Author Topic: intake/crankcase stuff  (Read 306 times)

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Offline 1manband

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Re: intake/crankcase stuff
« Reply #10 on: March 23, 2016, 05:14:15 pm »
learning as i go.

this is from a paper called "Surge Phenomena in Engine Scavenging" by Helmuth William Engelman (thesis).
probably the best paper on this topic.  64 pages worth.

sorry, i do not have a link, too big to post, maybe i could split it up somehow and post?

self explanatory.  range from about 1.95 to about 2.14.

now to plug in some numbers and see.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #11 on: March 23, 2016, 05:18:50 pm »
one thing you need to find first is Hz from RPM,

so, just divide motor RPM by 60.  done.

-------------------------
there is no mention of any of this in reference #2 K&W delivery ratio paper i was using....  just leaves you hanging after they post the formula.
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Re: intake/crankcase stuff
« Reply #12 on: March 23, 2016, 07:38:33 pm »
tried out a few different values in the formula.

easy to make them fall within the motor's rpm range.  looks like it can be of value.

this is the most basic of all resonance formulas.

will work out different formulas which look like they may give more accurate results.

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Offline 1manband

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Re: intake/crankcase stuff
« Reply #13 on: March 24, 2016, 04:33:11 pm »
side note:  the intake/crankcase res formula, much like exhaust formulas, are based on sound waves.  through experiments, folks found that they approximate physical testing of pressure waves.

sidetrack to some pressure things.  intake-crankcase tuning is interrelated to porting. since the size of the hole also affects the intake/crankcase Hz. this helps show what is ideal.

interesting thing at transfer port just close at higher rpm.

from reference #2 below.

......i see nobody caught my drift on the interesting comment?......will be back, have to draw something.
hiatus

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Re: intake/crankcase stuff
« Reply #14 on: March 24, 2016, 10:32:57 pm »
The drift I am seeing is that the larger the port and the longer the intake the lower the resonant frequency and it appears to me that it tends to come more in line with what your average chainsaw is going to turn in rpm's.   I am not good at all the math so I was more interested in a rule of thumb and this is what I seem to understand so far.  According to your last chart that is what appears to me.
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Re: intake/crankcase stuff
« Reply #15 on: March 24, 2016, 10:34:47 pm »
side note:  the intake/crankcase res formula, much like exhaust formulas, are based on sound waves.  through experiments, folks found that they approximate physical testing of pressure waves.

sidetrack to some pressure things.  intake-crankcase tuning is interrelated to porting. since the size of the hole also affects the intake/crankcase Hz. this helps show what is ideal.

interesting thing at transfer port just close at higher rpm.

from reference #2 below.

......i see nobody caught my drift on the interesting comment?......will be back, have to draw something.

Are you referring to the sound waves and pressure waves being similar to one another.
PP 505, 475, 445.

Offline 1manband

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Re: intake/crankcase stuff
« Reply #16 on: March 25, 2016, 10:55:08 am »
The drift I am seeing is that the larger the port and the longer the intake the lower the resonant frequency and it appears to me that it tends to come more in line with what your average chainsaw is going to turn in rpm's.   I am not good at all the math so I was more interested in a rule of thumb and this is what I seem to understand so far.  According to your last chart that is what appears to me.

not sure of a rule of thumb yet, you are right on with the concept.

but to me, the interesting thing was a couple of different things.

the graphs are showing the pressures within the crankcase. 

the author's stated that for maximum delivery ratio at a higher rpm:
a lower Pressure is more favorable for increasing DR at Transfer port close.  @t6 rpm, on the graph this condition was met.

however, again for maximum DR, they say that a higher crankcase pressure is favorable at intake port close.
this condition was not met on the graph.  it does happen though, at quite a higher rpm.

so, my head scratcher was, at what rpm is this happening at where both conditions are met?

drew some things on the graph to show some things. rpm is increasing, as you move down the page.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #17 on: March 25, 2016, 11:01:57 am »
side note:  the intake/crankcase res formula, much like exhaust formulas, are based on sound waves.  through experiments, folks found that they approximate physical testing of pressure waves.

sidetrack to some pressure things.  intake-crankcase tuning is interrelated to porting. since the size of the hole also affects the intake/crankcase Hz. this helps show what is ideal.

interesting thing at transfer port just close at higher rpm.

from reference #2 below.

......i see nobody caught my drift on the interesting comment?......will be back, have to draw something.

Are you referring to the sound waves and pressure waves being similar to one another.

that too.

that was my biggest head scratcher of all.  the sound waves and pressure waves, are supposed be similar.

none of these crankcase pressure graphs are showing any evidence of this at all.  they should be vibrating like a guitar string. and they are not.

could not figure out why.  then had to read read and read some more.  then i got it.
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Offline 1manband

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Re: intake/crankcase stuff
« Reply #18 on: March 25, 2016, 12:04:20 pm »
this is what i found.

the pressure graphs of the crankcase are not showing the vibrations waves at all.

only the ports are showing them.

so, the piston gets the wave motion going, based on rpm.  moves the air in the case, the air in the case then gets the waves going in the ports.

interesting thing is the intake likes about 4x the rpm, and the transfers like around 8x the rpm Hz.

for the guitar playing folks:  on the open "e" string.....after pluckng......harmonics at the 12th and 24th frets.
not exactly.....would need plenty more frets actually, but similar idea.

i like to know the "why" i guess......hahahaha.

screens are showing about 9500+ rpm



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Offline 1manband

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Re: intake/crankcase stuff
« Reply #19 on: March 25, 2016, 12:12:37 pm »
........and when you get the resonance thing going good........

picture the graph on the bottom of this link.......doing that in the intake and transfers.......!!!

link here:  http://newt.phys.unsw.edu.au/jw/Helmholtz.html
hiatus

 

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