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A more effiecent use of gasoline?

  1. Sep 15, 2004 #1
    This is not so complex or anything just meant as a simple school project..

    Much energy of that which is stored in gasoline for internal combustion engines are wasted as heat and in best cases 20% is changed into useful energy.

    So that means that ALOT of energy flows with the coolant water and exhaust stream (which also has Ke??) which is not used at all it just gives it off to the air.

    My question is would it be possible to somehow make use of this energy by eg the means of a modified Turbo that picks up the energy in the exhaust stream to drive a generator or by modiefying the cooling system (or both together) by removing the cooler and adding a condenser to condense another fluid which could spin a turbine which in turn would drive a generator? The aim is that the energy "collected" would be stored in a battery (which would be used as a buffert too) and would drive an electrical motor and the power accessories in the car to improve the effiency of the engine. The electrical motor would be used together with the combustion engine (by gearing) to, to some extent, easier the load of the combustion engine so that less energy (less gas) is needed. Thus getting better mpg.
    And when it powers the electrical accessories, the load would then too be lighter since the engines generator would not be used as much.

    Is it possible theoretically and practically??

    It would be real fun to build one if this is true...


  2. jcsd
  3. Sep 15, 2004 #2


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    Hybrid cars do essentially what you're suggesting. Some of the vehicle's kinetic energy is converted to energy stored in batteries for later use.Toyota's Prius is already on the market and many other manufacturers will introduce hybrids in the 2005 model year.
  4. Sep 16, 2004 #3


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    Hi Dan and Tide.

    When I hear about saving the energy wasted in an engine, I always think of designers and engineers working on it. The energy recycling is not always an efficient process. If you add a turbine for condensing the coolant, an electrical engine for additional power, and some batteries for energy storage, probably the weight of the car would be increased and the total fuel consumption would be larger.
  5. Sep 16, 2004 #4
    well then, guess that this project is spoiled. Anyone have a suggestion of projects possible with energy? supposed to be about 100 h big.. ??
  6. Sep 16, 2004 #5


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    Not really. Hybrids use wasted kinetec energy of the car and wasted kinetic energy from the engine spinning at idle. They don't recover wasted heat.

    Any car recovers wasted heat when you run the heater though: instead of the engine jacket heat being rejected into the air via the radiator, it goes into the heating air for the car. This is very similar to a concept called "cogeneration"...

    Cogeneration uses a typical natural gas or diesel electric generator to produce electric power. Then, the heat from the engine coolant and exhaust systems are used to make steam, which is used for heating or even cooling using something called an absorption chiller (you can actually use steam to create cold water).

    Many large buildings, large corporate complexes, and colleges use cogen plants. Because of the obvious large cost associated with building your own little power plant, its only economical for large installations.
  7. Sep 16, 2004 #6


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    You might want to compare the actual efficiency of car engines to the theoretical limits set up by the carnot cycle / otto cycle engines.


    the Carnot efficiency is summarized by the formula

    (Thot - Tcold) / Thot]

    and is the most theoreitically efficient heat engine possible. It works by heating and cooling an ideal gas to drive a piston.

    The otto cycle engine efficiency is summarized by very similar formulas, but the temperature ratio Tcold / Thot can be reinterpreted as being a function of the compression ratio, yielding the result

    eff = 1-r^(1-k)

    where r is the compression ratio, and k is the ratio of specific heats of air at constant pressure and constant volume (unless I got that backwards!).

    I'd look up which way the ratio is supposed to go, but I have to go eat breakfast now....

    Also note, there's some similar equations for the diesel cycle, which I won't get into, it's similar overall to the otto cycle. It turns out the compression ratio can usually be higher in a diesel engine with practical fuels, but it's not quite as theoretically efficient.
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