Combustion discussion
Jan 7, 2006, 04:42 PM
#31
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Originally Posted by ShaunSG
Adrian, you can read yourself into a ditch if you don't reference and combine it to more pratical approaches - which is what the top people in the industry do. Theory can only take you so far. For example, the guys who have an extreme grasp of fluid dynamics and lots of reasearch money still combine it with flowbench testing, swirl and tumble rigs, PPT and CFD. What do you know that the top guys don't?
Originally Posted by ShaunSG
This overconfidence is typical of engineers in training or fresh graduate engineers that have a general spirit of unwillingess to include actual and practical testing and work as a team and not alone.
I try very hard not to attack another person in an argument for the same reason I don't go around trying to justify my oppinions by telling people that I started college at twelve years old (I did). None of that makes ANY difference what-so-ever to the discussion, nor does it in any way justify ANY oppinion. The former is a logical fallacy known as "ad hominem" and the latter is "ad verecundiam". Implying that one should believe what "experts", or "top people", say simply by that fact alone is a logical fallacy and falls under the rubrick of ad verecundiam.
I am done with this thread and will not post any more in it, which I'm sure will please the rest of the "bandwagon". *sigh*
Jan 7, 2006, 06:39 PM
#32
Originally Posted by SaabTuner
Different vortices? Perhaps you're an FD major and I am not, but I have read my fair share of Fluid Dynamics (baroclinic generation forms, Rankine-Hugoniot jump condt. etc.) and it makes no sense to me that you'd have drastically different boundary layer properties. True the main vortex would "stick" to the piston if generated cleanly in swirl, but it could just stick to the cyllinder walls in tumble, depending on how it is generated. Because the primary vortex would be rotating in a different direction, the massflow currents around the boundary layers could be slightly, or dramatically, different, but it would depend on combustion chamber design and piston design as much as vortex angle.
If you really needed to "fix" something relating to swirl, you'll need to know exact swirl inclination, swirl ratio, and a whole host of other properties that you could not ever derive from merely a differentiation between "swirl" and "tumble". Aside from that, I originally intended only that the term "swirl" should be applied to all cases of swirling motion and that a more specific differentiation for most people would be merely an "intellectual excercise" since the difference is not meaningfull to most people.
So you wouldn't say that "tumble" is a form of spinning or swirling in a gas?
hahaha. They called it "maximum quench"? They didn't even change the quench at all; they changed the "squish". I guess that shows how well those terms are differentiated by "professionals".
You cannot change the cooling effect of the combustion chamber without either changing its temperature differential, coefficient of thermal conductivity, or surface area. They actually reduced the surface area, though the temperature differential might have increased. In either case, if the temperature differential increased, it was due to increased compression, not the quench pads since the differential would have increased across the entire piston surface.
I'm not saying that quench pads do not exist. I'm saying that they do not do any more "cooling" than the rest of the piston at a similar distance from the spark plug. Therefore, they do not do any more "quenching" than any other part of the piston. So they should be called squish pads and I will stand by that until I see some evidence that the "quench pads" do significantly more cooling than other areas of the piston, or even the head, at similar distances from the spark plug, already do.
But you know, we've spent so much time arguing about this. If we're not carefull, we're gonna get all mad and start hating on eachother. That's NOT what I wanted. I may be stubborn, and I refuse to back down without evidence, but I'm not trying to be an azz about it. I just don't agree. That's ALL.
So let's all sit back, get a few drinks, and enjoy being able to talk about this stuff in the first place.
Cheers,
-Adrian
If you really needed to "fix" something relating to swirl, you'll need to know exact swirl inclination, swirl ratio, and a whole host of other properties that you could not ever derive from merely a differentiation between "swirl" and "tumble". Aside from that, I originally intended only that the term "swirl" should be applied to all cases of swirling motion and that a more specific differentiation for most people would be merely an "intellectual excercise" since the difference is not meaningfull to most people.
So you wouldn't say that "tumble" is a form of spinning or swirling in a gas?
hahaha. They called it "maximum quench"? They didn't even change the quench at all; they changed the "squish". I guess that shows how well those terms are differentiated by "professionals".
You cannot change the cooling effect of the combustion chamber without either changing its temperature differential, coefficient of thermal conductivity, or surface area. They actually reduced the surface area, though the temperature differential might have increased. In either case, if the temperature differential increased, it was due to increased compression, not the quench pads since the differential would have increased across the entire piston surface.
I'm not saying that quench pads do not exist. I'm saying that they do not do any more "cooling" than the rest of the piston at a similar distance from the spark plug. Therefore, they do not do any more "quenching" than any other part of the piston. So they should be called squish pads and I will stand by that until I see some evidence that the "quench pads" do significantly more cooling than other areas of the piston, or even the head, at similar distances from the spark plug, already do.
But you know, we've spent so much time arguing about this. If we're not carefull, we're gonna get all mad and start hating on eachother. That's NOT what I wanted. I may be stubborn, and I refuse to back down without evidence, but I'm not trying to be an azz about it. I just don't agree. That's ALL.
So let's all sit back, get a few drinks, and enjoy being able to talk about this stuff in the first place.
Cheers,
-Adrian
certainly the meaning may not be of much significance to your common person... but the nomenclature and distinctions exist for a purpose. i see it as a convenience... but you don't see the same. i would say tumble is a type os spinning... it absolutely is... it's spinning normal to the piston... just as swirl is spinning parallel to the piston. they are equivalent... one is not within the other... cuz one has limitations the other doesn't and vice versa. just like how the normal to a surface can never be perpendicular to the surface... in a given vector space you need n amount of linearly independant basis vectors to describe the space, where n is the dimension of the space. and anything else can be described in linear combinations of these basis vectors. here we have a swirl space if you will... and one will be perpendicular in totality and one will be parallen in totatlity. everything in between is a combination of the two.
perhaps my idea of squish is different from yours... but squish is usually significant when there is a squish ring around the piston right? so that this "cavity" catches air and turbulates it while the piston moves nad then tosses it into the center of the cylinder through different kinds of spinning (as i will now call it for generality). if you have a flat piston... your squish is minimal as there is less to catch the air except for the area between the pison and the piston wall and the rin is what "catches" the air. i don't know why you're not adhereing to your previous definition of quench being the distance from the plug because in this "test" they would have defnitely changed that... both that and the squish if you would (by your definition of squish).
Jan 8, 2006, 05:45 AM
#33
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Adrian, I didn't mean to say you were against testing but that you lacked it. I'm sorry if you find it offensive that I think one should consider more strongly what the leaders in the industry are in agreement on - them having the brains, knowledge, testing.
I speak from the standpoint of a commoner as if I am talking to another (perhaps wrongfully since you may well be beyond a commoner - in fact you must be, having started college at 12). There is always the possibility that you may end up turning the industry upside down and set it right on its definitions of quench, and on detonation, etc. But from what I've observed, progression requires personal balance and network, not just pure brilliance. With all your brilliance you are far ahead of most as it is, but there are a couple of other essential qualities.
Remember the industry has no shortage of brilliant and balanced people. People with 5 PhDs by low 30s, etc. Organizations with huge resources that will spend millions to find a hundredth of a second. I cannot help but feel that in all their strength, that they would pass up anything at all, or accept error in anything that mattered.
Coming back to the possibility that you may be right and the entire industry (bandwagon) may be wrong, one is still left wondering why, when you can't find answers on an enthusiast forum, you don't search out a professional community and continue searching and discussing till you find answers. There are at least 2 english forums that could connect you to very good people. I believe one who is to eventually going to lead a tech revolution would possess some of this desire to connect with the right people in order to progress continually. Along with doing basics like fact finding on background rules on discussion topic, running numbers before speaking assertively on easily calculable kinematics, etc. All this is like the ABCs and yet here we are trying to talk about sentence structure - fringe inferring in an attempt to pick apart industry accepted truth.
Cheers
I speak from the standpoint of a commoner as if I am talking to another (perhaps wrongfully since you may well be beyond a commoner - in fact you must be, having started college at 12). There is always the possibility that you may end up turning the industry upside down and set it right on its definitions of quench, and on detonation, etc. But from what I've observed, progression requires personal balance and network, not just pure brilliance. With all your brilliance you are far ahead of most as it is, but there are a couple of other essential qualities.
Remember the industry has no shortage of brilliant and balanced people. People with 5 PhDs by low 30s, etc. Organizations with huge resources that will spend millions to find a hundredth of a second. I cannot help but feel that in all their strength, that they would pass up anything at all, or accept error in anything that mattered.
Coming back to the possibility that you may be right and the entire industry (bandwagon) may be wrong, one is still left wondering why, when you can't find answers on an enthusiast forum, you don't search out a professional community and continue searching and discussing till you find answers. There are at least 2 english forums that could connect you to very good people. I believe one who is to eventually going to lead a tech revolution would possess some of this desire to connect with the right people in order to progress continually. Along with doing basics like fact finding on background rules on discussion topic, running numbers before speaking assertively on easily calculable kinematics, etc. All this is like the ABCs and yet here we are trying to talk about sentence structure - fringe inferring in an attempt to pick apart industry accepted truth.
Cheers
Jan 8, 2006, 06:58 AM
#34
Any of you combustion chamber techies want to answer the question why mitsu abandonded the squish area on evo8 engines.
early 4g63 engines have a deck hieght of .065
evo8 4g63 engines have a deck height of .110
most engine builders prefer as little as .040-.030 squish
Are mitsu engineers stupid or do they know something we don't?
early 4g63 engines have a deck hieght of .065
evo8 4g63 engines have a deck height of .110
most engine builders prefer as little as .040-.030 squish
Are mitsu engineers stupid or do they know something we don't?
Jan 8, 2006, 09:09 AM
#35
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Where are you getting your numbers?
On the stock pistons for both early and late model 4G63..
What are the compression heights?
What are the dish or relief volumes ?
What are the gasket thicknesses?
Stock CRs?
Are the piston at zero deck?
On the stock pistons for both early and late model 4G63..
What are the compression heights?
What are the dish or relief volumes ?
What are the gasket thicknesses?
Stock CRs?
Are the piston at zero deck?
Jan 8, 2006, 02:22 PM
#36
Early pistons sit .015 below deck. EVO8 pistons sit .055 below deck. From my measurments.
DSM 89-94 7.8/1
DSM 95-99 8.5/1
EVO 1-9 8.8/1 (evo3 was 9.0/1)
DSM head gaskets compressed to around .042. EVO8 head gaskets compress to around .055.
EVO 8 pistons are nearly flat tops. Maybe 2-3cc dish volume. Dsm pistons had around 15cc dish on the early piston and around 10cc on the 8.5/1.
Chamber volume on dsm was 47cc, evo8 is a tad smaller at 45-46cc.
DSM 89-94 7.8/1
DSM 95-99 8.5/1
EVO 1-9 8.8/1 (evo3 was 9.0/1)
DSM head gaskets compressed to around .042. EVO8 head gaskets compress to around .055.
EVO 8 pistons are nearly flat tops. Maybe 2-3cc dish volume. Dsm pistons had around 15cc dish on the early piston and around 10cc on the 8.5/1.
Chamber volume on dsm was 47cc, evo8 is a tad smaller at 45-46cc.
Jan 8, 2006, 02:30 PM
#37
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Thanks for the compression ratios, but I wanted compression heights as in distance from wrist pin bore centerline to piston deck as installed. After I get this last bit of information I might be able to give you some possibilities for large piston deck to head distance.
Jan 8, 2006, 04:22 PM
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the lower deck/installed height is to acheive the desired CR (8.8:1), with a smaller chamber and less piston dish you need to gain volume somewhere.
i dont think you need squish areas when there is enough tumble from the cyl heads, squish areas are just there to increase mixture motion. I think with out them the combustion chamber is more resistant to detonation.
Im going to bet that the later evos have more tumble than the early ones.
also i think having a flat piston top helps with maintaining good flame travel verus having a dish or dome.
i dont think you need squish areas when there is enough tumble from the cyl heads, squish areas are just there to increase mixture motion. I think with out them the combustion chamber is more resistant to detonation.
Im going to bet that the later evos have more tumble than the early ones.
also i think having a flat piston top helps with maintaining good flame travel verus having a dish or dome.
Last edited by RFH; Jan 8, 2006 at 04:24 PM.
Jan 8, 2006, 05:52 PM
#40
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RFH,
Usually it isn't that simple. More dish can always be added to the piston unless its compression height is intentionally low or if there is a requirement for a very light piston to reduce loads. Both are usually found on engines that operate at higher RPM.
Tumble does mix in some ways but not in others like squish does. A lot of extremely well designed and performing pent roof 4V engines run tight squish.
Flame travel is good with a flat top but it is best with a profile that allows the flame front to propogate in all directions... which is a dish. There are many other factors involved in chamber design but talking strictly in terms of flame travel, a dished piston is best, followed by flat top, followed by domed or intruders of any kind.
Usually it isn't that simple. More dish can always be added to the piston unless its compression height is intentionally low or if there is a requirement for a very light piston to reduce loads. Both are usually found on engines that operate at higher RPM.
Tumble does mix in some ways but not in others like squish does. A lot of extremely well designed and performing pent roof 4V engines run tight squish.
Flame travel is good with a flat top but it is best with a profile that allows the flame front to propogate in all directions... which is a dish. There are many other factors involved in chamber design but talking strictly in terms of flame travel, a dished piston is best, followed by flat top, followed by domed or intruders of any kind.
Jan 8, 2006, 05:57 PM
#41
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Originally Posted by 4G63Rules
dsm compression height is 1.375
evo is 1.320 or 1.325
evo is 1.320 or 1.325
Jan 9, 2006, 07:48 PM
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shaun
you have some very good points, and i think you are right but i have a couple questions/comments.
1. you can run tighter squish in a NA engine than a TC, so yes i can see that and i think you would want to run as tight of a squish area w/o causing much detonation.
2.So my assumption is that they run huge squish clearance for detonation resistance becasue of the big cyl pressure of the Turbo and/or its to lower the over all turbulence/tumble because the increased mass flow from the turbo adds an increasing amount of energy to the flow and thus increases the mixture motion to a point which causes unstable combustion.
you have some very good points, and i think you are right but i have a couple questions/comments.
1. you can run tighter squish in a NA engine than a TC, so yes i can see that and i think you would want to run as tight of a squish area w/o causing much detonation.
2.So my assumption is that they run huge squish clearance for detonation resistance becasue of the big cyl pressure of the Turbo and/or its to lower the over all turbulence/tumble because the increased mass flow from the turbo adds an increasing amount of energy to the flow and thus increases the mixture motion to a point which causes unstable combustion.
Jan 10, 2006, 07:20 PM
#43
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Originally Posted by RFH
1. you can run tighter squish in a NA engine than a TC
So my assumption is that they run huge squish clearance for detonation resistance becasue of the big cyl pressure of the Turbo
or its to lower the over all turbulence/tumble because the increased mass flow from the turbo adds an increasing amount of energy to the flow and thus increases the mixture motion to a point which causes unstable combustion.
Thanks for the numbers you've provided. The only possibility I can come up with right now is perhaps HC reductions from running less squish at stockish power levels and cyl pressures. I may be able to come up with more when the weekend comes round. I haven't been able to give this much time - been very busy the past week.
All I know is that squish area is very important to racing engines both NA and forced inducted. I wish I knew more about OEM considerations in this area and what the effects of squish and quench are like at these much reduced specific outputs.
In the meantime... thanks for the ideas and if you have any more of them let's hear.
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