Purpose of High rpm Low Torque Engines

Discussion in 'Gas Engines' started by baboonslayer, Dec 21, 2010.

  1. RonL
    Joined: Nov 2010
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    RonL Junior Member

    Thanks, I had noticed the intent of gonzo's comment, after my post was made.:eek:
     
  2. mark775

    mark775 Guest

    You are generous.
     
  3. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    Turbines are exceptionally clean burning. The excess air that is present in the cycle provides very complete combustion. Essentially all of the fuel is burned and there are virtually no unburned hydrocarbons or carbon monoxide. High combustion temperatures can result in production of oxides of nitrogen, but modern lean burn combustion systems have made this an non-issue. A good gas turbine will have oxides of nitrogen emissions in single digits (below 10 ppm) and some are as low a 5 ppm.

    Where diesels require after treatment (which is expensive and maintenance intensive) turbines need none of that. While many marine diesel engines are unrestricted in their emissions, a large diesel capable of meeting Tier III standards is going to need a urea system to reduce emissions, and that is expensive. A reciprocating engine running on diesel fuel is a smudge pot compared to a modern turbine.
     
  4. Submarine Tom

    Submarine Tom Previous Member

    Yellow,

    While we're on the topic:

    Why are turbines (exhaust) so stinky?

    -Tom
     
  5. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    Turbines stink at idle if the fuel atomizaton isn't done properly, but most of it is a result of the fuel. Sulphur and other residual elements in the fuel cause a lot of the smell. As you power up, so long as the combustor is efficient they don't have much smell. Certainly less smell than a diesel running on the same fuel. Older engines (like JT-3's and J79's) are pretty dirty, and do emit smoke and stink to high heaven because of unburned hydrocarbons. When fuel got expensive in the mid to late 70's turbines started getting a lot cleaner.

    Depending on the fuel, turbines also have higher emissions on startup. That is because you have to get a combustable mixture in the air stream before it lights off and combustion is poor as the engine is coming up to idle. That results in a good bit of unburned fuel going out the exhaust before it gets up to idle. That is also one reason that turbines fell out of favor with the auto companines. It was difficult to control startup emissions and that is where 90% of the exhaust emissions from a typical engine happen.
     
  6. Submarine Tom

    Submarine Tom Previous Member

    Well that makes a lot of sense as they (Single and Twin turbo-prop Otters) idle on taxi here all the way across the harbour and if you're down wind, pee-yew.

    Thanks Yellow and OP for the hi-jack.

    -Tom
     
  7. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    How did you determine you were "using about 23.4hp" and "using close to 40hp"?
     
  8. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    DCockey, I just worked backwards from FastFreds #71 post. 1.18gph @ 7.13lbs/gal = 8.41lbs which divided by 0.36lbs/hr/hp gave me 23.36hp, i dont know if this is correct,which is why i was asking. I thought this was a good example for me to try the math since we ran light in one direction and under load the other way.
    Steve
     
  9. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    Thanks for the info.
    Do any turbines in any use have to meet emissions and who controls that?
     
  10. Joakim
    Joined: Apr 2004
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    Joakim Senior Member

    The same turbines are used in power plants, which have very strict emissions controls, at least in EU. They have to be measured for particles, NOx, SO2 etc. Modern turbines meet these without additional equipment like electrostatic precipitator (ESP) or flue gas desulfurization (FGD), which many other types of power plant need in order to meet the emissions control.
     

  11. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Reformulated fuels also have a huge influence of how clean the emissions are.
     
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