"Cé hé sin" (michael-m-mouse)
06/25/2015 at 09:10 • Filed to: Leyland, L60
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"Cé hé sin" (michael-m-mouse)
06/25/2015 at 09:10 • Filed to: Leyland, L60 | 4
| 10 |
It’s Thursday and so:
-The weekend is nigh
-It’s time for a two stroke
Last week we looked at the Commer TS3, a flat opposed piston triple used in the 1950s and 1960s. Today, to continue the opoc theme, we meet a tank and its engine.
Meet some Chieftain tanks trundling in a rather smoky manner down Straße des 17. Juni in Berlin on as it happens the following day, the 18th June 1989 which turned out to be a year of some significance for Berlin. What interests us is the smoke, which is coming from Leyland L60 multi fuel engines.
The L60 was intended to be able to run on any kind of fuel with a sufficiently low octane number that it would ignite under compression although diesel was its usual choice.
The L60 was an opposed piston two stroke engine with six cylinders, twelve pistons and a conventional crank set up - two, one at each end of the block. Unlike the TS3 it was fitted vertically. Also unlike the TS3 it was designed so that the upper crank only produced about one third of the power and was mainly used to power the supercharger and ancillaries while the lower crank provided most of the driving force.
Here’s a cutaway drawing by Terry Collins which dates from the days of actual drawings with paper and ink and not a computer in sight.
!!! UNKNOWN CONTENT TYPE !!!
Not that surprisingly for a Leyland engine it wasn’t very reliable and so the Challenger tank which followed the Chieftain used a Rolls Royce CV12, a conventional four stroke. The Challenger was followed by the Challenger 2, still the UK’s main battle tank, which has a Perkins CV12, actually the same engine as RR sold out to Perkins. Perkins in turn closed the factory which made their large diesels and there’s a shopping centre there now.
Leon711
> Cé hé sin
06/25/2015 at 09:31 |
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The Powershift in Steve's '12 Ford Focus killed it's TCM (under warranty!)
> Cé hé sin
06/25/2015 at 11:04 |
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Aww yeah, urban camouflage. It might be useless but it sure looks cool.
You can tell a Finn but you can't tell him much
> Cé hé sin
06/25/2015 at 11:47 |
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How do they get different amounts of power out of cranks that are absorbing power from the same cylinders? My first guess is different strokes on the two cranks, but I’m not sure that would actually do it.
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Cé hé sin
> You can tell a Finn but you can't tell him much
06/25/2015 at 12:12 |
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That’s a very good question which I was hoping nobody would ask! There’s an article about the smaller but similar Rolls K60
here
which describes how each pair of pistons is out of phase because of the need to uncover each port at different times. This means that ignition would take place when one of the pistons is not at the top of its stroke which is like reducing the stroke on that cylinder.
Snuze: Needs another Swede
> Cé hé sin
06/25/2015 at 14:36 |
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I think the the 1/3 power specification may be specific to the K60 based on the 20 deg. offset of the top crank. Do you know if this is true?
I ask because we had a Fairbanks-Morse 38-3-1/8 to run the backup generator on the sub when I was in the Navy. The top crank was only 12 deg. offset from the bottom. It still ran the supercharger and other ancillaries, but also had a relatively beefy drive-shaft gearing it to the bottom crank, which makes me think it was providing a fair amount of power to the generator.
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Cé hé sin
> Snuze: Needs another Swede
06/25/2015 at 14:43 |
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That may well be. I was assuming that the K60 and L60 (the tank engine) were the same basic design but in fact they’re not as the L60 uses its bottom crank to drive the blower.
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You can tell a Finn but you can't tell him much
> Cé hé sin
06/25/2015 at 15:46 |
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It must have something to do with the timing. It seems like it should be pretty easy to figure out a two stroke diesel cycle, but these are so different from a two or four stroke engine with a conventional layout that I just can’t quite get my head around them. They are definitely fascinating to read about and apparently I’m not the only one who thinks so. There is a lot of information, but unfortunately I haven’t found anything that actually goes into detail regarding the timing of the combustion/intake/exhaust events.
http://www.opposedpistonengines.com/page4.html
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Cé hé sin
> You can tell a Finn but you can't tell him much
06/25/2015 at 17:16 |
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And if we thought the L60 was hard to understand, there’s always the Deltic. One of those papers suggests a four crank Deltic (which should have had a name change!) but I don’t think they ever went that far.
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You can tell a Finn but you can't tell him much
> Cé hé sin
06/26/2015 at 11:38 |
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I’m pretty sure someone at Napier sold their soul to the devil. That is pretty much the only way to explain how the Deltic and the Nomad engines came into existence.
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Cé hé sin
> You can tell a Finn but you can't tell him much
06/26/2015 at 12:12 |
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Napier also built sleeve valve engines because they would, wouldn’t they?
There are still a few Deltics in use on the Royal Navy’s Hunt class minesweepers. They were chosen because of the lack of vibration (lots of cylinders so they kind of buzz when running) and low magnetic signature. They’re the last Deltics on active service.
There are a couple of preserved Deltic locomotives (they were the fastest trains in the UK for years) which get an occasional airing.