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Originally Posted by freebeard
My understanding, when rotary engines were introduced was that they had seals that wore excessively but were affordable, else seals that wear well but had unobtanium pricing.
Is silicon nitride expensive?
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The aftermarket silicon nitride seals for Mazda engines are something like 2400 a set, so yes. I think Mazda would be able to make them cheaper than that though, and I imagine it's possible to produce a plasma spray coated metal part that's much cheaper. Either way, in this day and age, it seems silly to use plain iron apex seals when there are more advanced materials.
As far as I can tell, silicon nitride powder is pretty cheap (you run an arc through silicon powder in nitrogen gas), but sintering it is very difficult. A process that can produce a thick coating on pieces of stainless steel might be very affordable.
Quote:
Originally Posted by cRiPpLe_rOoStEr
Due to the porting, much like a 2-stroke reciprocating engine, a Wankel has a quite narrow gap on its RPM range where it will operate more efficient. Sometimes I wonder if a power valve system similar to what used to be common on some 2-stroke motorcycle engines are likely to overcome such deficiency, or if Wankel would only make a comeback serving as range-extenders.
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The porting doesn't make it like a 2 stroke (which needs exhaust scavenging), it makes it like a motorcycle engine (4 stroke but no VVT). I believe the Renesis had 3 different intake ports to increase torque in different parts of the rev range, but fundamentally, a Wankel engine is happier at high speeds due to its high heat conduction losses.