On Wednesday, 20 August 2014 08:06:04 UTC+2, Glen Labah  wrote:
> In article , bob  wrote:
> 
> > To get the necessary performance, the RDC needed two engines.  Each was 
> > a 6 cylinder 10.8 L 275 hp (later models 300 hp).  A modern engine of a 
> > similar size might be the MTU 6R 183 TD, with 6 cylinder, 11 L, 422 hp 
> > and meeting modern emissions standards.  Larger engines are available, 
> > for example the Cummins QSK19, a 19 L 6 cylinder 750 hp engine used in 
> > a number of under-floor engine DMUs.  I can't find figures for fuel 
> > consumption, but I'll wager the modern engines are significantly 
> > better.  Twin engine DMU vehicless are definitely a thing of the past.
> 
> The thing is that with FRA car bodies the 422 hp would probably not be 
> enough.  The newest LIRR EMU cars are somewhere around 1,200 horsepower 
> to meet the performance they want.

It's the nature of the technology that electric traction will always be able
to pack far more power into a given size/weight than a diesel prime mover. 
For European type operations, somewhere in the 500 hp/vehicle range is
adequate for 100 mph operation 
and 750 hp/vehicle is adequate for 125 mph.  That's based on a ~45 Tonne
vehicle weight.  This is entirely within the capabilities of current
off-the-shelf under-floor engines[1].

> The Budd RDC also drove the inside axle of each truck, so at least two 
> axles were driven.
> 
> With a single engine, would you transmit the power to two trucks?  Or 
> would you transmit it to a single truck and link the axles so that both 
> axles on that truck are powered?

Common practice in Britain is for 2 axles per vehicle to be powered (giving
50% powered axles).  That's good enough for commuter-train levels of
acceleration, and in the kinds of routes where DMUs are common, 25% powered
axles would not pose a problem (
ie a single powered axle per car).  Considering that a locomotive hauling 6
cars only has 14% powered axles, even 25% is a huge improvement.

[1] with the caveat that new EU emissions regulations have just come in, and
the existing designs are not yet conformal.

Robin

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