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tonyslongez@cox.net wrote:
This may be a silly question but, (here goes) How does the air know?
how does the air know the length of the intake( runners) tubes versus the lenth of say a plenum? What if I have a really long plenum that acts like a long tube. how does the air know when it has reached an intake tube or port.
Do you understand what I'm trying to ask? air is air ! Is it all just a preasure game with these intakes?
How many different types of preasure are there?
I get the length part of it. I guess where I'm confused is the difference between a plenum and an intake runner, can a plenum act as an intake runner?
Air has mass. When you start sucking it down a tube, you get momentum. People usually don't think of momentum in tubes, but it can be significant. I was working as a security guard when one of the supervisors got overly busy and shut off valve to the main water supply pipe to quickly. It ruptured the pipe and create all sorts of commotion.
So, you've open the intake to your first rotor and started sucking air down it at a rate of 200mph or thereabouts. The rotor goes around a bit more and shuts the intake off. Where does that momentum go? Why, it bounces off of that cast iron rotors side, and back up the intake. The pressure will go right back out the intake and into the free airflow if there is nothing else to catch it, but if you play the game right you can have that pressure wave traveling down the intake of the other rotor just as it is opening up. This results in a little extra pressure to ram more air into that cylinder right before it closes. When it does close, there's a resulting pressure wave bouncing back. If the runner lengths are identical, the first rotor will catch the second's bounce.
On the exhaust, you want the opposite to happen. You want a negative pressure wave. It turns out, that when the positive pressure wave (cause by the exhaust opening up) hits a plenum, it reflects a negative wave back down the exhaust pipe. The maximum power situation is when that negative wave gets to the exhaust port just as it is opening for the next rotor face.
That's the FL30 view. Runner diameter, runner length, temperature, air density, the moon's phase and a thousand other parameters all seem have some effect on how those waves behave. That is where all the fun begins.
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