detectiveorange

I'm not sure if anyone here on the forum will be able to answer this question as it's more physics/chemistry related than mechanic related, but I figured I'd ask anyway.

To me, it makes sense that on peripheral ported engines, the exhaust gasses naturally exit through the exhaust port simply from pressure from the trailing apex. But on a renesis, I don't see how the exhaust gas can physically leave through the side exhaust port with the rotor spinning ridiculously fast. It seems like centrifugal force would keep the exhaust gasses pinned to the outside of the rotor housing like it does during the compression stage.

I know practically nothing about the physical properties of gasses so it may be a rather dumb question.

Any explanations? Or is the only real answer really "it just works"? haha

thanks in advance!

ilikecars

Short version, exhaust chamber is still at much higher pressure than exhaust header.

You are correct in thinking that not it will be more difficult for the exhaust to exit out of the side port, and this is a major reason Mazda used side ports. Mazda needed to improve the emissions of the rotary, so they used side ports to allow the air fuel mix more time to propagate and burn completely.

That being said, in fluid dynamics (gasses are still considered a fluid in most cases), outlets are often idealized as a free jet. This means that the exit pressure is atmospheric. With this assumption, it is fair to say that the exhaust is at a much higher pressure than the exit pressure. Because of the pressure difference, the high pressure exhaust tries to move to the lower pressure by exiting the exhaust chamber.

Remember that the gasses are being compressed against the side of the housing again further increasing pressure in the exhaust chamber. On a side note, the gasses would have a centripetal (notice spelling) force pointing to the center of the radius it is traveling in. My dynamics teacher taught us that centrifugal force is an imaginary force. A car traveling around a curve has a centripetal force pointing toward the center of the radius of the curve while the driver experiences a centrifugal force. This force is caused because the driver wants to continue moving in a straight line, but the seat is moving him the direction the car is moving.

detectiveorange

completely forgot about the basic concept of diffusion. I feel stupid now -_- lol

I see, so it seems like centrifugal force is just inertia that is felt, ya?

thanks so much for the detailed answer btw, it helped a lot!

nycgps

iTrader: (1)

its always been like that ...

detectiveorange

.............huh? o.O

ilikecars

No need to feel stupid. There is an assumption that has to be made about the exit pressure that isn't too obvious.

Centrifugal force is kinda the feeling of inertia, but I can't effectively explain it w/o plagiarizing this video. haha

wcs

iTrader: (2)

Dude.
First. This isn't a flame. AS the the ban hammer will come down faster than a fat kid on a Reese's Piece's

I thought you said you bought that book recommended to you in your Bridgeporting thread. https://www.rx8club.com/new-member-f...orting-249775/
"Street Rotary by Mark Warner"

Link posted again for any other noob members

The book answers these questions on page 55 the first page on the Exhaust System chapter.

Oh and another thing you might find interesting:
- The rotors are not spinning as crazy fast as you think they are.

For a rotary engine, one complete cycle = 3 eccentric shaft rotations = 1 full rotor rotation = 4 phases of combustion
This can be found on page 16 of the Street Rotary book.

Carbon8

iTrader: (4)

I will applaude the OP's curiosity, as opposed to most of the ridiculousness associated with this sub-forum and its members its inspiring to see someone in the search of enlightenment to be found asking the right questions.

As stated by myself and WCS already, the book quoted has all your answers. I know its a boring read, but its short I went threw it a couple times in the matter of a week.

ilikecars

I agree completely Mr. Hill. The pressure difference is the major factor that is causing the reactants to leave.

RIWWP

iTrader: (2)

Cars run on pressure differentials. Most of the world does too. There isn't much on the car that doesn't use/control/manipulate the basic principles of how fluids and gases move from locations of high pressure to locations of low pressure.

detectiveorange

I get the idea of diffusion. I was having a hard time imagining there's enough time for the exhaust to escape before the rotor covers the port.

Silly example, but if you breathe out, the pressure is higher in your lungs than the atmosphere thus you exhaust air. Duh. But no matter how fast you breath out, if something covers you mouth every quarter of a second or so (the rotor), you're never going to be able to breathe out fast enough.

After doing some reading, I understand that's the point of the side port. The unburnt exhaust gasses go around the housing for another chance to be burnt, right?

RIWWP

iTrader: (2)

Yup, completely agree.

I started understanding quite a bit more about numerous designs of all sorts of systems/components when I realized just how much the basic properties of pressure differentials are core to ... everything.

detectiveorange

On a completely random note, this is why I love cars. I could talk about theory and mechanics all day. I think probably the most interesting part about cars and engines to me....and y'know....going vroom vroom lol

bse50

In a Mazda you go Zoom Zoom, noob!

detectiveorange

Yes but you don't go "zoom zoom" in all cars lol. I like going fast no matter what car I'm in. Speed = fun