ESE's works engine tuner

[TZ350]

Looks like the dam is really upsetting all the other parameters?/ scavenging pattern!!

I was wondering about this myself. The hooks in the B ports force flow under the bulk incoming scavenge charge to help expel the previous cycles residual burnt charge, the raised exhaust port floor maybe impacting on this.

Maybe you could try lowering the centre of the port some, along the lines of the RSA exhaust port shape,



and radius the lower edge?

The narrow part of the exhaust window is the original RG50 port and the wider part above the dam is 85% of the bore width.

Without the dam we could have something that looks like the RSA exhaust port.

[AndreasL]

Ok, it's 2016.

Ryger please.

[TZ350]

Ok started on learning how to model a profiled exhaust in Engmod2T. Until we get the cylinder off again I can only guess at the real dimensions but my first effort more or less looks like the real thing.



Ran the simulation and generated data for the plot options.


In the Post 2t plot options for Thermo and Gas dynamics there is a choice for "Ex mach(1)", "Ex mach(2)" and "Ex machout". The help file does not explain what these are so I guessed that "Ex mach(1)" was the mach number at the exhaust port window, I have no idea what the other two are. In fact it looks like I have lost the entire help file, not sure why.



Mach numbers at two rpm points. I am not sure how to interpret these but I guess they are both choked for a bit after the exhaust port opens.

Some guidance by anyone who is familiar with Engmod about what the traces mean would be great.

[TZ350]

Looking at the pics my first reaction is to " fix " the insert - that is extend the floor all the way out to the flange face.

As I said earlier having the dam in place makes the exit area much bigger than that at the port - and we already know that the reverse scenario makes better power.

Having a much smaller area at the port may in fact work really well if the whole duct is reduced to suit, keeping the Mach number higher right down to the header.

TeeZee, try putting the measured data into EngMod and have a look at the Mach, down the duct length by varying the position of the Ex sensor.

Test it as it is now, then make the exit area much smaller as well - the power thrown up will be an indication of the result,but the Mach number gives us some insight into the actual effect.

In this case, maybe having a much smaller duct vol, with steps, like an old RS125, at the header, just might be a nice Xmas prezzy.

To make the sim really accurate, you will need to specify an actual step in the pipe input, as this has a big affect on the in and outflow calculations.

Found Wobs post on using Engmod to look at the mach numbers.



I would love some guidance on what the graph means.

[TZ350]

While I was trying to figure out what I had done to the help files I became distracted by this very interesting read on how to use Engmod's Post 2T program to investigate the cause of detonation in your simulation and how to design a solution.

[AndreasL]

I would love some guidance on what the graph means.

I had the same questions some pages ago that Wobbly gave some answers to.

Hope that help some.

[TZ350]

I had the same questions some pages ago that Wobbly gave some answers to.

Ok found it, thanks. Now to digest it.

wobbly, a EngMod question if you don't mind...

When designing a exhaust duct using EngMod, I think it's ExMach that should be used to check if we go sonic or not?

ExPMach, measured at the port(?), goes through the roof (>3) when the port opens so that can't be the right thing to use...

So what I'm planing is to reduce my exduct end area until we are about to kiss sonic. Can it be that simple really? Probably not...

Using ExMach, do we like to place our virtual transducer at the smallest cross section area of the duct, i.e. just before the header (if not using some sort of adapter/spigot that is). Normally I run it at 0mm but that might not be the best thing in this case?

I'm running some rough sims right now and we are getting closer to sonic when makin the duct area smaller...as expected. But with a single port, we might push it to far using this crude "technique"...

Do you have a graph from "a decent engine" showing what to look for regarding exhaust duct speed?

Here is a KTM250 for road racing I have worked on. This is not anywhere near "full noise " as it needs powerband width to cope with a 1500 rpm drop into 5th gear.

The Ex port at the face goes well sonic as the piston opens and closes - so the lifted floor has nothing to do with flow velocity, its all to do with A port short circuiting.

I am going to try a big radius on just the floor of a lifted port to see if it raises power by increasing the outflow Cd, without affecting the short circuit reduction down the sides where the corner rads are.

The transducer is set at the smallest area in the duct ( the cylinder face ) before the oval/round transition spigot, and this gave the best power - going smaller did not gain any power.

Going bigger did loose immediately, and it seems that in many engines going to around 0.8Mach at the exit seems to work best..

The stinger venturi just goes sonic for a short period, but again, this was the smallest area for best overall power without deto.

I could go bigger, and then i would need to add timing or increase com to compensate to lift the TuB number- and this lost band width.

As I have stated a hundred times the 75% area at the oval face will get you close every time, as will the 90% area for a single port.

Just remember that the sim will reduce the volume of the duct in a linear fashion, as you neck down the exit area, and this is the correct approach - not just weld up the last 20mm
as its easy to get at.

Also the sim has no idea there is a wall in front of the piston at BDC if you lift the port floor.
It cannot therefore adjust for any improved scavenging or trapping efficiency due to reducing the A port short circuiting - all its doing is reflecting the affect on in and outflow from a smaller port/duct exit.

TZ Keep in mind that my take on this is that the major effect is upon the A port short circuiting factor. If you look at ducts that have had the floor lifted alot the bulk flow goes sonic quite severely, and this I feel can override the positive effect of the A port trapping efficiency.

Try lowering the floor but leave as much infill in the bottom corners as you can. And at some stage try the big radius on the floor port corner only, as this will increase the outflow Cd but wont influence the trapping efficiency of the corners on the bad A port flow turning. The Aprilia ducts were CNC cut.

Another issue is that the added in dam has a crap heat transfer coefficient, and thus will be overheating the retained charge in the duct.

[Frits Overmars]

Hi Frits, are you saying that, that lower improvement in the Red line is more likely due to short-circuiting and not better trapping by the Dam? I thought we were doing well, but could it be, we have to re visit the "A" port angles.

No, I'm not saying that; I have no way of knowing. I just wanted to point out that it might be a factor to consider.

Our porting tools are pretty clumsy and not at all suited for 50's so the ports could be better shaped. We might have to bite the bullet and upgrade our tooling.

All you need for an unbridged exhaust duct is a round file.

we have not got as far as trying Wobblys suggestion of ... extending the dam further in the exhaust duct to keep up the gas velocity.

From what I could see on your pictures that was the first thought that crossed my mind. Looking in from the outside the dam looked more like a brick wall than a flow-aiding insert to me.

Hi Frits, Chambers did comment that it was not running as hot, at the time I thought it was a good thing. .... lots to think about....

Not running as hot should be a good thing, no doubt about it. It just depends on the reason why. Short-circuiting may aid in cooling the piston at the cost of some power.
Improved exhaust outflow may make the blowdown phase more effective, resulting in less spent gases entering the transfer ducts. and this would result in a lower cylinder temperature. Very desirable unless you want to retain a certain amount of exhaust gas in the cylinder in the interest of HCCI combustion.
The mechanical simplicity of a two-stroke can be quite deceptive...

You should be aware that this video probably shows a quite good CFD-generated impression of a rather poor scavenging system.

[TZ350]

Thanks Frits. ....

[breezy]

While I was trying to figure out what I had done to the help files I became distracted by this very interesting read on how to use Engmod's Post 2T program to investigate the cause of detonation in your simulation and how to design a solution.

i like this, enables a good understanding, easily,pictures and explanations, of the processes going on and the effects of each element..good post

[peewee]

Ok started on learning how to model a profiled exhaust in Engmod2T. Until we get the cylinder off again I can only guess at the real dimensions but my first effort more or less looks like the real thing.



Ran the simulation and generated data for the plot options.


In the Post 2t plot options for Thermo and Gas dynamics there is a choice for "Ex mach(1)", "Ex mach(2)" and "Ex machout". The help file does not explain what these are so I guessed that "Ex mach(1)" was the mach number at the exhaust port window, I have no idea what the other two are. In fact it looks like I have lost the entire help file, not sure why.



Mach numbers at two rpm points. I am not sure how to interpret these but I guess they are both choked for a bit after the exhaust port opens.

Some guidance by anyone who is familiar with Engmod about what the traces mean would be great.

this was mine. it matches the cylinder fairly well but engmod doesnt have enough detail options to get the window exact. i dont have the big round corners on the aux but its the closest i could get. im a dummy with all the tracer stuff so ill be following your posts

[wobbly]

The Ex Mach thing is easy to understand and use.
Once you are into the gas dynamics screen and chose Mach and your project rpm, then the graphical options are
ExPMach - this is the mach number at the port face.
ExMach1 - this is the mach at the sensor position you chose in the Engine screen - in this case we want to look at the Mach usually at the
duct exit, where the nozzle area is smallest.
ExMach2 - this is the mach in pipe 2 = the stinger in a normal single cylinder sim setup.

As the piston starts to open the port we have maximum pressure delta and the smallest area, so the initial flow goes sonic in the ExPMach trace.
Then the mach reduces as the area increases and the pressure drops - followed by an increase in flow due to the depression at the port created by the diffuser, this is then followed by the rear cone
pressure rise reversing the flow.
At the smallest area of the nozzle ( if one is correctly designed ) the Mach number will approach 0.8.
I have found that higher or lower affects the power.

Then we have the flow regime in the stinger, and again the best scenario seems to involve a short period of choked sonic flow, followed by a longer period closer to/below Mach 1.

[wobbly]

Sorry double post - please remove.

[TZ350]

ExPMach - this is the mach number at the port face.
ExMach1 - this is the mach at the sensor position you chose in the Engine screen - in this case we want to look at the Mach usually at the duct exit, where the nozzle area is smallest.
ExMach2 - this is the mach in pipe 2 = the stinger in a normal single cylinder sim setup.

Thanks Wob.

Also Neels has sent updates today and some info from the help file on Mach numbers.

In the Help file I was able to drill down through the index but was unable to open the related help document. As I have not needed the Help file for a while I am not sure when it stopped working properly for me. I probably inadvertently killed it when I was doing a re organization of the files.

Here is a PDF of the section of the Help file related to Mach numbers Neels sent me today.



Many thanks to Neels who goes to a lot of trouble supporting the EngMod2T program.

[husaberg]

Sorry double post - please remove.

You can do it yourself Wayne?
click edit post, then delete at the bottom left hand corner, then delete again.
http://www.kiwibiker.co.nz/forums/at...5&d=1424570781
http://www.kiwibiker.co.nz/forums/al...hmentid=309285

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https://youtu.be/MA2KmJMKFrQ?t=41s