Group: uk.transport · Group Profile
Author: MortimerMortimer Date: Aug 18, 2008 15:01
"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).
> 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.
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