Date: Sat, 19 Oct 2002 13:39:26 +0100
Reply-To: Clive Smith <clive.harman-smith@NTLWORLD.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Clive Smith <clive.harman-smith@NTLWORLD.COM>
Subject: Re: Increasing horsepower
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>The power recovery turbines are geared back to the crankshaft and
>may contribute something in the vicinity of 20% of the engine's power
output.
- which provided the exhaust pulse 'tuning' was not compromised (unlikely)
would be 20% reduction in sfc minus any lube/gear drive losses
, even 2 or 3% sfc is 'significant' in aviation fuel burn/fuel load terms so
this was quite an innovation.
However, what should be born in mind here is that scaling factors play a
large (sic) part. That is, these sort of gains just cannot be achieved in
smaller devices - so don't get your hopes up with that 999cc Asian import!
Without going into a treatise on deeper engineering and natural physical
world laws think about this. Scale down an engine or turbocharger till it is
much smaller, and you will find that it effectively produces less and less
effective power/compression as the losses go up proportionately and the
efficiency comes down, the two together creating a quite dramatic law of
diminishing returns. At a certain size you will find that a t-charger or
s-charger produces NO effective nett gain compression or in the case of an
engine, one barely able to overcome its own friction.
Note that all those big radials were big, very BIG. The Bristol Centaurus
was 50 something litres, the Wrights even bigger. Thus turbo-compounding
would not be particularly feasible at automobile engine sizes - not that
anyone ewas suggesting this - but it might save a few people some
brain-time. Things improve of course, but natural laws stay the same - I
knew someone here who produced one of the smallest gas turbines producing
nett thrust in the world, and he gained a PhD whilst doing so, a clever
configuration, think it produced about 25-40lbs of thrust, but the trick is
to get that at a reasonable sfc, rather than throwing lbs of fuel down the
drain per second to get this, so don't confuse this with others...
So at our scale, using compressors to fill the cylinder better is the best
use of a superchatger, howsover it is driven.
Clive
'88 Syncro Transporter
----- Original Message -----
From: "Angus Gordon" <agordon@BRIGHT.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, October 19, 2002 12:50 PM
Subject: Re: Increasing horsepower
> >This was called turbo-compounding, a very different thing from straight
> >supercharging, or straight turbocharging, the main benefit here being
fuel
> >efficiency...
>
>
> Well, as long as we're talking Connie's (is it still Friday?), they
> actually use the Wright R-3350 engine (not 3340 as reported). The power
> recovery turbines are geared back to the crankshaft and may contribute
> something in the vicinity of 20% of the engine's power output.
>
>
> Angus (aviation police)
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