Rotary capacity, yet again ....
02-09-04, 08:42 PM
#16
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Thread Starter
You say that using the "air consumed per 2-revs of output shaft" methodology is incorrect because it fails to take into account the internal gearing. The thing is, it isn't. For that methodology, there's two things that matter; air flow and output shaft speed. Period. You point out that if you were to look at the same measurement off of the camshaft of a piston engine, it would be equivalent to something twice the displacement. That's perfectly true... looking in terms of airflow at RPMs though, it works out the same either way. Thing is, looking at the rotary engine in terms of airflow per output shaft revolution allows direct comparison to other high performance engines; we have the same fuel requirements, airflow requirements and so on as a 2.6L engine tuned to a similar level of performance.
You need to compare the rotary to other engines with a swept volume of 654ccs. This is a reasonably large piston and I doubt there would be any production engines that rev to 9000rpm. Most will be more in the range of 6k to 7k.
A bit farther on, you say "Once the speed of an engine becomes too large the piston or rotor face has moved away from the fuel before the fuel has had enough time to push on the face. This is the main reason power of an engine drops off after a certain rpm. So the speed at which fuel can burn determines the number of times a chamber can expand and contract per minute." I'm sorry to say, but you're completely wrong. The speed at which the powerband drops off is because of breathing restrictions, on gasoline engines anyway. I attended a technical seminar a few years back on the effects of combustion chamber swirl on flame front propogation in a high speed research engine; IE a single cylinder motor approximating a Formula 1 engine. At 19,000 RPM, the flame front had reached the entire mixture by something like 20 degrees after the plug lit.
Oh yeah and just FYI, I can't think of a series offhand where you'd be restricted to a certain final drive ratio except for things like showroom stock where Mazda would have done that for you anyway.
Well, here's my thoughts overall, having read it. The theory you have come up with is technicially correct; yes, moreso than existing equivalence factors. You did a very good job bringing up your points and supporting them. It's ultimately not very useful though. The 2x displacement is used because it's handy; rotaries spin the output shaft about as fast as a built piston engine, so we have an easy thing to compare to to find parts. The standard displacement was defined to be the way Mazda rates it back in the early days of development of the things. Hell, I'm willing to bet there's some written SAE standard about such things around somewhere.
My personal view is that I don't really care to bother to equate it to any displacement. It would confuse the people at Mazda to ask for parts for a 3.9L rotary, the bits for a 2.6L one would cost more than I can afford, so I'm going to call it a 1.3. Or, they want to call it a 2.34L engine for autocross, so that works too, whatever. I'm rather more interested in power output than displacement.
My personal view is that I don't really care to bother to equate it to any displacement. It would confuse the people at Mazda to ask for parts for a 3.9L rotary, the bits for a 2.6L one would cost more than I can afford, so I'm going to call it a 1.3. Or, they want to call it a 2.34L engine for autocross, so that works too, whatever. I'm rather more interested in power output than displacement.
) for racing but the actual capacity really is 3.9 litres.
02-09-04, 11:43 PM
#17
spoon!
Originally posted by MikeC
This sort of comparison is fairly flexible. For example, it would be possible to determine that a F1 engine that runs to 19,000 rpm is twice the capacity of an engine that revs to 9500 but actually has the same capacity.
This sort of comparison is fairly flexible. For example, it would be possible to determine that a F1 engine that runs to 19,000 rpm is twice the capacity of an engine that revs to 9500 but actually has the same capacity.
Well, true. Again, see my general disdain for displacement as a measure of these things.
You need to compare the rotary to other engines with a swept volume of 654ccs. This is a reasonably large piston and I doubt there would be any production engines that rev to 9000rpm. Most will be more in the range of 6k to 7k.
Great point, this is the sort of info I'm after to try to make my article more accurate. However, the same thing still applies. If the rotary is doing 9000rpm then the fuel has the same time to enter the chamber as it has with a piston engine doing 6000rpm. This is the reason the rotary revs higher.
I accept that the rotary can be rated at the 2x displacement (although I would call this 2 thirds ) for racing but the actual capacity really is 3.9 litres.
) for racing but the actual capacity really is 3.9 litres.
I'm not disagreeing with you, merely saying that precedence is against you, no matter the fact you're right.
02-10-04, 01:21 AM
#18
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Sorry guys i will read it later from what i saw:
The only reason a 13b is more than 1.3 litres is the same reason the R26b is more than 2.6....
everyone else couldn't hack losing LEMANS
The only reason a 13b is more than 1.3 litres is the same reason the R26b is more than 2.6....
everyone else couldn't hack losing LEMANS
02-10-04, 02:08 AM
#19
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Thread Starter
Well, true. Again, see my general disdain for displacement as a measure of these things.
"The latest top of the line Detroit Diesel MBE 4000, which the company touts as "Big Power in a Small Package", with the 450 performance package (including turbo) makes 450 hp from a 12.8L inline six. It weighs "just 2,040 pounds". Big power in a small package. Good for transplant into Vettes."
Well, I'm just kind of saying that I don't see rotaries revving all *THAT* much higher. The Renesis, sure, but even that's only incrementally higher than some production boingers. You could argue that that's just street cars and that race tuned engines are turning higher RPMs, but... well, the factory race cars had about the same RPM ceiling as the Renesis.
Well, I say *an* actual capacity really is 3.9 liters. Wankel rated the things at the way Mazda does, so it could be argued that he gets to say. I'm not disagreeing with you, merely saying that precedence is against you, no matter the fact you're right.
02-10-04, 08:08 PM
#21
Rotary Enthusiast
Mike,
I fully agree with the comparison with a 3.9L 6 cyl boinger, with integral .67 OD before the output shaft. I include my note from this thread last year (08-25-03):
https://www.rx7club.com/showthread.p...hreadid=217838
" one rotor equals 3 pistons, but on a 'special' crankshaft with overdrive.
for the 13B, the best piston engine analogy is a very short stroke 3.9L 6 cyl, with a .67 overdrive gear built into the output end of the crank, before the flywheel.
at the flywheel, this gives the correct one combustion cycle per rev ( edit: per rotor, ie 2 per rev for each engine), and very smooth 270 deg power cycles for each piston, and 1.3L charge air displacement per rev.
my $.02 "
Not sure on your swept volume calculation though. Mabe I read it wrong. Point P displacement, normal to the rotor face, absolute or relative to the crank center, is simply 2xe over 270 degrees of e shaft rotation. This is intuitive from observing illustrations of TDC and BDC positions. The rest of the expansion is due to apparent motion of the housing surface. The effective displacement of the rotor face (projected) area is 3xe, but that includes the effect of the dynamic combustion chamber ... housing surface.
I fully agree with the comparison with a 3.9L 6 cyl boinger, with integral .67 OD before the output shaft. I include my note from this thread last year (08-25-03):
https://www.rx7club.com/showthread.p...hreadid=217838
" one rotor equals 3 pistons, but on a 'special' crankshaft with overdrive.
for the 13B, the best piston engine analogy is a very short stroke 3.9L 6 cyl, with a .67 overdrive gear built into the output end of the crank, before the flywheel.
at the flywheel, this gives the correct one combustion cycle per rev ( edit: per rotor, ie 2 per rev for each engine), and very smooth 270 deg power cycles for each piston, and 1.3L charge air displacement per rev.
my $.02 "
Not sure on your swept volume calculation though. Mabe I read it wrong. Point P displacement, normal to the rotor face, absolute or relative to the crank center, is simply 2xe over 270 degrees of e shaft rotation. This is intuitive from observing illustrations of TDC and BDC positions. The rest of the expansion is due to apparent motion of the housing surface. The effective displacement of the rotor face (projected) area is 3xe, but that includes the effect of the dynamic combustion chamber ... housing surface.
02-10-04, 08:48 PM
#22
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Originally posted by MikeC
I'd be interested to hear peoples opinions on this.
I'd be interested to hear peoples opinions on this.
For example, a 4-Stroke V8 may be rated at 5.0L based on the displacement of the swept volume of all its cylinders, no matter how many times the pistons produce a combustion cycle per crankshaft revolution. Now make that same engine into a 2-Stroke, and it is still rated at 5.0L, regardless of the fact that the pistons now have twice the combustion cycles as before.
OK, if you are with me so far, now look at the Wankel engine in the same manner. Its displacement is based on the swept volume of the rotor housing (cylinder), and it doesn't matter how many times the rotor (piston) produces a combustion cycle. The fact that the rotor has 3 faces has absolutely no bearing on the displacement of the rotor housing. In a similar manner, if there were such thing as a piston engine with one cylinder and three pistons that alternately traveled into the cylinder, its displacement would be based on the swept volume of that one cylinder, not on the 3 pistons.
Does this make sense now?
02-10-04, 11:30 PM
#23
Rotary Enthusiast
Originally posted by Evil Aviator
.... For example, a 4-Stroke V8 may be rated at 5.0L based on the displacement of the swept volume of all its cylinders, no matter how many times the pistons produce a combustion cycle per crankshaft revolution. Now make that same engine into a 2-Stroke, and it is still rated at 5.0L, regardless of the fact that the pistons now have twice the combustion cycles as before.
..... Does this make sense now?
.... For example, a 4-Stroke V8 may be rated at 5.0L based on the displacement of the swept volume of all its cylinders, no matter how many times the pistons produce a combustion cycle per crankshaft revolution. Now make that same engine into a 2-Stroke, and it is still rated at 5.0L, regardless of the fact that the pistons now have twice the combustion cycles as before.
..... Does this make sense now?
If you think a 9 lb cast iron 3 faced rotor wobbling aroung the e-shaft at 1/3 the e-shaft rpm is a single piston ... oh well to each his own. I visualize 6, clever, dynamic combustion chambers.
02-10-04, 11:43 PM
#24
Senior Member
Thread Starter
Originally posted by KevinK2
Mike,
I fully agree with the comparison with a 3.9L 6 cyl boinger, with integral .67 OD before the output shaft. I include my note from this thread last year (08-25-03):
Mike,
I fully agree with the comparison with a 3.9L 6 cyl boinger, with integral .67 OD before the output shaft. I include my note from this thread last year (08-25-03):
Once you understand this concept it is so obvious it is correct. Every other theory always has something that doesn't quite fit but this explains everything. It's one of those things that just clicks.
BTW, how did you arrive at this conclusion?
Not sure on your swept volume calculation though. Mabe I read it wrong. Point P displacement, normal to the rotor face, absolute or relative to the crank center, is simply 2xe over 270 degrees of e shaft rotation. This is intuitive from observing illustrations of TDC and BDC positions. The rest of the expansion is due to apparent motion of the housing surface. The effective displacement of the rotor face (projected) area is 3xe, but that includes the effect of the dynamic combustion chamber ... housing surface.
02-11-04, 12:15 AM
#25
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Originally posted by KevinK2
Got it. Forget combustion events per rev and total revs needed to complete a full engine cycle.
Got it. Forget combustion events per rev and total revs needed to complete a full engine cycle.
The displacement rating is based on static conditions, not dynamic conditions, otherwise you would need to also include other factors like compression ratio and volumetric efficiency.
Originally posted by KevinK2
Problem is bore area is projected rotor face area (same as defined by mike), effective stroke is 3xe, and number of dynamic holes is 6.
Problem is bore area is projected rotor face area (same as defined by mike), effective stroke is 3xe, and number of dynamic holes is 6.
02-11-04, 12:27 AM
#26
Senior Member
Thread Starter
No, you are getting back to the rotor issue, and that is causing the confusion. Forget the rotor. There is only one swept volume are per housing. The other two areas of volume NEVER function in the intake cycle.
02-11-04, 12:32 AM
#27
Rotary Enthusiast
but as u know, the swept volume method for boingers is any swept cylinder volume, regardless of what part of the cycle it should be at. could be any of 4 strokes. just bore area times stroke.
At that housing position, 3 different faces will cause 3 unique swept volumes as defined by the different faces, and each will be fired in 3 separate events.
At that housing position, 3 different faces will cause 3 unique swept volumes as defined by the different faces, and each will be fired in 3 separate events.
02-11-04, 12:41 AM
#28
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Originally posted by MikeC
Kevin is right, they are 3 independant chambers around the rotor. While one is on the intake cycle the other could be on combustion and the other on exhaust. They are all doing something. Just like a piston motor, while one is on intake another is on combustion etc.
Kevin is right, they are 3 independant chambers around the rotor. While one is on the intake cycle the other could be on combustion and the other on exhaust. They are all doing something. Just like a piston motor, while one is on intake another is on combustion etc.
There is only one point in the housing that functions as an area of swept volume. At no time do any other portions of the housing function in the intake cycle. Yes, the next face of the rotor will cycle through this swept volume area, but it is still the SAME swept volume area, not a different swept volume area.
OK, the piston example didn't work because I think that you guys don't understand piston engines, either. Lets try a racetrack analogy. There is one racetrack with three cars racing around the track. How many race tracks are there?
02-11-04, 01:39 AM
#29
Rotary Enthusiast
I personally built a fully prepared scca d-production engine, and tuned the tripple dcoe's. I know piston engines.
the 3 rotor faces combine with that part of the housing for 3, distinct intake cycles. our crude unofficial definition just says stroke all pistons in all bores, or all rotor faces thru a stroke in the housing (intake if u wish). The rotor faces are analogis to the piston faces.
until you can bust free and recognize that your 'cylinders' are dynamic and are rotating around the housing, you will be forever in the dark on this.
-----------------------------
Do a 'special' radial piston engine, 4 cyl'rs 90 deg apart, in plane. the 'head' is a fixed ring (like housing), around and sealed at the cylinder ends. head has plugs at 3 o'clock, so tdc at 3 and 9 (exh and intake ports), and bdc at 12 and 6 o'clock. a planetary gearset allows the housings to rotate (like rotor) 90 degrees for 270 degre rotation of the crank. would this 4 cyl engine be rated at just 1 hole, where intake occurs?
although it takes 3 crank revs for all cylinders to be stroked up and down, displacement shold be 4 x bore area x stroke.
the 3 rotor faces combine with that part of the housing for 3, distinct intake cycles. our crude unofficial definition just says stroke all pistons in all bores, or all rotor faces thru a stroke in the housing (intake if u wish). The rotor faces are analogis to the piston faces.
until you can bust free and recognize that your 'cylinders' are dynamic and are rotating around the housing, you will be forever in the dark on this.
-----------------------------
Do a 'special' radial piston engine, 4 cyl'rs 90 deg apart, in plane. the 'head' is a fixed ring (like housing), around and sealed at the cylinder ends. head has plugs at 3 o'clock, so tdc at 3 and 9 (exh and intake ports), and bdc at 12 and 6 o'clock. a planetary gearset allows the housings to rotate (like rotor) 90 degrees for 270 degre rotation of the crank. would this 4 cyl engine be rated at just 1 hole, where intake occurs?
although it takes 3 crank revs for all cylinders to be stroked up and down, displacement shold be 4 x bore area x stroke.
02-11-04, 06:30 AM
#30
Senior Member
Thread Starter
There is only one point in the housing that functions as an area of swept volume. At no time do any other portions of the housing function in the intake cycle.
OK, the piston example didn't work because I think that you guys don't understand piston engines, either.
There is one racetrack with three cars racing around the track. How many race tracks are there?
Did you read this this:
http://mikeonline.cable.nu:1863/misc/rotor.doc