Hydrogene powered boat

When you stop an engine at least one cylinder will be on the down position filled with exhaust gases, in this case water vapor.

 

H2 as a fuel is clean and light, puts out no carbon (if that is your concern), and no pollution.

Except that it has to be created /manufactured , a very inefficient process , next it has to be stored in a quantity to give the boat some useful range.

Usually in cylinders at 3000PSI .

Other than that its a great fuel.

FF

 

Pure Hydrogen is not an option on boats. As a fuel source it's way to scary, we don't even favour petrol due to it's volatility.
Binding hydrogen with carbon to form a lower calorific fuel that can remain liquid at normal atmospheric conditions must be the goal for renewable energy.

 

" must be the goal for renewable energy.


With hundreds of years of coal, oil and natural gas , why would one want to burn plants , peoples food to create at huge expense "renewable energy"?

Soon enough, 5-10- 50 -100? years we will have alternate power sources that will be cheaper than the current power,

no "renewable" need apply , unless its the cheapest source of power.

FF
"

 

Who said anything about burning plants or food?

Renewable is just a process of replacing what you have undone by adding work (energy).

In this case applying energy to re-assemble the carbon, hydrogen and oxygen bonds that are undone during combustion.
To me this is better than trying to build batteries to handle storage of electricity.
Dealing with Hydrogen in a pure form is not impossible but proved uneconomical.

 

There is no such thing as a "renewable resource", if completely true it would have to violate laws of thermodynamics.

Even solar power can not be replaced once spent, almost all processes on the earth require sun to create natural cycles, either long term or short. All add "heat" to the system through the sun's energy, and therefore entropy increases in all thermodynamic processes. The false fear of burning hydrocarbons is based on ignorance, like all superstitions. The releasing of the energy in hydrocarbons is just changing the form of something that was already put there by the action of the sun.

 

That's true only if you don't consider time.
But if you think of the fact that hydrocarbon fuel were slowly created by nature through a quasi-static process which went on during a 2000-3000 millions of years period, and that we have burned it nearly all in less than 200 years, you can get an intuitive grasp of the huge energy and chemical disequilibrium our intensive oil-burning is creating to the planet. And we should always bear in mind that ours is not a big planet, it has a finite diameter (an airliner can fly it around it in 50 hrs) and finite resources. So those fears are well-founded.

 

You have air + hydrogen => nitrogen + water. Say 20% of the exhaust volume would be water vapor, which has a density of less than 1 kg/m3 even when cold. In a big 1 liter cylinder you would have 0.2 liter of water vapor, which would condensate into about 0.1 g of water liquid.

How do you stop the engine? Normally you cut fuel input, thus even that 0.1 g is mostly flushed away, with air that may have a few vol% of water vapor to start with.

 

Which is enough to rust the cylinders and seize the pistons. Anyone that has rebuilt engines know how fast cast iron rusts. After honing cylinders and washing them to take the grit off, they get brown in a couple of minutes if not dried up and oiled.

 

So you are saying that ~20 vol% water in exhaust with hydrogen will kill the engine, but normal gasoline/diesel with ~10% will not? How much of that is left in the cylinder, if fuel is cut of to stop the engine and it runs say two seconds (~20 revolutions).

 

No multicylinder engine will run 20 revolutions after being stopped. It will run less than one.

 

How could it stop in less than one revolutions? 900 rpm = 15 rps so the engine should stop in less than 0.1 seconds? A flywheel of a rather small (~1 liter) engine stores a few hundred Joules of energy at 900 rpm. Wasting all that in 0.1 seconds equals to a few kW average power. A 1 kW starter easily turns such an engine even with cold oil.

 

Have you ever worked on engines? Just stop an engine and have a look see.

 

It does not need 20 revs, only two. With a typical 4 stroke engine, no matter how many cylinders, after 2 revolutions all the fuel mixture is swept from the cylinders. Each cylinder makes a complete cycle with each two revolutions. Particularly in a fuel injected engine the fuel is cut off along with the ignition, so there is not only no more combustion occurring, but there will not even be any fuel either.

I would say you likely get something like 10 to 12 revs or more even in a fast shut down. And beside, water accumulation in the cylinders has not been an issue, you will get H2O vapor as a product of combustion with all fuels, be it hydrogen, gasoline, Diesel, or ethanol.

This is a non-issue. I have worked on many engines, auto, off road and marine, and I have worked as an automotive engineer in several potions in the past. I have designed both engines and turbo systems for a number of different automotive applications. Take my word for it, residual water vapor in the cylinders due to combustion residue is not a problem. Moisture is a problem in long term storage due to condensation from day/night temp cycling, far more than H2O from combustion.

 

Yes I have, but I don't think I have ever paid much attension to how long it takes for an engine to stop. So I tried with my car (2005 2.2 liter 4 cyl gasoline by Peugeot) and judging just from the sound I think it took more than one second from turning the ignition off to full stop.

Then I took a close look at this video: http://www.youtube.com/watch?v=KjQ2f29VsPI

I think it takes about one second for the motor to stop from the point you hear a change in the motor sound. Slowing down in about one second from 15 rps to zero is several revolutions, maybe even 10.