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They would make engine out of ceramic, if it weren't so brittle. There has actually be attempts made to do so.
In fact, ceramics are so good at high temps, that a (very expensive) prototype of a ceramic engine was built, that required no oil because there was no reason to lower engine temperature.
Originally posted by rxtreme I thought oil was used primarily to reduce friction (which then, in turn, reduced heat), but friction also wears parts. Wouldn't any piston engine require something for lubrication?
Well, you can engineer ceramics to be more slippery than steel (quite a bit more actually). Don't know what the coefficient of friction on this engine was though. In the interest of fuel efficiency, you'd want the piston/cylinder interface to be as slippery as possible, but its not a material concern with these ceramics they were using. While ceramics may be brittle, they are harder than all-get-out. Iron, titanium, and all our other "super-metals" don't come close to having the hardness of ceramic. I forgot to mention, the pistons were ceramic too.
The goal was (with this engine) to be highly environmentally friendly. Think about how many gallons of used oil and engine coolant make their way into the environment. An engine that required neither would be a fantastic breakthrough.
Haven't heard much more about this engine since the preliminary data came out. I know it was wickedly expensive and extremely difficult to make. The brittleness problem was more-or-less solved, I guess, because they bench-tested it upto 1,000,000 miles with no failure (and hardly any noticeable wear in the cylinders). I think what killed the project (unless its still going, I can't find their webpage) was the fact that even in mass production, the estimated cost per engine would be (gulp) $50,000.