevant as I need them for a 10MW power station.

[Dezakin]

You can get industrial turbines in the 30% efficiency range between 1 and 10 megawatts sure. For the very efficient combined cycle plants (60%+ efficency) thats typically in the hundreds of megawatts.

I bet you could make smaller efficent combined cycle plants using kalina cycles on the bottoming end rather than the typical steam cycles, but its not done today.

[Aedo]

Dezakin - I thought that was the case and was sure someone here could confirm it! Thanks for your help - looks like reciprocating engines are the only current answer.

[Googolplex]

Its an interesting idea, but I suspect a novelty item.

Id like to point out that a turbine powered car is not new. In fact, there was a production turbine car being sold by Chrystler in the 60s.

All Im saying is do the same thing, except make it more modern and smaller (and therefore more efficient and clean) and this time use it only for electricity generation as part of a true hybrid car.

[Googolplex]

Dezakin - I thought that was the case and was sure someone here could confirm it! Thanks for your help - looks like reciprocating engines are the only current answer.

What makes you say that? The 30% he quoted is much more efficient than a reciprocating engine will be!

[ChumpusRex]

What makes you say that? The 30% he quoted is much more efficient than a reciprocating engine will be!

I don't think that's true.

Medium-sized diesel engines (for power generation, or heavy propulsion) have thermal efficiencies of around 35-40%.

The very largest reciprocating engines for ship propulsion can reach 50%

Reciprocating engines are the engine of choice for propulsion of large tankers - This includes LNG tankers, where supply of NG is not an issue (indeed the NG constantly boils from the tanks and has to be disposed of or reliquified).

The low efficiency of open cycle gas turbines has meant excessive fuel costs for those companies that use turbine powered LNG tankers. Careful accounting has shown that diesel powered propulsion engines and refrigeration plants are far preferable to turbine engines.

I came across some equations that allow a rough approximation for efficiencies of engines of various technologies (can't remember the source off hand - will try and find it)

Reciprocating engines (high compression)
Eff = 40 - 10 * e ^ (-0.0032 * P)

OCGT:
Eff = 35 - 15 * e ^ (-0.0003 * P)

CCGT:
Eff = 50 - 10 * e ^ (-0.00005 * P)

P = rated power (kW)
e = base of natural logarithms

For a 1MW system these equations solve as follows:
RE = 40 - 10 * 0.04 = 39.6%
OCGT = 35 - 15 * 0.74 = 23.9%

[Aedo]

Dezakin - I thought that was the case and was sure someone here could confirm it! Thanks for your help - looks like reciprocating engines are the only current answer.

What makes you say that? The 30% he quoted is much more efficient than a reciprocating engine will be!

ChumpusRex has answered this in detail and I have quoted efficiency figures for new 1.5-2MW reciprocating engines which exceed 40%. I really wanted to find a turbine solution but it just doesn't exist at this time.

[Curmudgicus]

Check out infiniacorp.com. They make stirling engines, which are extremely high efficiency external combustion engines.