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The air powered locomotive

The air powered locomotive

The air powered locomotive

(OP)
http://www.aircaraccess.com/images/3stage%201.jpg

The compressed air powered locomotive has had a long, if quiet, career. The setup shown above is one of the later and more succesful designs.

I am very interested to know why they reduced the pressure from 150 to 30 atmospheres before using it in the engine. My only thought was that the 30 atm holding tank allowed the air to warm up a bit before hitting the piston, and perhaps 30 atm was as much as they wanted in the engine itself - 450 psi is a fair pressure.

Of course one thing worth pointing out is that they probably weren't worried overmuch about efficiency.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: The air powered locomotive

I wonder if it was just a conversion of a standard steam design.

Assuming it was, it was probably easier to stick a reducer in than than to uprate all the engine components and fiddle around with cylinder volumes at TDC.

A.

RE: The air powered locomotive

Long ago I visisted a couple of mines that use air powered engines to pull ore cars.  The air tank was about the size of an 800 gallon butane tank. I don't know the pressure.  
It was more of a put-put than a train. Probably a 2" gage.
It hauled ore and tailings.  
The tailings went to a big dump that is now a site targeted for clean-up. They didn't get all the mercury out of the rock and now its being leached into the creek, the river and ocean.

RE: The air powered locomotive

(OP)
Thanks BE, that is a fun page. I suppose it seems wasteful, but maybe that first pressure reduction dried the air out enough to prevent the engine itself from freezing up internally.

Although 450 psi is not very high compared with peak pressures seen in an IC engine, the pressure is sustained for much of the cycle (depending on the cutoff ratio) and that has a big effect on the strength required for each part.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: The air powered locomotive

I think I read an article about air powered locomotives in Compressed Air Magazine (Ingersoll Rand) several years ago.
I tried to search their archives but for some reason was unable.

http://www.compressedairmagazine.com/index.asp

There were quite a few of these locomotive in mines near my home. They were nearly all gone by the 1960's.

RE: The air powered locomotive

As a guess;
Isn't it easier to design a compressed gas engine to run on a fixed pressure than on a constantly decreasing pressure?
The displacement must be great enough for the engine to still work at the end of the day when the storage tank pressure is low. That much displacement may tend to over-perform in the morning if full tank pressure was applied.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: The air powered locomotive

(OP)
Sure. But the usual way to cope with that would be to vary the cutoff. That is the point on the power stroke at which the intake valve closes.

If you run with the intake valve open for the entire power stroke you run at the full reservoir pressure. If you close the intake valve just after the start of the power stroke then the air that is in the cylinder expands adiabatically. The latter is far more efficient. That's what you do on a steam engine, when you are cruising along you change the cutoff to minimise the steam consumption.



Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: The air powered locomotive

It's probably simpler/cheaper to design a pre-set pressure regulator, that never has to be touched for anything other than maintenance purposes, into the air supply to the engine  than to design an automatic pressure regulated valve cut-off or train operators to vary it manually and trust them to use it properly.

Additionally, stepping down the pressure after the tank means all the engine plumbing and controls can be made to a lower pressure rating.  

RE: The air powered locomotive

I see that the Indian car maker TATA is talking about marketing a compressed air powered car. This is looping right back into history.
B.E.
 

RE: The air powered locomotive

At 30 bar, you can use cheap commercial air valves, and there's less risk of a Diesel explosion if you introduce a little oil into the gas stream to lubricate the engine.

 

Mike Halloran
Pembroke Pines, FL, USA

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