Benefits of tapered quench for NA applications?

[hoffman900]

The squish surfaces may be parallel or tapered. If the squish surface is lengthy and the clearance is
tight and the rpm is high, mixture can become trapped in the squish volume. It cannot escape into
the main chamber and will increase in pressure locally. This will add considerable gas pressure to
the upper ring land and ring crevice. Combined with the temperatures of the squish surfaces, auto-
ignition can occur in the crevice volume, resulting in ring land detonation.

To avoid trapped squish band mixture, the squish band surfaces are tapered; the outside clearance
being tight and the chamber side clearance being larger. This allows the trapped mixture to escape
into the chamber. The included angle may vary from 1 to 3 degrees depending on specific design.
For calculation purposes, we use the mean clearance dimension.

The squish surfaces may be flat or angled. In addition to squish velocity, the direction of the
squish jet must be considered. For a shallow bowl, the squish surface may be flat. For a deep
bowl, such as a hemi, it may be angled upward toward the spark plug. The shape of the chamber and
piston top will determine the optimum squish jet direction.

I guess that answers my earlier question about putting it in the head or piston then. I'm looking at a semi-hemi (I'm not sure what else to call it) with quench pads that make the combustion chamber an oval between the two valves and a plug that isn't too far from centreline but is very close to one of the pads. Putting an angle on the pads in the head would 'point' the squish slightly more into the chamber than otherwise. Putting an angle on the pistons would remove more metal (lowering compression is good for my case) but point the squish the wrong way.

So you say 1-3 degrees. Others say 4, with extreme cases (which appear to remove the squish action almost entirely) as 12 degrees.
I ran the numbers on the engine in question and a 4 degree taper would have the squish area start to burn 4 degrees earlier (assuming 3mm clearance was required for a burn of any significant speed). I need more research...

Read the paper I linked to earlier by Honda. It’s literally the same design and see how it scales.

There is also a SAE paper from Chrysler when designing the “new Hemi” regarding this as well.

It should be noted how the OEM world and aftermarket differ. The OEM’s are using high tumble designs (4v/cyl) in very high output turbo situations, which assists in speeding up combustion and makes it more consistent, where the aftermarket is still “softening” things.

Combustion is very hard to understand on a high level and harder still to control it. Think about what Darin said about vacuum of lifting up a flat piece of wood off the floor and pumping losses, but Dr. Andy Randolph, who is a combustion engineer, works at ECR and has worked at Hendricks, says they the run the NASCAR engines to the point that with carbon build up at the end of a race weekend, it’s just starting to kiss the head. Maybe there are some pumping losses, but if there is, it isn’t anywhere near as much as inconsistent and incomplete combustion will give you.

[BradH]

...

I can hardly wait to become even more confused.

Welcome to my world.

I did have an interesting discussion with my oldest son when he was taking physics in High School about changes in rod length & angularity and the effects on cylinder wall loading. However, when we had a parent / teacher meeting sometime later and I mentioned this to his teacher, I was left with the impression his perspective is if it's not on his test, why bother? Sad...

[BLSTIC]

The squish surfaces may be parallel or tapered. If the squish surface is lengthy and the clearance is
tight and the rpm is high, mixture can become trapped in the squish volume. It cannot escape into
the main chamber and will increase in pressure locally. This will add considerable gas pressure to
the upper ring land and ring crevice. Combined with the temperatures of the squish surfaces, auto-
ignition can occur in the crevice volume, resulting in ring land detonation.

To avoid trapped squish band mixture, the squish band surfaces are tapered; the outside clearance
being tight and the chamber side clearance being larger. This allows the trapped mixture to escape
into the chamber. The included angle may vary from 1 to 3 degrees depending on specific design.
For calculation purposes, we use the mean clearance dimension.

The squish surfaces may be flat or angled. In addition to squish velocity, the direction of the
squish jet must be considered. For a shallow bowl, the squish surface may be flat. For a deep
bowl, such as a hemi, it may be angled upward toward the spark plug. The shape of the chamber and
piston top will determine the optimum squish jet direction.

I guess that answers my earlier question about putting it in the head or piston then. I'm looking at a semi-hemi (I'm not sure what else to call it) with quench pads that make the combustion chamber an oval between the two valves and a plug that isn't too far from centreline but is very close to one of the pads. Putting an angle on the pads in the head would 'point' the squish slightly more into the chamber than otherwise. Putting an angle on the pistons would remove more metal (lowering compression is good for my case) but point the squish the wrong way.

So you say 1-3 degrees. Others say 4, with extreme cases (which appear to remove the squish action almost entirely) as 12 degrees.
I ran the numbers on the engine in question and a 4 degree taper would have the squish area start to burn 4 degrees earlier (assuming 3mm clearance was required for a burn of any significant speed). I need more research...

Read the paper I linked to earlier by Honda. It’s literally the same design and see how it scales.

There is also a SAE paper from Chrysler when designing the “new Hemi” regarding this as well.

It should be noted how the OEM world and aftermarket differ. The OEM’s are using high tumble designs (4v/cyl) in very high output turbo situations, which assists in speeding up combustion and makes it more consistent, where the aftermarket is still “softening” things.

Combustion is very hard to understand on a high level and harder still to control it. Think about what Darin said about vacuum of lifting up a flat piece of wood off the floor and pumping losses, but Dr. Andy Randolph, who is a combustion engineer, works at ECR and has worked at Hendricks, says they the run the NASCAR engines to the point that with carbon build up at the end of a race weekend, it’s just starting to kiss the head. Maybe there are some pumping losses, but if there is, it isn’t anywhere near as much as inconsistent and incomplete combustion will give you.

I have read that Honda one, a couple of times. I'll try find the Chrysler paper. I do wonder what the expected power gains were if it was a turbo engine and they raised boost levels instead of compression.

Engine Analyzer + won't give me cylinder pressure or let me set timing, but I could possibly get an approximation if I make a knock limited engine and alter compression then boost for the same knock limited ignition timing.

Mercedes M139 (new AMG A45 motor, 410hp from 2.0L on pump gas stock) has no squish, moderate tumble, tiny valves, circular dish piston. Only the extended plug boss looks unusual. Its secret to power is detonation resistance and 30psi (at 9:1 it's low compression for even a turbo DI motor)

[BLSTIC]

I have read that Honda one, a couple of times. I'll try find the Chrysler paper. I do wonder what the expected power gains were if it was a turbo engine and they raised boost levels instead of compression.

Engine Analyzer + won't give me cylinder pressure or let me set timing, but I could possibly get an approximation if I make a knock limited engine and alter compression then boost for the same knock limited ignition timing.

Well it's off-topic, but for those interested, I made a knock-limited engine (944 SOHC) at 9:1, 10psi and it was limited to 13 degrees at 4000.

9:1 10psi 13deg 256ft-lb Baseline
10:1 10psi 11deg 260ft-lb 1.56% gain
9:1 12psi 11deg 269ft-lb 5.08% gain

(note, using EA+, it's probably not too accurate for this kind of work, I need me some EngMod4T)

[David Redszus]

Mercedes M139 (new AMG A45 motor, 410hp from 2.0L on pump gas stock) has no squish, moderate tumble, tiny valves, circular dish piston. Only the extended plug boss looks unusual. Its secret to power is detonation resistance and 30psi (at 9:1 it's low compression for even a turbo DI motor)

Look at the A45 piston tops. They are dished with a circumvential collar. The direction of intake flow in a four valve head
provides more than adequate tumble, as does the piston dish collar. But the mixture tumble is in the piston bowl.

More important is that Gasoline Direct Injection (GDI) engines are not prone to detonation. Kinda like a diesel.

Reduced chamber turbulence will not reduce detonation; it will increase the possibility of detonation.
Squish velocity increases flame speed but if ignition is advanced, the pressure curve moves toward TDC
and could produce pre-ignition.

Once again. in-cylinder pressure curve measurement tells us what we really, really need to know.

[Alkyfool]

A pic of supposed Bob Glidden Boss piston I found on facebook.

This has been a great discussion.

My recollection when ideal situation where you get supersonic burn (flow) in a tube, to stop it you must increase the area, like a step header. A decrease in area would speed it up until it hits the wall and reflects that it sees the increase in area with the 4 to 12 degree expansion.

Similarly accumulator grooves between first and second piston ring are very small, how do they control detonation...a change in area. Seems so small how could they work?

BG Boss Piston.jpg

[BLSTIC]

Has anyone done tapered quench on a chamber without a mill or CNC? I'm thinking of how to apply it without expensive machinery, even if I had to make up guides and jigs, but can't quite picture how to do it

[The Iron Icon]

Has anyone done tapered quench on a chamber without a mill or CNC? I'm thinking of how to apply it without expensive machinery, even if I had to make up guides and jigs, but can't quite picture how to do it

Not saying it wouldn't work without a machine but I'd think you'd have so much time and money in a jig to do it properly that you wouldn't come out ahead.

But as for how, I might would try to see about using the intake guide as an indexing point and then build from there. You would need it very ridgid to make a cut in only part of chamber.

[David Redszus]

One of the most important lessons taught to me by an old timer was to make a mold of the combustion
chamber with valves and a piston at near top center. The volume shape that the flame fireball must
traverse is complicated and not easy to visualize.

I asked the old man where he learned such a thing. He said it was back when they were building and testing
B-29 bomber engines.

[DCal]

I did that with Paraffin wax, left the deck area about .125 thick. It's very eye opening because you can see in 3D the relationship of top of the piston to chamber, valves and the spark plug. That got me started on rounding the sharp domes and valve reliefs.

[BCjohnny]

Having done only very simple tests, indeed nothing that might stand up to the scientific method, there is nevertheless a very clear correlation between minimum area, not necessarily volume, and flame propagation

You can literally 'switch' the flame off with a minimal reduction in area

This is partly why I consider there is a secondary, or tertiary etc, 'mechanical timing' phenomenon occurring, regulating the rate of pressure rise and promoting complete charge combustion (power and emissions), that you don't necessarily need fancy instrumentation to comprehend

This mostly relates to older, understandably compromised, two valve designs

[69427]

I did that with Paraffin wax, left the deck area about .125 thick. It's very eye opening because you can see in 3D the relationship of top of the piston to chamber, valves and the spark plug. That got me started on rounding the sharp domes and valve reliefs.

I had to make a mold of our GMPP 12363391 combustion chambers using "US Chemical Icing Polyester Finishing Putty USC-26006 " for our 427 so I could send it to J&E to get a custom dome made for a 13.5 compression ratio since there was no off the shelf pistons.

I would think this would also have to be done if a taper chambered was to be used to get the most benefit.

[GARY C]

I thought about this idea in 2006 after letting one end a 4x8 sheet of 3/4" plywood drop on the shop floor and watching the dust blast across the shop,

I have been thinking about this plywood scenario and can't help but think about dropping a book flat against a floor and the resulting bang it makes when the two surfaces come together. Would the same thing be happing when the squish pads of the piston and head come together creating a sonic boom in the chamber? In Darin's video he also talks about these surfaces being pulled apart and creating a vacuum between them.

I would think keeping a very tight clearance (allowing for piston rock) out by the cylinder bore and tapering it to the center would be beneficial.

Drop it flat on a dusty floor and then stand it on end and let it fall on a dusty floor and note the direction of flow, the opposite would occur to some degree with a reverse action but I think it would be to a lesser degree.

Another thing presented on a tapered or grooved chamber is that it allows flame to travel into areas at TDC that a flat quench would not.

[frnkeore]

Does this tapered quench area, have to be parallel, blowing up, towards the chamber? Can it be only on the piston, blowing down, into the piston recess?

[frnkeore]

Does this tapered quench area, have to be parallel, blowing up, towards the chamber? Can it be only on the piston, blowing down, into the piston recess?

No one has a opinion on this?