Using compressed air on boats

[hansp77]

I am not up to the science or engineering involved,
but compressed air cars and transport are being taken very seriously within the ecological modernization and sustainable development discourses.
While there may be an argument regarding performance compared to combustion engines, the technology offers the potential for (near to) zero-emission transport.
Of course one has to look at the source of power for compressing the air in the first place (alonside emissions involved in the manufacturing and transport of the engine/car/boat, etc), however these processes could in theory (and practice in most developed countries) be powered by green or renuable energy sources.
Initially air-engines may or may not be economically viable alternatives for individuals (depending on situation)
however, if anything along the lines of the 'polluter pays' principle or carbon tax comes on line (which in some form or another seems both inevitable and rational), then the technology appears to offer some serious potential.
The beauty of this technology is that it is stored energy. That means that peak usage times can be covered by a lower slower constant baseload of power.

if you can suspend your disbelief...
imagine the 'petrol station'- a fresh smelling place (along with the roads and tunnels), most probably roofed entirely in solar panels, possible connected to some form of windpower, trickle charging battery banks that power electric air compressors into systems of underground tanks, also connected to a green electricity power grid for emergency back up (and to make maximum use of storing cheaper off-peak electricity).
Imagine out to sea, along select appropriate trade routes (with the best wind, sun and wave conditions), similar versions, like oil rigs, powered by massive wind turbines, solar and wave/tidal sources, where tankers and cargo ships (assisted by kite/sail) can refuel (Oil rigs themselves could possibly generate power/compressed air by utilizing the natural gas that they burn off).
Sail-and power-boats incorporating air tanks as ballast within the design (possibly to be assisted with water ballast to acount for an emptying tank?).

May seem a bit dreamy, but with the right market incentives, compressed air engines could be a very big and very cool thing.

One not-so-nice foreseable side effect of compressed air cars that I have read about is when they crash into each other (as they inevitably will). While design precautions can be taken for most foreseable situations or uses, it might be a bit hard to design a tank strong enough for for two hoons to have a head on collision at over 150kmh (hopefully not in a crowded place ).
Maybe we'll all be driving slower, and all be happy, and peace will reign under a glorious sunset of flying pigs...
Maybe I should scrap that last sentence.

[Poida]

Before I get into figures and calculations I like to look at common sense and gut feeling first.

By the way Mike thanks for the regulations on compressed air, but my boat's only 6 metres and it won't make the trip to Denmark to get the "Danish Maritime Authority" certification.

A lot of talk is about how efficient the car is running on compressed air. But, what about, as I mentioned in a previous post, the expense of compressing the air in the first place? It is like doing the internal combusting of an internal combustion engine putting it into a car and saying, "WOW," that's efficient.

I get scuba tanks filled, you have two problems,
1. The amount of power to compress 30 bars of air.
2. The time it takes, and when you get your tank filled from a compressor even a small scuba tank takes quite a bit of time. I know of one re-filler who had invested in large storage tanks which filled the tamks fast, he went bloke.
3. Compressing air creates heat so after the compressing you have to have a coolers and filters.

Think about this rationally, if all the cars lined up at the bowsers were filling up with compressed air, imagine the size of compressors they would need and the banks of storage.

Not to mention, which I will the maintenance costs of servicing the compressors.

Sorry but I can't see it.

And a boat that uses compressed air, and the air is replenished by an electric motor? If we are talking about an air driven boat where is the electricity coming from? A generator driven by an air motor. Are we talking perpetual motion here.

At least at my age I'll be dead before they prove me wrong.

[hansp77]

a bit long, but if you are interested,
from a 2004 (publicly available) academic paper,
http://web.fu-berlin.de/ffu/akumwelt...85%20wells.pdf
Peter Wells and Dr. Renato J. Orsato The Ecological Modernisation
of the Automotive Industry page: 379-80

Motor Development International (MDI) is the
company formed to bring to market the ideas of the inventor of the compressed air
engine, Guy Negre (Wells, 2002). The technical concept and the business plan have
generated much controversy in the automotive industry, and doubts over both re-
main.
However, the case is reported here as indicative of a different means of combining
product technology and business model. In this vehicle, compressed air is held in a
suitable canister. As such, compressed air represents stored energy. The compressed
air is then fed into a cylinder and allowed to expand, and in so doing the expansion
provides the motive force to push a piston and hence turn the engine. There is no
combustion, so there are no emissions at the point of use other than air- though of
course overall emissions performance depends upon the energy source used to com-
press the air. A useful attribute of the technology is that any sort of dedicated infra-
structure would not be technically difficult or expensive to install – air refilling points
could easily be added to existing petrol stations for example. Simple air compressors
could be run from domestic electricity and re-charge the cylinders overnight. The de-
tailed design of The Air Car is more complex than the above suggests, for example it
involves an innovative articulated connecting rod to allow the piston to be positioned
at top dead centre for a longer duration in the cycle than is normally the case with an
internal combustion engine. The engine develops maximum power at 3,500 rpm and
maximum torque at just 800-1,300 rpm. The slow speed and low temperature of ope-
ration (air in the cylinder head reaches 400 C maximum) mean than vegetable oil is
sufficient for lubrication, and the oil will last up to 50,000 km.
The car is positioned and performs rather like a battery electric vehicle without the
weight and cost penalty of high performance batteries. Compared with contemporary
petrol and diesel cars the range, top speed and acceleration are limited. An interesting
by-product of the technology is that the exhaust air is at minus 15 Celcius, so air con-
ditioning for the cabin is easy to obtain.
The engine concept has various non-automotive applications. However, MDI have
designed a vehicle structure within which the engine and tanks can be placed. The ve-
hicle is available in four basic body styles that reflect the urban / commercial vehicle
focus of the product: family car; van; taxi; and pick-up.