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I Love Ingenuity

May 18, 2012

Way back in my school days when we were doing the physics of the car engine I asked my physics teacher why we couldn’t invent a car that used an engine to get going and then engaged the wheels back to the engine to provide a sort of perpetual motion car and negate having to use petrol quite so much. The answer is, it’s a non-workable idea. The energy from the wheels would be lost in friction and heat and the amount going back into drive would be so small the car would immediately start to slow down you’d need to start the engine again within a few seconds.

So with that knowledge I read this story on the Sky News website and got a school days flashback ( The article is about a man in China who has invented an electric car which incorporates a fan and generator to add charge to the battery and provide extra range.

I love this kind of thing, its by doing things like this that we as a human race learn. Its experiments like this that drive ingenuity and invention and they should be encouraged.

Here Comes the BUT…

However, in this particular case its not as clear cut and judging from some of the related comments (and other discussion I have seen on the story), that not everyone understands why this idea is flawed from the start and will never take off. Much like the school boy me, who was thankfully eager to learn.

It basically boils down to the efficiency of electric generators. They do not convert 100% of the energy they are given into electricity. The conversion process takes some of that energy.

How this translates to the news article

The car in the question has to carry the extra weight of the fan and the generator, this makes the car heavier and means more energy is required to get it up to speed. The wind resistance of the fan on the front also increases the energy required. These two elements combined mean that the battery in the car will have to provide more energy to get the car to go compared with the same car with the fan, generator and related ancillaries removed. This difference is the amount of energy being put into the fan at the front of the car when it is driving the generator. That’s not strictly true, there are other factors at play but for this simplification it explains the point well.

This is where we get to the kicker. The energy that is put back into the battery will be less that the energy used to drive the fan; namely less than that required to carry it in the first place. In other words, the battery would provide more range if the man featured simply took his invention off the car.

If the idea was true and had genuine potential, it would be used in industry already. The fact its not shows the truth. This is something that has been played with a long time ago and modern physicists know exactly why it won’t work and no longer even bother to consider it.

I’ve seen variations of this idea come up before. In my car club days it would come up in the form of people asking why they can’t just plug their air conditioner into their car air intake and provide extra power due to the cold air going into the engine.

Its pretty much the same principle, the weight and energy used by the air-conditioner will be greater than that that provided by the cold air flow, thus the benefit is erased.

Learn by experimentation

OF course people should try things out because we learn by experimentation. However, when its something as basic as this that has been known about for many years, it is useful to have a critical thinking mind set and a basic education to understand why it won’t work in the first place to save yourself a whole heap of time.

Though with the number of people who are obviously thinking it’s a decent idea, perhaps our schools out to run this form of experiment each year to demonstrate just why this sort of thing is a fool’s errand.


From → comment, Motoring

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