In a message dated 7/10/2010 8:37:57 P.M. Eastern Standard Time,
ceengland@bellsouth.net writes:
The
points above make me ask a question I've wondered about for years.
I've
seen it mentioned several times that best power in a rotary is with
relatively low water (or was it oil?) temps; around 160 degrees. I
assume that's empirical data, & don't question it. But when the
discussion turns to efficiency, I wonder if that principle (yes, I had
to look up which way to spell it...) still applies.
When the fuel and air are already a mixture flowing through the intake
manifold, you have a target for infrared energy from the rotor face as the
intake port opens. Not as bad on a side port as on a periphery port. The energy
expands the mixture rapidly and so less cylinder filling results. Just air with
no fuel mixed in does not suffer as much energy absorption.
So the cooler the oil inside the rotor the less charge lost to heating. And
injection directly into the chamber after the port has closed would be ideal. As
on the proposed X-16 engine.
Decades ago, I read of Japanese car manufacturers
experimenting with
all-ceramic engines without any cooling systems to get
efficiency up by
keeping the engine's heat in the combustion chamber. If
we make an
assumption that with synthetic oil & better quality 'soft'
seal
materials the rotary can be safely run at higher temps, say in the
220
degree range, would that be enough to improve BSFC? Obviously nowhere
near the temps where a ceramic engine could operate, but would it be any
help at all in compensating for the large swept area of the rotary
combustion chamber?
Charlie
Racing rotaries and flying rotaries is not an exercise in efficiency.
Racing engines get little over 4 MPG.
Car engines are designed to be most efficient between 2,000 and 3,000 RPM
where it spends nearly its entire life. A 100% efficient engine would convert
every pound of fuel into work, and the engine and the exhaust temperature would
remain at ambient at all times.
This would mean that every BTU had been converted, and none was lost to the
engine.
So you see the ceramic experiments. The ceramic is a good insulator and can
withstand massive heating with little loss of strength. Called adiabatic
engines. See Smokey Yanuck.
Smokey lined his aluminum heads with water glass because they absorb too
much heat if left stock.
The object is to retain as much heat as is possible in the combustion
chamber. Smokey had the same problem with the hot intake over expanding the
incoming mixture, so he provided a turbo that ran at just a few pounds to
maintain flow direction in the manifold.
Smokey had a gag for preventing detonation in very high compression
engines. Nobody found out how he did it. He let Detroit engineers drive his
Mercury Capri beater with his adiabatic engine. It would not detonate even
starting out in 4th gear. The intake manifold ran inside the exhaust system.
Detonation is charge temperature dependant.
How much fuel any particular engine needs to make each HP is a function of
its design.
As you lean past best power, you use less fuel, but the HP is coming down
as well, and the BSFC stays about in the same area. At very low speeds where
burn time is long and lean mixtures can burn completely, better BSFC is
possible, but total Hp will be well down.
The airplane is a dyno. Just make changes and watch the tach.
Lynn E. Hanover
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