ESE's works engine tuner

[Muhr]

If anyone thinks it's interesting with water CFD

blue is weak circulation

The exhaust duct above the exaust flanch is the hot spot Iam working on ringt now.

[wobbly]

In the new file we have a Blowdown Power Capability of 30.4 Hp and a Transfer Power Capability of 34 Hp.
The original file showed the Inlet as capable of 33.71Hp so that is close to the new transfers.
What you now need to do is increase the Aux Exhaust port area or timing to get up around 34 Hp as well for the Blowdown.
If you dont,then the low Blowdown will have all the bad consequences I explained before.
The actual overall Ex port effective area is redundant,and is usually low, meaning in practical terms the duct volume will be lower - a good thing..
Another thing I noticed is that you have conventional port stagger ie A port opening first - but the boost port is up at the same timing as the B port.
To get the mid power advantage of this scavenging regime the boost needs to be lower as well.

[ken seeber]

Makes me wonder why Aprilia went with the intake side offset cylinder head for ditech, as it's already proven not to be that great. To get the plug to the hot side?

One of the ideas I've pondered experimenting with, is to offset the chamber to the exhaust side. That approach is proven to work very well in 4-strokes allowing a lot more compression and reduced ignition lead, but can't say what to anticipate in 2-stroke. Should at least improve the piston cooling and charge vaporization somewhat. Easy to try though.

Jannen,
To locally contain the vertically downward injection stream, it was very clear (at Orbital) from the start that having some sort of bowl in the piston “reflected” the spray. This was key to low load type settings to achieve stratification, hence reduced HCs and increased BSFC.
At higher loads, this “reflection“ wasn’t required, as we were even injecting before BDC, particularly at higher rpm.
The sequence of development was to start off with an axisymmetric arrangement (referred to as Type 25), as per the central piston. Then, with time, the Type 23 (on the left) was developed, offering much improved characteristics for the 3 cyl, 85 hp, 1.2 litre automotive engine application (circa 1990). Unfortunately I don’t have any pics of the head shape, but it was flat with a well radiussed rectangular bowl above the bowl in the piston, this being above the inlet or transfer side.
As Wob has pointed out, the MSV difference from one side to the other is all over the place and, even knowing very little about this subject, can see it not conducive for a max power shape. However, as it was an auto engine where we were focussed on emissions and fuel consumption.
In setting the engine maps, particularly at high loads, we used a term MBT. This, within Orbital, meant minimum advance for best torque, slightly different to the alternate meaning of maximum brake torque. One tool was apply a realtime statistical analysis to the combustion pressure trace (we used Kistler 601 pressure transducers. Then, knowing a predetermined allowance for the onset of detonation, this determined the ignition timing at this point.
I wasn’t close to the Aprilia Ditech project, this was mostly conducted from Italy, but am pretty sure the same general combustion chamber shape & piston bowl were used, albeit scaled down. Have no idea of swapping the head around might achieve. One thing to be aware of is that it’d definitely be undesirable for the protruding piston bowl to run into the flat head face.
Just for a giggle, I have included on the RHS an early cross flow scavenged piston (probably ex Mercury or OMC). This should offer you the worst of everything, although I do believe the idling and low speed operation wasn’t too bad.
Disclaimer: As all this was around 30 years ago, putting me into dementia territory, there could be a touch of bullshit in the above.

[F5 Dave]

Dementia aside I've been looking forward to hearing about your previous vocation even if it isn' directly racebike related

[Jannem]

The issue with any offset to a chamber in a 2T is that no matter what, you end up with the MSV off the scale on the wide squish side, and no MSV on the other.
This was a huge issue in the old TZ250G model, that would detonate as soon as the jetting was even close.

Did it loose power going with less ignition lead?

[Muhr]

If anyone thinks it's interesting with water CFD

blue is weak circulation

The exhaust duct above the exaust flanch is the hot spot Iam working on ringt now.

Port flow

[shnaggs]

Port flow

Muhr, What are you using for the coolant CFD? Still Fusion360?

[Muhr]

Muhr, What are you using for the coolant CFD? Still Fusion360?

In a sense, I'm using a plugin called Simscale. Fusion does not have CFD

[SwePatrick]

Muhr, What are you using for the coolant CFD? Still Fusion360?

Add a moving piston to the simulation =)
Edit: and decreasing pressure in crankhouse as the pistons moves.

[SwePatrick]

I have stumbled upon a problem.
To shape the B-transfers as i want i need more material above the transfers next to the 'water'.
At the outside of cylinder i can just add with welder, no problems.
But inside the waterjacket above the transfers is a problem.

I had this idea first with just wash with some acids and pour down a epoxi to build some material to grind in above the transfers.
But, then i got the next idea, how about do the same cleaningwork but then melt aluminium and pour down raise 'bottom' of cooling jacket.

This method has been used to save old ironheads for fourstroke engines when needing more meat to grind in.

Will it 'stick' to the surface good enough to secure a seal between the materials?

Rgds

[shnaggs]

In a sense, I'm using a plugin called Simscale. Fusion does not have CFD

Thanks, I didnt think Fusion had CFD, although it does have some sim stuff, so thats why I was asking.

[jonny quest]

Ken Seeber, the DiTech SR 50 has a domed piston.

[Tim Ey]

I have stumbled upon a problem.
Will it 'stick' to the surface good enough to secure a seal between the materials?

Rgds

Nope. It will have air to the barrel because of the thermal shrinking.
But if you pour in Aluminium, remove it afterwards and screw it in place with 2K glue in between it is dead serious.

[wobbly]

Simple solution to adding alloy above the transfers,within the waterjacket,is to acid clean it then use alloy stick weld repair rods.
The trick is to weld upward , so the molten flux runs down hill away from the weld pool.

The TZ250G had to run retarded timing to stop the det, and this did loose power but allowed leaner jetting so it would at least rev out as it should.
Then when you got it to rev, the pistons would fall into the idiot designed inlet port and would destroy themselves in about 100Km - the whole team that designed that piece of shit
cylinder should have been shot.

[SwePatrick]

I tried almost your way wobbly, just a couple of minutes ago.
I didn´t reach as you describe so i just started to weld,(material was about 1mm thick) and i pushed in a lot of weldingrod and heated and heated so it 'sinked' down into the waterjacket, had the cylinder upside down.

In middle of progress: