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 01:04:25 GMT
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Viewed:
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2909 times
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> (the 645 and 710 are 2 cycle, but have 4 exhaust valves per cylinder... no
> Intake of course since they're fuel injected Diesel, but these are not OP,
> they're conventional single piston per cylinder)
The big advantage of a OP engine is that you get good scavange air flow via the
two ends of the cylinder being open at the same time. So, yes, it is in some
ways more complex (timing gears between crankshafts, rather than valves), in
other ways they are far simpler (no head, easy cross flow for air exchange).
I know we no longer have any OP engines (CF/RCN). When I got in (1996) we had a
training engine that was a 3 cyl. FM OP at the Fleet School. Not sure how long
it had been apart, but I never saw it run.
On the other hand, I have run GM 268A's, and reheaded one. They are also a 2
stroke, with a Roots blower for scavange air. (on a aluminum block, with
Stainless/austenitic heads...non magnetic :). They tended to leak oil. Lots of
oil.
It's all about air exchange- it is far easier to 2D model airflow from end to
end than for a cross scavange engine. Since computer modeling has taken over,
the limits of 3D airflow modeling have basically disapeared, and large engines
(Sulzer RTD @ 95 MW, ect) are done that way. Two stroke suffers in that it MUST
have turbocharging or supercharging to run, whereas a 4 stroke does not suffer
that absolute requirement.
James Powell
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Message is in Reply To:
 | | Re: BNSF new paint
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| (...) Well now I'll display MY ignorance... I know that a lot of 2 cycle engines are valveless but I did not think it was mandatory that they not have exhaust valves. Anyway, I am pretty sure the FM is 2 cycle, I think the Alco 244 was (but too lazy (...) (20 years ago, 26-Jan-05, to lugnet.trains)
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