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Old 13-11-2018, 12:27   #16
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Re: Hydrogen 15x more power dense than diesel?

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There is a reason Elon Musk chose kerosene over liquid hydrogen for his rockets
Several reasons actually! ease of handling, storage volume, flammability, warmer storage temperature, lubricating.

Not as efficient, though.
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Old 13-11-2018, 13:32   #17
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Re: Hydrogen 15x more power dense than diesel?

Hydrogen has been used as a fuel since the industrial revolution. Coal gas is over seventy percent hydrogen, the rest is carbon monoxide and small amounts of methane. During the war when domestic petrol was as rare as hen's teeth, farmers and buses and cars got by by making hydrogen as they went by getting a container of coke or anthracite glowing nicely, then letting water into it to produce steam which was then reduced to hydrogen and carbon monoxide plus carbon dioxide. They called it Water-Gas. The cleaner the coal--the less scrubbing the gas had to go through before it could be used in an internal combustion engine. Particle filters and bubbled through water was about it.

Simpler versions, but less efficient just burned the coke in reduced oxygen and produced carbon monoxide--which would also run an internal combustion engine but far less efficiently, but without having to carry a tank of water..

The advocates of the hydrogen economy are not intending to electrolyse acidulated water using excess wind and solar and tidal sources, while releasing the oxygen component into the atmosphere, or bottling it for uses requiring high purity. It would be GREAT of that were the case--and it should be the case.

What the fossil fuel industries have in mind is to make it from coal. Watch out for the bastards in the fossil fuel industry and their rentlings in power. They will destroy your little planet and make another Venus out of it. Unless they are stopped it is a certainty--but moving on--Making hydrogen from coal produces no oxygen--just more greenhouse CO2. No advantage whatsoever.


For a yachtsman, the way to store Hydrogen in small quantities is in a rubberised bladder--it is how it was done in WW2 when buses ran on it. They had a large rubberised canvas bladder on the roof. Only those with a good compressor could store it in bottles. The atomic hydrogen cutters used in precision industry use hydrogen stored in cylinders cylinders of steel lined with special paint--but I think the paint is just for prevention of corrosion. It may also provide some seal.

The easiest way to produce hydrogen is in an electrolytic cell using caustic soda solution as an electrolyte. These use a stainless steel container and stainless steel electrodes. Plans for them exist on the internet--but it is essential the gasses produced do not mix.

The Russians ran jet engines on hydrogen as well as piston engined aircraft--but it was impractical unless liquefied, and in this condition it is used as rocket fuel, at which hydrogen excels. The second stage of the Atlas-Centaur space launch vehicle was hydrogen fuelled..It mixes 2:1 with liquid oxygen in the combustion chamber to form nothing but high pressure steam.

As power for a yacht, the easiest way would be to use it in a fuel cell to produce the power for an electric motor. That way, excess power from solar while at anchor could be used to pr9oduce a bladder of hydrogen to use in a fuel cell. Not all that practical, but possible.
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Old 13-11-2018, 18:38   #18
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Re: Hydrogen 15x more power dense than diesel?

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I believe you're confusing the energy released by burning hydrogen versus using it with a catalyst and oxygen in an electrochemical reaction - a fuel cell - to generate electricity.

The Wikipedia table I linked to that lists hydrogen being about 1/4 the energy density of diesel is (I believe) talking about the energy released by burning hydrogen vs burning diesel.

And yes a fuel cell doesn't store electricity, it generates it.
Confusion is a daily event for me.

But can you, or anyone else, elaborate on the physics of how a gallon of hydrogen (produced from sea water via an electrolyzer on board) sitting next to a gallon of diesel (bought at the fuel dock) can with the assistance of a fuel cell, wind up producing 15 times the electrical or mechanical energy of that gallon of diesel running an internal combustion engine for alternator charging of batteries or as mechanically coupled propulsive force to the propellor.

If so, I sure want one.
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Old 13-11-2018, 20:18   #19
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Re: Hydrogen 15x more power dense than diesel?

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1/4 of the power sounds about right if this table this table is accurate - which lists diesel at 35.8 MJ/L and hydrogen at 700 atmospheres as 9.17 MJ/L.


BUT as MartinR said, they're probably talking power cells.

Hydrogen in a Refinery at 700 Atmospheres is worthy of respect on a boat --- not on your life.

In a refinery you can afford to use top quality materials, welded pipe, and lots of testing to ensure quality before you risk peoples lives. The Refinery does not move around.

If you think boat parts are expensive buy stuff of acceptable quality to use in a refinery.

Think about it, how many boats have serious problems because someone saves less than 100 dollars?
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Old 13-11-2018, 20:19   #20
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Re: Hydrogen 15x more power dense than diesel?

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I believe you're confusing the energy released by burning hydrogen versus using it with a catalyst and oxygen in an electrochemical reaction - a fuel cell - to generate electricity.

The Wikipedia table I linked to that lists hydrogen being about 1/4 the energy density of diesel is (I believe) talking about the energy released by burning hydrogen vs burning diesel.

And yes a fuel cell doesn't store electricity, it generates it.
Right you are. In any event, "Electricity" in the context here is really electric energy. Electric field in a capacitor is the only steady state form of directly storing electric energy that I can think of. Everything else we have is just energy storage in chemicals which then can be converted to electric energy.

I remember reading many years ago about the next big thing to replace gasoline. It was hydrogen stored in a solid chemical which releases it gradually. So the tanks containing this solid chemical and operating at low pressure, would be relatively safe. You would just pull into a service station and exchange discharged tank for a charged one. Charging just requires putting hydrogen back into the tank at higher pressure so it can be absorbed by the chemical. Any chemical engineers here might be able to identify what the substance was that can temporarily store hydrogen at low pressure.
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Old 13-11-2018, 20:23   #21
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Re: Hydrogen 15x more power dense than diesel?

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Confusion is a daily event for me.

But can you, or anyone else, elaborate on the physics of how a gallon of hydrogen (produced from sea water via an electrolyzer on board) sitting next to a gallon of diesel (bought at the fuel dock) can with the assistance of a fuel cell, wind up producing 15 times the electrical or mechanical energy of that gallon of diesel running an internal combustion engine for alternator charging of batteries or as mechanically coupled propulsive force to the propellor.

If so, I sure want one.

a gallon of hydrogen at what pressure. Without that figure, the question is meaningless
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Old 13-11-2018, 23:25   #22
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Re: Hydrogen 15x more power dense than diesel?

^^ at whatever pressure is needed to keep it liquid
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Old 14-11-2018, 04:10   #23
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Re: Hydrogen 15x more power dense than diesel?

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They have tried to develop hydrogen as car fuel for decades now, and have not been able to make it work reliable. Neither for direct combustion nor for fuel cells.

Fuel cells for stationary applications are in use, though.
Perfect fuel from an environmental point of view otherwise.
The problem with hydrogen as a fuel from an environmental perspective is getting the hydrogen in the first place.

Right now there are basically two answers. You either start with a bunch of electricity and use it to split water apart to make hydrogen - losing energy every step of the way, so by the time you use a fuel cell to convert the hydrogen back into electricity you'll be lucky to have a quarter of the original amount, or you convert a longer hydrocarbon by some sort of controlled combustion process.

That's what the coal gas reference above was; the newer preferred version is steam reformation, which splits water in the process and thus makes more hydrogen - but you're still lucky if you get 75% of the energy content of the source fuel in hydrogen, and you'll get about as much electricity if you just burn the source fuel in a modern combined cycle plant.
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Old 02-02-2021, 14:45   #24
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Re: Hydrogen 15x more power dense than diesel?

scuse the necro post but I felt like commenting on here as i'm researching zero emmisions strategies at the moment.

for me the issue of energy density isn't so much about sustainability per se. It's more about safety.

Diesel is about 10Kwh per litre, and as a stable liquid fuel it's easy to manage. you can work out the range of a vessel with a 400L tank for a certain cruising speed or rpm, and be aware of how far you'll get against bad weather.

Electric motors will probably convert more KWh from their fuel that an I.C.E but regardless, the point is that most of the time, you will never need that stored energy, however when you do it may be critical to survival.

So how can you get to a similar level of safety margin with electric propulsion? 4000 KWh in a 400L diesel tank, would take several tons of batteries, or what size fuel cell stack?
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Old 02-02-2021, 15:42   #25
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Re: Hydrogen 15x more power dense than diesel?

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^^ at whatever pressure is needed to keep it liquid
Actually, you can not pressurize hydrogen into liquid form, as you can with propane. No matter what the pressure, it stays a gas (or very technically a supercritical fluid) unless you cool it to cryogenic temperatures, like less then -240C.

A point often ignored, or simply not understood, by hydrogen fuel fan boys.

No question hydrogen is a great energy storage medium, just one that is very, very, very difficult to handle on a retail scale.
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Old 02-02-2021, 15:49   #26
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Re: Hydrogen 15x more power dense than diesel?

That sounds like a complete nonsense to me.

Perhaps true if you fuse hydrogen atoms to form Helium. That is what the Sun does--it is called a nuclear fusion reaction--and it is not possible on any vessel so far--.
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Old 02-02-2021, 15:54   #27
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Re: Hydrogen 15x more power dense than diesel?

A slip neighbour and local celebrity, Red Green, AKA Steve Smith, converted one of his diesels on his houseboat/barge/studio/party central to run off hydrogen. He also converted his Chrysler 300 too run off hydrogen.

His onscreen personas is a humbling handyman of the 'Possum Lodge's. Not so bumbling in real life.
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Old 02-02-2021, 16:00   #28
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Re: Hydrogen 15x more power dense than diesel?

Liquid hydrogen in cryogenic storage has a density of 0.07x water where Diesel is about 0.75x water so there is already a 10x factor for energy density. so you would have to carry 10x less



Next if you look at the heat of combustion, Hydrogen comes in at 61 000btu/lb whereas diesel is at 19 300 btu/lb. Thats another factor of 3.16x between hydrogen and diesel. So taking that into account you would need 31.6x less hydrogen than diesel (by mass).


The process of producing hydrogen is not very efficient. Nor is the energy recovery 100% in a fuel cell. Whether using electrolysis or steam reforming, both processes are about 70% efficient. With electrolysis, producing the electricity in the first place has additional efficiency penalties. With steam reforming one is basically using steam and natural gas. If one had a way to just burn the natural gas, the overall efficiency might be better, especially since that opens up the possibility of coming up with your own methane sources...


On the fuel cell end, the system efficiency is 55-60% at best so multiply 0.6 x 0.7 = 0.42 or 42% efficiency. Now multiply 31.6 x 0.42 = 13.27 would be the final conversion from water to hydrogen to power in the fuel cell to electricity to drive your electric motor (from an energy density point of view).


If you are flying rockets, the light weight is without doubt an advantage. But for a displacement boat - doubt it is much of a factor at all. And provides a very complex system with a lot to go wrong... If you plan to make your own hydrogen wherever you are, well, then you will need your own nuclear reactor to go the electrolysis route and still a lot to go wrong, why not just drive the electric motor directly from the reactor in that case, or use steam ?
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Old 30-07-2021, 06:51   #29
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Re: Hydrogen 15x more power dense than diesel?

Apparently, many of you have never seen a lead acid battery explode. I had a 1970s car battery explode as I raised the hood on the car. Chunks of battery the size of soft balls grazing my forehead. Not a common event, but not necessarily a rarity either. Battery was apparently low on electrolyte and allowed hydrogen to build in the cells. What ignited it was not apparent.
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Old 30-07-2021, 14:25   #30
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Re: Hydrogen 15x more power dense than diesel?

No. Because it isn't--there is no practical way to store liquid hydrogen aboard.
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