Combustion Flame Speed

beth · Post by **beth** » Thu Aug 10, 2006 7:11 pm

I don't understand what the piston displacement per degree is? If you mean the amount of cc above the piston that is lost per degree I don't understand the 324cc figure.

putztastics · Post by **putztastics** » Thu Aug 10, 2006 7:19 pm

Whew, hope I got the fps changed to fpm before anyone saw it.

I wonder if quench flow and port/chamber flow need to be analyzed separately.

The vortex Darin mentions is obviously an artifact of port/chamber flow because quench flow effects were not present. Chamber modification fixed it with the resulting effect of supressing detonation. A quench pad modification like a groove might also trip the vortex resulting in a similar detonation supression effect. Or the groove might have a completely different way of supressing detonation.

It seems apparent the groove does supress detonation.

I wonder if the ideal groove might be concentric with the bore with intersecting grooves towards the chamber - like an E with a curved back.

putztastics · Post by **putztastics** » Thu Aug 10, 2006 7:21 pm

beth wrote:I don't understand what the piston displacement per degree is? If you mean the amount of cc above the piston that is lost per degree I don't understand the 324cc figure.

Piston movement in volume per degree of crankshaft rotation.

From PipeMax....

beth · Post by **beth** » Thu Aug 10, 2006 7:26 pm

I believe there is only squish velocity just before TDC. As the piston rises the pressure above it is rising equally until the very end when the surface friction in the squish becomes such a restriction to horizontal movement that pressure builds until it is physically expelled. This is why after a certain amount of clearance the squish flow stops. These are my ideas not something in stone. The use of squish area finish and its relationship to squish flow is what I was starting to work with when I retired. There may be something there.

beth · Post by **beth** » Thu Aug 10, 2006 7:28 pm

putztastics wrote:
beth wrote:I don't understand what the piston displacement per degree is? If you mean the amount of cc above the piston that is lost per degree I don't understand the 324cc figure.
Piston movement in volume per degree of crankshaft rotation.

From PipeMax....

but it could never be 324cc in one degree unless it's an ocean liner

Greenlight · Post by **Greenlight** » Thu Aug 10, 2006 7:32 pm

putztastics wrote:How much does the piston move up between 30 before TDC and TDC?

On a 350 sbc (3.48" stroke, 5.7" rod) the piston moves 0.2995" in that 30 degrees of crank rotation.

beth · Post by **beth** » Thu Aug 10, 2006 7:38 pm

I wonder if quench flow and port/chamber flow need to be analyzed separately .

Yes, they are completely different happening at different times. Darin's photo is during intake flow not during squish.

putztastics · Post by **putztastics** » Thu Aug 10, 2006 7:50 pm

beth wrote:
putztastics wrote:
beth wrote:I don't understand what the piston displacement per degree is? If you mean the amount of cc above the piston that is lost per degree I don't understand the 324cc figure.
Piston movement in volume per degree of crankshaft rotation.

From PipeMax....
but it could never be 324cc in one degree unless it's an ocean liner

You're right, that's WAY wrong. That column has to have a different meaning. I'm away from that computer for a while so cannot figure it out right now.

So scratch that volume per degree baloney please.

I don't call myself putz for nothing......

putztastics · Post by **putztastics** » Thu Aug 10, 2006 8:25 pm

Called my son at the other computer and got it figured out.

That column is cylinder volume at whatever specific crankshaft position in degrees.

So...

displacement @ peak piston speed is 6cc per degree

at 30 BTDC it is 4.05cc per degree

at 20 BTDC it is 2.81cc per degree

at 10 BTDC it is 1.44cc per degree

Man this is embarassing, I better shut up for a while now....

beth · Post by **beth** » Thu Aug 10, 2006 9:25 pm

Man this is embarassing

No it's not, it's all very interesting. Thanks so much for the info, this is all good mind candy. I'll be seeing squish in my dreams tonite.

beth

Mark Workman · Post by **Mark Workman** » Thu Aug 10, 2006 10:42 pm

Gordon Blair breaks the squish effect down into increments of crankshaft rotation, and mathematically determines the velocity, squish pressure ratio, and kinetic energy of the squished mixture for each increment. He further categorizes the type of combustion chamber as central, offset, total offset, or deflector. The resulting squish velocity curve starts at zero at point of intake port(valve) closing, and rises exponentially to point of maximum squish velocity before TDC.

For an engine with:

Bore= 70mm

Stroke= 70mm

Rod Length= 125mm

Trapped (dynamic) compression ratio= 7:1

Squish area ratio= .5

Squish clearance: 1.2mm

At 5000 rpm,

For a central chamber, Max squish velocity(MSV)= 20.9meters/second. Max Squish Pressure Ratio(MSPR)= 1.094. Both occured at 10° BTDC. Total Kinetic energy(TKE) due to the entire squish process = 6.94mJ.

For an offset chamber, MSV= 28m/s, TKE= 12.5mJ.

For a Total offset chamber, MSV= 46.5m/s, TKE= 35mJ.

For a deflector chamber, data shown in the book is the same as the other chambers, but for an additional .6mm squish clearance, to 1.8mm: MSV= 49.5m/s. TKE= 56mJ.

I would consider a typical 23° chamber to be a totally offset design, while the more sophisticated chambers like are pictured in this post tend to straddle the boundaries. Looking at some of the better chamber types in use today, it is also pretty obvious that higher squish velocities do not necessarily mean more power. Quality seems to be as important as quantity.

These figures, as seen in a cylinder with more competitive dimensions as most of us are more familiar with, will of course be different. Mainly because the squish clearance does not grow proportionally with increasing displacement, and the TKE will be greater because more mass is being accelerated in a larger cylinder. I guess the point is that squish behavior is very quantifiable, and I'm sure there is a very elite group of people with a pretty good understanding of how it all relates to the end goal. It sure isn't me. But it makes for very interesting reading.

Unkl Ian · Post by **Unkl Ian** » Thu Aug 10, 2006 11:10 pm

But isn't squish behavior going to change with engine speed ?

beth · Post by **beth** » Thu Aug 10, 2006 11:16 pm

It says 5000rpm

Silverback · Post by **Silverback** » Fri Aug 11, 2006 4:51 am

Oh man... where did the pictures go? I wanna see (throwing a tantrum...)

Darin Morgan wrote:Pictures

Even amount of quench on both sides and quench about 260° around cylinder.

.150 thick quench on intake side

Vortex generation on quench pad

Chamber mod stops vortex generation

som32 · Post by **som32** » Fri Aug 11, 2006 6:07 pm

Just thinking out loud, someone throw an idea that groove might act as a sparkplug for quench area. well,if its wide enough and deep enough to support flame travel to other side of chamber through it (when piston is near tdc) wouldn`t it reduce the possibility of detonation? (forming sort of pointed-jet flame)
If I remember right Automotive breath tried grooves that pointed to exh valve. How did it work?
And this thread started from flame travel speed... well I gues its still touches the subject:javascript:emoticon('

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