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Author Topic: perpetual motion  (Read 983 times)
creagmor
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« on: January 23, 2016, 01:16:42 pm »

It has been said that the next best thing to knowing something is knowing someone who does know it, and I’m professing ignorance on a particular subject.

Someone once told me of a plan whereby, with some slight modifications to the head of a gasoline engine, one could burn hydrogen in it. The hydrogen would be produced by putting a certain chemical into water to separate the hydrogen from the oxygen, and since the end product of the combustion is water this could be reused indefinably. Due to entropy, and other factors, I know that there is no possibility of it working in real life; I’m just not certain why.

Without a doubt there are many of you folks who are considerably better educated in this area than I am. Is it possible that someone would consider filling me in as the reason for the impossibility of it?   
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Narsil
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« Reply #1 on: January 23, 2016, 01:55:26 pm »

The easiest way to understand this is that any molecule has a specific energy state, mostly determined by the bonds connecting the atoms together.

In the combustion of hydrogen you have 2H2 + O2 ----> H2O + energy

The energy released is the net difference in energy between the molecules on the LHS of the equation and those on the right.

It therefore follows that to turn water back into  hydrogen and oxygen you need to ADD  at least the same amount of energy to water as you would get from burning it, (in practice it is a lot more). So even without considering entropy there is no new energy going into the system and so no way to extract useful work.

People often mumble vaguely about 'catalysts' in cracking water to make hydrogen but no catalyst can change the energy required for a reaction, they can speed it up certainly but not change the end state.
« Last Edit: January 23, 2016, 01:59:34 pm by Narsil » Logged







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creagmor
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« Reply #2 on: January 23, 2016, 03:16:26 pm »

Thank you very kindly sir, for your speedy and informative reply. I may have the details wrong, but I know my son has some kind of container into which he puts water - and baking soda (I think) - and somehow this increases the oxygen intake in his car, and thus his mileage by about 4 miles to the gallon, but of course that is a horse of a completely different colour.
« Last Edit: January 23, 2016, 03:29:51 pm by creagmor » Logged
Narsil
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« Reply #3 on: January 23, 2016, 04:07:49 pm »

There are systems where a small amount of water is injected into the cylinders. The thermodynamics of this get a bit complicated but in essence the principal is the same as a steam piston engine. This doesn't actually add any additional energy to the system but it can, at least in theory, allow more useful work to be extracted from the heat generated by combustion and it can be beneficial in controlling combustion and cooling.

There are however practical difficulties in implementing it, in particular any condensation in the cylinders is very bad news.
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Maets
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« Reply #4 on: January 26, 2016, 02:08:15 pm »

I have seen systems that use electricity to break water into oxygen and hydrogen, which is then added through the intake and burns as part of the combustion in the engine for a major claim in gas mileage. The water is not recycled, you need to fill up the water tank occasionally.  The electricity is "extra" from the alternator. Number of systems like this out there.  No idea if they actually gain you anything.
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creagmor
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« Reply #5 on: January 26, 2016, 07:58:50 pm »

Maets: Thanks. This may have been what my son was doing. it was some years ago that we discussed this so I don't exactly remember all of the details. As I said he told me he increased his fuel efficiency to the point where he gets an extra four miles per gallon. The proposed system wherein the water is recycled is a completely different idea.
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