> 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.
>