Basic rotary theory question
 

From what i understand our rotary engines are supposed to burn oil, and if so i have a few questions. Do rotary engines have oil injectors in their oil pans? Does it have a oil dip such as a piston engine that splashes oil around to lubricate moving parts? How does this work lol.

great question, i think this diagram and information with it may help to answer your question.

The MAZDA RX-7 86-88 technical page

^The perfect link Scott.
Oil is used for lubrication and cooling....not unlike most piston engines. It's a pressurized system, not much splashing or dipping going on. Journal bearings on the rotors and e-shaft (rough equivalent to a crank).The injectors are in the housings. A very small amount is injected into the chamber at the intake phase. This lubricates the hard seal to side plate interface, and helps compression. Again, not unlike oil rings in a piston.

I assume they are wet sumps?

yes.

Now, this is something that I don't understand. As far as I know, in a rotary oil doesn't naturally return to the bottom of the crankcase as it happens with piston engines. It has to be brought back there through dedicated oil passages. Is this correct?

In that case, why would the engineers decide to place the oil pan beneath the engine? Wouldn't it be just as easy (or just as hard) to place it elsewhere? You could then lower the engine even further in the chassis, and there would be no complexity drawback, as all of the additional equipment for a "dry sump" setup is already there.

Am I missing something?

Regards,

Andrea.

no.. it is more correctly termed a version of a "dry" sump,, the crank does not whip in an oil bath like a traditional wet sump
.. just slung underneath for practicality of making the smallest package

oil is directed everywhere it needs to go under pressure from the pump
.. all vent or drain eventually back to the sump
.. oil from within the rotors returns via the centre plate with gravity

I suppose that was not directed at me, but it does nevertheless answer my question, as I didn't know that part of the oil return path was by gravity. I thought it was all under positive pump pressure. That explains the position of the oil sump then.

Andrea.

Apparently, these engines require as much oil cooling as well as water cooling...... somewhat like a Porsche air cooled motor, which is oil cooled.

Yes, an oil cooler is a must. Just had a failure with mine when I bench-tested my new 13B and it was certainly a high-pressure system too. lol

Thanks guys! I had recently bought an rx7 and i'm trying to wrap my mind around rotary engine theory without having to tear down the engine(yet.)

Great book for anyone owning a rotary. The first couple chapters discuss basics.
---->

good book