rotary engines: 2 or 4 or ... stroke ???
03-19-04, 03:31 AM
#26
Senior Member
Originally posted by SuperPhly
but we rev higher... so you'd have to do the converting of the gears to see how many hits we get per gear and compare that same number to that of a 4/6 cyl. Wouldnt that do us justice? I mean... we've got to have an engine thats better and more powerful than a 4 banger geo metro..................
but we rev higher... so you'd have to do the converting of the gears to see how many hits we get per gear and compare that same number to that of a 4/6 cyl. Wouldnt that do us justice? I mean... we've got to have an engine thats better and more powerful than a 4 banger geo metro..................
03-19-04, 03:39 AM
#27
Senior Member
Originally posted by shinjuku
now this has always confused me!!!
I thought that if u followed theprogress of one face of the rotor it achieves the 4 cycles in 3 crank revolutions rather than a piston doing it in 2 revolutions?
But b/cos there are 3 faces to each rotor that means there are three 4 stroke cycles happening per rotor at the same time (but at different stages of course!)
so per rotor in 3 revolutiosn of the crank three compression 'strokes' have occured. wouldn't this be the same as a 2 cylinder 2 stroke?
help confused!
now this has always confused me!!!
I thought that if u followed theprogress of one face of the rotor it achieves the 4 cycles in 3 crank revolutions rather than a piston doing it in 2 revolutions?
But b/cos there are 3 faces to each rotor that means there are three 4 stroke cycles happening per rotor at the same time (but at different stages of course!)
so per rotor in 3 revolutiosn of the crank three compression 'strokes' have occured. wouldn't this be the same as a 2 cylinder 2 stroke?
help confused!
You've pretty much got it. You're first paragraph is correct but you are confusing it in your second and third. One face goes through the 4 strokes same as a piston motor, the only difference being that the output shaft spins further for the same number expansion/contractions of the chamber. Think of the other faces as different pistons. If you compare a 3 piston motor with a single rotor motor it's very similar. While no 1 piston/rotor face is firing no 2 piston/rotor face is inducting and no 3 is on exhaust. Pretty much exactly the same just the output shaft spins 1.5 times more with the rotary.
Hope this helps.
03-19-04, 04:45 AM
#28
Senior Member
Originally posted by KevinK2
Not dead as long as misleading info is still posted ...
50% longer pulse, for same disp, is smoother, not more power.
work done on piston or rotor face is the integral of pressure force times stroke. assume pressure drops linearly from tdc to bdc, gets you ave pressure of P. ave force thru stroke = P x piston (or r-face) area. face area times stroke is just displacement for that piston or rotor face.
so work done for a power pulse is just displ times ave chamber pressure, say units are psi x sq-in x in = in-lbs. whether it takes 1/2 rev or 3/4 rev, it's still same work done per rev. so at 6000 rpm, same work done in .01 sec, or in-lb/sec which means same hp.
just smoother.
Not dead as long as misleading info is still posted ...
50% longer pulse, for same disp, is smoother, not more power.
work done on piston or rotor face is the integral of pressure force times stroke. assume pressure drops linearly from tdc to bdc, gets you ave pressure of P. ave force thru stroke = P x piston (or r-face) area. face area times stroke is just displacement for that piston or rotor face.
so work done for a power pulse is just displ times ave chamber pressure, say units are psi x sq-in x in = in-lbs. whether it takes 1/2 rev or 3/4 rev, it's still same work done per rev. so at 6000 rpm, same work done in .01 sec, or in-lb/sec which means same hp.
just smoother.
I just wrote this long and involved post just to realise I had written pretty much the same thing as you in different words! I was going to say you can use the graph of volume by crank rotation to work all this out and it doesn't matter a stuff what's translating that volume into crank rotation.
Only thing I would add is that it's not smoother, it's the same smoothness as a 6 cylinder motor.
a more interesting question is the mechanical efficency in creating torque, for a slider crank mechanism (boinger), vs a rotor face. another paper for MikeC ...
03-21-04, 10:51 PM
#29
Rotary Enthusiast
Originally posted by MikeC
... Only thing I would add is that it's not smoother, it's the same smoothness as a 6 cylinder motor.
... Only thing I would add is that it's not smoother, it's the same smoothness as a 6 cylinder motor.
03-22-04, 04:01 AM
#30
Senior Member
Originally posted by KevinK2
.. and not likely as smooth as a v12 jag. I was not clear but meant smoother as compared to a 4stroke boinger with same 2 bangs per (eaasential) crank rev, ie a 4 piston 2.6L 4stroke.
.. and not likely as smooth as a v12 jag. I was not clear but meant smoother as compared to a 4stroke boinger with same 2 bangs per (eaasential) crank rev, ie a 4 piston 2.6L 4stroke.
BTW, have a look at this really bad sketch.
http://www.rx7store.net/orderstatuslogin.asp
This is something along the lines of the radial engine you described except with 3 cylinders. I didn't realise until I sketched it out how similar it is to the rotary, eg
- general operation is the same, inlet, compression, combustion and exhaust happen in the same locations.
- 270* expansion
- sucks 2.6 litres of air over 2 revs
- 654cc swept volume
- single inlet, exhaust and spark plug shared between 3 chambers
- chambers rotate at 1/3 crank speed
- same torque fluctuation graph
- sum of the volume of all chambers at any point in time is the same
The interesting thing is that if you fix the cylinders and allow the outside to rotate then it sucks 3.9 litres of air per 2 revs. So the air sucked per 2 revs can vary for exactly the same engine.
Thread
Thread Starter
Forum
Replies
Last Post
datfast1
Old School and Other Rotary
18
06-20-19 10:53 PM
Under PSI
3rd Generation Specific (1993-2002)
19
09-23-15 11:47 PM
