Subject:
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Re: BNSF new paint
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Newsgroups:
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lugnet.trains
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Date:
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Thu, 27 Jan 2005 01:20:45 GMT
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Viewed:
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2941 times
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> > They are probibly a lot more efficent when whey do have exhaust vales. A
> > basic two stroke doesn't clear the cylinder of exhaust very efficiently. • Snip
> Oh ya, no doubt.
Atually, from what I remember of the movies we watched @ school, the air
exchange can run up to about 98% clean air in a loop type arrangement. That's
using something like 200% excess air in order to clear the cylinder of
combustion gasses.
> I think one of the reasons for this whacky two piston, one cylinder, central
> combustion chamber arrangement is that in an exhaust port system, with the
> proper amount of lag between cylinders, you can arrange the exhaust to happen
> at a moment when there is a lot of compression in the cylinder giving a nice
> blast... Not sure, would have to study that Deltic animation or whatever to > be sure.
Nope, you don't use the cylinder compression at all. You use either tubocharger
or supercharger to give a positive air pressure above the exhaust rail pressure.
(at least in more modern (1940+) designs...the earlier diesels did some darn'd
strange things, look up Hamilton engines for one...)
> > However in the two cylinder one combustion chamber arrangment you can't have
> > cylinder head mounted valves, because there isn't a cylinder head. This is why
> > I'd be surprised if there were 2 stroke with exhaust values, or 4 stroke
> > versions of this engine design.
>
> Nod. BUT it can't be a completely uniform cylinder wall, there have to be at
> least some cutouts for the fuel injectors. The FM pistons have S shaped
> depressions for fuel injector (spray paths?) stuff.
It isn't completely uniform. Again, going from memory, the ports are different
shapes (intake and exhaust), and there are 3 injector assemblies for each
cylinder. But it is far more uniform than a head across the top of a
'conventional' diesel is :).
> So arguably if you had good valve timing you could have valves with curved
> bottom surfaces that fit into the cylinder sidewalls, or some sort of ported
> arrangment.
You don't need to worry. Because you are using Uniflow to clear the cylinder,
there is no need to have curved bottom surfaced valves. The cylinder skirts are
the valves.
The advantages of using the more conventional Uniflow design (exhaust valve in
head, intake by piston movement) are given in my marine engineering book as a
shorter piston skirt. (= less momentum per piston, smoother running).
James P
(I knew my diploma in Marine Engineering would come in handy for SOMETHING!)
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Message is in Reply To:
 | | Re: BNSF new paint
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| (...) Oh ya, no doubt. I think one of the reasons for this whacky two piston, one cylinder, central combustion chamber arrangement is that in an exhaust port system, with the proper amount of lag between cylinders, you can arrange the exhaust to (...) (19 years ago, 26-Jan-05, to lugnet.trains)
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