ESE's works engine tuner

[41juergen]

My definition for crankcase compression ratio is

(volume below the piston dome at TDC) / (volume below the piston dome at TDC - cylinder capacity)

and for me, volume below the piston dome at TDC includes the transfer duct volumes.

Of course this is just a geometric approach. One can argue that crankcase compression can only begin when the inlet is closed, and it ends when the transfers start opening.
So the crankcase compression ratio is just a number. The crankcase volume, in combination with the transfer ducts and above all the exhaust system, determines the engine's pressure fluctuations and resonance frequency.

Of course that makes sense (as always for your statements )
@Wob: when you say, a well designed reed engine should have a CCR of approx 1.3, is that with the transfer volume included?

[philou]

Have you ever measured a crankcase volume?

[41juergen]

Have you ever measured a crankcase volume?

Yes, my 3XV / 4DP engine has on the left cylinder 565 ccm and on the right cylinder 510 ccm. On my 125ccm engine with a 4DP cylinder and a spacer plate (to match the 110 mm rod) I got 630 ccm (needs a re-work to get the CCV down)..

[wobbly]

Neels CCR " definition " isn't different than the accepted method.
In the code it automatically removes the duct volumes when you use the calculator.
Thus if the duct or port area changes it will update the CCR.
Alternately you can input the actual CCR as measured manually, and use the Transfers Included radio button.

Re the CCR with reeds - yes 1.3 is the measured ratio with transfers included.

[philou]

565 cc = 1,28
510 cc = 1,32
630 cc = 1,25

[41juergen]

Neels CCR " definition " isn't different than the accepted method.
In the code it automatically removes the duct volumes when you use the calculator.
Thus if the duct or port area changes it will update the CCR.
Alternately you can input the actual CCR as measured manually, and use the Transfers Included radio button.

Re the CCR with reeds - yes 1.3 is the measured ratio with transfers included.

Thank's a lot, so the CCR number shown in Neels code is slightly different to the "accepted method" (what of course is not a problem, plus the benefit of the automatic update when changing the goemetry of the transfers)..

[wobbly]

Just to be clear , although the code displays a " non standard " output it is using the normal CCR ratio including the transfers when running the sim.

[Vannik]

Although not 2T but 4T, this video showing the inlet pulses is very insightful. It shows how through an rpm sweep the number of pulses in the inlet system decreases as the rpm value increases and the inlet system goes in and out of tune. What I find interesting is how the last pulse slowly disappears until the next pulse becomes the dominant pulse. This effect is what causes the fluctuations in the torque curve of a 4T engine.

https://www.youtube.com/watch?v=Axro8WRa_dQ

[Gradella23]

Splatter , yea buddy that cage looks dead cool , now try the step under the reed tips , it worked well for me in the TM R1 and now the R2 as well.
The company I used originally to print stuffers used a process of putting the part in a box with I think acetone fumes , this fused the surface into a smooth shiny finish.

if i understood you're using something like this? more or less angle in relation to the reed surface?

[Frits Overmars]

My definition for crankcase compression ratio is (volume below the piston dome at TDC) / (volume below the piston dome at TDC - cylinder capacity)
Of course this is just a geometric approach. One can argue that crankcase compression can only begin when the inlet is closed, and it ends when the transfers start opening.
So the crankcase compression ratio is just a number. The crankcase volume, in combination with the transfer ducts and above all the exhaust system, determines the engine's pressure fluctuations and resonance frequency.

Come to think of it, I do not use the crankcase compression ratio nor the combustion chamber compression ratio anywhere in my sim.
Instead the code calculates the crankcase and combustion chamber volumes for each crankshaft degree.

For me, these compression ratios are only useful for comparing engines of different displacements. But even then I do not use the Crankcase Compression Ratio CCR.
I use the Crankshaft Volume Ratio CVR between TDC crankcase volume and cylinder displacement.
I find this just as useful in comparing engines with different displacements, but the math is much simpler.
Here is an example, using the Aprilia RSA values of 124,8 cc cylinder displacement and 675 cc TDC crankcase volume.
The Crankcase Compression Ratio CCR is 675 / (675 -124,8) = 1,2268
The Crankcase Volume Ratio CVR is 675 / 124,8 = 5,409
Now suppose we want the same crankcase ratio in a 100 cc engine. So cylinder displacement CC=100, and TDC crankcase volume CV must be calculated.

When using CCR, calculating the required TDC crankcase volume CV goes like this:
CCR = CV / (CV - CC)
CV / (CV - CC) = CCR
CV = CCR x (CV - CC)
CV = CCR x CV - CCR x CC
(CCR -1) x CV = CCR x CC
CV = CCR x CC / (CCR - 1)
now we enter the current vallues:
CV = 1,2268 x 100 / (1,2268 -1)
CV = 122,68 / 0,2268 = 540,9 cc

For those who are still with me, let's repeat the calculation using the Crankcase Volume Ratio CVR. I promise it won't take long.
CVR = CV / CC
CV = CVR x CC
entering the current values:
CV = 5,409 x 100 = 540,9 cc
Piece of cake, isn't it?

[ranasada]

come to think of it, i do not use the crankcase compression ratio nor the combustion chamber compression ratio anywhere in my sim.
Instead the code calculates the crankcase and combustion chamber volumes for each crankshaft degree.

For me, the ratios are only useful for comparing engines of different displacements. But even there i do not use the crankcase compression ratio ccr.
I use the crankshaft volume ratio cvr between tdc crankcase volume and cylinder displacement.
I find this just as useful in comparing engines with different displacements, but the math is much simpler.
Here is an example, using the aprilia rsa values of 124,8 cc cylinder displacement and 675 cc tdc crankcase volume.
The crankcase compression ratio ccr is 675 / (675 -124,8) = 1,2268
the crankcase volume ratio cvr is 675 / 124,8 = 5,409

now suppose we want the same ratio in a 100 cc engine. So cylinder displacement cc=100 and crankcase volume cv must be calculated.
When using ccr, calculating the required tdc crankcase volume cv goes like this:
Ccr = cv / (cv - cc)
cv / (cv - cc) = ccr
cv = ccr x (cv - cc)
cv = ccr x cv - ccr x cc
(ccr -1) x cv = ccr x cc
cv = ccr x cc / (ccr - 1)
now we enter the current vallues:
Cv = 1,2268 x 100 / (1,2268 -1)
cv = 122,68 / 0,2268 = 540,9 cc

for those who are still with me, let's repeat the calculation using the crankcase volume ratio cvr. I promise it won't take long.
Cvr = cv / cc
cv = cvr x cc
entering the current values:
Cv = 5,409 x 100 = 540,9 cc
piece of cake, isn't it?

x : 100 = 675 : 124,8
more simple

[Frits Overmars]

x : 100 = 675 : 124,8
more simple

If you say so Ranasada .
But something else puzzles me.
What magic did you use to convert most uppercase letters in my above quoted post to lowercase? Only some capital letters at the beginning of sentences have survived.
A conversion like this doesn't exactly make the formulas any easier to read. So why ?
Initially I suspected the quoting algorithm of the forum to be the culprit. But after looking at a number of other quotes, the forum seems to be innocent...

[ranasada]

If you say so Ranasada .
But something else puzzles me.
What magic did you use to convert most uppercase letters in my above quoted post to lowercase? Only some capital letters at the beginning of sentences have survived.
A conversion like this doesn't exactly make the formulas any easier to read. So why ?
Initially I suspected the quoting algorithm of the forum to be the culprit. But after looking at a number of other quotes, the forum seems to be innocent...

not my fault...
maybe for having modified my post?

[Grumph]

Of course that makes sense (as always for your statements )
@Wob: when you say, a well designed reed engine should have a CCR of approx 1.3, is that with the transfer volume included?

Further to this : What is left in or removed from the inlet tract when reed CCR is measured ? Everything out and an external plate across the cavity ? Leave the reeds and stuffer in and put a plug in the carb mount rubber ?

What's accepted practice ?

[41juergen]

Further to this : What is left in or removed from the inlet tract when reed CCR is measured ? Everything out and an external plate across the cavity ? Leave the reeds and stuffer in and put a plug in the carb mount rubber ?

What's accepted practice ?

I use tape to make sure the reeds are closed and no oil can escape through the reed plates...and have the reed cage installed. And also make sure no oil can escape through the aux ex ports or power valves.