In cylinder turbulence/ burn rate

[automotivebreath]

Clint Gray of TFX Engine Technology Inc. (Combustion Pressure Analyzers)
was kind enough to share some of his knowladge on combustion.
tfxengine.com

From what he has to say there is plenty of improvements to be found
in the area of combustion.

Measurable Heat Energy – the heat energy that is being used to
generate pressure and torque/power (does not include heat lost to the
engine components).

Total Heat Released - the measurable heat release plus the heat
that is lost to the metal surfaces.

Application Efficiency Value - how efficiently the heat energy is
converted to power applied to the crankshaft via pressure

Indicated torque/power generated on the power stroke depends
only on the amount of Measurable Heat Released and how efficiently
(Application Efficiency) the energy released is applied to the crankshaft
via pressure.

The goal is to get higher heat energy release and higher application
efficiency at the same time, not just one at the expense of the other.

Energy released before roughly 10 ATDC (not BTDC) and after roughly
20 ATDC is inefficiently applied.

Typically 70% of the measurable heat release energy is released in the
15-20 ATDC range on a decent tune-up. I'm not saying this is the most
efficient way possible because it is not; it is just what we typically see.
If 70% of the heat is released by 15-20 ATDC then the flame front
must have covered more than 70% of the mixture by this point.

The trick is to maximize heat release from the A/F mixture, minimize the
amount of heat release before about 10 ATDC, maximize the heat release
before about 20 ATDC and finish up the burn as quick as possible after
20 ATDC. A tall order? Yes. Anyone thinking that they are already there
should think again.

100% energy release can be as early as 20 ATDC, more typically 40-80
ATDC and in some applications doesn't finish by exhaust valve opening.

[DavidVizard-GFN]

Originally Posted by automotivebreath

Hi David, As a reminder to start planning an article on mixture motion, I'll post
in this thread from time to time. I hope you can find the time to fit it in, it's a
interesting subject. I personally believe we are only beginning to touch on
the benefits of in-cylinder turbulence.

Anyone interested? Jump right in.


The designer of this port has taken the concept of swirl to extremes, to me it
looks like he created a high RPM fuel/air centrifuge.

It seems we have gone a full circle here. AB posted this way back and the question it left us with was ' does that ramp in the port do anything constructive. Hopefully the article on the 7 Liter Corvette Heads answers that.

7 Liter Corvette Heads - can they be improved upon?

[Cammer]

The article clearly illustrates choices head porters face every day.

Following the philosophy of "First Do No Harm", will go a long way to advancing a head artist's education!

The word on the street says the OEM boys are getting with the program and producing some good work.

David, thank you for sharing this article!
______________________________

Let us stir the pot!

Turbulence and laminar flow?

Stir in a dash of swirl?

Homogeneity?

Momentum?

Forward flow, reverse flow?

Stay tuned!
_________________

[automotivebreath]

Talking with drag racers over the years, discussion on swirl is fairly rare.
Recently two articles have drawn my attention to the importance, one
the LS7 writing the other PolyQuad four valve power concept. Both have
opened my eyes on the importance of swirl in generating low RPM torque,
how to generate swirl and advantages of 2 valve or PolyQuad designs as
they relate.

Surprisingly removing the 7 liter port dam reduced flow, I for one have been
guilty of removing such features with out flow bench access thinking I was
improving cylinder filling. It makes me realize just because removing looks
to improve flow that's not necessarily so. Now we know it has two purposes,
to enhance port induced swirl as well as improved VE.

The one thing that catches my attention is both the 7 liter example and the
one I posted earlier appear to change the direction of natural swirl,
this generates the question; What are the advantages of doing this?






The PolyQuad writing provides details on the subject of swirl and tumble that
are rarely discussed, perhaps because many like myself are not aware of the
fine details of port generated mixture motion. Additional questions will
certainly follow.

Originally Posted by DavidVizard-GFN

...this begs the question as to what a PolyQuad head does better than a
current and typical four valve per cylinder head?

...conventional four valve head has no natural tendency to swirl – but it does
have a tendency to ‘tumble’ the charge. The following illustration shows the difference between the two.



Not unreasonably a first inclination would be to assume that both types of
mixture motion would work equally well. Up to a point they do but as the
piston nears the top of it’s stroke these two forms of mixture motion diverges
in characteristics. The tumbling charge motion breaks down to small tumbling
eddies where as the swirl, as it gets compacted in the chamber can speed
up while still retaining it’s swirling motion form. This swirling motion in
conjunction with a well placed spark does a good job of effectively and
rapidly burning the charge. On the other hand the tumbling action seen most
often in four valve engines tends not to produce enough charge motion at
low speed to produce as good results as the two valve engine swirl. Also
tumble can be almost cancelled out when high compression ratio’s are used.

[Pinhead]

As far as I can tell, port induced tumble and swirl play pivotal roles in Larry Widmer's Soft head technology. It has to be able to be implemented elsewhere.

Originally Posted by big block fiero

But those dimples on the back side of the valves, I'm real glad you guys spilled the beens on that one. Even the wizard seemed a little interested. I still haven't dyno'ed it yet but I will in a couple weeks.

Have you got any dyno results?

[mpgmike]

I find it interesting how I arrive at a certain technology independently of others, only to find out somebody else already did it. I bought a Power Plate for carb'd engines back in the late '90s. My /6 Duster went from an already impressive 29.8 mpg best to a whopping 44.7 mpg! The power went up just as dramatically. The key was the heated, tapered cones with 20 pitch threads turned in them.

I figured out a way to implement this on modern PFI engines; turn screw threads into the intake ports. As an extension of the Powre Lynz (as I call them) I put the intake valves in the lathe and turned screw threads into the back sides of them. Later I found out that Metric Mechanic was already doing this (patent expires any day now).



Mike

[Pinhead]

And I found out that Metric Mechanic is in Kansas City!!!

[seattle smitty]

It's interesting to see where dimples have gone since some porter thought about golf balls. I always felt that dimples worked like vortex-generators on aircraft wings, to minimize flow-separation over convex surfaces. On a golf ball, the dimples don't help much until the air starts flowing past the point of maximum diameter (non-rotating golf ball here). Therefore, for my own engines I dimple the short-turn surface with the hope of keeping the flow attached somewhat better as it goes around the bend, but that's all the dimpling for the ports.

But now people dimple a lot of surfaces, such as the backside of those valves, where flow separation is not an issue. On those surfaces the dimples are said to shear liquid fuel into the airstream. Maybe so, but it doesn't look right to me. Seems like the best shearing action will be over the sharp, ground edges of the valve, and that big surface features on the back of the valve just creates drag. You'll never see vortex-generators on the leading edge of a wing, or on the nose of an aircraft.

OTOH, if big surface features on the back of the valve are there to transfer more heat into the fuel and air/fuel, maybe that helps . . . ???

[MadBill]

Not wanting to paint myself into a corner with an irreversible wrong move, I first used a glue dispenser to dot the SSR of an inlet port of my ZL1 BBC with tiny 'Hersey's Kisses' in an attempt to emulate vortex generators to eliminate the stall at 0.800" and above.
Lost 5 CFM and didn't help the stall condition...

[seattle smitty]

Well sure, Bill, I mean whoever heard of Hersey's Kisses on a golf ball! I'm just waiting for the aluminum rolling mills to start turning out 7075 Alclad sheet with dimples all over, so I can build a super-slippery homebuilt airplane!!!