ESE's works engine tuner

[breezy]

The exhaust gas is not fed back into the cylinder; it never leaves the cylinder because we make sure that there is not enough blowdown time.area to get rid of it all.
That is why I emphasized the absence of auxiliary exhaust ports that would otherwise increase the blowdown time.area. And yes, this occurs in two-strokes already.
The best-known control mechanism is the exhaust power valve used in the Honda Activated Radical combustion engine.
Attachment 323927
But once you have established HCCI, you can also control it via the mixture strength. With HCCI you can make the mixture as lean as you wish and the fact that very lean mixtures are no longer spark-ignitable doesn't matter because they will still be compression-ignited as in a diesel.

thanks Frits, great source of information in the file, should keep me quiet for a while. ive got a 50cc motobecane for my test engine.. very poor porting... couldnt get it to fire up untill i removed the exhaust!!

[wobbly]

The engine that the asymmetric reed cage came from was a late model KTM250 and yes it had a very odd entry angle into the case.
In the KZ10 the factory has progressively straightened out the carb/manifold to get flow symmetric into the cage, and at the same time tilted the cylinder back
and the reed mount face downward - all to get incoming flow directed upward within the case toward the transfer entries.
Having the reed cage tilted, but with very good flow guides, will increase the upward tilt of the entering flow even more.
I will have to try all manner of varying petal stiffness and backup combinations to find what is best.
The centerline of the carb entry is offset vertically, as are the bolt mounting holes, so that there is no shrouding with all the petals at full lift.
I believe what is really needed though is a very small exit area from the reed cavity but with an extra pair of scalloped ducts down the reedbox/case sides to
promote the flow that comes out the sides of the reed cage - and maybe something like the reed cage pictured.
Better yet a VeeForce W cage, with double the reed tip curtain area - I have just recieved a pile of freeby parts from them to test in Italy.

Although its technically illegal in the KZ2 class engines I have welded the Ex port floor upward 3mm and filled in the bottom corner rads.
It "looks " identical " to stock, but makes around 1.5 Hp everywhere.
I believe that then radiusing the bottom edge would promote short circuiting flow at BDC so have not tried that idea.
Of course welding/filling in the duct to make the exit area way smaller would be very illegal and obvious - but if someone happened to scrape the duct port core
prior to casting at the factory - then the rule regarding " no added material " would not be broken - would it, he asks hopefully.

[teriks]

Although its technically illegal in the KZ2 class engines I have welded the Ex port floor upward 3mm and filled in the bottom corner rads.
It "looks " identical " to stock, but makes around 1.5 Hp everywhere.
I believe that then radiusing the bottom edge would promote short circuiting flow at BDC so have not tried that idea.
Of course welding/filling in the duct to make the exit area way smaller would be very illegal and obvious - but if someone happened to scrape the duct port core
prior to casting at the factory - then the rule regarding " no added material " would not be broken - would it, he asks hopefully.

Well, the radius idea might come in handy if you happen to scrape a bit too much of that duct core.
Of course its a shit load of work to test such feature, wish I had the means to do it myself..

[jfn2]

wobbly, which side is up and which side is down? Straight side up?

[peewee]

almost like that hole was never even there and suprisingly I didn't melt the corner off but I cant consider it successful until I see the engine run without piston failure

[jamathi]

How about, when you have raised the exhaust floor enough to loose power, you add a nice radius to promote flow, while maintaining the small duct area.
In a way that could give a good hint if the (potential) gains comes from the reduced area or the potentially reduced short circuiting.

That would certainly have been done.
With a higher exhaust port floor the ideas behind it were 2:

1 to reduce short circuiting, although a certain amount is necessary.
2 to be able to try wider A-ports.

[jamathi]

Well, the radius idea might come in handy if you happen to scrape a bit too much of that duct core.
Of course its a shit load of work to test such feature, wish I had the means to do it myself..

At Aprilia we made our own casting models, and core boxes.
But still scraping the cores was used, above all when I started working there.
And I started by boring out a STD ROTAX cylinder exhaust duct and fitting an insert which also worked well.
That was in 1995.
The STD ROTAX exhaust duct was really way too big, I think they still make their cylinders the same way.....

The place were the CNC machining was done was not far from us.
So sometimes I would test a cylinder on the dyno, then have it re-machined, and test it again.

When the auxiliary ducts were still a bit small I tried to raise the exhaust port underside.
The engine lost power, so it needed all the exhaust port surface for blowdown.

[Dutch Fisher]

And I started by boring out a STD ROTAX cylinder exhaust duct and fitting an insert which also worked well.

Jan did you bore out thru into the exhaust duct water channel and seal it back up with the insert?

[husaberg]

- but if someone happened to scrape the duct port core
prior to casting at the factory - then the rule regarding " no added material " would not be broken - would it, he asks hopefully.

if someone scraped the core, assuming they were that clumsy. Imagine If they inadvertently dipped some other parts in ceramic glue and it fell in some sand, well that would be unfortunate as well.

[teriks]

That would certainly have been done.
With a higher exhaust port floor the ideas behind it were 2:

1 to reduce short circuiting, although a certain amount is necessary.
2 to be able to try wider A-ports.

Im thinking of one more potential benefit:
The smaller duct area should result in a longer column of fresh gas in the duct, this could reduce the thermal load on the piston a bit at lowish rpm, when the return pulse is too early.
Also you should get slightly less dilution of the fresh gas, if not for the longer column, but at least due to the increased difficulty of mixing fresh and exhaust gas in a narrow duct.

At Aprilia we made our own casting models, and core boxes.
But still scraping the cores was used, above all when I started working there.
And I started by boring out a STD ROTAX cylinder exhaust duct and fitting an insert which also worked well.
That was in 1995.
The STD ROTAX exhaust duct was really way too big, I think they still make their cylinders the same way.....

The place were the CNC machining was done was not far from us.
So sometimes I would test a cylinder on the dyno, then have it re-machined, and test it again.

When the auxiliary ducts were still a bit small I tried to raise the exhaust port underside.
The engine lost power, so it needed all the exhaust port surface for blowdown.

Could work quite well on my ring-less engines where one can make the exhaust port ridiculously wide then.

Thanks for great info Jan, as always!

//Thomas

[jonny quest]

High ex port floor help with less shortcircuiting, or perhaps better flow path for returning mixture?

On bridged ports, I've found power by widening bottom close to transfers

[Frits Overmars]

High ex port floor help with less shortcircuiting, or perhaps better flow path for returning mixture?

Better blowdown outflow coefficient and stronger exhaust pulses due to smaller turbulence losses, less mixing of spent and fresh gases because of a smaller exhaust duct cross-section area where spent and fresh gases are in contact with each other, less short-circuiting, and a better flow coefficient for the returning mixture.

[wobbly]

Been a while that someone felt the need to ask me "which way is up ", im not telling, you will have to wait for the dyno results to be published.

[WilDun]

The best-known control mechanism is the exhaust power valve used in the Honda Activated Radical combustion engine....... once you have established HCCI, you can also control it via the mixture strength ........ the fact that very lean mixtures are no longer spark-ignitable doesn't matter because they will still be compression-ignited as in a diesel.

Having grown up on a farm I was aware that a diesel's "throttling" was done by controlling the amount of fuel coming in and was aware that petrol (gasoline?) should not be compressed to the high diesel compression figures - and of course the theory that to be more efficient an engine must breathe a cool charge, these theories now seem to have been blown right out of the water!

My questions are:-

1. Does it all mean that the good old "simple"carburettor will be back in favour (better for a fully homogenized charge?).

2. Does it mean that squish (and therefore squish clearance with it's inherent problems) is no longer necessary with HCCI?
In theory, could a thin disc (very thin biscuit like) combustion chamber formed by a flat top piston and the bore sealed off by a flat cylinder head be sufficient (simple description) and still achieve the high compression ratio necessary for HCCI?

3. Does a cool fresh charge no longer matter for cylinder filling? ie. in the case of HCCI.

4. Is it now necessary to have a bulky expansion chamber exhaust? seeing that as you say, the spent charge has not all actually left the cylinder and therefore I assume that none of the fresh charge will have gone either (to be pushed back in as in a normal high performance two stroke).

5. Or am I way off track - maybe I should just have stuck with farming?

[Frits Overmars]

...petrol (gasoline?) should not be compressed to the high diesel compression figures

Two things might happen if you put petrol in a diesel tank.
1: the temperature rise caused by the compression might not be sufficient to ignite the petrol/air mixture, so no combustion at all.
2: the temperature might be borderline; unlike diesel fuel that will start burning as soon as it is injected, a large amount of petrol may be injected in the combustion chamber before ignition begins, and then it begins with a head-removing bang.

1. Does it all mean that the good old "simple" carburettor will be back in favour (better for a fully homogenized charge?).

I hope not. The drawback with pulsed injection is that not every bit of air gets a bit of fuel administered. In this respect a carburettor is better. But continuous injection is better still. I designed such a system for 35.000 rpm model engines for which it would be impossible anyway to find injectors that are fast enough.
It is one of the many projects that are still awaiting completion...

2. Does it mean that squish (and therefore squish clearance with it's inherent problems) is no longer necessary with HCCI?

You're probably right about that, Will. Squish will no longer be required for flame spreading, though it may still contribute to homogenizing the fuel/air mixture.

In theory, could a thin disc (very thin biscuit like) combustion chamber formed by a flat top piston and the bore sealed off by a flat cylinder head be sufficient (simple description) and still achieve the high compression ratio necessary for HCCI?

In theory that would be a yes. But it would yield an unfavourable volume/wall surface ratio, meaning big heat losses.
Anyway, the head shape also plays a role during scavenging so I'd stick with the present shape for now.

3. Does a cool fresh charge no longer matter for cylinder filling? ie. in the case of HCCI.

It would seem so, wouldn't it? But the cooler the charge, the more mixture mass we get in the cylinder and that is what we need to make power.
It may mean that we will have to compress this cool mixture even more in order to achieve HCCI.

4. Is it now necessary to have a bulky expansion chamber exhaust? seeing that as you say, the spent charge has not all actually left the cylinder and therefore I assume that none of the fresh charge will have gone either (to be pushed back in as in a normal high performance two stroke).

That bulky pipe can charge the cylinder with 1 bar overpressure (2 bar absolute) at exhaust closure. Without it we could not hope to make anything like decent power.
What I was trying to say is that with limited blowdown time.area not all spent charge has left the cylinder when scavenging starts, so fresh and spent charge mix, and the fresh charge gets heated. That won't impede it from washing through though.

5. Or am I way off track - maybe I should just have stuck with farming?

I'd say your dead on track Will. And it may seem like I've got all the answers, but HCCI is a new and partly virgin territory for all of us
(which makes me wonder: can there be such an animal as a partly virgin?).