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Hybrid Efficiency

  1. Feb 4, 2006 #1
    What is the actual gain in efficiency in a hybrid?
  2. jcsd
  3. Feb 4, 2006 #2


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    By hybrid, are you referring to a hybrid automobile or propulsion system.

    It's efficiency is a function of how it is used.

    An automobile engine, which is idling much of the time (stop & go traffic, aka grid-lock), will have low efficiency because it produces energy, but not work when the vehicle is stopped. If an energy storage system is applied, then the energy produced by the engine can be stored for later use, particular when demand is high.

    Automobile engines are most efficient (that is when converting thermal energy to work) when they are driving at optimum speed without cycles of acceleration/deceleration or braking.
  4. Feb 4, 2006 #3
    Thank you for the reply

    I am asking about the hybrid automobile. I am asking because I read in quite a few places that the fuel efficiency gains offered are 80-100% which is very unbelievable.
  5. Feb 5, 2006 #4


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    When you ask about efficiency, do you mean fuel economy?

    Again, the gains are highly dependent on use. If you're measuring 'efficiency' as 'miles per gallon', then obviously if you're sat in a traffic jam and aren't moving, then your 'efficiency' will approach zero. And more hybrid-specific, - if all you're doing is motorway miles, and the petrol engine is on all the time, the advantage of having an electric drive will disappear because you'll just have a smaller engine working harder, and you'll be lugging around a load of redundant weight in the form of batteries.

    For reference, the EPA combined figure for the Prius is 55mpg, which is something easily achievable by a decent Diesel (as Wolram will tell you!). When you take into account the extra resources needed to actually build hybrids at the moment, and the extra resources needed to dispose of them at their end of life, you do start to wonder just how environmentally friendly they actually are.
  6. Feb 7, 2006 #5
    I also haven't seen anywhere where there's been real world road testing done in places where the weather (temp) varies greatly and where there are alot of hills. I'd liek to see what the efficiancy of these cars are and what problems develope over the course of a year or more in places like New England and the Northern Midwest where they get snow.
  7. Feb 7, 2006 #6
    popular mechanics just did a huge article on this subject, their bottom line was that people who paid more up front for a hybrid car are barely if at all saving any money on it, so i would have to say that shows that yes, the hybrid's efficiency is much improved, provided you use it the way the testing was done, but is it efficient on the wallet? doubtfull
  8. Feb 8, 2006 #7
    True but the govt. is also providing a 3400$ tax credit on hybrids.
  9. Feb 8, 2006 #8
    did not know that, that does make it a bit better, but in any case, im pretty sure this issue is still on the shelf if youre intrested, it has alot of real testing information, it directly compares the hybrids to their pure ice counterparts and to eachother.
  10. Feb 8, 2006 #9


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    Frankl, it has always been some what puzzling to me that hybrids can offer any improvement in efficiency at all. I mean, when you get right down to it, you're basically adding a step. I think it's mostly a testament to the innefficiency of the internal cumbustion engine.
  11. Feb 10, 2006 #10


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    The thermochemical to mechanical conversion of an ICE, or any thermal to mechanical conversion system, is what it is. The bigger problem is the way in which a machine is used. Engines in cars in slow traffic or stop-and-go traffic still produce energy, whether there is movement or not. As idle time is increased, the efficiency (and fuel economy) decreases.

    The optimal way to use an ICE is maintain optimal speed for as long as possible in the usage cycle. In urban areas, that is impossible.

    The hybrid concept does allow for some collection and storage of energy that would otherwise be discharged to the environment. Later, when there is an increased demand for mechanical energy, the electrical energy storage system (batterises) can supply the energy rather than the ICE. However, the hybrid system (to which Lurch alludes) requires to parallel systems - a thermal to mechanical system (engine + transmission) and a thermal - electrical to mechanical system (engine + generator/motor + storage (battery)). I am assuming that the motor/generator is one in the same, as in railroad locomotives which use the motors as generators when in dynamic braking mode, and I assume the generator/motor is somehow integrated into the transmission system. Of course, the motors could be separate from the generator, which simply adds mass and more complexity to the system (with more points of potential failure).
  12. Feb 10, 2006 #11
    I had read that with the increased cost of purchasing and maintaining a hybrid, the extra gas mileage didn't allow you to break even until nearly 80,000 miles. So they may be better from an environmental standpoint, but not really from an economic one.
  13. Feb 10, 2006 #12


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    I'm not even so sure about the environmental standpoint. When you consider the extra resource needed to manufacture the batteries, and the possibility of needing to replace the entire battery bank after 10 years and then to safely dispose of them, and that you only get the same kind of economy figures as a Diesel, I don't believe there's currently much in it.
  14. Jul 22, 2006 #13


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    hydraulic hybrid - urban driving

    This year 2006, UPS (trucking) is working with a consortium including Eaton Corp, to test efficiency of hydraulic-combustion-hybrid engines on their fleet. ref1 and ref2

    I note this isn't a new concept, but appears to be gaining significant attention by manufacturers. They are embracing the idea of storing energy wasted during braking, into hydraulic tanks, and releasing that energy in subsequent acceleration cycles. It is especially efficient in stop-and-go urban driving.
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