Date: Fri, 19 Jul 2002 11:16:13 +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: Sleeve valve engines - off subject
Content-Type: text/plain; charset="iso-8859-1"
>> Much better efficiency than any poppet valve engine could ever give, and
much more power.
Thats why Formula 1 cars use them - NOT!
Yes, the British took up Knights ideas in the 20's and 30's and worked and
worked and worked and worked ... and finally, started to get these sleeve
valve engines reliable and the oil consumption down. Bristols mainly,
but there were others. By 1943 the numbers of sleeve valve engines flying
over Germany daily was greater than any other type, mainly 2 and 4-engined
bombers.
Although the Bristol Centaurus was their ultimate engine, the workhorse was
the Hercules, rated variously at about 1650 - 1800 HP, by 1945 it had an
MTBO of 3,000 hrs - an unheard of figure for a piston aero engine, and a
military rated one at that - most others were in the 1000 hr range if they
were good engines. These were all air-cooled double-sleeve engines.
Bristol's (and one man in particular, Sir Roy Fedden) had developed the
metallurgy, functional designs and especially the production technology to
finally make sleeve valves reliable, efficient and powerful. I don't know
how many Hercules engines were produced but an awful lot. Churchill visisted
the factory once just to see the remarkable production lines, and said
'...without, doubt, without your engines, we could not have taken the war to
the Nazis in Germany as succesfully as we have ', referring to the 1,000
bomber raids. Sir Harry Ricardo was also instrumental in the development of
the sleeve valve engine in the UK, as he was in almost every thermodynamic
device of the era!
The Napier Sabre 24 cylinder 'H' engine was a watercooled sleeve-valve
engine of 2,000, 2,500 and ultimately 3,000 HP but without Bristol's being
'told' to make their production technology available, it would never have
had it's teething troubles solved. The Hawker Typhoon and later Tempest with
this engine were the fastest of their day, the Tempest's thin-wing airframe
effectively combating early onset of compressibility and maintaining
stability and control at the speeds now attainable - circa 450mph - and
regularly being dived at over 500.
[There are sound files on the web of this remarkable engine starting up
(cartridge starter), taxiing, taking off and flying past - quite a howling
monster]
With today's synthetic lubricants matters would be a lot different, and
easier, but vegetable oils (the sweet smelling castor bean-based Castrol R)
were still being used in motorcycle racing circles into the 70's, such is
their film strength.
Almost unknown, Rolls Royce (the poppet-valve kings, sodium-filled exhaust
valves etc) were moving very much towards sleeve valves as the war's end
approached, having 3 large development projects running for some very
interesting engines. The last of these, a lightweight engine designed for a
short-range Spitfire style interceptor, was said by one RR engineer
(responsible for its turbocharger installation) to be 'without doubt, the
finest aero-engine even built'. Called the Crecy, it produced just over
5,000 BHP - and was a sleeve-valved two-stroke! 6 were built, and one
eventually ran for 6000 hours, not only was there no perceptible wear
detected after this, but sfc (specific fuel consumption) at altitude was
found to be not far short of the best of the day - it wasn't designed for
range, but lightness and time-to-height - a sprint engine. It was 90 degree
V-12, single sleeve valve engine, the turbocharger receiving 36,000 exhaust
pulses per minute! Note that by their nature, two-strokes and sleeve valves
are both much more immune from detonation problems than 4-stroke poppet
valved engines. This was the culmination of 8 years work on this engine, the
original spec. being laid down by the i.c. guru of all time, Sir Harry
Ricardo, to an air ministry requirement. RR had obviously mastered
sleeve-valve design and production, but for the advent of and a shift in
resources towards the gas turbines then coming off the production lines (at
Bristol's as well), these would have become the ultimate piston engines.
Sir Roy Fedden and P&W's chief engineer became friends early on and P&W
started several sleeve valved projects as a result, one being an in-line
engine with separate barrels.
Keith Duckworth, of Cosworth V8 fame, built a single sylinder sleeve valved
engine some years ago, as a technology demonstrator - apparently it's
specific output was not far from that currently being achieved by their
Grand Prix engines.
The British Napier 'Deltec' diesel engine was developed after the war as a
powerful railway engine (3,000 hp) and was of 2-stroke, opposed piston
design in a triangular configuration with geared crankshafts (combustion
chamber in a perfect uninterrupted enclosed cylinder) - variants are still
running today, and it was also used in high-speed marine applications
(MTB's). When I was at college we had one of these in a pumping house to
compress the air for the supersonic wind tunnel. Some sleeve valved engines
are, I believe still used on the railways in Canada and South Africa.
Production costs of double-sleeve and even single sleeve valve engines are
considerably higher than the well understood engines of today, and unless
something changes radically in the world of auto engineering, I doubt we
shall see their like again.
If you're interested in the history of these engines -
http://www.marss.com/media/sleeve.pdf is good and Rolls Royce's Historical
Society sell a book about the RR Crecy V12.
Apparantly, some Napier Sabres 'might' still be powering unlimited power
boats.
Or go to Oshkosh and witness a Hawker Sea Fury's 2,500 BHP Bristol Centaurus
whining past - quite a sight - and quite a sound - an engine so succesful,
it was built for over 30 years, from 1938 to 1970.
Clive Smith
'88 Syncro Transporter
----- Original Message -----
From: "SpaceKommander" <jboldway@BEE.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, July 19, 2002 1:09 AM
Subject: Running on tap water - didn't work!
> I'm angry. I filled my tank with water and tried to run it to get some
fuel
> economy benefits but the damn engine quit after only a few seconds on
> running on tap water. Who thought up this idea?
> Seriously, in 15-20 years there will be a change in engine design as
people
> realize designs from the 1930s are the best way to assemble and run
> engines. Two words - sleeve valve. Everybody is familiar with poppet
valves
> which get roasted in exhaust gasses. WWII engines such as Centaurus and
> Perseus and Knight auto engines of the 1930's used something called sleeve
> valves. It's waaaay too complicated to go in to but just say the poppet
> tulip shaped valves which bang in to the heads were eliminated and a
> circular sleeve surrounding the cylinder with ports machined in the sleeve
> and cylinder did the job. Much better efficiency than any poppet valve
> engine could ever give, and much more power. Steel and aluminum Sleeve
> valve engines are complicated and extraordinarily expensive. However,
> ceramics make the sleeve valve engine seem like a likely candidate for any
> new engine development as they can operate at much higher engine
> temperatures than any poppet valve engine could ever stand without
> introducing failed valve heads or detonation due to excessive exhaust
valve
> temperatures - there are no "valves!" - and no shock of valves slamming on
> to cylinder head - a smooth sliding action. Ceramics don't suffer the
> thermal expansion problems. Plus some things like a steel connecting rod
> surrounded by a ceramic which puts the steel under constant stress loading
> can be made using concepts of SPG style pressed together cranks and a one
> piece connecting rod of lightness and strength. Imagine an engine without
a
> complicated cooling system. Ceramic sleeve valve engines also allow things
> such as no valve springs and operating at temperatures far in excess of
> anything currently running as the thermal distribution is much more even -
> no super hot exhaust valves. Sleeves that contact the cylinders most of
the
> time or form a "port" to relieve exhaust without much thermal transfer.
> That, folks, is the future of gasoline internal combustion engines. We
> still have the 14.7/1 air/gas ratio, but operating at higher temperatures
> gives more power.
>
> Next is the conspiracy to repress the soda carburetor.
>
|