home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > performance & modifications

Reply
 
Thread Tools Display Modes
Old 02-23-2007, 07:46 PM   #1
jmclay
Board Member
 
Join Date: Dec 2005
Default Fast Burn, Small Combustion Chamber

Fast Burn, Small Combustion Chamber

I was looking at a 530 head and wondering how to end up with a small CC, shaped and located so that it's mixture would complete the burn more quickly, and be displaced by the piston crown in such a way as to maximize mass flow out of the valve. From what I read a compact CC, designed so that the travel distance of the flame front is significantly reduced, is key to fast burn; and fast burn is key to significantly better performance. In addition, a crown that more fully displaces the volume in the vicinity of the intake valve, corraling the mixture towards the exhaust port, is important to more complete ejection out of the exhaust valve. So, make a piston that's crowned under the intake valve, and if needed, dished under the exhaust valve. But as I looked at the distance from the plug to the farthest extent of the CC under the exhaust valve, it didn't look much different than the distance to a similar point under the intake valve. The CC could be moved and positioned for better ejection, but the propagation distance was essentially unchanged. Would it not take as long to burn the mixture with/without the dome?

If that all makes sense, how can one make a fast burn motor out of a B230? Any way I slice it, I don't see a way to significantly reduce the required combustion propagation distance. Am I missing something?

What else affects combustion propagation speed?

Trying to understand this.

John
jmclay is offline   Reply With Quote
Old 02-23-2007, 08:05 PM   #2
740ATL
Guest
 
Default

tight squish! Decrease the piston-to-head clearance via block decking or thinner headgasket.

The man to talk to is Stealthfti. Surf performance for anything with his name in it, and check out his pbase site at www.pbase.com/stealthfti... specifically his engine builds.

Mike
  Reply With Quote
Old 02-23-2007, 08:13 PM   #3
jmclay
Board Member
 
Join Date: Dec 2005
Default

Quote:
Originally Posted by 740ATL View Post
tight squish! Decrease the piston-to-head clearance via block decking or thinner headgasket.

The man to talk to is Stealthfti. Surf performance for anything with his name in it, and check out his pbase site at www.pbase.com/stealthfti... specifically his engine builds.

Mike
Thanks Mike,

I'm on board with the tight squish part of the equation, but the CC modifications as they relate to shortening the combustion time is a tough nut for me to crack.

John
jmclay is offline   Reply With Quote
Old 02-23-2007, 09:01 PM   #4
Stereophile33
Board Member
 
Stereophile33's Avatar
 
Join Date: Nov 2003
Location: Portland, OR
Default

Quote:
Originally Posted by jmclay View Post
Fast Burn, Small Combustion Chamber

I was looking at a 530 head and wondering how to end up with a small CC, shaped and located so that it's mixture would complete the burn more quickly, and be displaced by the piston crown in such a way as to maximize mass flow out of the valve. From what I read a compact CC, designed so that the travel distance of the flame front is significantly reduced, is key to fast burn; and fast burn is key to significantly better performance. In addition, a crown that more fully displaces the volume in the vicinity of the intake valve, corraling the mixture towards the exhaust port, is important to more complete ejection out of the exhaust valve. So, make a piston that's crowned under the intake valve, and if needed, dished under the exhaust valve. But as I looked at the distance from the plug to the farthest extent of the CC under the exhaust valve, it didn't look much different than the distance to a similar point under the intake valve. The CC could be moved and positioned for better ejection, but the propagation distance was essentially unchanged. Would it not take as long to burn the mixture with/without the dome?

If that all makes sense, how can one make a fast burn motor out of a B230? Any way I slice it, I don't see a way to significantly reduce the required combustion propagation distance. Am I missing something?

What else affects combustion propagation speed?

Trying to understand this.

John
John,
You need a piston that biases the burn to the exhaust side. A great piston can make up for a mediocre chamber, bu the Volvo 8v head is ideal for fastburn stuff. The head needs some work, but combined with pistons you can get there.

Checkout some of the work that Michael May did back in the day..
__________________
in quasi-retirement...
Stereophile33 is offline   Reply With Quote
Old 02-23-2007, 10:09 PM   #5
jmclay
Board Member
 
Join Date: Dec 2005
Default

Quote:
Originally Posted by Stereophile33 View Post
John,
You need a piston that biases the burn to the exhaust side. A great piston can make up for a mediocre chamber, bu the Volvo 8v head is ideal for fastburn stuff. The head needs some work, but combined with pistons you can get there.

Checkout some of the work that Michael May did back in the day..
Thanks Jonathan,

Not to be difficult, but trying to see what the fundamental mechanisms are, so I have to ask:

* Why the exhaust bias? What does that do? I thought it really improved gas ejection by squishing everything towards the exhaust valve.
* Am I missing something that affects mixture burn speed? I'm assuming that squish is part of getting more complete mixing & burn as well as knock resistance, but is not a fast burn of the CC contents primarily related to how far the flame front must travel? Is that fundamentally incorrect thinking, and some other mechanism speeds the burn up?

What am I missing?

John
jmclay is offline   Reply With Quote
Old 02-23-2007, 10:33 PM   #6
fryea
Board Member
 
fryea's Avatar
 
Join Date: Mar 2005
Location: Tacoma, WA
Default

John -

Have you been to www.theoldone.com ? It has got a lot of information on the stuff you are curious about. Look at the articles section. More specifically, check out this article

http://www.theoldone.com/articles/Th...5FHead%5F1999/
fryea is offline   Reply With Quote
Old 02-23-2007, 11:05 PM   #7
jmclay
Board Member
 
Join Date: Dec 2005
Default

Quote:
Originally Posted by fryea View Post
John -

Have you been to www.theoldone.com ? It has got a lot of information on the stuff you are curious about. Look at the articles section. More specifically, check out this article

http://www.theoldone.com/articles/Th...5FHead%5F1999/
Thanks Fryea,

Actually that's the main article that has me asking all of these questions; it's easy to see generally how to shape a piston to reduce the CC volume under the intake valve and increase it under the exhaust. What I don't get, aside from the benefits of better mixing, extreme turbulance/swirl and preventing the fuel from changing to liquid phase, is how that (the relocated CC) speeds the burn. Maybe those ARE the reasons, but I thought that shortening the distance the flame front had to travel would be part of it, an important part at that. Maybe that's my mistake. One of the other articles, at least on first read, implies (actually says) that the burn is slower and doesn't have the extreme pressure spike of other systems. And that that yields a larger area under the pressure curve, between the BME points, so more torque. Maybe it's not really what I think is meant by "fast burn".

I'm also trying to figure out just why placement of the CC over the exhaust valve is the "sweet spot"? What is it about that placement that rings the bell?? I figured it had to do with that placement doing a better job of squishing the molecules out the exhaust valve, but I don't know if that's it, or part of it.

Just to make sure I'm not misunderstood: I don't doubt for a second that these guys know what they're doing. I'm just trying to figure out the underlying mechanisms in order to see how they might be best applied to our 8V heads. To illustrate my point, if flame propagation distance happened to be THE big deal (aside from mixing and exhaust squishing) then maybe flat tops and no head welding would be a decent 80% solution for the DD. Then again, maybe the exhaust squishing is paramount for best scavenging, and that's the real story.

I don't know. The more I read, the more questions I have.

John
jmclay is offline   Reply With Quote
Old 02-24-2007, 12:39 AM   #8
stealthfti
Board Member
 
Join Date: Aug 2006
Location: sanction rescinded
Default

Quote:
Originally Posted by Stereophile33 View Post
John,
You need a piston that biases the burn to the exhaust side. A great piston can make up for a mediocre chamber, bu the Volvo 8v head is ideal for fastburn stuff. The head needs some work, but combined with pistons you can get there.
+1

John,

two ways to help you out:

1) a correction of terminology: when the piston is at TDC, after the compression stroke and at the beginning of the power stroke, the volume of space above the piston crown and below the cylinder head is the "ignition chamber".

the "combustion chamber" is in actuality the volume of space above the piston crown and below the cylinder head....when the piston is at BDC.

The ignition chamber is not a set exact size:
...because the piston is moving, albeit not very much or very quickly, at TDC, but it IS moving. Therefore a variable volume.
...and the starting time to measure the volume of the ignition chamber is when the spark plug is 'fired'.....the beginning of the ignition.

The combustion chamber is HUGE by comparison. It's size measurement commences when the ignition is complete, and the combustion commences. That point in piston travel is hopefully somewhere between 12degrees ATDC and 20 degrees ATDC....aka the LPP, or locus of peak pressure. The end of measurement of the size of the combustion chamber is taken when the combustion is completed...the default value being BDC. The desired value is at exhaust valve opening, but that is seldom the case.

My point: reworking the size of the ignition chamber to make it as small as possible improves the quality and speed of the ignition process.
...the smaller the size of the IC, the less distance the flamefront has to travel to completely ignite all the air-fuel mix.
...working with the sizing of the IC would be the squish wave, generating hyperturbulence in the igniting air-fuel mixl which also helps speed up the rate of ignition; assisting in completing the ignition by the time the piston has reached the LPP.

Faster completion of the ignition assists in shortening the time it takes to complete the combustion....the 'burn'.

...And it also helps to make sure that the maximum amount of force can be applied to the piston crown when the piston does reach the LPP.

2) an experiment that you can perform at home:

you will need:
...3 sheets of paper, cut into circular shapes. All the same size circles.
...some matches, or a Zippo.
...a grille
...a timer
...a fire extinguisher, for safety reasons...

take one of the circular pieces of paper and lay it on the grille. [if you are not using the barbeque grille, then do be sure to set up the grille on a non-combustible surface such as a concrete driveway; and away from any other combustible items...like the house or the car.]

take a match, or the Zippo, and set the piece of paper on fire....on it edge. Time how long it takes for the entire piece of paper to be engulfed in flame; and time how long it takes for the piece of paper to be completely burned...when the flame dies out.

take the second piece of paper and lay it on the grille. Set it on fire: this time in the middle of the piece of paper. Time as before: how long before the entire piece of paper is engulfed in flame; and how long before the flame goes out.

take the third piece of paper, and wad it up into a ball. Not a super tight wad, but definitely wadded up. Set the paper wad on the grille. Set it on fire. Time the completed ignition, and the completed combustion, as you did with the first two pieces of paper.

Compare the timed results.

The first piece of paper will have taken the longest time to be completely ignited, and also the longest time to be completely burned up.

The second piece of paper will have ignited completely faster than paper #1, and will have completely burned faster as well.

the paper wad will have completely ignited the fastest; and burned up the fastest.

the first piece of paper represented what goes on in a non-squish, non-fastburn motor.

the second piece of paper represented the centrally located spark plug of a pent roof motor

the paper wad represented a fastburn motor.

Your point regarding the sweet spot under the exhaust valve assisting in the final push of the exhaust gases out at the end of the exhaust stroke is one of the pluses of the fastburn configuration: what assists in making the nice and tight ignition chamber will also help empty the cylinder at the end of the exhaust stroke.

HTH

TF
stealthfti is offline   Reply With Quote
Old 02-24-2007, 01:48 AM   #9
klr142
Turbo, what?
 
klr142's Avatar
 
Join Date: May 2004
Location: OR
Default

Quote:
Originally Posted by stealthfti View Post
HTH
Absolutely. As always, thanks for the lesson.
klr142 is offline   Reply With Quote
Old 02-24-2007, 03:10 AM   #10
hudson
Board Member
 
Join Date: Apr 2005
Location: Ontario, Canada
Default

I really like how www.theoldone.com doesn't back up anything they say with real numbers.
__________________
hudson
  • '68 145 & '71 142 projects
hudson is offline   Reply With Quote
Old 02-24-2007, 03:43 AM   #11
linuxman51
BRANDSCHUTZVORSCHRIFTEN!
 
linuxman51's Avatar
 
Join Date: Dec 2002
Location: mont, AL
Default

Quote:
Originally Posted by hudson View Post
I really like how www.theoldone.com doesn't back up anything they say with real numbers.
careful there bud, you're playing with stealth fire.
__________________
"They bum rushed them in their own crib, they drank all their beer, they partied with their ladies and they left with the trophy"

Now with in-house Dyno tuning!

Megasquirt Tuning!
Plug and play LH 2.4 Megasquirt, now with stealth mode!
linuxman51 is offline   Reply With Quote
Old 02-24-2007, 05:04 AM   #12
automotivebreath
Board Member
 
automotivebreath's Avatar
 
Join Date: May 2006
Default

Here's a quote from Larry Wildmer along with a picture of a piston he designed for
air cooled engines.



Quote:
Originally Posted by Larry Widmer
I used the "dome" to purge the dead area about the intake-side of the chamber. Remember that this is a turbo piston, and while we increased the compression (especially compared to other turbo pistons that utilized dishes), the tendency for detonation was greatly reduced and the engines realized considerably more power.
************************************************** *

And a picture and quote on the May Head:



Quote:
Originally Posted by Jaguar power train engineer
I'm quite familiar with the May Fireball head. Over here
on 5 star 100 octane fuel that engine was supplied with
a 12.5 : 1 CR in production!

In retrospect however we've moved on: although that chamber had
good initial burn characteristics, (0-10 %), later in the cycle it didn't
burn all that fast. Also, that engines CR made it supremely suitable
for part load operation, but it was quite knock limited all the way up
the rev range even with quite modest VEs at WOT. For after market
performance applications of this engine I reccommend using the flat
head as the ports flow better then thge swirl inducing May ones.It
should be noted that one CAN have too much of a fast initial burn
that leads to knock also!"

"In addition to those comments
I think squish/quenching the intake side of the chamber the way
the Jag may head did is actually good for combustion stability.
This means the engine can run lean and still remain stable
without running into the lean misfire limit. In modern day terms
it can also mean that the engine can have a high EGR tolerance
at part load and still have stable combustion-again good for
fuel economy if you design your package to take advantage of
this."

"In terms of tumble, swirl and squish-for me squish is used in
tandem with tumble.
Swirl decays less then tumble ( as the piston comes up)and isn't
so confined and contrained to peak gas velocities during the
intake stroke. Squish can be used to make the tumble motion into
smaller eddies -which is ideal to speed up combustion in some
situations."

"Squish on its own, as here doesn't neccesarily do much (It takes
place too late in the cycle and the speed at which the crown
approaches the head at lower engine speeds is fairly slow).
In practice this may seem rather vague, as it often is with
combustion, it's alot less clear cut even in terms of trends
then something like maximising your VE for full load
performance."

"To be fair to the old May head -in the V12 it was barely lower
then the more conventional flat head design in terms of outright
WOT performance -but this was WITH the high CR versus the lower
CR!"

Last edited by automotivebreath; 02-24-2007 at 05:18 AM..
automotivebreath is offline   Reply With Quote
Old 02-24-2007, 04:41 PM   #13
jmclay
Board Member
 
Join Date: Dec 2005
Default

Quote:
Originally Posted by stealthfti View Post
+1

John,

two ways to help you out:

snipped by jmc

Your point regarding the sweet spot under the exhaust valve assisting in the final push of the exhaust gases out at the end of the exhaust stroke is one of the pluses of the fastburn configuration: what assists in making the nice and tight ignition chamber will also help empty the cylinder at the end of the exhaust stroke.

HTH

TF
Thanks Thomas.
Not arguing, and I understand the analogy, but I'm not sure I understand the fit. Right, wrong or incomplete, here is where my thinking goes:

I see two ignition chamber plan views, footprints if you will, for our 8V motors. One is what the current shape is, sort of a slice, taken long ways out of a short potato. Not a cross section slice, a long ways oblong flat slice, about a half inch thick or whatever it is. The other footprint available, with a suitable piston dome under the in valve, is approx one half of that, so cut the longways slice in half, but to maintain the same SCR, stack the halves on top of each other. Twice the depth, half the plan area/shape. The piston has the dome under the in valve and a dish under the out valve, again for a same/same SCR. What has happened to the required flame front propagation distance? To my eyes, not much: It's about the same distance, eyballing it.

Again, I don't doubt the results or expertise of LW, you and others for a second, I just don't understand it completely. There seems to be a missing detail, and I need to figure out what.

* both scenairos have roughly the same distance from the spark plug to the farthest distance in the IC
* both scenairos have the fuel/air molecules at the same energy levels (closeness to each other)

Wouldn't it then take as long for complete ignition of one as for the other, assuming a uniform radial propagation (which may be a large assumption)? One radiates through an angle of 180 and the other an angle of 90 deg, but the flame front propagates away from the plug in all directions at the same speed. The FF gets to the far sides of both IC arrangements at the same time, MOL, or so it would seem to me.

OR is there something else at work, like the lower volume-aspect-ratio (a deeper IC) of the domed arrangement resulting in better atomization/more intense and large swirls and shock waves, that sort of thing, speeding the ignition? That ought to be able to make a diff., no?

I have to run for now but please let me know what you think.

I did manage to get what appears to be a good head, this AM at the PnP.

Thanks,
John
jmclay is offline   Reply With Quote
Old 02-24-2007, 10:15 PM   #14
stealthfti
Board Member
 
Join Date: Aug 2006
Location: sanction rescinded
Default

Quote:
Originally Posted by jmclay View Post
...What has happened to the required flame front propagation distance? To my eyes, not much: It's about the same distance, eyeballing it.

...There seems to be a missing detail, and I need to figure out what.

* both scenarios have roughly the same distance from the spark plug to the farthest distance in the IC
* both scenarios have the fuel/air molecules at the same energy levels (closeness to each other)

Wouldn't it then take as long for complete ignition of one as for the other, assuming a uniform radial propagation (which may be a large assumption)?
Yep, the physical distance from the spark plug to the other side of the ignition chamber hasn't changed...or not by very much.

BUT, are you really sure that 'the fuel/air molecules at the same energy levels' is correct?

Why so? because with squish action/squish wave and fastburn configuration, the dynamics of what is going on in that space has been altered considerably.

The 8V SOHC head design is excellent as a swirl inducer during intake. 'tangental ports' [aka tangential ports] being the operative research term.

The 8V SOHC head also has a very good squish area to total area percentage: the potential for excellent squish action is already there.

Add in fastburn configuration, via piston crown layout rather than very expensive weld/re-tempering/re-machining of the head itself, and the total amount of hyperturbulence of the air-fuel mix...AND of the igniting air-fuel mix...has been increased A LOT. This increased hyperturbulence, along with the higher compression of the air-fuel mix, has changed the 'energy levels of the fuel/air molecules': it's higher than before.

To answer your question of what happened to the distance: it was shortened. dynamically.

The other side was not brought closer to the spark plug physically. The flamefront has been blasted to the other side dynamically. This speeds up the rate of the ignition, shortening the time needed to complete the ignition:

...just like it would be if you actually brought the other side of the ignition chamber closer to the spark plug.

I very much understand that it takes a while to get it figured out in your mind's eye. BTDT

Some research into swirl induction, tumble [which applies more to 4V per cylinder layouts], turbulence, squish wave, and flame front propagation will give a lot of details, along with some very insightful CFD graghings of what is going on during intake, compression, and ignition.

An experiment that you could try, illustrating hyperturbulence:

you will need:
...an empty tuna can
...an empty #10 coffee can
...2oz of gasoline
...a nomex fire suit
...some matches, or a Zippo
...a timer
...a fire extinguisher
...a large concrete or gravelled area
...an assistant to operate the timer and [if the need arises] the fire extinguisher

out on the large concrete area, set the tuna can down
pour 1oz of gasoline into the tuna can
ignite the gasoline
time how long it takes for the gasoline to burn

next, take the #10 coffee can, and set it down FAR away from anything flammable
put on the nomex fire suit
pour 1oz of gasoline into the coffee can
with your assistant operating the timer, and with the fire extinguisher at his/her side, at a safe distance from you and the coffee can:
...ignite the gasoline in the coffee can, and then give the coffee can the best kick you can muster; and time how long it takes for the gasoline to burn.

[hopefully, your assistant will only be occupied with operating the timer at this moment, and not the fire extinguisher trying to put the fire out engulfing your leg]

compare the burn times.

the kicked coffee can gasoline will burn up a lot faster than the same amount of gasoline in the tuna can.

...that's what hyperturbulence does.

aka, the way to dynamically shorten the distance between two points.

TF
stealthfti is offline   Reply With Quote
Old 02-24-2007, 11:32 PM   #15
jmclay
Board Member
 
Join Date: Dec 2005
Default

Quote:
Originally Posted by jmclay View Post

* both scenairos have roughly the same distance from the spark plug to the farthest distance in the IC
* both scenairos have the fuel/air molecules at the same energy levels (closeness to each other)

Wouldn't it then take as long for complete ignition of one as for the other, assuming a uniform radial propagation (which may be a large assumption)? One radiates through an angle of 180 and the other an angle of 90 deg, but the flame front propagates away from the plug in all directions at the same speed. The FF gets to the far sides of both IC arrangements at the same time, MOL, or so it would seem to me.

OR is there something else at work, like the lower volume-aspect-ratio (a deeper IC) of the domed arrangement resulting in better atomization/more intense and large swirls and shock waves, that sort of thing, speeding the ignition? That ought to be able to make a diff., no?

Thanks,
John
Quote:
Originally Posted by Stealth

Yep, the physical distance from the spark plug to the other side of the ignition chamber hasn't changed...or not by very much.

BUT, are you really sure that 'the fuel/air molecules at the same energy levels' is correct?

Why so? because with squish action/squish wave and fastburn configuration, the dynamics of what is going on in that space has been altered considerably.
That's what I wanted to flesh out.

No, I don't think the molecules are at the same energy level, even though I stated as much. What I was actually thinking was that they were in the same proximity to one another (same SCR), and then got sloppy in my summary statement.

So, the key to fast burn isn't necessarily a shorter distance for the flame front to travel, though nice if you can get it, it's making it travel farther, faster by generating a substantial increase in shocking the bejeezus out of the mix; pressure waves, macro mixing, whatever. This sounds like the next level of squish, in the sense that it relates to generating even more intense physical action within the IC.

I'm guessing that the "half plan area/2x depth" IC (the one you'd get with domed pistons in my example) would generate more violent wave, and macro mixing.

Ignoring the effect of port induced swirl for a moment, which I'd expect to be the same in both IC configurations, here is what I'm thinking:

In a stock head/piston most of the fluid movement (due to piston movement) is up. You get some wavefronts across the final IC from the squish band, but mostly the fluid is being compressed upwards. In the domed arrangement you get all of that but in addition, you get the increasing macro flow mixing and shock mixing ACROSS the IC because of the displacement of the volume under the in valve, due to the dome, particularly as it gets to TDC.

If that's MOL the diff, then now I can see why there could be an effeciency diff between the two IC configs, even though they are of the same volume and SCR.

Jonathan is working on getting Endyn to make some domed pistons, as well as modified heads, for the redblocks. I'm pretty eager to get a set of the pistons, possibly a head too.

Now I wonder how EZ116K will adapt. Will it's spark timing logic adjust to leverage the potential of an engine that does less negative work?

John C
jmclay is offline   Reply With Quote
Old 02-24-2007, 11:36 PM   #16
automotivebreath
Board Member
 
automotivebreath's Avatar
 
Join Date: May 2006
Default

Hi stealthfti,

I just love your experiments, especially the one with the coffee can.

You are the first person I have heard describing the ignition chamber.
Where can I find more information on the subject?

Jmclay, sorry for thread hi jack, here’s some good reading on squish
action and turbulence.

http://home.earthlink.net/~scloughn/id21.html

Quote:
Originally Posted by Neels van Niekerk
As rpm increases so does MSV, and so does the available kinetic
energy that can be converted to turbulent intensity. If this does get
converted the burn rate will increase.
automotivebreath is offline   Reply With Quote
Old 02-25-2007, 01:27 AM   #17
stealthfti
Board Member
 
Join Date: Aug 2006
Location: sanction rescinded
Default

John, you are on the right track. It is the greatly increased turbulence that makes the difference.

Swirl plays a very important part in that. [And the 8V SOHC head is excellent for swirl.] A good swirl is speeded up during the intake stroke, and speeded up even more during the compression stroke. That has been checked out and confirmed via CFD analysis and via experimental observation in purpose built test motors. A lot of the swirl research has been done in the context of 2V per cylinder 4 stroke diesel motors; the tangental intake porting has been proven to be excellent for swirl induction.

Pent roof motors [4V per cyl] do not have swirl; they have tumble. Which is less 'organized' than swirl, but can be optimized to do [similarly] what swirl does. Endyn's rollerwave pistons for the pentroof motors work to maximize the tumble velocities.

I also look forward to seeing what Endyn comes up with.

RE what EZ116K does or can do with a tight squish motor: preliminary findings by me on the motors I've done is that it does okay. A LOT more work to explore what can be done either via the timing curve mods [term18-19 procedure] or via chipping needs to be done. I will soon be starting some of that testing.

What EZ116K can do with a fastburn motor? That has not even been started on to find out, because no one [that I have heard of or about] has really done a fastburn 8V redblock. That is going to be changing.

AB...am glad you like the experiments.

regarding the 'ignition chamber'...

I can't claim originality for the term, but what and how I described it is what I came up with and wrote out. I came up with the term and description because most of the reading that I have done on the combustion events in a spark ignited gasoline motor talked about 'completing the burn' by the time the piston reached the LPP. Or points to that effect.

As I would read those articles and papers, that comment about 'completing the burn' did not quite click. Because I could still visualize watching the flames shooting out the shorty pipes on the sides of a top fueler at Irwindale, when I would go to the drags there. I 'knew' that the burn wasn't being completed with the piston just after TDC. NO effin' WAY!

So what was going on? and what was supposed to get finished by the time the piston reached the LPP?

I would have to say that it was the research I did on aircraft piston engine detonation experiments and research that started to nail it down. It hit me that it wasn't the full completed burn of the air-fuel mix by the LPP that was being called for, it was the completion of the igniting of the air-fuel mix by the LPP.

Once I 'saw' that, and then started applying that description to the research work I was reading, it all fell into place.

So, I would have to say, that for some really good info on what goes on during the ignition and combustion processes, reading up on the aircraft piston engine studies and research into detonation and preignition would be a good place to start. The NACA reports and papers dating back to pre-WWII times are very good.

Car maker type research, via SAE papers or other organizations like COMODIA, also have excellent material. One thing to remember though is this: with the car makers, a lot of the emphasis is on MPG or emissions effects. With piston powered aircraft, the emphasis is on keeping the motors alive and running. Cuz if the motor blows up, people usually die. You don't get to park your plane on a cloud and call a tow truck.

That is a nice link for info. In the context Mr. van Niekerk has, side port 2 strokers, it is very different from the 4 strokers we discuss, but his findings are interesting.

With our overhead valves and 4 strokes, we have the benefits of swirl or tumble available. But the man's comments and findings re squish velocities are instructive nonetheless. Bike guys have been using squish bands for a long time to make power.

TF
stealthfti is offline   Reply With Quote
Old 02-25-2007, 08:56 AM   #18
jmclay
Board Member
 
Join Date: Dec 2005
Default

Quote:
Originally Posted by jmclay View Post
If that's MOL the diff, then now I can see why there could be an effeciency diff between the two IC configs, even though they are of the same volume and SCR.

Jonathan is working on getting Endyn to make some domed pistons, as well as modified heads, for the redblocks. I'm pretty eager to get a set of the pistons, possibly a head too.

Now I wonder how EZ116K will adapt. Will it's spark timing logic adjust to leverage the potential of an engine that does less negative work?

John C
I have only a basic macro understanding of how the EZK systems work but based on that my reaction is that their algorithms are based on a premis that doesn't fit a reduced-negative-work-engine. If they try to advance timing to the point of knock (within limits) then won't the ignition occur sooner that than optimum? I remember that there were some EZK pin combinations that would RETARD the entire spark map. Maybe that will be an initial help but it seems like I saw some comments about substantial ignition timing changes (multiples of 10 deg?) for fast burn/reduced negative work engines; I need to double check, because if so then that's a vital element, I think.

Gaining mpg/power at retarded timing would seem a way to tell if uniform ignition and combustion is being completed in less time.

Reduced negative work IS, ultimately, the operational characteristic that generates these performance improvements, if I understand the fundamental principles?

With luck the LH systems won't need to think about the world in a new way.

John
jmclay is offline   Reply With Quote
Old 02-26-2007, 12:51 AM   #19
automotivebreath
Board Member
 
automotivebreath's Avatar
 
Join Date: May 2006
Default

TF, thanks for sharing your insight on the “ignition chamber”.

When studying combustion it is easy to forget about what happens in the cylinder after peak pressure is reached, writings never seam to provide details, it gives the impression that the burn is complete by 15 – 20 degrees ATDC. In practice that’s hardly the case, as you mentioned it is possible for the fuel to continue burning when the exhaust valve opens. In worse case scenario the burn can continue until the overlap period and overcome the fresh charge in the intake manifold. With this said, when considering modifications to an engine the effect the modification has on flame speed should be considered.

As for the link to the "Squish Action” article, yes it all about two strokes but good reading none the less. Unfortunately information on squish action and its role in the engine is difficult to find. When reading information written by the highly educated they always refer to mean squish velocity. This leads me to believe that they don’t fully understand how to tailor squish to a specific application. Sure MSV is important but IMO it’s hardly the most important factor. I would think that converting kinetic energy into turbulence is the objective.

With four stroke engines squish action is normally compromised in favor of high VE. Large valves consume the chamber leaving little room for squish area. That’s where Larry Widmer fits in. He not only understands the importance of turbulence in the ignition chamber but he also knows how to generate the needed turbulence. Much of the world can’t understand what he is doing because they underestimate the importance of turbulence in the combustion process.
automotivebreath is offline   Reply With Quote
Old 02-26-2007, 02:02 AM   #20
stealthfti
Board Member
 
Join Date: Aug 2006
Location: sanction rescinded
Default

John,

Less negative work is one of the advantages; there are others as well. A higher detonation threshhold for one; decreased octane requirements....premium becomes an option rather than a given....is another.

How well can EZ116K adapt to a fastburn 8V? I have not built a fastburn 8V yet, so I can only give a definite answer of: I don't know.

I do know that EZ116K can and does take tight squish well in stride, especially the decreased octane requirements. 7 PSI or 10 PSI, even 14 PSI was not a problem...on 87 octane. I am certain that there is room for optimization of EZ116K for tight squish motors.

I will say that, from what I have seen so far on the tight squish motors that I have built, I think that EZ116K can take fastburn in stride as well, that there will definitely be room for optimization, and that that most likely will be via fastburn-specific chips. Time will tell.

AB,

you're welcome. I liked that squish action article, and what he's working at doing. I look forward to reading more from the man.

Partly why there is a lack of information on squish is because most MFRs are concentrating on the pent roof motors, which lack squish area. A few years back, Toyota came out with a taper squish pent roof motor, to try to take advantage of what squish area was available. I haven't kept track of it, so I do not know what they've done with it since.

The MFRs have been doing things to improve the tumble that the pent roofs generate, in efforts to increase the turbulence...a different path to reach essentially the same objective: lots of turbulence to promote a good, clean burn. The research on cylinder turbulence, and the methodologies developed to enhance it in the pent roof motors, may not be directly applicable to the 8Vs, but is informative and helpful.

TF
stealthfti is offline   Reply With Quote
Old 02-26-2007, 02:39 PM   #21
automotivebreath
Board Member
 
automotivebreath's Avatar
 
Join Date: May 2006
Default

TF,
It is my opinion that the major design fault of the pent roof design is lack of adequate squish area. Tumble is a critical element of turbulence generation best used in conjunction with squish. Tumble creates large scale in-cylinder flow, this helps with air fuel mixing and flame kernel stretch. Effective squish breaks the large scale flow into small vortexes needed for fast flame speed.

The pent roof design has an ideal spark plug location, great VE potential and if designed correctly intake flow generated tumble. This combined with additional energy from piston movement will develop the flame velocity needed for efficient combustion, reduction in ignition advance requirements and resulting reduced pumping losses.

You mention taper squish, I use this picture to understand the term reverse squish, in-cylinder flow generated at the beginning of downward piston movement. I will try to locate more information on the Toyota design you mention.


automotivebreath is offline   Reply With Quote
Old 02-26-2007, 03:32 PM   #22
Stereophile33
Board Member
 
Stereophile33's Avatar
 
Join Date: Nov 2003
Location: Portland, OR
Default

Its interesting that you guys bring up the Toyota research. LW was approached in the late 80's to develop his deal in a pentroof design. They build an entire motor around his piston/head combination.

I look forward to seeing more info AB.
Stereophile33 is offline   Reply With Quote
Old 02-26-2007, 05:47 PM   #23
jmclay
Board Member
 
Join Date: Dec 2005
Default

And another thing; I wonder if the squish and mixing provided by simple flattops, set up for good squish, would yield most of the benefits of a domed piston? Seems like with a flattop you'd suddenly have a substantially larger squish area that is detonation resistant and which smacks the mixture with serious enthusiam, thereby generating much more shock and macro turbulance, as compared to the little dished tops in the B230F.

It's not a $ thing to me, the dometoped pistons are well within my budget, but I wonder just the same. I guess that ultimately the domes can provide a higher SCR, so their potential is greater from that reality, but if SCRs in the 10s is all one is after, maybe flattops are a good option??

Just thinking out loud,
John
jmclay is offline   Reply With Quote
Old 02-26-2007, 06:35 PM   #24
Stereophile33
Board Member
 
Stereophile33's Avatar
 
Join Date: Nov 2003
Location: Portland, OR
Default

plus the dome tops can bias the mixture to one side and actually take better advantage of the squish band.
Stereophile33 is offline   Reply With Quote
Old 02-27-2007, 01:00 AM   #25
klr142
Turbo, what?
 
klr142's Avatar
 
Join Date: May 2004
Location: OR
Default

Quote:
Originally Posted by Stereophile33 View Post
plus the dome tops can bias the mixture to one side and actually take better advantage of the squish band.
Please expand... Thanks.
klr142 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 04:39 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.