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Could I attach a little fan to power a motorcycle alternator to be more efficient then running off the engine? Attach any where facing the wind on the vehicle to increase mileage from eliminating strain on the regular alternator while driving.

Could a AC compressor be circumvented to reduce strain on the car engine in this way as well?

By displacing the tension applied to these primary parts from high train from changing RPMs from shifting by having a softer and more consistent steady air driver increase efficiency? The original alternator would only kick in at an idle or have a deeper cycle battery.

With impellers wind can be restricted to prevent over speed on the fan. It would just look like an extra air scoop on the hood. It could also spin the air into a cold air intake increasing efficiency. A small weighted fly wheel or kinetic storage devise can buffer wind gusts.

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    The engine has to overcome rolling resistance and drag through air resistance... all you would do is increase the drag due to air resistance and increase system losses. – Solar Mike Sep 16 '18 at 20:07
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    @Muze no, putting a turbine in the air intake to power a generator will partially block the intake, reduce the air flow to the engine, and reduce the engine power. You can't get "something for nothing" from this or any similar ideas. If you want to get more air into the engine you would have to supply electricity to the drive the fan - and you have just invented an electrically powered turbocharger, of course. – alephzero Sep 16 '18 at 20:18
  • @Muze sorry, I don't even know what your last comment means - but I think you are trying to invent a perpetual motion machine with these ideas, and nobody has yet succeeded in making one of those work! – alephzero Sep 16 '18 at 21:39
  • @alephzero Not at all. Just a more efficient and reliable power supply. – Muze Sep 16 '18 at 21:40
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    @Muze - the "impeller creates a vortex" is nothing but laughable. It does nothing but make a restriction in the intake tract. Just a waste of money. – Pᴀᴜʟsᴛᴇʀ2 Sep 16 '18 at 21:43
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The question was somewhat unclear, at first I was assuming the question was about installing a wind turbine to a car to make motive power. Yes, somewhat counterintuitively, such a wind powered car will work if properly designed, even if you have a headwind! No law of physics would be violated: conservation of energy is satisfied and the conservation of momentum is satisfied (you are using the wheels to transfer the momentum of the wind to become added momentum of planet Earth). The performance of such a wind-powered car would be horribly low, though (I expect any wind turbine whose weight the car is capable of supporting would result in at most 1 km/h speed, probably much lower than that).

However, if I understood the question correctly, it was instead about using some magical fan thing to help the alternator, relieving the engine from working hard to power it.

There are very well-established laws, the first and second laws of thermodynamics.

The first law of thermodynamics is the conservation of energy. You cannot create or destroy any energy, you can just change its form (note: mass is one form of energy according to Einstein). If you install a fan, you have to power it somehow, e.g. with electricity. Any energy you use to drive the fan can reduce the energy to run the alternator, but that energy has to come from somewhere. It is coming from the battery, charged by the alternator, driven by the internal combustion engine. So, the very engine whose load you are about to decrease has to drive the increased load of the fan.

Typically, the efficiencies are nowhere close to 100%. In this very setup, I assume the "help" to the alternator would be so minimal that >99% of your energy would be wasted and less than 1% of it would actually help the alternator.

The second law of thermodynamics says that disorder (entropy) only increases and never decreases. This gives the maximum efficiency for heat engines and refrigerators / AC systems. For AC and refrigerator, it can be over 100%, but for an equivalent heat engine, it is less than 100% by the same amount, so that the AC/refrigerator efficiency times equivalent heat engine efficiency is always at most 100% -- so no free lunch there, either.

Both of these laws are extremely well tested. Any violation of these laws could be exploited to demonstrate a working perpetual motion machine.

So far, nobody has demonstrated a working perpetual motion machine despite numerous attempts. By the sheer number of people attempting it, I'd say these laws are the best-tested laws of physics.

There are, however, some ways to obtain wasted energy in a car, turning it to useful energy:

  • Turbochargers use exhaust energy and exploit it to cram more air into the engine, creating more power and better fuel economy
  • In theory, you could use a device similar to a turbocharger to create electricity, charging the battery.
  • The turbocharger should make it apparent that the exhaust contains lots of wasted energy. A better cycle such as simulated Atkinson cycle instead of Otto cycle can help to turn more of that energy into motive power (and is used at least in Toyota hybrids).
  • The efficiency of an alternator is actually quite poor. Modern hybrids use motor-generators instead that have better efficiency.
  • Regenerative braking can charge the battery, turning braking energy into useful energy.

By the way, if you think you could omit the fan and drive the wind turbine by the headwind a car typically experiences when driving fast, that would increase the wind resistance, thus increasing the load of the internal combustion engine.

  • Please explain the first and last paragraphs... you seem to be arguing both sides and promoting perpetual motion, in violation of the very laws you quote in the 3rd paragraph... – Solar Mike Nov 25 '18 at 20:41
  • Wind turbine doesn't need power does it, I thought a wind turbine built up and provided power by the wind-force needed to spin the blades – hello motto Nov 25 '18 at 22:04
  • The first paragraph doesn't violate perpetual motion. You CAN extract power from wind, like any wind turbine does. The wind turbine creates some extra drag, so if the car is driven by an internal combustion engine, it has to supply more power. – juhist Nov 26 '18 at 19:45
  • Oh, and the wind power originates from fusion reactions in the sun, if the winds are natural, or from the internal combustion engine, if the winds are due to ordinary headwind experienced during high-speed driving... So there is a source of energy. – juhist Nov 26 '18 at 19:46
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A small wind generator wouldn't do any good if the car was sitting still. One that would generate 1000 watts from a 5 mph wind and was 40% efficient would require 1000* (70/5) /.4 = 35000 watts to move 70 mph. That's about 47 hp. That's would probably cut your gas mileage in half.

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