Chainsaw Repair
How To Basics - Carb Fixes + Mods - IPL and Service Manuals => How To Basics and Fixes => Topic started by: 1manband on June 04, 2015, 09:44:27 pm
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jonsereds 52
first 1/2 of photos.....crankcase volume at BDC.
2nd 1/2 of photos........crankcase volume at TDC.
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Super cool. Thanks for sharing!
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1.4 to 1.50 would be a common ratio on cr125 or other modern dirt bikes. The tz250 GP bike is around 1.4 as well. Interesting
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...looking at it again this morning.......made couple of errors.. at BDC, there is 5cc more volume of goop. another error i found was forgetting to subtract out about an inch and a half of connecting rod volume....possibly a few cc's.
will correct this. don't see the end result changing much at all, even if i fix these errors.
....thought it would be a lower ratio, too.
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So the 1.85 ratio represents a smaller case volume vs the bike motors? (1.4 ratio)
I'm assuming the bigger ratio would equate to higher crankcase pressure and result in moving more fuel/air per time unit than the larger case bike motors.
I'm wondering how this plays into the bike T/A graphs and if they are co pletely skewed towards the bike motors with their different crankcase volume/ratio?
End result COULD be equal if you have a small motor moving air faster for less duration vs. The large motor moving air a bit slower for LONGER duration but I'm not sure the Blair Jennings data works this way or there are losses from moving the fuel air at higher pressures. (Perhaps more short circuiting)
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...and this would help to explain the 'time' element being off.
want to look at few other things that go along with this as well.
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the two corrections up-thread:
Total BDC volume = 94 - 40 + 18 +21 = 93 cc
Total TDC volume = 21 + 48.4 + 94 - conn rod vol 1.2cc = 164.6 cc
ratio: 164.6/93 = 1.76
1.76:1
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one of the things which i was looking for by doing this, was how much air/fuel mix volume was moving in per single rpm.
estimate (based on crankcase volume, ratio, and motor displacement): approximately 14.6 cc total per rpm.
not much. hahaha.
previously.....cc'd the transfers they were approx. 4cc each.
........not really within the scope of this discussion but interesting to me at least.
edit: adding reference. blair page 392. top of page.
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...have not had much available time lately. had to reread my previous posts.
anyhow, sometimes a tiny scrap of information can shed some light on motor gizzards.
did not show how I came up with with an estimate of how much a motor ingests into a crankcase on every stroke. (it also gives me an opportunity to correct myself).
blair did an example of this crude estimate in his 'book,' below is using a j'red in similar fashion.
given:
jonsereds 52
49cc displacement
TDC crankcase volume = 164.6 cc
BDC crankcase volume = 93 cc
crankcase compression ratio = 164.6/93 = 1.77:1
delivery ratio = 0.5
(delivery ratio is amount air-fuel mixture, that is ultimately used for combustion. In other words... the cylinder volume is 49 cc total. If this total cylinder volume could be filled completely, the delivery ratio would be 1:1, or de = 1. a saw motor which I found data for, had a de = 0.5, so only half of the entire cylinder volume is filled…..if its good enough for blair's saw motor, should be good to use for an estimate).
de = 0.5 was chosen, because that is what blair was using.
de of 0.5 = 49 cc/2 = 24.5 cc
(this is very poor because the more air-fuel that can be squeezed in there, the more heat can be made, and more output can be had).
fwiw, the de also = torque curve.
as it relates to this motor's crankcase in particular:
(24.5 cc)/(TDC crankcase volume) = 24.5/164.6 = 0.1488 x 100 = 14.88%
only 14.88% of the total crankcase volume is being filled on every stroke.
case volume ratio (comp ratio), in this particular saw is very loose, at 1.76:1
taking this a step further....
each individual transfer port cc'd out to be 4 cc by measuring. 8 cc total.
so, as the piston descends to BDC it is squeezing down on at least 24.5 cc of new mixture on every stroke, and sending it up through 8 cc of transfer port total volume.
hypothetically...... in order to cram 24.5 cc into the chamber itself, one would need
24.5 cc + 8 cc = 32.5 cc of mix to do so, because the trans are holding 8 cc of the charge.
…...who gives a frog you say!
...hope it may shed some light on effect of transfer port volumes, expectations of realistic modification gains within a motor, etc.
the chamber size w/piston at TDC measured out at a volume of 4 cc.
if some of the 24.5 cc mix did not leak out the exhaust (which it does) .......then 24.5 cc's gets squeezed into 4 cc.
i had no idea that so little A-F charge enters the motor on every spin. changed the way i think about things motor.
none of which would have happened if i did not get the calculator out.
*there is a good paper on 'crankcase delivery ratio' on the interweb that shows how crankcase volume and port sizing are connected to delivery ratio if anyone does decide to take more interest.
hope it helps
-joe
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link to the crankcase volume paper from previous post: http://www.bridgestonemotorcycle.com/documents/crankcase_volume6.pdf
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I have always wondered the crankcase volume differences in the husky 50 special and the partner 5000 plus. Seems like folks preferred the partner 5000 top on the husky 50 special crankcase. Always wondered the difference in them or not.
Very neat reading by the way. 8)
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Good info.
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link to the crankcase volume paper from previous post: http://www.bridgestonemotorcycle.com/documents/crankcase_volume6.pdf
some things from this paper:
the paper uses Vc/Vs (this is slightly different than crankcase volume ratio).
Vc = crankcase volume cc @ BDC
Vs = motor displacement cc
using the jonsereds 52 as an example:
crankcase volume at BDC = 93 cc
motor displacement = 49 cc
so, Vc/Vs = 93/49 = 1.9
......The larger this number, the more crankcase volume there is.
Figure #18
-Effect of Intake Duration on crankcase pressure. (Carby sizing also plays a big role).
....if you are interested in whys/hows of intake reversion, and whats going on....possibly worth a read.
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Joe, shows the potential pitfalls of hogging out transfer ducts and loosing more of the already small charge that makes it into the chamber. Cool stuff. Thks
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.....i may need to clarify.
the example saw motor in this thread has a box muffler. pipe motors crankcase requirements can differ, because they are highly influenced by the pipe.
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...taking a look at crankcase pressures which were used in a saw motor in gb's writings:
(more of an fyi thing, as i have no way of measuring these in the jon's 52. so it is not apples to apples comparison).
lowest crankcase pressure = 0.8 atm = 11.7 psi
highest crankcase pressure = 1.5 atm = 22.0 psi
now, here is the interesting part . (hahaha, if these ramblings of mine were indeed interesting at all).
crankcase pressure builds well before intake closes. goes from 0.8 atm to 1.1 atm
so, 0.8 atm (11.7 psi), is only 3 psi below atmospheric pressure.
...since, atmospheric pressure = 1.0 atm = 14.7 psi at sea level. so, at anything under 1.0 atm, air-fuel mix (delivery ratio), is entering the motor.
this is the reason where pipe motors put out 3x the power of box muff motors.....they pull it down well below 0.8 atm in the crankcase...pulling in a bigger gulp, ie. more delivery ratio.
after intake is closed, goes from 1.1 atm to 1.5 atm, so, about 22 psi is being forced up the trans ports. some of this pressure is gained from blowdown, so crankcase pressure has to overcome this.
another interesting thing, (and i say this loosely), how do crankcase comp degree measurements give any inclination as to any of this? hope someone can explain this to me, because i am not seeing this at all.
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I was shown abit different way to do crankcase volume mainly so it works with my TSR program , the way I was shown a 3120 ends up at 1.47 to 1 ratio , You want 1.20 to 1 ratio . That much changes will produce alot more power but takes about double the fuel to produce it and to get the 1.20 ratio your pretty much outside the case so alot of extra machine work , If you got the time the best thing is to machine a new crankcase so you can make more volume and 2 carbs on it to get enough fuel to make it run
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.....i read a good thread on a bike site, that a couple of aprilla race motor engineers chimed in on. talking about all that stuff.
edit: just remembered that some of the thread was in italian. it switched to english the last 30+ pages. interesting read.
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alot of it is BS mainly because its impossible to reach the amount that is claimed it can do , its all just theory but its a dam good place to start figuring . Biggest thing is the parts cannot stand that pressure if you can get enough fuel to it , bike engines are far better built to start with than a chainsaw so the crank can stand alot more pressure . One thing that had my mind working was at 1.20 to 1 ratio on the computer dyno in the TSR program it showed almost double the hp compared to 1.47 to 1 but was going to burn pretty much 2 -1/4 fuel lines of alcohol/ nitro to keep it running so way more fuel than what a single carb could produce
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i'm with you ehp. the bike thread was based on reed block motors. pipe has huge effect.
my program does not account for crankcase volumes as of yet, but it will in the future. when i worked the numbers with the calculator, for a piston ported/box muff motors.....only saw about a 5% increase in fuel charge entering the crankcase when just the volume was changed, depending on rpm.
have not estimated a pipe motor with numbers. not really an interest of mine.
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found it again, link here:
http://www.pit-lane.biz/t117p320-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked
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Please help me understand the putty. Is it the volume underneath the piston? I believe you could get accurate volume at bdc without the putty but then there is no way to measure the underside of the piston at tdc correct? Unless you did this with cylinder on which is the no drilling thing, drill the piston to let air out I assume? I have so many questions.
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Interesting thread that I had not seen and need to read more carefully. I'm still confused as to the definition of crankcase volume and exactly what volume this includes. Does it include the volume under the piston? Everything under the piston at BDC? Is transfer volume included?
Then there is the question of what volume is this being compared to - it makes sense to me to compare it to displacement, but ratios will of course be different if a different denominator is used.
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Please help me understand the putty. Is it the volume underneath the piston? I believe you could get accurate volume at bdc without the putty but then there is no way to measure the underside of the piston at tdc correct? Unless you did this with cylinder on which is the no drilling thing, drill the piston to let air out I assume? I have so many questions.
yes, the only reason for the putty is to help find the volume on the underside of the piston itself, when it is at BDC.
yes.
the last one, yes, kind of the idea....but it is not really just to let the air out. maybe the following will help to picture it using the "drill the hole in the piston crown method."
to get BDC case volume: with cylinder removed, piston at BDC. seal the piston skirt to the case deck with heavy grease. fill the case and underside of piston with a measured amount of oil via the drilled hole. done.
one could measure the oil being put in there with a syringe and a length of tubing.......(buret or graduated cylinder would work too).
the reason for the putty, is just to do all this without trashing a piston. not really a big deal, but it you are using 'one off' custom stuff, this can get expensive in a hurry.
the volume of under the piston is an additional portion of the case volume. like in the first photo shown in this thread, the entire piston does not disappear below the case deck at BDC, so the volume of the piston that is above the case deck has to be measured some way is all.
hope it helps.
i will clean up the thread a bit.
reducing the case volume, can gain some rpms. hope to show just how many as well.
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Interesting thread that I had not seen and need to read more carefully. I'm still confused as to the definition of crankcase volume and exactly what volume this includes. Does it include the volume under the piston? Everything under the piston at BDC? Is transfer volume included?
Then there is the question of what volume is this being compared to - it makes sense to me to compare it to displacement, but ratios will of course be different if a different denominator is used.
just volume at TDC divided by volume at BDC. some don't include the transfer port volumes, some do.
the volume under the piston is included at BDC. the volume under the piston is included at TDC as well.
without transfer ports volume included:
case volume @ TDC = 200 cc
case volume @ BDC = 100 cc
so, the case volume ratio = 200/100 = 2.00
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with transfer ports volume included:
say, motor has only 2 trans ports, each trans port measured out at 5cc each. so, 10cc total trans volume.
case volume @ TDC = 200 cc + 10 cc = 210 cc
case volume @ BDC = 100 cc + 10 cc = 110 cc
then, case volume ratio becomes = 210/110 = 1.91
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the difference in ratios is 0.09
rounding it off = 0.10
up to you, to decide whether to include them or not.
.....the folks who got the ball rolling on this case volume thing as referenced by the article linked in the thread, calculated the ratio differently.
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Thanks for the reply. Life threw me a wild pitch that hit me, so my saw play time has dropped huge amounts. When I get back on my feet I'm going to check a few for fun.
Sent from my iPhone using Tapatalk
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Thanks for the reply. Life threw me a wild pitch that hit me, so my saw play time has dropped huge amounts. When I get back on my feet I'm going to check a few for fun.
Sent from my iPhone using Tapatalk
..sometimes life = dodge-ball game, with multiple hits to the cranium and testes. eventually the swelling goes down.
vegetable oil leaves a sticky film that needs to be cleaned using a brush. think that something like transmission fluid would be better thing to use instead. easier to flush out, and better for the seals.
will you be drilling?
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This is a topic that interests me - I've been reading that people believe that the case volume can be too small and that this will hurt performance, but I do not see the logic in that. The swept volume of the case will always be the same on both sides of the piston, so there must always be "enough" volume. The only thing I can think of is that a full circle crank might block flow to the transfer entrances, but otherwise I can't see the problem with reducing case volume. It seems like less should always be better.
When drawing mix into the case you can have at best one atmosphere of pressure to push it in, and any extra volume just reduces that pressure differential and makes for less efficient pumping. When pushing mix up the transfers you can generate much more pressure, but initially must push against the residual combustion pressure in the cylinder.
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from what i gather from the nagao & shimamoto paper, reducing the case volume too much can cause the charge to blowback through the carb at lower rpms they were testing, with porting kept the same.
reasoning they had was the pressure builds up too fast in the case. as the case pressure rise fills the transfers too quickly, a portion of the charge goes back out the intake with a small case, at lower rpms.
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(above must happen because the case pressure gets equal or greater than atmospheric before the intake port closes......my words not theirs here).
the case has harmonic cavity resonance and wave pulses. changing volume, length of port, port diameter, carb size........ can all change the pulses as well. at a certain rpm the pulses become tuned to rest the motor. at others they are out of phase. intake tuning.
suggest sticking to the paper, not my ramblings.
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it has been abit, but have made some progress in the crankcase volume thing, along with many setbacks.
long story with not much to say.
first tried to get through some of the multi variable calculus formulas in that paper, to be able to get crankcase pressures. so far a no go. it's not like riding a bike. been 25 years.
someone younger needs to take a shot at it while it is still fresh.
after that, tried to find an easier way to get it done. got distracted and off course with some p-v diagram stuff and heat transfer (thermodynamic stuff) i found from a working program available from a university. cool stuff, you could plug in some numbers, and it spits out the whole intake/compression/expansion/blowdown cycle on a graph, along with power output. another graph shows just how much heat the motor tosses around.
of interest was that raising the compression ratio way up, forms two pressure spikes in the chamber. one before ignition, and a primary pressure spike when it lights off. there is more to learn there. but after some time, read some more of blair to figure out why the numbers were off. long story short, imo would stick to blair's methods, and abandon the regularly used p-v graph altogether for two stroke use.
on another note, figured out some things of interest. these were derived from page 178 of the paper i quoted earlier in this thread.
found how and succeeded to make a graph of the delivery ratio of a chainsaw motor based on the time area of the motor, how to find optimal crankcase compression ratio for a particular rpm, and lastly how to find the case volume in cc, needed for that particular rpm.
that's all for now. one mans interest is another mans boredom i guess. hahaha. time to crack a beer. peace out.
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that's all for now. one mans interest is another mans boredom i guess. hahaha. time to crack a beer. peace out.
It's interesting stuff to me Joe, but sometimes I just don't have the mental energy left at the end of the day to do more analytical stuff with spreadsheets and calculations. So much of what is written in the texts seems to be mostly empirical stuff.
I'm more interested in trying to visualize what happens. So as I said previously, here there is no pipe, and no way to increase the volume of air drawn in beyond what the piston can pull in under (at most) 1 atmosphere of pressure. Then it pushes that up the transfers with slightly higher pressure.
The swept volume is always larger than the effective displacement because it is gated by the port timing - the ports are only closed for a fraction of the swept volume. Combined with the extra volume that will always exist in the case and transfers, it's hard to see how it could ever get "crowded" in the case - there is always more volume than needed. What would be the negative effect of too little case volume? Would the pressure during primary (case) compression get too high? That just seems unlikely.
If you look at a theoretical engine with durations of:
Intake =160, Exhaust = 160, Transfer = 120, Blowdown = 20, Primary (Case) Compression = 40
That primary compression represents only 34% of the swept displacement, and it occurs while the crank is centered around 90deg - so over half the cylinder's swept volume is still exposed.
The intake has about 41% of the swept volume to pull in air (if you assume it's stops pulling at TDC - I know the air continues to move beyond that, but it's only from inertia), and at 1 atmosphere of pressure.
The transfers have 25% of the swept volume to push the mix into the cylinder, but that is pushed not pulled, so it's at more pressure.
It seems to me that the advantages of having a small case volume are to improve the efficiency of pulling in air and pushing it up the transfers, and I'm having a hard time visualizing what the negatives are - at least with no pipe.
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that's all for now. one mans interest is another mans boredom i guess. hahaha. time to crack a beer. peace out.
It's interesting stuff to me Joe, but sometimes I just don't have the mental energy left at the end of the day to do more analytical stuff with spreadsheets and calculations. So much of what is written in the texts seems to be mostly empirical stuff.
I'm more interested in trying to visualize what happens. So as I said previously, here there is no pipe, and no way to increase the volume of air drawn in beyond what the piston can pull in under (at most) 1 atmosphere of pressure. Then it pushes that up the transfers with slightly higher pressure.
The swept volume is always larger than the effective displacement because it is gated by the port timing - the ports are only closed for a fraction of the swept volume. Combined with the extra volume that will always exist in the case and transfers, it's hard to see how it could ever get "crowded" in the case - there is always more volume than needed. What would be the negative effect of too little case volume? Would the pressure during primary (case) compression get too high? That just seems unlikely.
If you look at a theoretical engine with durations of:
Intake =160, Exhaust = 160, Transfer = 120, Blowdown = 20, Primary (Case) Compression = 40
That primary compression represents only 34% of the swept displacement, and it occurs while the crank is centered around 90deg - so over half the cylinder's swept volume is still exposed.
The intake has about 41% of the swept volume to pull in air (if you assume it's stops pulling at TDC - I know the air continues to move beyond that, but it's only from inertia), and at 1 atmosphere of pressure.
The transfers have 25% of the swept volume to push the mix into the cylinder, but that is pushed not pulled, so it's at more pressure.
It seems to me that the advantages of having a small case volume are to improve the efficiency of pulling in air and pushing it up the transfers, and I'm having a hard time visualizing what the negatives are - at least with no pipe.
hey chris.
what you have shown here is about all the information one could gleam from looking at this using just degree durations and volume displacement. i don't disagree with the conclusions.
my point of contention, when i posted that a case can be too small is that 'every case is too small.'
the point being, that at any motor rpm, that is less than the peak torque rpm, the case is too small. at peak torque rpm, it peaks to a value 'as good as its going to get.' lastly,at any rpm higher than peak torque rpm, it is too large.
looking at this, like you have is a good way to visualize it.
looking at it, adding in both time areas and rpm, lets one look at it a little more clearly.
if somebody works the heavy math involved, to add in pressures and mass flow, we could look at it exactly the way those two guys did who wrote the paper. in this last way, their calculated numbers matched values that were closely approximated to the results obtained from the actual physical tests performed on the motor. (would be cool to be able to graph the pressures and mass flow at any rpm).
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don't know if many folks have read that paper?
the paper's graphs were very confusing to me at first because of the way they are set up.
for example, the term ...... no/n ........ no, is the 'optimum rpm'. 'optimum rpm' is the peak torque rpm. where the case volume is best suited. and n, is just the particular rpm is running at.
so, when you look at no/n, it is peak torque rpm divided by motor rpm.
small values of no/n, are high rpm operation.
large values of no/n, are low rpm operation.
the graphs display high rpms, closer to the left side bottom, while low rpm is further to the right side of graph. backwards to what i am used to.
hope it helps.
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So thanks to a recent storm I had many hours of shoveling gravel off my yard and dragging the lane with a box blade, which gives lots of time to think about this kind of stuff.....
from what i gather from the nagao & shimamoto paper, reducing the case volume too much can cause the charge to blowback through the carb at lower rpms they were testing, with porting kept the same.
reasoning they had was the pressure builds up too fast in the case. as the case pressure rise fills the transfers too quickly, a portion of the charge goes back out the intake with a small case, at lower rpms.
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(above must happen because the case pressure gets equal or greater than atmospheric before the intake port closes......my words not theirs here).
the case has harmonic cavity resonance and wave pulses. changing volume, length of port, port diameter, carb size........ can all change the pulses as well. at a certain rpm the pulses become tuned to rest the motor. at others they are out of phase. intake tuning.
suggest sticking to the paper, not my ramblings.
I am not convinced of this explanation (yet). On a piston ported engine the intake open event is symmetrical, and no other ports are open at the same time. So from a low speed/static point of view, whatever volume of air it draws in, the same volume will be pushed back out. However, if the case volume is larger than the volume it draws in, it is not necessarily the same air that goes back out - some fuel mix stays in the case. And the case volume is always bigger than what is drawn in. In my example engine upthread the intake is open for 41% of the swept displacement (and the piston is moving through TDC, exposing the maximum volume cylinder), and that does not count transfers and the con rod slot.
I'll come back to this...
hey chris.
what you have shown here is about all the information one could gleam from looking at this using just degree durations and volume displacement. i don't disagree with the conclusions.
my point of contention, when i posted that a case can be too small is that 'every case is too small.'
the point being, that at any motor rpm, that is less than the peak torque rpm, the case is too small. at peak torque rpm, it peaks to a value 'as good as its going to get.' lastly,at any rpm higher than peak torque rpm, it is too large.
looking at this, like you have is a good way to visualize it.
looking at it, adding in both time areas and rpm, lets one look at it a little more clearly.
if somebody works the heavy math involved, to add in pressures and mass flow, we could look at it exactly the way those two guys did who wrote the paper. in this last way, their calculated numbers matched values that were closely approximated to the results obtained from the actual physical tests performed on the motor. (would be cool to be able to graph the pressures and mass flow at any rpm).
If we imagine the case volume at the extremes it is useful to see how things respond to that variable. So imagine a very large case volume - maybe there is a huge tank under the cylinder. Then when the piston rises the volume in the case is changed by only a small percentage, and since air is compressible then that small change in volume causes a proportionately small change in pressure - and there is not much pressure difference to drive the movement of air into the case. So the volume of air intake is very small.
Next imagine if we could reduce the case volume to equal the displacement. Now the volume of air drawn in is as large as it can be (higher volumetric efficiency), and what is spit back out is too. As rpm goes up there is simply less time for moving the air, but it is still symmetrical so I don't thing rpm changes the picture.
Now is the spit back situation improved in any way by drawing less fuel mix into the case (larger case volume)? I don't see how it could be.
In a running engine there may well be a continual flow of air into the case that causes a bias towards retaining more of the air drawn in, but a smaller case volume will still make it a better pump.
So I'm still struggling to come up with some mechanism whereby lower case volumes are bad (at least without a pipe). It might be some secondary effect like the small case volume restricting flow to the transfers, but that could be mitigated by placing the transfer inlets in line with the con rod slot - such as under the exhaust port like in many modern saws......
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do think you are bringing up some interesting points. i like the way the paper explains all this.
what i get out of it, so far.
both the time area of the ports and the case volume, are changing the amount of mass flow (delivery ratio) and pressures.
and, both time area and case volume change with rpm in opposite ways. time area values gets smaller, and case volume becomes to large at higher rpm. opposite of that at lower rpm, so the time area is too large, while the case is too small.
on the discussion page, shweitzer says "with small volume and low speed, the crankcase discharges too fast into the cylinder, and during the rest of the transfer period, there is reverse flow."
thinking, since the time area is too large at lower rpm, it also allows the ease of filling the transfers too quickly with little resistance. once the trans are filled with fresh mix, it happens during the time where the pressure back-flowing in the trans, from the cyl to the case is quickly stalling flow. for the remainder of the time, the piston, still on the down-stroke is just pushing the remainder of the intake charge out through the carb, and easier way out.
as rpm increases, this all goes away. and the delivery ratio is just controlled mainly by the time areas. at least that is what the graph looks like when set it up like they say to. it follows the shape of the time areas changing with rpm.
that is all i have absorbed so far. hope it is correct?
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without working out the heavy math, there is really no way i can to make any further headway on this. so, my view of how time area is influencing the delivery ratio in opposite ways as compared to crankcase volume, may not be the on the mark. from what information i can go on at this time, comparing the time area delivery ratio graph i worked out, to the shapes of crankcase delivery ratio graphs as shown in the paper is not a definite. what looks and quacks like a duck, may not be a duck at all.
leaving this alone for others to explore further.
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time*area delivery ratio graph vs. rpm (graph setup as per the paper):
compare this to the crankcase volume/delivery ratio graphs vs. rpm, and draw your own conclusions.
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I still need to wade through all the details of this paper. However, I think it is important not to lose sight of what the authers were trying to accomplish. They state this in the opening paragraphs:
By changing the crankcase volume and lengths of the exhaust and inlet pipes, the authors have experimentally investigated the effect of the crankcase volume on the delivery ratio, and the effect of exhaust and inlet systems to compensate for the drop in delivery ratio caused by increasing the crankcase volume.
So once again it is all about the pipes, which makes sense because that effect is so dominant. But what if there is no pipe? Here, the only real hint seems to be in the following graphs, if we look at both intake and exhaust as "shortest" (i.e. untuned). However these graphs don't go any lower than a case to swept volume ratio of 2, so even here it may not be relevant:
Figure 6 shows that there is no rpm relationship to the delivery ratio - the delivery ratio peaked at some rpm, and it didn't matter what the case volume was.
Figure 9 shows that even by 3000 rpm, with no tuned pipes increasing the case volume reduces delivery ratio.
I don't know why the no pipe lower rpm plots in Figures 7 & 8 show larger case volume is better - perhaps because there is so much time that other effects dominate, or maybe because the no pipe situation was not really the focus of their efforts and some other effect was going on.
Still, I think what little data there is in this paper about engines with no tuned intake or exhaust confirms that at reasonable rpms smaller case volume is always better.
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Going back to Figure5, which is also for no tuned intake or exhaust, take a look at the smallest case volume (which is still pretty large at 2.44). Not only is the rpm of max delivery ratio moved up, but it does not fall off as fast as for larger case volumes. The peak is wider and flatter.
It is really hard to tell extrapolate this data to the the little engines used in saws at 10,000rpm with no pipes.
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believe that figures #5 and #6 are showing the same thing.
lost some things on my laptop after an update, and lost ability to take screenshots. will be back, when i get it sorted out.
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I still need to wade through all the details of this paper. However, I think it is important not to lose sight of what the authers were trying to accomplish. They state this in the opening paragraphs:
By changing the crankcase volume and lengths of the exhaust and inlet pipes, the authors have experimentally investigated the effect of the crankcase volume on the delivery ratio, and the effect of exhaust and inlet systems to compensate for the drop in delivery ratio caused by increasing the crankcase volume.
So once again it is all about the pipes, which makes sense because that effect is so dominant. But what if there is no pipe? Here, the only real hint seems to be in the following graphs, if we look at both intake and exhaust as "shortest" (i.e. untuned). However these graphs don't go any lower than a case to swept volume ratio of 2, so even here it may not be relevant:
Figure 6 shows that there is no rpm relationship to the delivery ratio - the delivery ratio peaked at some rpm, and it didn't matter what the case volume was.
Figure 9 shows that even by 3000 rpm, with no tuned pipes increasing the case volume reduces delivery ratio.
I don't know why the no pipe lower rpm plots in Figures 7 & 8 show larger case volume is better - perhaps because there is so much time that other effects dominate, or maybe because the no pipe situation was not really the focus of their efforts and some other effect was going on.
Still, I think what little data there is in this paper about engines with no tuned intake or exhaust confirms that at reasonable rpms smaller case volume is always better.
sorry, i cannot post the screenshots. best i can do. EDIT <<<<<<hahaha fixed it. silly windows.
believe it is best to use the words from the paper in my reply.
imho:
the first one shows the graphs being similar.
the second one shows what i used to come up with the graphs i made.
the third one addresses, part of the intent of the paper.
i'm looking at the 'untuned' pipes as being the 'shortest-shortest' as well.
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Looking at Figure 5 again, and thinking about the engines used in this paper, which are 200cc and 150cc with power peaks at 3600rpm.
What I see is that when the case volume is very large, then you can get a good delivery ratio at low rpm, but it falls off quickly once you go higher in rpm. That makes sense because there isn't much pressure differential to move the air, but if you go slow enough eventually it fills. Go beyond that and it falls on its face since there isn't enough time to move the air.
However, once you get close to the peak power rpm (where presumably the port timing was optimized), and you get the case volume down small enough, then it no longer falls off with rpm. Now the delivery ratio isn't so much a peak as a threshold.
This makes sense to me because the relationship between the pressure differential and the case volume isn't linear. As the case volume goes down the pressure differential goes up fast, and therefore the velocity goes up fast too. So as the case volume goes down you can move the air much faster and then you don't have this effect where there isn't enough time to achieve the full delivery ratio.
So if we look at our smaller engines at 10,000rpm it appears to me that smaller case volume is better, and we will not easily make case volumes small enough such that the delivery ratio will fall off at practical rpms for these engines.
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This is a graph of the pressure volume relationship from https://en.wikipedia.org/wiki/Boyle's_law:
(https://upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Boyles_Law.svg/363px-Boyles_Law.svg.png)
If you define the volume as the ratio of Vc/Vs as in the paper, the graph is even more extreme/less linear:
(http://chainsawrepair.createaforum.com/index.php?action=dlattach;topic=4974.0;attach=17529;image)
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Looking at Figure 5 again, and thinking about the engines used in this paper, which are 200cc and 150cc with power peaks at 3600rpm.
What I see is that when the case volume is very large, then you can get a good delivery ratio at low rpm, but it falls off quickly once you go higher in rpm. That makes sense because there isn't much pressure differential to move the air, but if you go slow enough eventually it fills. Go beyond that and it falls on its face since there isn't enough time to move the air.
However, once you get close to the peak power rpm (where presumably the port timing was optimized), and you get the case volume down small enough, then it no longer falls off with rpm. Now the delivery ratio isn't so much a peak as a threshold.
This makes sense to me because the relationship between the pressure differential and the case volume isn't linear. As the case volume goes down the pressure differential goes up fast, and therefore the velocity goes up fast too. So as the case volume goes down you can move the air much faster and then you don't have this effect where there isn't enough time to achieve the full delivery ratio.
So if we look at our smaller engines at 10,000rpm it appears to me that smaller case volume is better, and we will not easily make case volumes small enough such that the delivery ratio will fall off at practical rpms for these engines.
yep.
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This is a graph of the pressure volume relationship from https://en.wikipedia.org/wiki/Boyle's_law:
(https://upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Boyles_Law.svg/363px-Boyles_Law.svg.png)
If you define the volume as the ratio of Vc/Vs as in the paper, the graph is even more extreme/less linear:
^^.......this graph, if volume was on the y-axis, rpm on the x......
so close. since volume changes with piston movement........
set it up so that it's sqrt vc /rpm and you got it. (like in the paper)
(you will need a need to pick a known example case volume, and a certain peak value for rpm).
.......from there a simple ratio will get you case volumes and crankcase compression ratios for all other rpm points.
i did not think it beneficial to post this info yet, because it is useless without porting to a certain similar rpm point using time*areas?
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......very tough to convince you of anything........hahahahaha.
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time*area delivery ratio graph vs. rpm (graph setup as per the paper):
compare this to the crankcase volume/delivery ratio graphs vs. rpm, and draw your own conclusions.
peace
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......very tough to convince you of anything........hahahahaha.
LOL, I'm a bonehead for sure!
But look at the red curve of Figure5 again. This is at 3000rpm, or if scaled to an engine with a 10,000rpm power peak, it would be at 8,333rpm. The red curve does not peak and fall off, it plateaus. This is because once the case volume gets low enough the pressure differential gets very large, and you can no longer get ahead of the flow rate.
(http://chainsawrepair.createaforum.com/index.php?action=dlattach;topic=4974.0;attach=17527;image)
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Oh - I'm not sure Crankcase Compression Ratio is the same as the Vc/Vs ratio they used. It's still not clear what all is included anyway. If it is supposed to be the same, then it's probably because their setup could only add volume.
EDIT: I think CCR is the ratio of the swept volume plus the case volume to the case volume, or: CCR = (VC +VS)/VC
That is different from VC/VS
If you calculate it out, VC/VS = 2.44 works out to a CCR of 1.41, which is what Engine A is listed as.
So for the red line of Figure 5, the VC/VS = 2.44 is getting pretty close to the practical limit of what you could achieve, and it still is at almost full delivery ratio by 2,500rpm. That scales to about 7,000rpm for an engine with a 10,000rpm power peak, so practically it would be very hard to reduce the case volume down so far that you push the peak delivery ratio up above your power band.
I'd still like to know if the transfer volume is included - it should be.
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......very tough to convince you of anything........hahahahaha.
LOL, I'm a bonehead for sure!
But look at the red curve of Figure5 again. This is at 3000rpm, or if scaled to an engine with a 10,000rpm power peak, it would be at 8,333rpm. The red curve does not peak and fall off, it plateaus. This is because once the case volume gets low enough the pressure differential gets very large, and you can no longer get ahead of the flow rate.
(http://chainsawrepair.createaforum.com/index.php?action=dlattach;topic=4974.0;attach=17527;image)
glad you are having fun with it.
if you are on board with graph #5, being similar to #6......? x-axis scale on #6, has a big 3000 to 6000 jump.
motor A's hp peak is at 3600 in stock form. thinking it may only rev a few grand or so higher?
the only way to get an better handle on that would be to plug in it's numbers, which i have not done. will have to look into that. would be a good check.
i have not been focusing on pressure and mass flow, with this so much. when the math came to a dead end, lost interest. will rekindle that angle again eventually. the fuel's mass compared to the air's is much greater. kind of like wind trying to blow sand around on the beach. takes a lot to get it moving because of the mass difference. as rpm's rise, velocity naturally increases, looking just at pressure differentials may be bit deceiving because it is compressible flow. lots of things going on.
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Oh - I'm not sure Crankcase Compression Ratio is the same as the Vc/Vs ratio they used. It's still not clear what all is included anyway. If it is supposed to be the same, then it's probably because their setup could only add volume.
EDIT: I think CCR is the ratio of the swept volume plus the case volume to the case volume, or: CCR = (VC +VS)/VC
That is different from VC/VS
If you calculate it out, VC/VS = 2.44 works out to a CCR of 1.41, which is what Engine A is listed as.
So for the red line of Figure 5, the VC/VS = 2.44 is getting pretty close to the practical limit of what you could achieve, and it still is at almost full delivery ratio by 2,500rpm. That scales to about 7,000rpm for an engine with a 10,000rpm power peak, so practically it would be very hard to reduce the case volume down so far that you push the peak delivery ratio up above your power band.
I'd still like to know if the transfer volume is included - it should be.
imo, think that the difference in the numbers is not that big a deal. does sound silly i know. for the following reason......
both results are interchangeable when using them just to scale a graph. thinking that you will not buy into this. hahahaha.
ok, put another way, the end purpose of figuring any of this out is not to see just how much beer you can drink while juggling numbers in a calculator.
for any of this to be useful for anyone, the end goal is to find the estimated case volume needed for a certain rpm.
both CCR methods, while different, give the same result when a rpm point is equated to it. the shape of the graph does not change.
so, the CCR is just along for the ride. think you will find that the author's use this interchangeably, if you stick to the way they set the graph up in the relationship using sqrtVc/rpm, that i quoted.
trans volume....up to you. if 0.1 or so CCR makes a difference? wouldn't think it would change anything as far as the graphing is concerned. 10cc looks to only have an impact when you are way way up in the rpm range, possibly well beyond physical limitations anyway.
as you have already found, achieving the proper case volume runs into physical limitations very quickly, and it's doubtful that they can be met.
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Another way to look at the reasons behind the peaking of the curves:
Larger case volume means lower pressure difference and lower velocities. Lower velocity means more time to move the air. Therefore larger case volumes represent a time delay in moving the air.
However, port timing is always symmetrical about TDC. So at least at lower rpm there should always be some case volume/time delay that best matches the port time events, trapping the most air before the ports close or some such (probably the transfers would be most important).
At smaller case volumes/higher velocities and higher rpm possibly inertial effects start to come into play, making the shape of the red lined plot different.
i have not been focusing on pressure and mass flow, with this so much. when the math came to a dead end, lost interest. will rekindle that angle again eventually. the fuel's mass compared to the air's is much greater. kind of like wind trying to blow sand around on the beach. takes a lot to get it moving because of the mass difference. as rpm's rise, velocity naturally increases, looking just at pressure differentials may be bit deceiving because it is compressible flow. lots of things going on.
I'm not sure there was any fuel in the tests done in this paper? Also, the fuel is in vapor form in a engine, so its mass should just join that of the air - not quite like blowing sand.
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Oh - I'm not sure Crankcase Compression Ratio is the same as the Vc/Vs ratio they used. It's still not clear what all is included anyway. If it is supposed to be the same, then it's probably because their setup could only add volume.
EDIT: I think CCR is the ratio of the swept volume plus the case volume to the case volume, or: CCR = (VC +VS)/VC
That is different from VC/VS
If you calculate it out, VC/VS = 2.44 works out to a CCR of 1.41, which is what Engine A is listed as.
So for the red line of Figure 5, the VC/VS = 2.44 is getting pretty close to the practical limit of what you could achieve, and it still is at almost full delivery ratio by 2,500rpm. That scales to about 7,000rpm for an engine with a 10,000rpm power peak, so practically it would be very hard to reduce the case volume down so far that you push the peak delivery ratio up above your power band.
I'd still like to know if the transfer volume is included - it should be.
imo, think that the difference in the numbers is not that big a deal. does sound silly i know. for the following reason......
both results are interchangeable when using them just to scale a graph. thinking that you will not buy into this. hahahaha.
ok, put another way, the end purpose of figuring any of this out is not to see just how much beer you can drink while juggling numbers in a calculator.
for any of this to be useful for anyone, the end goal is to find the estimated case volume needed for a certain rpm.
both CCR methods, while different, give the same result when a rpm point is equated to it. the shape of the graph does not change.
so, the CCR is just along for the ride. think you will find that the author's use this interchangeably, if you stick to the way they set the graph up in the relationship using sqrtVc/rpm, that i quoted.
trans volume....up to you. if 0.1 or so CCR makes a difference? wouldn't think it would change anything as far as the graphing is concerned. 10cc looks to only have an impact when you are way way up in the rpm range, possibly well beyond physical limitations anyway.
as you have already found, achieving the proper case volume runs into physical limitations very quickly, and it's doubtful that they can be met.
i deserve a good kick in my backside. ignore my ramblings above. did not see this before i plugged in numbers from motor A. using a chainsaw motor the difference was slight, with motor A is is quite large.
will post up some motor A stuff today.
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i deserve a good kick in my backside. ignore my ramblings above. did not see this before i plugged in numbers from motor A. using a chainsaw motor the difference was slight, with motor A is is quite large.
will post up some motor A stuff today.
Actually I agree with you, in the sense that CCR or VC/VS are just two different ways of measuring the same effect. It will change the shape of the graph by changing the X-axis scale, but it does not change the meaning at all.
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graph is motor A from paper
top blue line is crankcase volume.
black is Vc/Vs
red is crankcase comp ratio.
idea is, that you can see what volume/CCR value needed for a particular rpm.
wanted to include the time area delivery ratio and crankcase delivery ratio graphs on this plot. when i added a 5th range, the graph went to crap.
liking this spreadsheet software, but the graphing functionality needs some work. going to have to show the delivery ratio stuff on separate graph.
as far as saw motors go, it is a little off. does not seem to account for straight line, non changing situations, because of the way it is set up.
delivery ratio of a saw is pretty well close to flat. think it could be tweaked using bsfc's, not sure. will throw some photos up of the saw graphs later.
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first photo is motor A from paper again, yellow highlight, showing that everything lines up fine.
second photo is saw motor set for 5500 rpm. the CCR is off.
third photo is the same saw motor now set at 4500 rpm. there is about a 1000 rpm spread on either side of 5500. but far off from 4500.
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OK, the relationship between CCR and VC/VS is straightforward, but I'm not sure what you are calculating with the rest of it.
I have been more focused on trying to understand the big picture effects - what happens as case volume changes. Near as I can tell from the data they provide, without a pipe it would be near impossible to make the case volume too small on most saw engines, unless you were going for an rpm band well below what is typically used in a modern saw engine.
The recommendation I have seen before is (I believe) for a case volume of 120% of the displacement, but I'm never sure what that includes. VC would clearly include the volume under the piston and the transfers, but I don't know if the rule-of-thumb does. It would be tough to achieve this. Still, these are significantly smaller numbers than the 2.44 minimum they used. Looking at the 2.44 and 2.99 plots of Figure 5, you can see that things are different at higher rpm compared to the larger case volumes. What happens if you go smaller still? There just isn't any data here to show that.
I tried to make a plot of the rpm of the peak delivery ratio vs. VC/VS from Figure 5, but there are not many data points, and looking at only the peak ignores what is happening at rpms above the peak.
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OK, the relationship between CCR and VC/VS is straightforward, but I'm not sure what you are calculating with the rest of it.
yes, straightforward. to get the CCR and Vc/Vs, you need just two things. case bdc volume, and swept volume. a plot can easily be made for different volumes. taking it a step further, put rpm in the mix at peak DR. peak DR, for any motor has to be below peak hp rpm. there is a slight rise at peak tq. check the curves in the paper. blair shows this much clearer. for a high rpm motor they are pretty flat. used that single rpm or close to it in my graph. a user input value. best guess. that rpm, is placed between values of rpm, in 500 increments. after peak torque rpm, the time*areas of the ports are getting too small. so, the time*area is in control. the rpms are showing what the CCRs an Vc/Vs would be along their curves if there was air enough. nothing fancy.
it is a close estimate. until someone figures out the heavy math, best that can be done, as i had mentioned before. since the Vc/Vs is always going to be a curve, and CCR is always a straight line. they will never line up with rpm and the case volume, to the right of their point of intersection. none of this matters at all, unless you really like to make things go, by balancing the case to the porting using rpm.
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CCR = (VC+VS)/VC
VC/VS = 1/(CCR-1)
They are both ratiometric (dimensionless) ways of relating case volume to swept volume - all the plots in the paper could be reformatted to use CCR instead of VC/VS, and it would change the shape of the plots but the meaning would be exactly the same. The relationship between the two measures is not related to rpm, and I'm confused as to how you are introducing this term?
You can actually set the two equal and try to solve it:
VS2+VCVS-2VC=0
https://www.wolframalpha.com/input/?i=a^2+%2Bab-2b%3D0 (https://www.wolframalpha.com/input/?i=a^2+%2Bab-2b%3D0) (had to use c for VC and s for VS)
But it still doesn't mean anything.
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will post up the estimated crankcase delivery ratio graph in a few minutes, was at a extended union contract update dinner. working 11-1/2 months without a contract is not cool. returned with a few brain cells lost last eve to even reply.
since, i am unable to prove the relationship to you, as i have described, if i can get the time in the next few days, by using only values given for motor A......will post up all six graphs, similar to the ones referenced in the paper so you can compare values. after i post those up, will email you working copies of the graphs, for you to do as you like with. don't really want to spend the time to rework what has been shown in the paper, but that is what i am willing to do. those graphs are of no use to me. my purpose was/is different.
its all cool, always need proof of things myself.
will check out the link later.
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Graphs and charts are fine Joe, but I tend to approach problems from concepts first, and since I do not know what you are trying to show they may not be meaningful to me.
To that end, VC and VS are fixed for a given engine design. The authors devised a way to vary VC and look at how that effected delivery ratio at various rpm. Still, for each value of VC, both VC and VS are fixed and not a function of rpm, so equating different combinations of them (VC/VS vs. CCR) tells you nothing about delivery ratio.
It is delivery ratio that is a function of rpm and VC and VS. If you could come up with a way to model Figure 5 for an un-piped engine that might be useful, but it would be very complex - and it appears that if you tune the engine for typical saw rpms, then the simple model of smaller-case-volume-is-better will suffice in most cases anyway. In my opinion that is what Figure 5 shows, and I think if you look at what the manufacturers are doing it confirms this. It might technically be possible to make the case volume so tight that the rpm of max delivery ratio moves higher than the port timing can be set up for, but I think in practice this would be very difficult to do.
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some motor a things. at this point, i can say that i have seen enough of this motor. hahaha.
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Graphs and charts are fine Joe, but I tend to approach problems from concepts first, and since I do not know what you are trying to show they may not be meaningful to me.
To that end, VC and VS are fixed for a given engine design. The authors devised a way to vary VC and look at how that effected delivery ratio at various rpm. Still, for each value of VC, both VC and VS are fixed and not a function of rpm, so equating different combinations of them (VC/VS vs. CCR) tells you nothing about delivery ratio.
It is delivery ratio that is a function of rpm and VC and VS. If you could come up with a way to model Figure 5 for an un-piped engine that might be useful, but it would be very complex - and it appears that if you tune the engine for typical saw rpms, then the simple model of smaller-case-volume-is-better will suffice in most cases anyway. In my opinion that is what Figure 5 shows, and I think if you look at what the manufacturers are doing it confirms this. It might technically be possible to make the case volume so tight that the rpm of max delivery ratio moves higher than the port timing can be set up for, but I think in practice this would be very difficult to do.
the graphs are just an estimate from the relationships the authors gave folks like us to picture what the curves look like.
the values for DR are lower than actual, as you can see. that is all there is with this. i understand that.
the only difference with the graphs(mine) i posted before all of this, is that rpm is plotted with a changing case volume. the graphs are not meant to be compared to any of the graphs in the paper. my purpose is different. i for one have never seen a chart of this.
i agree with making case volume as small when raising rpm point within reason. for me it would be just to know how small, or how big to leave it for matching the case to peak torque point at whatever rpm i am after. physical limitations would stop you before reaching those goals.
its just numbers.
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........some folks like rc plane guys for example, may not need a small case. depends on what you are trying to do i guess?
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now here is a head scratcher.
same saw.
first saw graph = estimated t*a DR
2nd graph = estimated crankcase DR
peak rpm points are chosen. best guess. disregarding the differing number values........due to these being estimates.
the t*a peak rpm is pretty close to what it actually is, imo, because it matched up with blair recommendation t*a values for that size motor at that rpm.
the crankcase peak rpm, may or may not be at the right rpm point. my best guess is that it is somewhere between peak tq and peak hp rpm. saw specs say 8300 hp peak, 11400(max) ? if i remember right.
somewhere it gets air to run up there.
if t*a peaks, at 5500......maybe the crankcase actual rpm of DR peak is higher.....? and if so, it may tightrope between the two peaks? or is t*a in control of DR as i was thinking previously?
what say ye?
so this is what i am looking at:
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think i will heed chris' advice and leave the whole Vc/Vs and CCR separate from the various peak DR's.
there is no way i can be sure the CC DR is at peak tq rpm, and even less sure that it would be located at that peak tq rpm point for all different sizes and porting configurations of motors and cases. there are definite trends, as y'all can see, but that is all i have to go on with using these estimates so far.
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here is a working program,
figures out CCR and Vs/VC, based on your crankcase volume.
screenshots to follow.
the working program, is found right below this sentence.
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So here's a question: If the rpm of peak Delivery Ratio is dependent on case volume, does it also depend on combustion chamber volume?
I've been playing around with two 42cc Poulan engines with different combustion chamber volumes, and thinking about the impact of that. Obviously larger combustion chamber volumes negatively impact compression ratio, but do they also trap a larger volume of fuel/air mix?
Clearly combustion chamber volume can't be zero or way too big, but what is optimal?
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So here's a question: If the rpm of peak Delivery Ratio is dependent on case volume, does it also depend on combustion chamber volume?
I've been playing around with two 42cc Poulan engines with different combustion chamber volumes, and thinking about the impact of that. Obviously larger combustion chamber volumes negatively impact compression ratio, but do they also trap a larger volume of fuel/air mix?
Clearly combustion chamber volume can't be zero or way too big, but what is optimal?
my understanding at this point, is that two factors control what ultimately becomes a motor's delivery ratio. ie. case volume and porting.
in the first part of the paper on case volume, porting was held constant, while they tested differing case volumes.
i found another paper in which testing for delivery ratio was done by keeping the case volume the same, and changing porting only.
found here (starts on page 17): http://www.vintagesnow.com/SledU_Folder/delivery_ratio-1.pdf
combustion chamber......so far, i have not found mention of this affecting delivery ratio. i was not on the lookout for this while reading and may have missed it?
while this may or may not be completely true, my belief is the optimal case sizing has to match the porting sizing for a overlapping range of rpms to work well. still learning on this. read 4 papers on this so far, just slogging through it all. two sources mention that delivery ratio is the most important factor for making power, for motors which lack a tuned exhaust.
thought the estimate i was working on for case size/rpm would have ended better. the error between optimal and estimated, increases with rpm. they are two straight line style plots. could post it. too bad it was not more accurate.
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The combustion chamber question was not from a paper, just my own musing. The more fuel/air you can trap in the combustion chamber, the more energy is stored in there at ignition. Delivery Ratio is a way of measuring that by comparing the trapped volume to the displacement.
So if you can increase the volume available to trap that fuel/air by increasing the combustion chamber volume, do you increase deliver ratio? You still have to turn whatever is trapped into mechanical power effectively, so DR is not the only factor by far - and a larger combustion chamber (lower compression ratio) may really hurt in doing that.
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The combustion chamber question was not from a paper, just my own musing. The more fuel/air you can trap in the combustion chamber, the more energy is stored in there at ignition. Delivery Ratio is a way of measuring that by comparing the trapped volume to the displacement.
So if you can increase the volume available to trap that fuel/air by increasing the combustion chamber volume, do you increase deliver ratio? You still have to turn whatever is trapped into mechanical power effectively, so DR is not the only factor by far - and a larger combustion chamber (lower compression ratio) may really hurt in doing that.
see where you are going with this.
imo, combustion chamber size sets compression. since compression is pressure and the higher the pressure the higher the heat, and the more heat, the more power. so i would side, on that the smaller the chamber - the better. because of the whole pressure cooker idea.
the heat, got me onto the whole otto cycle p-v diagram/heat transfer thing a few weeks ago. there is a free program that looks at this. it is what is used for both 4st and 2st. it is way off for 2st, when i plugged in heat data numbers for a 2st, from blair's book. he came up with a better way to look at this. anyhow, you could plug in different values for compression ratios, and use the program to get your own conclusions.
<edit> added the link here: http://ronney.usc.edu/spreadsheets/
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for those who still have interest in this kind of thing, something to look into, is volumetric efficiency. this is basically what folks call delivery ratio these days.
there are lots of views on this. an interesting thing is that once you find the VE, you can find the CFM the motor needs for a certain amount of power/torque at an rpm. so, a very basic dyno curve like simulation can be had. this was the initial reason for my interest in delivery ratios.
like i mentioned, unless someone stays at a holiday inn and figures out the heavy math, the best that can be had is an estimate. using the crankcase DR, therefore is out for me. the T*A DR is what i will be using, since the values are based on the simple porting program found somewhere here in another thread.
when i find things of interest that may help folks in these papers and such, i post what may be useful. i'm over the rehashing of jennings to the point that it causes effects similar to the acidic juices of pre-vomiting in my throat after a night of heavy bourbon consumption. hahahaha.