Date: Mon, 16 Feb 2004 22:52:40 -0600
Reply-To: Stan Wilder <wilden1-1@SBCGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1-1@SBCGLOBAL.NET>
Subject: Re: "green" cars (NVC)
In-Reply-To: <3527.192.168.1.101.1076991555.squirrel@www.presslab.us>
Content-Type: text/plain; charset="iso-8859-1"
Depolymerization combined with cleaner & hotter engines (ceramic?
turbine?) seems likely for the future.
Ryan
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Ceramics, really?
You can be forgiven for finding the idea of ceramics in engines
unbelievable. After all, aren't they too brittle and breakable to be useful
where mechanical stress and movement are encountered? The types you're used
to sure are, but new formulations are appearing that are remarkably tough,
so much so they look promising for components from wrist pins to valves.
USACA (the United States Advanced Ceramics Association, which includes such
companies as Allied Signal Aerospace, Allison, Caterpillar, Coors, Dow
Corning, Dupont, GE, IBM, Kyocera, Martin Marietta, Rolls-Royce, Textron,
3M, etc.) states that intensive R&D has yielded dramatic improvements in
ceramics, including:
Silicon nitrides now have twice the room temperature strength, three times
the high temp strength, and 10,000 times the fatigue life of previous
versions.
Manufacturing yields of useable parts have increased from 2-5% in 1980 to
40-50% today.
A ceramic turbine rotor has run over 1,000 hours in a prototype engine.
Monolithic ceramics are demonstrating that they can take impact, tip rub,
and minor damage without catastrophic failure.
Ceramics are not only resistant to high temperatures, they're also good
insulators, so can be used to keep those btu's where you want them and to
protect metal parts. They have exceptional wear characteristics too,
especially in areas where lubrication is sparse or non-existent at start-up.
And how about components that weigh less than half as much as their metal
equivalents? They'll cut parasitic losses, allow higher operating speeds,
and enhance smoothness by reducing reciprocating mass. These are the kinds
of advantages those relentless engineers can't leave alone.
Already out there
Ceramics have been used in automobiles for years. There have always been
spark plug insulators, after all, and don't forget water pump shaft seals,
catalytic converter pellets and monolithic cores, and oxygen sensors. And
some breakthrough applications have been around for a while, but are unsung.
For example, Porsche installed cast-in-place aluminum titanate ceramic
exhaust port liners in the 944 because they helped insulate exhaust heat
from the engine, so the cooling system could be made smaller. Since the
exhaust stream lost less heat, the turbocharger operated more efficiently.
There was also some benefit in more complete combustion, which reduced HC
emissions and catalytic converter light-off time.
The team of Isuzu and Kyocera has offered silicon nitride diesel glow plugs
since '81, which heat up many times faster than the metal type. Mazda and
Toyota started using ceramic diesel precombustion chambers in the
mid-eighties to retain heat, thus keeping combustion temperature high and
improving cold running characteristics. Mitsubishi has put ceramic rocker
arm pads into production.
An impressive application is the ceramic turbocharger rotor. Introduced in
late '85 on a number of Nissan 300 ZX's, it's much lighter than its metal
counterpart so has less inertia and reaches boost rpm more quickly, which
reduces turbo lag considerably. This benefit wasn't only noticed by the
Japanese: Garrett AiResearch created a ceramic-rotor turbo for Buick, which
put it into the limited-production Regal Grand National GNX -- one of the
hottest cars in the world back then. Boost time was cut in half.
Too high
But availability of the best materials imaginable won't get them into
engines if the car makers aren't interested. Even if they can demonstrate
better performance and durability, the auto manufacturers want them to cost
the same as metal.
Ceramics suppliers understand this and have been working for years to get
costs down. For instance, in the mid-eighties Champion Spark Plug was
looking for a way to utilize its excess ceramic-making capacity, and came up
with a patented material called "Ceraform ZTA" (Zirconium Toughened
Alumina). It cost about 1/7th as much as other ceramics, yet was easy to
form and met the physical requirements for flexural strength and impact and
thermal shock resistance that are necessary for many engine parts. The
company successfully demonstrated valves, seats, guides, and piston pins,
but so far there have been no takers among the auto manufacturers.
With what's called "the economies of scale," ceramics will come way down in
price. It's probable that these will include monolithic silicone nitride,
which is as strong as metal, but doesn't like impact, and has only 1/10th
the flaw tolerance of steel. Then there are ceramic composites that consist
of a silicon nitride matrix with silicon carbide "whiskers," hair-like
strands that make the stuff 40% more resistant to internal cracking than
non-reinforced monolithic materials.
The manufacturing techniques required to eliminate flaws is a major factor
in the current high price. Another is that "net build" is necessary. In
other words, the part has to come out of the mold at precisely the right
size because you can't do any machining.
First, the valve train
These modern materials lend themselves especially to valve train
applications. Wear could be reduced at pushrod tips and rocker arm fulcrums,
or cam followers with OHC, which would stabilize valve train performance
over the life of the engine. Ceramic guides could cut oil consumption, and
seats of the same material wouldn't erode or recede even though the lead is
out of gasoline.
These are low-risk/low-return parts. The most significant benefits would
come from a more daring step: ceramic valves. The 60% weight reduction would
allow higher engine speed and/or lower friction and less parasitic loss.
Plain lifters could be substituted where expensive roller tappets are now
used.
Beyond valves, there are ceramic wrist pins that weigh much less than metal,
yet are so much stiffer they can be made considerably smaller in diameter.
Rings are a possible application, too. Perfect Circle is researching a
ceramic coating with fabulous wear characteristics. Or, how about
compression rings of a titanium nitride-based cermet? They've been tested
for 100 hours at full load and rpm with no appreciable wear and, amazingly,
no breakage. Cylinder liners are a logical extension, then pistons with
ceramic crowns, completely non-metallic pistons, and ceramic-insulated
combustion chambers.
Blue sky
The ultimate the idea can be taken to is the low heat rejection Diesel
(LHRD), sometimes called the adiabatic diesel (really a misnomer because
"adiabatic" means a total lack of heat loss, which is as elusive an
achievement as absolute zero). In this ideal powerplant, all the Btu's in
the fuel would be converted into useful work in the cylinders and by a
turbocharger. There'd be no waste heat, so the cooling system could be
eliminated and levels of efficiency would be fantastic.
An exciting prospect, but really just a goal to work toward that will
probably never be fully achieved. The technological breakthroughs needed are
formidable, especially in the area of lubrication -- no known oil, even
synthetic, could withstand the temperatures involved, and with solid oxide
lubes you lose the necessary benefits of liquids. As a spokesman for one
ceramics company told me, "It makes sense to insulate a diesel to some
degree, but it's my view that you'll be getting incremental improvements and
you'll get to the point where it's not worth the next step."
The other futuristic possibility is an efficient and relatively inexpensive
gas turbine, most likely a tiny unit that could bring practicality to the
hybrid. That is, an electric car with an internal combustion-powered
generator to provide acceptable range once you drive out of congested areas
where ZEVs (Zero Emissions Vehicles) are required. The metal turbines that
have been around for decades waste heat like mad, and require expensive
alloys and complex machining, but those drawbacks could be eliminated with
ceramics. That would give us a smooth, nearly emission-free engine that
could run on any flammable liquid from drain oil to scotch. There's even the
possibility of burning powdered coal. But, as with the LHRD, we're talking
21st century.
No problem
Will all this affect auto service and repair? Not very much. There would be
no procedural changes at all for ceramic exhaust port and intake manifold
liners, pushrod tips, rocker arm pads and fulcrums, and lifters. While
valves, seats, and guides would require more careful handling, they probably
wouldn't wear out. There'd be no chance of cutting faces and seats in the
normal way, but, again, they shouldn't need anything but maybe a little
lapping to get rid of deposits. After all, there can't be any corrosion, and
it would take almost unimaginable heat to burn out the sealing surfaces.
The thing to remember about all this is that alternative materials will be
introduced gradually, a part here, another there the next year as the
manufacturers see performance and durability improvements that are cost
beneficial.
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