ESE's works engine tuner

[TZ350]

Good thinking. But remember that, even with 192° exhaust timing, at low revs the first return pulse will arrive at the cylinder too early.
You ought to combine it with a trombone pipe.

Good idea, thanks, a trombone pipe has been a bit of a dream, it may be possible ....

High rpm means diminishing blowdown time.area, so the pressure of the spent, hot gases in the cylinder at the end of the blowdown phase will increase.

If you close the throttle as well, the scavenging pressure is sure to drop below this cylinder pressure, the spent gases will enter the transfer ducts and you'll get detonation like you've never seen before.

Knowing that lowering the pressure in the pipe at the lower end of the rev range increases power there (Red line). I was thinking of having a rotary pressure bleed valve activated by the same servo as controls the PV. So as the PV closes the exhaust port pressure bleed opens. The pressure bleed valve could be a drum with a slot so the valve area opens/closes quickly.



Pressure bleed, Red open, Blue closed.

[philou]

The fospipe concept works on low bmep engines ?

I have to make an exhaust for a friend who has mounted a husqvarna 360 engine in a chassis of 125 rs aprilia :rayure:

I do not have the original exhaust to have a starting base.
The original is not suitable for circuit use. Allez terrain motorcycle

[Frits Overmars]

Knowing that lowering the pressure in the pipe at the lower end of the rev range increases power there (Red line). I was thinking of having a rotary pressure bleed valve activated by the same servo as controls the PV. So as the PV closes the exhaust port pressure bleed opens.

Bleeding the pipe will drop the average pipe pressure but this will hardly speed up the blowdown phase which is already partly sonic. And you cannot speed up a sonic flow by lowering the downstream pressure. Bleeding may work indirectly to some extent as it will weaken the exhaust pulses and therefore the engine power and the mass of exhaust gases.

[Frits Overmars]

The fospipe concept works on low bmep engines ?

Yes, you can compensate by entering a low value for the speed of sound; that should get you in the ball park.

[philou]

thank you very much

[breezy]

Yes, I think so!

Thanks for reply.

[lohring]

As I have a little bit of a problem visualizing the air flow through cylinder transfers I asked a CFD guy at work to show me his tools and if he at the same time could do a quick flow visualization of the RSW cylinder. With my limited 3D knowledge a made a bottom end (crankcase substitute, not perfect or anything like the original..) to connect to the cylinder and we put the piston at BDC. I asked him to send 0,04 kg/s into the bottom inlet channel to see how it looked like. I hope it is not that far from an air flow that could be seen. Changing the flow between 0,01 to 0,04 kg/s did not change the flow pattern so much, if I remember correctly.

I think we got close to 0,16 bar pressure difference from inlet to outlet at this flow.

Please note that it is a steady state flow right through the cylinder and without the actual very transient situation during operation. I guess it cannot be much more simplified than this. Can it possibly indicate how the flow would look like just before the return pulse stops the flow and pushes back into the cylinder? See pictures attached.

Please note that all pictures represents 0,04 kg/s even if otherwise stated.

Jan Thiels statement that the flow is attached to the bottom of the transfers, is clearly also observed in the simulations!

Attached is an Article I edited from two articles. the second is a CFD analysis of an Aprilia cylinder that is very interesting.

Lohring Miller

[DaisyB]

Yes, you can compensate by entering a low value for the speed of sound; that should get you in the ball park.

Errr, just how low Frits?
Cheers

[wobbly]

ATAC in general works much lower down the powerband than a powervalve does, and cannot be gradually reduced in its effect.
It works very well to reduce the effect of the pipes return pulse being way too early at lower rpm, but this effect kills the power badly as soon
as the pipe efficiency starts to rise - thus the valve connecting the Helmholtz chamber to the pipe must be switched instantly at a specific rpm.
In a 125 race engine the ATAC would be off at around 8000 rpm, where as the PV may not be closed fully to within 1000 rpm of peak power.

[136kg136ps]

Thanks for that Wob,and to Frits for the tip on reducing the speed of sound.

[Norman]

Attached is an Article I edited from two articles. the second is a CFD analysis of an Aprilia cylinder that is very interesting.

Lohring Miller

Yes, very interesting. Thank you. I understand the importance to have good flowing transfers in combination with the very best flow pattern..

[Frits Overmars]

Yes, you can compensate by entering a low value for the speed of sound; that should get you in the ball park.

Errr, just how low Frits?

That's not a serious question, is it Daisy? Because if it was, I would need to know about a hundred things regarding your engine before I could give a more or less accurate estimation.
Just pick a value between 350 and 550 m/sec, build a pipe, see where the rpm of maximum power is, and if it is not where you want it to be, adapt your picked value accordingly. If your first pipe isn't already in the ball park, your second one should be. It's not that difficult.

[Haufen]

Attached is an Article I edited from two articles.

Thanks, looks interesting! Could you please provide links / information on the two original articles, too?

[lohring]

Thanks, looks interesting! Could you please provide links / information on the two original articles, too?

Unfortunately, I lost the links to the articles. A google search didn't find them either. I'll look some more.

Lohring Miller

[Vannik]

Unfortunately, I lost the links to the articles. A google search didn't find them either. I'll look some more.

Lohring Miller

One part of the article.