are there any boats running compressed-air engines?

[ijason]

greetings.

i while ago i found a very interesting website detailing a company which was producing transit buses and passenger cars which were both powered completely by compressed-air engines. sadly, i can't seem to find the link, so i can't provide it...

has anyone heard of any boaters using compressed-air engines? what do you think about the viability?

apparently the advantages are substantial - beyond not having to buy fuel. the motors themselves have dramatically fewer parts, and don't suffer from the wear of combustion going on inside them. the pistons (or rotors) are moved via simple expansion of the air. apparently they are also lighter-weight for HP produced than traditional engines. the process is actually endothermic, so you have a ready source of cooling while your engines are running!

[kerosene]

yes -the gas cools down when it expands. However it heats up when you compress it - and that energy is lost when the air was compressed in the 1st place.

Besides the efficiency issue with the energy wasted as heat there are mechanical losses. How bad - not sure.

It is important to understand that the air is not fuel but a a battery. As boats use quite significant amount of energy this can't be solution for every boat. Might work for casual put put boat that is used every now and then - especially if the energy for compressing is cheap - solar, wind etc.

I doubt it has as good efficiency as the latest and greatest battery tech but simplicity might be a huge factor (and subsequently the price).

I have been playing with the idea of having big compressed air storage tank on my parents' farm. Have compressed air run machinery (lower HP and smaller machinery would be required) that use switchable tanks. Ie you work for 4 hours on the filed - come to the barn replace to a full tank and hook the empty one to be filled from the big storage.
The big storage tank could be filled with wind/solar over the year.

Just a playful idea - probably not feasible - after all farming machines like boats really use their HP and the energy need is pretty high. Might end up spending more time filling tanks than plowing...

On a boat you could have the tank in the boat - no need to replace it as you probably wouldn't be in such hurry to seed your crops.

[steele m.a.]

Running a vessel on compressed air is virtually as simple as running it
via hydraulic motors.
Hydraulic motors offer a 1/1 hp transfer , and instantaniously deploy.
So does a compreesed air motor , the difference being :
1 : the compressibility of the compressed air makes it more unpredictable
than hydraulic .
2 : compressed air motors don't self lubricate the way hydraulic motors do.

There is another difference , air offers more buffering between compression
and power delivery.Because it's compressible , it wil absorb drivetrain
shock to a certain extent.

[ijason]

@kerosene. i don't doubt that air-powered engines could have the grunt to move a boat. there are active transit-buses using compressed air engines very successfully, and any motor that moves a full-sized bus would be able to move a boat. a boat of limited size, of course.

the real question for me is range. i have no information on how big the air-bladder needs to be for those buses to go 200 miles between re-charging.

speaking of having the tank refill by solar brings up a follow up question; would it be viable to have a solar/turbine powered compressor that you could then use to refill your air once you've docked? i.e., sail for 3 days to a destination and then park the boat in the sun for a week to refill

[ijason]

@steel m.a., wouldn't it be a simply task of putting in an oil-pump? to take care of the self-lubrication i mean. surely that's not a problem that was unforeseen by designers.

[steele m.a.]

Very true , actually , most air compressors leave a little oil in their
air as they compress it.
The advantage , however , of running on compressed air , usually leaves
you asking the question : why not just run on hydraulic oil ?
Air runs cool , and , if you tap out of an acumulator , as you suggest ,
you have a supply handy , which can easily be re-filled.
The ideal compromise seems to be an air/hydraulic system.
Instead of changing out pressure cylinders , which are usually very
heavy and securely mounted , it's easier to simply hydraulically
re-charge them.
You charge air pressure into your compressed air tanks using an
onboard hydraulic pump.

[ijason]

@steel m.a., ah well i'm already on the bandwagon for a hydraulic drive ship, although a popular consensus is that you lose a good deal of energy due to mechanical inefficiency. which would be much reduced by direct-driving a propeller from a compressed-air engine.

as for another reason for using air over hydraulic is the potential for storing energy. i think an electric drive motor would be easier, but i am not at all hopeful for the ability to motor for 3 days on batteries/solar panels, and then recharge the batteries with only a week or so in the sun. whereas i'm more optimistic about being able to store enough compressed air for a 3 day run. and i have a hunch you'd be able to much more efficiently run a compressor off a wind-turbine or solar panels than you'd be able to charge batteries. at least, at the scale of energy required to drive a boat for 3 days.

[kerosene]

I am sure it can be done - and yeah I have no doubt of the peak power either - more so the total energy storage capacity. Even though a city buss might have 200-300 hp motor it rarely needs to step on it and use more than fraction of the power - on a boat you often have engine working on pretty hard steady load.

I doubt solar panel or wind turbine pumping air will be a magical solution compared to same setup with batteries - it is still about available energy and small energy collection devices (solar or wind) are quite limited in their output.

[FAST FRED]

and i have a hunch you'd be able to much more efficiently run a compressor off a wind-turbine or solar panels than you'd be able to charge batteries. at least, at the scale of energy required to drive a boat for 3 days.

A hunch can not replace the Laws of Physics. Darn!

Every form of storage incurs losses , Darn.

FF

[ned L]

Other than the difference of storing the compressed air ahead of time, or producing it as you need it, how would a compressed air driven vessel really differ from a steam driven vessel? they are both vapor/gas under pressure?

[ijason]

@ned. the difference between a compressed-air motors VS steam depends on which way steam is being used.

modern nuclear vessels use steam turbines to drive electric generators, which in turn drive electric motors. ye olde steam vessles used a boiler to create steam with enough pressure to turn a crank via expansion chamber (i believe).. and as such are very similar to modern compressed-air motors. i think that modern compressed-air motors enjoy the rewards of being new technology; better efficiency, better simplicity, longer duty life... but i believe are very similar to old steam engines.

[ijason]

@fast fred. hey now, don't go polluting theory with fact!

of course every storage option involves loss, but what do you think about the efficiency of using a wind-turbine to turn a compressor head VS a wind-turbine to turn a generator which then charges a battery... it seems like the battery option has another step and thus another chance to loose efficiency. fewer steps = more storage, right?

[kistinie]

Efficiency and trust of an air motor in water ?
I have been told it was low ?
0.3 to 0.5 ?
more ...less you think ?
who did the test ?
Air drill
air compressor
a propeller and measure...
if air is blowed off the body of motor far behind propeller and body of motor could give a cool torpedo effect
too close air will make you lose density of water including air, far you will only get the thrust i think

To grease motor i would try an animal oil, many should work, a lot of huile d'olive and other ones will certainly do interesting results, all these oil work incredibly well on brass and can go to the sea in final, low temp are fine for non petrol oils.