Mortimer wrote:
> "John Wright"
pegasus.f2s.com> wrote in message
> news:w5ydnd_9eOCZczTVnZ2dneKdnZydnZ2d@pipex.net...>> Mortimer wrote:
>>> "John Wright"
pegasus.f2s.com> wrote in message
>>> news:8qSdnbHAfJTBdzTVnZ2dnUVZ8gidnZ2d@pipex.net...
>>>>>>> The original Junkers Jumo was an opposed piston diesel engine, the basis
>>>> of which became (when the Brits got hold of it) the Napier Deltic, which
>>>> was also an opposed piston design, but with more cylinders - usually in
>>>> a triangular form hence the name.
>>> Was the Junkers version of the engine a two-stroke like the Deltic
>>> railway locomotive engine? Is there a technical restriction to having a
>>> conventional inlet valve and exhaust valve per cylinder pair and having
>>> four-stroke operation? Or was it influenced by the more frequent power
>>> strokes (one per crankshaft rotation rather than one per two rotations)
>>> at the expense of efficiency and complete combustion.
>> Yes it was a two stroke, most probably as a way of keeping the weight
>> down. I think you could have a valved four stroke opposed piston engine
>> but you couldn't use poppet valves as are used in petrol or diesel engines
>> nowadays, you'd probably have to use a sleeve valve like some of > the
>> Bristol radial engines and the Napier Dagger, Rapier and Sabre engines of
>> the late 1930s or early 1940s
>
> Ah yes, of course: poppet valves would need a curved cylindrical profile to
> match that of the cylinder wall, which would need a nifty bit of machining
> to create!
>
> Given the mixing of inlet and exhaust gases, and the fact that for part of
> the stroke both the inlet and exhaust ports are open simultaneously, it's
> always amazed me that two-stroke engines work at all without wasting most of
> the inlet fuel straight out of the exhaust pipe (at least for petrol
> engines - for diesel all you are wasting is some of the inlet air).
A lot of 2 stroke diesels use what they call scavenging pumps - like
turbochargers or superchargers in normal usage. I think the Deltic in
the Class 55 was like that, unlike most other big rail diesels it wasn't
turbocharged.
>> Talking of railway Deltics I think the most thrilling noise I ever heard
>> was a Class 55 with 11 coaches on full power going through Durham
>> station - I was on the platform at the time. Shortly followed by a heavy
>> coal freight with a pair of Class 37s at the front. Tractors indeed.
>
> Yes, it's a very evocative sound! It's a shame that the cutaway working
> version of the Deltic in the National Railway Museum doesn't have a
> recording of an Deltic-powered loco at full throttle as an accompaniment.
There are six preserved Class 55s around, some with main line clearance,
so the sound is not lost. Some interesting stuff on youtube as well. An
interesting trainista point is that the Class 55 and Class 37 share
bogie and traction motor design - they're basically interchangeable.
I still occasionally get special trains with two class 37s in charge
going past the house. Janet, my wife, wonders why I rush out of the door
when this happens and I'm around. More healthy to get a charge out of
the noise of a Class 37 than Fern Britton in a bikini :-) IMHO anyway.
--
John Wright
"What would happen if you eliminated the autism genes from the gene pool?
You would have a bunch of people standing around in a cave, chatting and
socialising and not getting anything done!" - Professor Temple Grandin
