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What are examples of high efficency engines?

  1. Aug 28, 2014 #1
    im looking for engines that are known for being extremely high effiency.

    im not just talking about high efficency consumer engines, but highest records, etc

    also, consumer level is nice as well, but please tell me that they are consumer level if you do list them.

    please list electric engines, nuclear(if there is such), or what ever else, except rockest. thanks:)
  2. jcsd
  3. Aug 28, 2014 #2


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    Staff: Mentor

    What have you found in your reading so far?
  4. Aug 28, 2014 #3


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    Staff: Mentor

    The question is very vague, so it is difficult to answer in its current form. Could you be more specific about the types, sizes, uses, etc you are interested in and for what purpose?
  5. Sep 10, 2014 #4
    engines like jet engines.

    ok, for example, a electric motor powering a propeller isnt that efficient. the motor itself my have some efficency, then there is the propeller, i am looking at the net efficiency of power put in vs total thrust. (dont put aircraft, or other veihcle or anything into account, just the eingine)

    so, there is motor, then there is jet engines, i am looking for numerical value in percentage, even though they vary quiet vastly, please give me ones that are common and ones that are peek efficient. if you know of any other engine, especially high efficiency ones.
  6. Sep 10, 2014 #5


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    That, still far too vague and it sounds like far too big of a task for you to reasonably expect it to be done for you. Worse, it doesn't appear that you really know what you want or how to do or express it (your example makes little sense).

    You are going to need to do a bunch of work yourself and we still need to know what this is for. For example, from your example of an electric-driven propeller:

    What kind of vehicle? Air boat? Airplane? Hovercraft? Model or manned?
    For efficiency, what units? Joules per passenger-km? SFC? % is not necessarily a useful measure.
    What is the purpose? Homework? Designing a personal jetpack and want to know how to power it?

    Why don't you start by outlining a very specific scenario for us.
  7. Sep 10, 2014 #6


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    The thermal systems which have the highest efficiencies are the marine slow-speed diesel engine (approx. 54%), a turbo diesel auto engine (approx. 40%), or a combined cycle gas-turbine power generator (approx. 60%). Some of these power plants are installed into vehicles; some are stationary, but they all are leaders in turning the energy of the fuel into usable work.


    Scroll down to see the section titled 'Fuel Economy'.

    On top of these engine thermal efficiencies, for instance, the slow-speed marine diesel, you will have to factor in losses in shaft transmission (about 2-3%) and the propulsive efficiency of a propeller. (Propulsive efficiency in ships varies considerably depending on the hull form of the vessel and the speed. Marine propellers have about 70% max. efficiency in converting engine torque to thrust output).
  8. Sep 22, 2014 #7
    ok, the main thing i am looking at is aircraft propulsion. so, i am looking for amount work done, for the energy. for example, i saw somewhere, a rc aircraft(i do realize there is a range) thrust to the energy used was around 18 percent when using this one specific propeller.

    im looking for data like this. My main goal is(i have a specific design in mind) aircraft propulsion. so list tell me about the efficient engines. but the reason i ask for all engines is because, one could be adapted to work with aircraft if the engine is so efficient. so list all engines with highest amount of work done(like the thrust of motor, propeller combination). thanks.
  9. Sep 22, 2014 #8


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    18% is really awful for a propeller - a well designed prop operating at its design advance ratio should be more like ~80% efficient. For a remote controlled aircraft, I'd expect it to be a bit worse (due to the small scale and lower engineering effort compared to large aircraft), but I would think you could do a lot better than 18%.

    As for the most efficient aircraft propulsion? I'd guess that it's probably a turbodiesel engine powering a propeller. Jets don't tend to be quite as efficient as props, though some of that is also skewed by the fact that the energy requirements for flight are much lower at slower speeds, and prop aircraft tend to fly slower (so even if jets had the same thermal and propulsive efficiency, they would require more fuel to go the same distance).
  10. Sep 22, 2014 #9


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    Still vague and still poorly formed. Though you seem to think not, in terms of "efficiency", an electric driven propeller is about as efficient as it gets for a model aircraft. Electric motors are on the order of 90% efficiency while gas engines are on the order of 30%...then, spinning the same propeller. This is in addition to the fact that you are mixing and matching units in a way that doesn't make sense: % efficiency only applies to energy input and output and that's not compatible with force (thrust).

    Of course, for a model aircraft, why does 1/3 the "efficiency" matter if you can get 10x the energy density from fuel vs a battery? So maybe it is weight density of energy or thrust to fuel weight ratio that matters?

    So: is this a model aircraft? Airplane or helicopter (quadrocopter?)? What is this "specific design" you have "in mind"? Are you looking for speed or range/longevity?

    Please stop making us guess what you are asking about.
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