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Old 10-06-2008, 12:32 AM   #21 (permalink)
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what about a jet engine/turbine in the bed of a pickup? Just last week the guys and work and I were discussing mounting a small jet engine in the bed of my truck for highway purposes... and of course for showing off. Rig it up so when the turbine powers up, the tailgate drops, and BAM! flames and power from the bed

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Old 10-06-2008, 07:27 AM   #22 (permalink)
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Quote:
Originally Posted by kane66 View Post
For all those people representing metro's. Found a Turbine engine mounted to a metro torque converter and auto transmission. 100 hp. and only weighs 68lbs. From what I've read turbine engines are 60% efficient, as apposed to ICE's 30%. It's a lot of money to double your FE but it would be awesome.
Keep in mind that, while the efficiency of gas turbines climbs with practically each passing day, older gas turbines tend to be EXTREMELY inefficient. And I would be willing to bet that what we are looking at here is hardly state of the art.

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I Don't Believe It

Gas turbines only surpass ICE's after they pass the 100,000 HP level - what turbine people call Frame 8s. That little heat loss thing, y'know.

It might fit, and it would probably go like a scalded dog. But like the Hyabusa engine in a Smart it would get lousy MPG.

Did you ever stop and ask why - in a hypercompetitive auto market - nobody ever offered a turbine?
Actually, there is a REALLY good reason why automakers aren't offering a turbine - cost. Not only are there hefty costs when it comes to developing the things. But turbines are also VERY expensive to build. Although they have FAR fewer moving parts than an ICE (and by the way, a turbine actually IS an internal combustion engine!), the parts themselves must be manufactured to VERY exacting tolerances, and out of highly expensive heat-resistant materials. Add to this the fact that a truly efficient turbine would likely be of the more expensive axial flow design (as opposed to cheaper and less efficient centrifugal designs), and you can see that it would be virtually impossible to build a cost effective turbine - at least any time soon. Anyway, the automakers currently have all bets on fuel cells (and NOT turbines) for future automotive propulsion. So I would not expect to see any turbines.

As for the 100000HP threshhold, this is not the barrier that you make it out to be. For instance, Capstone Turbines (a manufacturer of microturbines) currently has a 200HP gas turbine on the market for electrical power generation with an ELECTRICAL efficiency of around 33%, or probably about 36-38% efficiency at the power take off! Their 60HP version has an electrical efficiency of 28%, or about 32-33% at the shaft. True, neither is 50-60% efficient. But both are still well in excess of what is possible with a conventional gasoline engine. In fact, the 200HP unit is well within the range of diesel efficiency. Of course, compared to a diesel, it will burn MUCH cleaner, run MUCH smoother, and require MUCH less maintenance. It would also be able to run on a VERY wide variety of different fuel.

Another interesting microturbine is the Wilson microturbine. It is still somewhat in the research stage. But with its special heat exchanger, mostly axial-flow design, and ceramic turbine blades, this turbine promises an efficiency of 55% at the shaft, or 50% to electricity. Yes, it is not a production unit. But given the efficiencies of the Capstone units (which are available right now), as well as all the advantages that this turbine has over the Capstone turbines (more efficient heat exchanger, axial flow design, ceramic turbine), these figures seem completely believable. Oh, and this is a 400HP turbine. Imagine having THAT under the hood of a Civic! Although it might be on the big side as far as power, it would probably still be more efficient than a conventional ICE - especially if run in hybrid configuration with battery power around town. Now THAT'S what I call 'flower power' right there!

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The big complaint from the consumers was poor fuel economy at idle and lower speeds. Unfortunately, this wasn't something further refinement could alter very much, since high rpm is inherent in gas turbine operation. I suspect this was the main reason that the U.S. Government ended its support for Chrysler's turbine research--the Goverment's goal was to lower fuel consumption in vehicles, not increase it, never mind the fuel flexibility.
Besides the fact that their turbine was probably not NEARLY as efficient as the aforementioned microturbines, the efficiency of Chrysler's design certainly suffered due to the fact that they simply geared the turbine to the wheels of the car through a conventional transmission - the turbine HAD to run under conditions where efficiency would be low. Had they been able to use some sort of hybrid drive at the time (so that battery power could be used during low speed operation), the outcome might have been considerably different.

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Old 10-06-2008, 09:47 PM   #23 (permalink)
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Tell you what, StorminMatt. Why don't you hit these guys websites and post to this forum the heat rates for these little turbines and prove me wrong.

I would be astonished if any of them get under 12,000 BTU/Kwh. A common diesel works in the 7,000 to 9,000 BTU/Kwh range.

Airplane designers like turbines for their reliability. A PT6 will has a MTBF of three pilots' careers. They are easy to maintain.
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Old 10-06-2008, 11:48 PM   #24 (permalink)
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The PT6 is also a design that's about 45 years old. Comparing it to what might be done today seems rather like comparing the O-360 in my Cherokee to my Insight's engine.
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Old 10-07-2008, 04:47 AM   #25 (permalink)
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Quote:
Originally Posted by Big Dave View Post
Tell you what, StorminMatt. Why don't you hit these guys websites and post to this forum the heat rates for these little turbines and prove me wrong.

I would be astonished if any of them get under 12,000 BTU/Kwh. A common diesel works in the 7,000 to 9,000 BTU/Kwh range.

Airplane designers like turbines for their reliability. A PT6 will has a MTBF of three pilots' careers. They are easy to maintain.
Capstone does not provide this figure on their website. But according to Capstone, their 200KW turbine operating at 59F, 14.696psia, and 60% humidity has an exhaust gas temperature of 535F, and rejects heat at a rate of 1 350 000 BTU/hr. Under these conditions, the ELECTRICAL output is 190kW. If you divide 1 350 000 BTU/hr by 190kW, you get a heat rate of 7105 BTU/kWH - certainly not bad at all. Of course, this does not take into account ALL possible heat losses. But, unlike a piston engine, the VAST majority of heat produced by a turbine is lost through the exhaust.

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Originally Posted by jamesqf View Post
The PT6 is also a design that's about 45 years old. Comparing it to what might be done today seems rather like comparing the O-360 in my Cherokee to my Insight's engine.
Good point. Turbines in those days couldn't even achieve 20% efficiency, and were HORRIBLY dirty. High power output, light weight, low maintenance, and sleek, aerodynamic profile were the only things turbines had going for them at that time. But when Barcroft Labs at over 12000ft in California's White Mountains decided to ditch their aging diesel genset a couple of years ago, they chose a pair of Capstone turbines over another diesel genset. This certainy speaks volumes about modern gas turbines.

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Old 10-07-2008, 08:15 AM   #26 (permalink)
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I "do" gas turbines for a living (past 25 years). Mostly with aeroderivatives used in power generation or propulsion. They are very inefficient, spending most of their energy keeping themselves running. They would also run on diesel fuel or natural gas if they were to be put in a car/truck - remember there is no spark keeping these running, just an ignitor or two for initial light-off.

It would just be too cool to have one in a production vehicle though. It would be more of a "proof of concept" than anything else. Emissions would be the problem with these however. I don't think you you could ever get them remotely clean enough these days to even consider putting one in a production vehicle.

Looks to me like there is a lot of cut and paste, "everything I learned about gas turbines I learned in the past few google searches" going on here. Interesting discussion none-the-less.
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Old 10-07-2008, 03:44 PM   #27 (permalink)
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I "do" gas turbines for a living (past 25 years). Mostly with aeroderivatives used in power generation or propulsion. They are very inefficient, spending most of their energy keeping themselves running.
If indeed they are inefficient, then why are so many used in utility power generation? Sure, that's at a different size scale than an auto or light aircraft turbine, but if an IC engine were indeed more efficient than a turbine, then why are these applications not using large "diesel" engines running on natural gas, instead of gas turbines?
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Old 10-07-2008, 03:59 PM   #28 (permalink)
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Hey - I to am in the power industry ( only 12 years though)..

The current base load power plants running simple cycle gas turbines are operating in the 40 - 50% thermal efficiency range ( depending on the age of the equipment and how advanced it is).

the "BEST" domestically produces power plant efficiency (operating in Combined Cycle) is going for 60% thermal efficiency. This is usign Steam as part of the hot gas path cooling loop to increase efficiency - advanced materials and coatings for the hot sections - even making 12 inch long blades out of a single granular crystal of material.

These are not IDEAL but are what the Gas Turbines are operating at.

I do not know the relative efficiency of the Aeroderiviative units. Probably a little worse but not a TON worse. IN the power world - the aerodrivative engines are awsome for Reliability as well as start time ( full load operation in 7 minutes) may not seem like much to Non-power people - but to get the HP rotor spinning up to +10,000 RPM and get 60 MW on the grid from a stopped rotor is fast.

Micro turbines were the RAGE a decade ago - then kinda went away.
From an efficiency point of view - when you get smaller in size - the Tip Losses start becomming a larger % of the equation ( Tip losses cover the ability to completely limit airflow Around the ends of the blades - where no work is extracted - compared to air going through the blades - and doing work).

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Old 10-07-2008, 07:49 PM   #29 (permalink)
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You really expect me to believe that a small-diameter single-stage centrifugal gas turbine gives you 30% efficiency? 30% efficiency equates to a heat rate of 11, 376 BTU/kwh.

If a company is not willing to guarantee a heat rate they are selling snake oil.

Check out this:

http://www.ringpower-systems.com/360...%20Gensets.pdf

0.327 lb/HP-hr equates to 6,540 BTU/HP/hr or 38.9% efficiency To get better thermal efficiency youíd have to go to a LM6000 (54,000 shp) to beat this medium speed engine.

People do stuff for a reason, sport. Gas turbines have their niche but automobiles, trucks and locomotives arenít a part of it. And professionals donít believe company propaganda unless the company is ready to back up what they say.

This Capstone outfit looks shady to me.
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Old 10-07-2008, 08:07 PM   #30 (permalink)
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I had forgotten how poorly conventional turbines scale... It makes me wonder how this guy is coming along? Like a turbine, it is a brayton cycle engine. It looks he's finally getting into developing the second (and most important) half of this engine: the expander.
Star Rotor Engines
The compressor side seems to be pretty efficient.

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