rotary engines: 2 or 4 or ... stroke ???
04-22-02, 03:47 PM
#1
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rotary engines: 2 or 4 or ... stroke ???
How much stroke is a rotary engine?
i think the rotary engine isn't a 2- or a 4 stroke engine.
is it a 3 stroke?
anyone any idea how much stroke the rotary engine is?
Andreas.
i think the rotary engine isn't a 2- or a 4 stroke engine.
is it a 3 stroke?
anyone any idea how much stroke the rotary engine is?
Andreas.
04-22-02, 07:37 PM
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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!
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!
04-22-02, 08:47 PM
#6
Banned. I got OWNED!!!
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!
It takes two full crank shaft revolutions to complete a "4stroke cycle"
In two full crank shaft revolutions there are 4 chambers that have fired. i.e same as a 4cyl 4 stroke (4 seperate power pulses)
This is because the crank shaft sensor or dizzy is geared down 2:1.
For EVERY crank rev there is a front rotor power pulse and a rear rotor power pulse, it take three crank revs to fire ALL three sides on each rotor ONCE....do not let this confuse the issue.
So when comparing engines (mostly 4cycle engines) you need to look at how much work they do and in a 4cycle it takes 2 full crank shaft rpm for the engine to one complete cycle. In a wankel rotary in takes only one crank shaft rpm to complete it's cycle (like a two stroke) but it does it using the 4 stroke cycle. It does this via geometry and gearing or the rotor to the crank. easy as that
This is why when comparing our engines to a 4cycle piston motor you need to double the capacity i.e. 1.3lt X 2 = 2.6lt which is what it realy is when you do mass flow calculations.
When comparing our engines to 2 stroke piston motors it is a 1.3lt because this is what it is in one crank rpm the difference is that unlike the 4 stroke piston engine in HAS COMPLETED ONE FULL CYCLE just like the 2 stroke piston engine (excepet using the 4 stroke system) In mass flow calculations both 2 stroke piston and wankel rotary need to have thier capacity doubled.
Last edited by RICE RACING; 04-22-02 at 08:52 PM.
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04-25-02, 02:41 PM
#8
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I thought the rotary was the same as a 12cyl engine because each Rev of the crank you get 6 hits... same as a 12cyl...
A piston engine gets 1/2 the number of cylinder power pulses per rev. Ie. 6cyl = 3PP/Crank Rev.
I guess what I have read to understand is that the rotors don't do a 360 per crank rev.. thus we have the rotors rolling around a smaller eccentric shaft... that movement is vital and probably the most important to the theory of the rotory...
Hmm, interesting...
A piston engine gets 1/2 the number of cylinder power pulses per rev. Ie. 6cyl = 3PP/Crank Rev.
I guess what I have read to understand is that the rotors don't do a 360 per crank rev.. thus we have the rotors rolling around a smaller eccentric shaft... that movement is vital and probably the most important to the theory of the rotory...
Hmm, interesting...
04-25-02, 04:26 PM
#9
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Originally posted by SuperPhly
I thought the rotary was the same as a 12cyl engine because each Rev of the crank you get 6 hits... same as a 12cyl...
I thought the rotary was the same as a 12cyl engine because each Rev of the crank you get 6 hits... same as a 12cyl...
04-25-02, 11:05 PM
#10
Senior Member
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..................
04-25-02, 11:43 PM
#11
Banned. I got OWNED!!!
There are pluses and minuses for every engine type, The 13B must be doing something right to still be in production after almost 30 years with no real geometrical changes, however Piston engines I feel are getting a jump on us in many areas and we can no longer use revs as an excuse.
The biggest thing we have going for us is Capacity for engine physical size and how cheap the motors are relative to the power you can reliably make compared to a 4 cylinder piston engine.
Oh and you just cant beat the sound of a wankel in any form, they have character......I do not know any one (who is into them) who will say that they do not stir up emotions inside you evertime you hear one, let alone drive one
The biggest thing we have going for us is Capacity for engine physical size and how cheap the motors are relative to the power you can reliably make compared to a 4 cylinder piston engine.
Oh and you just cant beat the sound of a wankel in any form, they have character......I do not know any one (who is into them) who will say that they do not stir up emotions inside you evertime you hear one, let alone drive one
03-09-04, 10:30 PM
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Technically speaking, the rotary is a 2 stroke in principle. And in the same fasion has no valves, but ports that are uncovered by the "piston".
1. Compression/Intake (at the same time)
2. Expansion/Exhaust (at the same time)
The ignition takes place in between the cycles, just like a two stroke.
Simple!?!
1. Compression/Intake (at the same time)
2. Expansion/Exhaust (at the same time)
The ignition takes place in between the cycles, just like a two stroke.
Simple!?!
03-09-04, 11:35 PM
#13
Originally posted by Rtrpwr
Technically speaking, the rotary is a 2 stroke in principle. And in the same fasion has no valves, but ports that are uncovered by the "piston".
1. Compression/Intake (at the same time)
2. Expansion/Exhaust (at the same time)
The ignition takes place in between the cycles, just like a two stroke.
Simple!?!
Technically speaking, the rotary is a 2 stroke in principle. And in the same fasion has no valves, but ports that are uncovered by the "piston".
1. Compression/Intake (at the same time)
2. Expansion/Exhaust (at the same time)
The ignition takes place in between the cycles, just like a two stroke.
Simple!?!
1 intake - sucks the air in to full chamber volume
2 compression - squishes the chamber back down to min volume
3 combustion - the plug fires and the chamber expands to full volume
4 exhaust - the chamber pushes the exhaust out down to min chamber volume
It is just that each of the 3 chambers per rotor are in some phase of this continuous cycle at any given time, and it takes 3 full rotations of the eccentric to complete the cycle for all three of the rotor's chambers. It fires as often as a 4-cylinder 4-stroke, or a 2-cylinder 2-stroke, but the combustion cycle has four clear and distinct phases just like a piston 4-stroke.
-Max
03-10-04, 10:02 AM
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Actually. You can't directly compare a piston engine to a rotary. But if you did the engine would be a 6 cycle. Yes, that is 6.
In a 2 Cycle. The crank rotates 1 full revolution. A compression stroke and a combustion stroke. That is 2 strokes of the piston in turn that makes 2 180* rotations of the crank.
In a 4 Cycle. The crank rotates 2 full revolutions. An Intake stroke, compression, combustion and, exhaust. that is 4 strokes of the piston in turn that makes 4 180* rotations of the crank.
On a rotary it is a little different since it had no pistons but, since on a piston engine 1 stroke of the crank is 180* then the rotary will be 6 strokes. 2 180* rotations of the crank for intake, 2 180* rotations for compression and, 2 180* rotations for exhaust. That makes 6 180* rotations of the crank before the same combustion chamber comes full circle on the rotor. 6 cycles.
But like I said before. You really can't directly compare them since "cycle" is a piston engine term.
Easy enough right?
All engines run the same combustion "steps", the stroke or cycle is relative to the piston. Every combustion engine needs an intake, compression, combustion, and exhaust. Even 2 cycles, they just do several of them during the 2 strokes.
In a 2 Cycle. The crank rotates 1 full revolution. A compression stroke and a combustion stroke. That is 2 strokes of the piston in turn that makes 2 180* rotations of the crank.
In a 4 Cycle. The crank rotates 2 full revolutions. An Intake stroke, compression, combustion and, exhaust. that is 4 strokes of the piston in turn that makes 4 180* rotations of the crank.
On a rotary it is a little different since it had no pistons but, since on a piston engine 1 stroke of the crank is 180* then the rotary will be 6 strokes. 2 180* rotations of the crank for intake, 2 180* rotations for compression and, 2 180* rotations for exhaust. That makes 6 180* rotations of the crank before the same combustion chamber comes full circle on the rotor. 6 cycles.
But like I said before. You really can't directly compare them since "cycle" is a piston engine term.
Easy enough right?
All engines run the same combustion "steps", the stroke or cycle is relative to the piston. Every combustion engine needs an intake, compression, combustion, and exhaust. Even 2 cycles, they just do several of them during the 2 strokes.
Last edited by OneOfFew; 03-10-04 at 10:29 AM.
03-10-04, 11:09 AM
#15
Rotary Enthusiast
Originally posted by RICE RACING
OK, If you look at thet crank angle sensor or the distrubutor which fires the Chambers your talking about then the following happens.
It takes two full crank shaft revolutions to complete a "4stroke cycle"
In two full crank shaft revolutions there are 4 chambers that have fired. i.e same as a 4cyl 4 stroke (4 seperate power pulses)......
...... When comparing our engines to 2 stroke piston motors it is a 1.3lt because this is what it is in one crank rpm the difference is that unlike the 4 stroke piston engine in HAS COMPLETED ONE FULL CYCLE just like the 2 stroke piston engine (excepet using the 4 stroke system) In mass flow calculations both 2 stroke piston and wankel rotary need to have thier capacity doubled.
OK, If you look at thet crank angle sensor or the distrubutor which fires the Chambers your talking about then the following happens.
It takes two full crank shaft revolutions to complete a "4stroke cycle"
In two full crank shaft revolutions there are 4 chambers that have fired. i.e same as a 4cyl 4 stroke (4 seperate power pulses)......
...... When comparing our engines to 2 stroke piston motors it is a 1.3lt because this is what it is in one crank rpm the difference is that unlike the 4 stroke piston engine in HAS COMPLETED ONE FULL CYCLE just like the 2 stroke piston engine (excepet using the 4 stroke system) In mass flow calculations both 2 stroke piston and wankel rotary need to have thier capacity doubled.
For 2 stroke comparo, another way to say same thing is that each chamber takes 3 revs to complete it's cycle, so with 3 chambers per rotor, one of the 3 chambers will fiinish it's cycles and fire each rev. Each rotor is then like .65L 2-stroke cylinder, only with respect to aspiration and firing per rev. The 2-stroke is firing the same cyliner each rev, while the wankel is firing one of 3 different chambers each rev.
03-10-04, 12:01 PM
#16
Rotary Enthusiast
Originally posted by OneOfFew
Actually. You can't directly compare a piston engine to a rotary. But if you did the engine would be a 6 cycle. Yes, that is 6.
In a 2 Cycle. The crank rotates 1 full revolution. A compression stroke and a combustion stroke. That is 2 strokes of the piston in turn that makes 2 180* rotations of the crank.
In a 4 Cycle. The crank rotates 2 full revolutions. An Intake stroke, compression, combustion and, exhaust. that is 4 strokes of the piston in turn that makes 4 180* rotations of the crank.
On a rotary it is a little different since it had no pistons but, since on a piston engine 1 stroke of the crank is 180* then the rotary will be 6 strokes. 2 180* rotations of the crank for intake, 2 180* rotations for compression and, 2 180* rotations for exhaust. That makes 6 180* rotations of the crank before the same combustion chamber comes full circle on the rotor. 6 cycles.
But like I said before. You really can't directly compare them since "cycle" is a piston engine term.
Easy enough right?
All engines run the same combustion "steps", the stroke or cycle is relative to the piston. Every combustion engine needs an intake, compression, combustion, and exhaust. Even 2 cycles, they just do several of them during the 2 strokes.
Actually. You can't directly compare a piston engine to a rotary. But if you did the engine would be a 6 cycle. Yes, that is 6.
In a 2 Cycle. The crank rotates 1 full revolution. A compression stroke and a combustion stroke. That is 2 strokes of the piston in turn that makes 2 180* rotations of the crank.
In a 4 Cycle. The crank rotates 2 full revolutions. An Intake stroke, compression, combustion and, exhaust. that is 4 strokes of the piston in turn that makes 4 180* rotations of the crank.
On a rotary it is a little different since it had no pistons but, since on a piston engine 1 stroke of the crank is 180* then the rotary will be 6 strokes. 2 180* rotations of the crank for intake, 2 180* rotations for compression and, 2 180* rotations for exhaust. That makes 6 180* rotations of the crank before the same combustion chamber comes full circle on the rotor. 6 cycles.
But like I said before. You really can't directly compare them since "cycle" is a piston engine term.
Easy enough right?
All engines run the same combustion "steps", the stroke or cycle is relative to the piston. Every combustion engine needs an intake, compression, combustion, and exhaust. Even 2 cycles, they just do several of them during the 2 strokes.
It functions just like a 4 stroke boinger, and id directly comparable. Each stroke is actually 3xe in (curved) length, and takes 270 degrees of e-shaft rotation to complete. 4x270 = 3 revs.
03-10-04, 12:16 PM
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Define "Stroke"
If you define stroke as the completion of a "phase" in combustion (ie. intake, compression, combustion, exhaust) then all engines are 4 stroke. Even 2 strokes have to complete these "phases" but they are called 2 stroke for a reason, because the engine takes 2 strokes to complete them (up then down).
The only thing in common that piston engines have in common with a rotary is a crank. That is why I use the 180* rotation of a crank to decide what a "stroke" is... One throw of the crank.
If you define stroke as the completion of a "phase" in combustion (ie. intake, compression, combustion, exhaust) then all engines are 4 stroke. Even 2 strokes have to complete these "phases" but they are called 2 stroke for a reason, because the engine takes 2 strokes to complete them (up then down).
The only thing in common that piston engines have in common with a rotary is a crank. That is why I use the 180* rotation of a crank to decide what a "stroke" is... One throw of the crank.
Last edited by OneOfFew; 03-10-04 at 12:21 PM.
03-10-04, 12:41 PM
#18
Rotary Enthusiast
stroke and cycle seem to be used to descirbe the maximum translation of the piston in a 2 or 4 stroke boinger, = 2 x crank pin offset. goes back to days of otto.
stroke for wankel is the motion of the rotor face, perpindicular to it's apex-to-apex planer surface, during a full expansion or compression cycle. this is a curved line, vs strait line for boinger.
180 degrees of crank rotation has no significance in the wankel where each chamber stroke/cycle/'step' takes 270 degrees of rotation.
stroke for wankel is the motion of the rotor face, perpindicular to it's apex-to-apex planer surface, during a full expansion or compression cycle. this is a curved line, vs strait line for boinger.
180 degrees of crank rotation has no significance in the wankel where each chamber stroke/cycle/'step' takes 270 degrees of rotation.
03-10-04, 03:08 PM
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Good explination. I agree. Your defonition of a rotary stroke I have not thought of before but it sound practical consitering the application. I admit, I was even pressed to find a logical number consitering the differences. I figured 6 because if a piston engine took 3 rotations to get a given cylinder back to TDC of compression it would be 6 stroke but it was still "fuzzy" reasoning to convert it to a rotary.
03-10-04, 11:20 PM
#22
Rotary Enthusiast
Originally posted by jeremy
this is an old, old, dead horse.
kink in the cogs. compare length of power pulses between a piston and a rotary.
this is an old, old, dead horse.
kink in the cogs. compare length of power pulses between a piston and a rotary.
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.
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 ...
03-12-04, 01:57 PM
#23
look at the brain on kevin! are you a mechanical engineering student? anyway, here's a good article on that with less math.
http://www.dragsport.com/dept/tech/2/
http://www.dragsport.com/dept/tech/2/
03-12-04, 03:29 PM
#24
Rotary Enthusiast
Originally posted by jeremy
look at the brain on kevin! are you a mechanical engineering student? anyway, here's a good article on that with less math.
http://www.dragsport.com/dept/tech/2/
look at the brain on kevin! are you a mechanical engineering student? anyway, here's a good article on that with less math.
http://www.dragsport.com/dept/tech/2/
I'm an ME/PE, and have consulted in the field applied mechanics for decades. Usually ME students know just enough to be dangerous .... been there. You learn the real deal in practice.
03-19-04, 03:29 AM
#25
Senior Member
Originally posted by jeremy
look at the brain on kevin! are you a mechanical engineering student? anyway, here's a good article on that with less math.
http://www.dragsport.com/dept/tech/2/
look at the brain on kevin! are you a mechanical engineering student? anyway, here's a good article on that with less math.
http://www.dragsport.com/dept/tech/2/
All rotational angles are quoted for the output shaft (eccentric shaft/crankshaft), not the rotor. Both engines burn a compressed fuel-air mixture to develop rotational power. Both are four-stroke engines. However, one big difference between them is that the recip has 180 degrees per stroke (or 4 x 180 = 720 degrees per thermodynamic cycle) while the rotary has 270 degrees per "stroke" (or 4 x 270 = 1080 degrees per thermodynamic cycle). Yeah, you may have to think about that one for a bit, but trust me, it's true.
This has some good and some bad consequences. Assuming that both engines have similar maximum rpm's (and I think that is roughly true), it means that the rotary has 1.5 times as many milliseconds to accomplish each "stroke". This is one reason why rotaries breathe so well - they have more time (in milliseconds) to draw in and spit out the mixture. They also have more time for the power stroke - a real plus to get the most out of the combustion gas, especially at high rpm. Now the bad part. The rotary also has 1.5 times as many milliseconds to transfer heat from the burning mixture into the oil and water. This is one reason why rotaries waste more heat in the process of staying cool. Another consequence is that, if you only consider one flank of one rotor, the rotary only gets 2/3 as many power pulses as the recip. However, there are actually 3 flanks to each rotor, each at a different point in the thermodynamic cycle, so each complete rotor actually gives 2 times as many power pulses (3 times 2/3) as a 1 cylinder recip. Confused?.
This has some good and some bad consequences. Assuming that both engines have similar maximum rpm's (and I think that is roughly true), it means that the rotary has 1.5 times as many milliseconds to accomplish each "stroke". This is one reason why rotaries breathe so well - they have more time (in milliseconds) to draw in and spit out the mixture. They also have more time for the power stroke - a real plus to get the most out of the combustion gas, especially at high rpm. Now the bad part. The rotary also has 1.5 times as many milliseconds to transfer heat from the burning mixture into the oil and water. This is one reason why rotaries waste more heat in the process of staying cool. Another consequence is that, if you only consider one flank of one rotor, the rotary only gets 2/3 as many power pulses as the recip. However, there are actually 3 flanks to each rotor, each at a different point in the thermodynamic cycle, so each complete rotor actually gives 2 times as many power pulses (3 times 2/3) as a 1 cylinder recip. Confused?.
I know this sounds like I'm splitting hairs but this is a very important distinction.