In cylinder turbulence/ burn rate

[automotivebreath]

Yes pinhead, the author of the "Fire In The Hole" article, Ray T. Bohacz is
fully aware of the importance of efficient combustion. This is evident again
here in his "Understanding Spark Advance" writing.

With the current inches is everything mentality, a fast burn is more important
than ever. The trend is to go with the maximum bore size that the spacing
allows, resulting in increased burn distance. Combine this with maximum RPM,
getting the flame to keep up with the piston becomes a top priority.

UNDERSTANDING SPARK ADVANCE

"...Any conversation about spark timing is actually a discussion of the gas
exchange process, and the theory of flame speed and burn rate. During
combustion, the spark travels slower than the piston, which is why it's
necessary to give it a head start. Combustion in an engine is dependent upon
the ability of the flame front, originating at the spark plug, to travel into
regions of unburned mixture. This occurs by means of conduction, diffusion,
radiation, and the convection of heat. The unburned mixture portion is then
heated and compressed, and it ignites. Conduction and the diffusion of heat
from the burned charge into the fresh charge, and vice versa, are of great
importance during the expansion, or power, stroke.

This sheds a different light on the old saying that airflow in an engine is
king. All the airflow in the world will do nothing without an efficient and
powerful combustion event.

Although the exact speed of the flame front during ignition is not easily
determined, the consensus of most engineers is a rate of 10 to 25
meters-per-second (m/s). Many factors affect the speed the flame,
and thus the amount of spark advance the engine requires to produce
the best-possible power without entering an abnormal combustion
(like detonation or pinging)..."

[Pinhead]

Wasn't there someone on MPGResearch that was developing some type of sensor to detect peak cylinder pressure? He was talking about using the ionization in the plug gap to detect it somehow... That would be a handy tool to determine the flame speed and optimum ignition advance.

[automotivebreath]

I did hear of the combustion Ion testing from the MPGResearch site, very
interesting concept. Ionization current is a method using the spark plug as a
sensor in the engine. The air fuel mixture does not conduct electricity very
well. Once the mixture begins to burn it has many highly conductive free
electrons due to the chemical reactions. An electrical potential is put across
the spark plug after it fires and the current is measured during the
combustion event.

Here's some information on it: Ion-Sensing and Interpretation

"When using the spark plug as sensor, a DC-bias is applied to the gap and the
current that goes through the circuit is measured, the current is called the
ionization current"

"In an ideal combustion reaction, hydrocarbon molecules react with oxygen
and generate only carbon dioxide and water. In the combustion there are
also other reactions present, that include ions, which go through several
steps before they are completed. These ions, and several others, are
generated by the chemical reactions in the flame front. Additional ions are
created when the temperature increases as the pressure rises.

The processes creating the ionization current are complex and are also
varying from engine cycle to engine cycle. Figure 8 shows ten consecutive
cycles of the cylinder pressure and the ionization current operating at
constant speed and load. "



Cycle to cycle variations are always present in the combustion. The plots
show ten consecutive cycles at stationary engine operation that clearly
exhibit the cyclic variations.

"The ionization current typically has three phases: a phase related to ignition,
a phase related to ions from the flame development and propagation, and a
phase related to pressure and temperature development. In Figure 10, the
three phases of the ionization current are displayed. Each of these phases
has varying characteristics and they also mix together in complicated ways.
In the ignition phase, the ionization current is large, with reversed polarity.
Due to the high current in the ignition the measured signal shown in the figure
is limited. What can be seen in Figure 10 is the ringing phenomenon in the
coil after the ignition.'



Ionization current showing three clear phases, ignition, flame front, and post flame.

"In the flame-front phase, the high level of ions associated with the chemical
reactions in the flame produces one or more characteristic peaks. The ions
generated by the flame have different recombination rates. Some ions recombine
very quickly to more-stable molecules, while others have longer residual times.
The result is a high peak which after some time decays as the ions recombine."

"In the post-flame phase the most stable ions remain, generating a signal that
follows the cylinder pressure due to its effect on the temperature and molecule
concentration. Ions are created by the combination of the measurement voltage
and the high temperature of the burned gases, since the temperature follows
the pressure during the compression and expansion of the burned gases, when
the flame propagates outwards and the combustion completes. The ionization
current thus depends on the pressure."

[big block fiero]

Hello again automotive breath and david vizard. So much effort has been made to reduce surface area and now this concept comes along (metric mechanic head). this just has to reduce thermal efficiency because there is just to many cuts. As I have discussed with automotive breath I think just one planned cut nearer to the plug could have a shearing effect that could cut flame front turbulence across the rest of the chamber (sort of like a chin spoiler on the front of a car) could have some merit but the rest of the chamber I think would be better off with less surface area. Nothing scientific hear, just my gut feeling.

"it dosent take but country smarts to solve a problem" quote by smokey yunic.

[big block fiero]

All this talk of increased chamber turbulence to the point that fuel is being vaporized in the cylinder thru large surface area vortex configurations and tight squish clearances. Smokey yunick thought vaporization would be better if it were completely done much sooner upstream some distance in the intake track. With all these high turbulence ideas why not then inject the fuel right in the cylinder and vaporize it then, this would allow the inlet track to be only air then you could avoid centrifugal sepparation of the mixture. Higher turbulent chambers run better with larger fuel droplets anyway.

Conversely to this, take the example of the summander sigh grooves (popular science article). The groove in the quench area shoots a velocity at the spark plug as it fires. More precombustion vaporization occurs at the plug and the fasination is that he reports a notable gain if the quish clearance is increased (less chamber turbulence!) and the engine has a notable increase in lower speed operation with no loss in high speed operation. This goes along with vizards example that a squishless engine needs good vaporization and can produce a very wide power curve.

david, Ive read and own almost all your books and have found that you sort out allot of misinformation and you consistently present original thought.

Matt kneen, mpls mn.

[rookie]

This thread has gone way beyond my scope of intelligence but when I saw the name Big Block Fiero I could not help but think what a scary ride that would be. And how much nitrous should we put on it?

[automotivebreath]

Originally Posted by big block fiero

"it dosent take but country smarts to solve a problem" quote by smokey yunic.

Welcome to GoFastNews Matt! I enjoy the “country smarts” you bring to
the discussion.

I can see that the metric mechanic may be able to see some benefits from his
efforts but if so it comes at a huge costs; therefore I can not agree with his
methods. It’s difficult to imagine that he is seeing enough benefit to justify
the huge increase in surface area. In addition the grooves on the back side
of the intake valve surly have a negative impact on cylinder filling, no good
when maximum performance is the ultimate goal.

It does appear that other methods would provide similar benefits with out the
disadvantages; perhaps he has so much time and money invested he’s not
willing to turn back.

[automotivebreath]

Originally Posted by big block fiero

...take the example of the summander sigh grooves popular science article.
The groove in the quench area shoots a velocity at the spark plug as it fires.
More precombustion vaporization occurs at the plug and the fasination is
that he reports a notable gain if the quish clearance is increased (less
chamber turbulence!) and the engine has a notable increase in lower
speed operation with no loss in high speed operation...

I have modified more than forty engines with different variations of grooved
squish pads much like you describe. To date, the most impressive example
was Glenn Elliser’s SBF Mustang. Cutting one groove in the squish area
pointing at the plug combined with opening of the squish clearance eliminated
a starting line detonation problem and brought of new found performance. The
result was so much of an increase of power that a rear end gear change was
required to control the car at launch.

[Pinhead]

Originally Posted by automotivebreath

In addition the grooves on the back side of the intake valve surly have a negative impact on cylinder filling, no good when maximum performance is the ultimate goal.

I was under the impression that the low-lift flow actually increased due to the effect it has on the boundary layer. I'm pretty sure one of his PDF's mentioned somewhere around 40% increase. In addition to helping to vaporize the fuel.

Edit: Don't know where I got 40%.. It was 5%.

[big block fiero]

Originally Posted by Pinhead

I was under the impression that the low-lift flow actually increased due to the effect it has on the boundary layer. I'm pretty sure one of his PDF's mentioned somewhere around 40% increase. In addition to helping to vaporize the fuel.

I am sceptical of any intake flow increase especially relating to any modification that is on top of the valve inside the chamber, and 40%, no way.
Unless you are referring to mods that are at the underside of the valve but even then I remain sceptical and again, 40%, no way.


David vizard has tried and tested (on a dyno) many theoretical profiles to get to where he is at today and has never made any unbelivable 40% claims. He has found improvements that accumulativly add up but not 40% above a properly done, modern, high flow, performance valve job.

David Vizard, I hope you read this or mabe I should post this in a different thread but it kind of fits into what were talking about -------- I realize that many nascar builders have gone to 55 degree valve seat angles and with that the port to valve centerline angles, RPM horsepower curve, and many other things contribute to the trend for this application. What application is best suited to the 30 degree valve seat angles that you had supported against the trend for a more conventional 45 degree seat. Some diesles have 30 degree seats and are low RPM but I dont know how many are currently running these angles. You have run these angles at a much higher RPM but I dont know if you continue to do so. I have built a sprayed boosted engine with 30 degree seats so I could justify a decrease in valve duration. I havent read any where of you saying anything about this but I believe the boosted low lift flow on the intake side can really get moving before the piston does and so this could allow for a smaller intake valve and hence a larger exhaust valve within the chamber space that is available. I have no scientific supporting data to confirm my guesses as to the best valve event timing for any 30 degree boosted engine and there may be drawbacks that I havent realized. Also would you not run 30 degree seats on the exhaust valve of a sprayed motor.

matt kneen mpls, mn.