ESE's works engine tuner

[husaberg]

Lengthening the belly will disturb the optimum relations, as will lengthening the header. So the pipe in its lengthened version will not be the optimum for the low resonance rpm dictated by the length. But it will be a hell of a lot better than using an exhaust power valve that spoils the 180° effective exhaust timing, necessary for true resonance.
And a pipe shortened beyond its optimum may not show the optimum length relations between its components either, but it will be a lot more effective in overrev than artificially raising the exhaust gas temperature by retarding the ignition, or by weakening the mixture strenght through closing a power jet, which has the disadvantage that not all inhaled air is used for combustion.

Do I understand this correctly, given sufficient blow down and exhaust STA an exhaust duration of 180 deg would be the optimum at any rpm?

Thanks Frits ..... gives me a bit more to think about.

Interesting i was assuming that Frits meant an exhaust valve that varied the effective height of the port?

Follow up question sorry.

In the Aprilia cylinders (I assume you are talking about the racers; not the RS250 street bike with Suzuki engine) the blades (there are two of them, one on top of the other) only control the main exhaust port.

Yes i was meaning the blades on the Aprilia race bike.
What i was meaning was the blades seemed very thick in profile. So i was just wondering if they also controled the exit of the AUX EX ports.
I was also wondering if anyone other than Kawasaki with the KIPS z(The AUX being higher than mainport) had tried this as it would seem if the blade was shaped similar profile to bellow it may be able to control the AUX ports as well so if they they (the AUX EX Ports) were positioned higher than the mainport EX port without seamingly hampering low down power.

http://www.dootalk.com/reports/images/TS_Sep08_05.jpg
http://www.kiwibiker.co.nz/forums/at...1&d=1334572289
The profile is a top view looking down.

[trevor amos]

Dmcca ,
I have the exactly same problem , thought i`d done something real stupid , not being the smartest computer user on the planet , and have tried to
correct it ? I intended to email Neels to seek advice , however , if you could post his solution i might not have to bother him , again . He must get
exasperated continually rescuing dummies like me !

Gratefull thanks if you are able to help ! Trevor

[speedpro]

The slippery pipe style of thing made by Peter Steadman had a closed end on the cone and the exhaust outlet was from the side of the centre section. As far as I'm aware he had a push-pull system to move a completely internal rear cone back and forth. He didn't perservere with it but I'm not sure why.

[dmcca]

Dmcca ,
I have the exactly same problem , thought i`d done something real stupid , not being the smartest computer user on the planet , and have tried to
correct it ? I intended to email Neels to seek advice , however , if you could post his solution i might not have to bother him , again . He must get
exasperated continually rescuing dummies like me !

Gratefull thanks if you are able to help ! Trevor

Ive heard back from Neels and sent him a couple of files he requested... Im sure he'll get back to me whenever he has something. Im thinking its user error as this particular project was causing problems from the beginning just trying to accurately model the exhaust and inlet port... the numbers that i thought should be correct caused other errors before this latest one and i had to keep manipulating them to get the sim to run. Havent had that before on any other project.

and dont worry i feel bad emailing him with issues too, but if you dont ask you'll never learn!

[dinamik2t]

I believe this problem has to do with "open ends" in the lines that form port shapes.
In an aux exhaust port for example: if I input a radius of 1mm and the vertical and horizontal line cannot be connected with that radius value, then there is a shape where radius line either is above vertical/horizontal lines or too far from them to create a 'closed shape'.
Both cases create a discrepancy, as Dat2t says, that seem to cause the inflown/subsonic error in the simulation process.

The same thing can happen in the combustion chamber CADing and it seems to happen in inlet/exhaust pipe modeling too - but I don't know why there.

As Wob said in the past, since EngMod utilises ports shapes to calculate time-area only, there is not problem to shape a port of the same area with different sizes/radiuses. In reality you can then apply the correct radiuses.

I guess it's something logical since a computer cannot handle everything with human logic. A radius of 3mm has a fixed shape and it cannot connect two orthogonal lines that are not properly coordinated to each other, to be connected with that radius.
As for the pipe modeling, sometimes it helps to re-compose and re-save a model - or re-start the computer.

[Frits Overmars]

....Yes i was meaning the blades on the Aprilia race bike... I was just wondering if they also controled the exit of the AUX EX ports. I was also wondering if anyone other than Kawasaki with the KIPS had tried this

Kawasaki was by no means the only one to control the auxiliaries as well as the main exhaust with a power valve. Jan Thiel and yours truly incorporated it in the 1992 Rumi GP125; Maxter uses it on their KF125 kart engine, KTM has it on their MX-engines and no doubt there will be others.

[Frits Overmars]

Do I understand this correctly, given sufficient blow down and exhaust STA an exhaust duration of 180 deg would be the optimum at any rpm?

The short answer is yes. But why is it that each time you people sit down for five minutes to write a question, I have to sit down for two hours to write an answer?

When the exhaust port opens, a pressure pulse starts moving through the exhaust pipe. It is reflected at the end cone and it should be back at the cylinder just before the exhaust port closes.
Next a part of this reflected pulse bounces off the partly-closed exhaust port and a residual pulse starts moving down the exhaust pipe. This residual pulse too is reflected by the end cone and starts moving back to the cylinder. Ideally it will arrive at the exhaust port just when the port opens again. Then the cylinder pressure and the pressure of the residual pulse combine their energy and the resulting pulse will be stronger than the pulse from the previous cycle. And the combined pulse from the next cycle will be stronger still, and so on; we have achieved true resonance.

Some may argue that we want a low pressure in the exhaust pipe when the port opens because then the spent gases will experience less resistance while leaving the cylinder. But that is not true. Gas flow depends on a pressure difference ratio. But once that ratio reaches 2, the flow velocity will reach Mach 1, the speed of sound. Raising the pressure difference any further will not raise the flow velocity any further.
The cylinder pressure at exhaust opening can be as high as 7 bar and the pressure of the reflected pulse will be about 2 bar. Thus the pressure ratio is well above 2, so lowering the pressure in the exhaust duct outside the cylinder will not do any good to the flow.

What has the exhaust timing got to do with the 'true resonance' I mentioned above?
The initial pulse starts moving at Exhaust Opening and it has to be back at Exhaust Closing, or a little earlier. This pulse travels with the speed of sound and its journey up and down the exhaust pipe will take t seconds.
The residual pulse starts moving at Exhaust Closing and it has to be back at the next Exhaust Opening. This pulse also travels with the speed of sound and its journey up and down the exhaust pipe will also take t seconds.
So from EO to EC takes t seconds and from EC to EO also takes t seconds. In English: the exhaust port should be open just as long as it should be closed.
Assuming that the crankshaft rotates with a uniform speed, this means that the crank angle during which the exhaust is open must be equal to the crank angle during which the port is closed. So both angles must be 180°.

I developed this line of thought some 40 years ago, but when I first published it in 1978 (in the motorcycle magazine Moto73 of which I was the technical editor) everybody called me crazy. Some people still do, but I got used to it .

Above I made a couple of assumptions. The crankshaft does not rotate with a uniform speed, but at high revs the deviation is negligible. In case you really want to know, I did the math for the Aprilia RSA125. At a nominal rpm of 13,000 the minimum rotation speed is 12970 rpm @ 107° after TDC and the maximum value is 13031 rpm @ 356° aTDC. What's more significant: the deviation in crankshaft position from truly uniform rotation is always less than 1°. So that really is negligible.

Second assumption: both the initial pulse and the residual pulse move with the speed of sound. Not true: the pulse pressures in exhaust waves are so high that acoustics rules do not apply any more. We are dealing with gas dynamics here and the stronger a pulse, the faster it moves. Since the residual pulse is weaker than the initial pulse, they move at different speeds. But we will leave this aside for now.

Third assumption: the initial pulse starts moving as soon as the exhaust port starts opening. More or less true, but we are not interested in the first weak appearance of the pulse; we want to know when the pulse reaches its maximum amplitude. And that requires a certain amount of open exhaust port area. It turns out that for our desired theoretical exhaust timing of 180° we will need a geometrical exhaust timing of about 190°, depending on the shape of the port: does it open gradually or does it open over its full width all at once.

The obvious question will be: why has the Aprilia RSA125 a geometrical exhaust timing of about 200°? True, at 190° the maximum torque value would be higher, but the engine would not want to rev because the blowdown time.area would be too small.
The 200° are a compromise: a bit less torque and a bit more revs; as long as the torque decline is smaller than the rpm rise, we gain horsepower.

[trevor amos]

Hi Frits ,
From our perspective thats an easy one , we don`t know enough to ask long questions , but you know so much , a short answer is`nt
enough , that makes us very lucky indeed !

Regards , Trevor

[Frits Overmars]

Hi Frits , From our perspective thats an easy one , we don`t know enough to ask long questions , but you know so much , a short answer is`nt enough , that makes us very lucky indeed !

Thanks for the flowers, Trevor. I prefer short questions anyway. Well, the next couple of weeks I will go walkabout in Germany, so I may be absent here for a while.

[TZ350]

Thanks Frits for your answer about the 180 deg port duration.

Attachment 262139

Here is a simulation of the Trombone effect. Datum is at 14500 and it went -30mm and extended +45mm, for a total slide movement of 75mm. Seems to be more more of an effect at peak power than at the lower revs.

Its a very interesting idea, being able to extend the power peak like that .... now what could I do with that

[Frits Overmars]

.....Here is a simulation of the Trombone effect. Datum is at 14500 and it went -30mm and extended +45mm, for a total slide movement of 75mm. Seems to be more more of an effect at peak power than at the lower revs.

That Dutch trombone pipe moved from +70 mm length to -20 mm length, so its effect was concentrated on the lower revs (although raising max.rpm from 14,500 to over 17,000 rpm was a welcome bonus).

[husaberg]

The short answer is yes. But why is it that each time you people sit down for five minutes to write a question,

“The important thing is to not stop questioning. Curiosity has its own reason for existing.”


“Only the one who does not question is safe from making a mistake.”


“Wisdom is not a product of schooling but of the lifelong attempt to acquire it.”

[wobbly]

The tech term for what Frits is describing is Superposition of the Ex pulse.
This is easily described in a sim, where a residual pressure ratio is seen sitting at the Ex port when it is opening.
The "new " pulse is added to this residual, and a very large pressure ratio exits down the duct to the header.
The larger the initial ratio, the larger the amplitude of the wave in the diffuser - this creates a deeper depression around BDC, and it is this that initiates the biggest mass flow
from the transfers.
The lower Ex timings of 190 and below create larger residual pressure ratios,over a wider band, and thus these work with a good pipe design to use "resonance" to increase band width and also peak power.
Big problem though is this whole concept is at odds with maximising blowdown to allow good peak power and more importantly, overev power.

The sim shows RGV100 making serious power with the superposition pulse going down the duct - off the scale.

Re the trombone pipe results you did sims for TeeZee.
Look carefully when you say it seems to affect the top end "more ".
At 9000 the lowest reading is 13 Hp, the highest reading is 17 Hp, thats an increase of 4 Hp, thats 31% more power in the bottom end, that then allows the thing to rev to 17,000.
Seems a not bad result.

Re the powerjet temp result you mentioned.
The effect of the solenoid powerjet is as you described - this I only discovered recently with a datalogger that I could set the sample rate of the EGT high enough to read the temps quick enough - along
with some exposed junction probes.
I was testing a RS125 on the dyno and it was making NO power past 12500, looking at the data you could see the egt drop from 640 C to 580 in around 400 rpm.
After fixing the fact some idiot had left out the rpm plug in the loom, the solenoid now switched on at 12200, and the temp stabilised at 650 past 12500 and the thing than reved out to 13500 +.
So the powerjet switching isnt making the mixture "lean"as such, it is simply maintaining the correct mixture, and thus the temp in the pipe.

[TZ350]

Re the trombone pipe results you did sims for TeeZee.
Look carefully when you say it seems to affect the top end "more ".
At 9000 the lowest reading is 13 Hp, the highest reading is 17 Hp, thats an increase of 4 Hp, thats 31% more power in the bottom end, that then allows the thing to rev to 17,000.
Seems a not bad result.

Hi Wob and Frits, thanks, I should have said I was looking at width of power spread possible and the effect seems more pronounced in real terms at the top than lower down which is very usefull, and maybe if the Trombone was combined with an ATAC valve to spread the bottom more we could have a real tractor on our hands.

I hope no one else sees the benefit in this ...... as this is massive.

[wobbly]

What I am about to try next on a project is to use a powervalve to drop the port timing below 190, along with the slider header.
This will combine the beneficial resonance effect along with the variable pipe length to give killer mid range off corners as well as top end revs.