You still haven't told me where you went to school, what kind of degree you got, or what your experience is. Till then, I will side with the other guy's website.
And it seems like you aren't a native English speaker, so I will pardon your demeanor on that account.
Re-Tuning G35 engines to run on lower Octane
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smockers83
- Posts: 3889
- Joined: Sat Oct 28, 2006 12:07 pm
- Car: 2006 G35 Coupe
Re: Just a reminder... (adren77)
I think (personally) a better way to describe higher octane gas--it has more of a controlled burn than a lower octane.
Re: Just a reminder... (Sentientbydesign)
Sentientbydesign and others who want to know:
First of all, when a clutch is clamped to a flywheel, they are both considered a single walled solid. At this point, you technically have only 2 surfaces (two outer surfacs). While the thermal conductivity of the clutch and the flywheel are slightly different because of the porous nature of the clutch material and the solid metal of the flywheel, and also there thicknesses, in engineering terms, when clamped together, they are considered a single piece of material wall, since both materials are expected to spin at the same RPM. However, both materials are technically different but expected to function as a single unit.
However, the heat from the engine heats up both materials. Thus, when both materials are clamped together, the flywheel will accumulate slightly more heat than the clutch because the thermal conductivity of the flywheel is usually higher than that of the clutch. This is why your clutch is made of a material that naturally does not conduct as much heat as the flywheel, while some level of grip is sacrificed, thus leading to potentially to slipping. There are better materials than the materials used in making your clutch. But the engineers have to consider how much heat that material can absorb and dissipate before the clutch starts to fail. This is why your clutch is made of an asbstos type material that is less prone ot heat absorption and quick to heat dissipation. Ceramic materials are even better, but they are expensive. Ceramic means clay. Clay is a good conductor and dissipator of heat.
In the process of the clutch and flywheel spinning, the linear expansivity of the flywheel will be greater than that of the clutch, thus increasing its surface area for more heat accumulation, while the surface area of your clutch isn't as affected because of the relatively lower thermal conductivity of the clutch material. Your flywheel does expand as a result of heat absorption, but your clutch does so only in smaller amounts.
When the flywheel and the clutch are clamped together, on either side of the flywheel and the clutch system walls, you have a thin wall of air on both sides. That thin wall of air is called a thermal boundary layer.
The rate of heat transfer per unit area, called the heat flux on the side of the flywheel is usually slower and less than the heat flux on the side of the clutch. And according to Fourier's law, which is dq/da = -k dt/dn, heat will move from a region of a hotter surface to a region of a colder surface. Assume the surface of the flywheel to be isothermal regardless of the heat it is absorbing from the engine, for ease of understanding.
Thus, the heat flux on the side of the clutch system, as a result of the heat transfer from the flywheel to the clutch system, based on Fouriers law, increases the temperature gradient of the air at the thermal boundaries on either side of the clutch and the flywheel.
This heat gradient in addition to the heat continuously generated by the engine, causes expansion of the surface area of the flywheel and the clutch, thus reducing grip and clutch reliability---this is what partly leads to slipping of the clutch. Slipping is accelerated under these conditions if the clutch is not fully depressed or fully engaged. Clutches don't slip by themselves, they do so slip as a result of improper engagement or disengagement in addition to the effects of temperature on the flywheel and the clutch material itself. During this phenomenon, the porous material of your clutch will tend to disintegrate, which is what causes the burnt clutch smell. Slippage may not have occured at that time. However, this process is a precursor to slippage.
Thus, in order to reduce slippage or the potential for slippage, a third thermal boundary has to be introduced. That thermal boundary is in between the clutch system and the flywheel when they are disengaged. It is a small area for the air. Air will fill up any area if a vacum does not exist. However, what is important is that the small area contributes another area for further heat transfer away from either the cluth material or flywheel, from a region of cold to a region of warmth, according to Fouriers law.
During this period, the air inside and close to the walls of the bell housing which covers the flywheel and the clutch system, are touching the bell housing metal, and consequently loosing heat by conduction to the bell housing, while air on the outside and close to the bell housing, is absorbing the heat being conducted by the bell housing. All this is happening as the engine continues to generate more heat.
Thus, the air in side and close to the bell housing gets cooler and returns to the clutch system and flywheel by convection to absorb more heat to be transferred outwards through the bell housing. This is why the bell housing is made of a material which has a higher thermal conductivity than the cast iron used in making many flywheels. This material has to be able to dissipate heat very fast. Cast iron is also cheaper to make.
The more a thermal boundary is introduced close to the gripping surfaces of the flywheel and clutch system, the better heat can be transferred from the clutch, and the less damage you do to your clutch, assuming the clutch is operated porperly.
The clutch is subject to heat impact. And because a clutch is made up of a porous material, the dust form the clutch in an enclosed chamber can actually ignite on its own. When you have an enclosed space with powdery substances, explosions are common, especially if you don't have an efffective ventilator. This is what led to the recent explosion of a sugar factory in Savannah Georgia. Thus, among one of many reasons why clutches can ignite on their own, without explanation and forewarning. Much of the heat from a clutch does not come from its spining with the flywheel. Much of its heat comes from the engine. And to reduce this heat, you will have to increase the surface area for cooler air to come in contact with the clutch and flywheel, no matter how small the area. Thus, the reason to disenage the clutch from the flywheel for a few seconds.
When a clutch is clamped to a flywheel you effectively have only two surface (outer surfaces) areas for heat to be effectively dissipated by the air. When you disengage the clutch from the flywheel, you increase the surface area for heat dissipation to four (two inner surfaces and two outer surfaces), and your Fouriers law holds in this case because, the heated surfaces of the clutch and flywheel automatically is absorbed by the air in between the two surfaces, thus reducing the possibility of slip from heated surfaces.
As you will recall, I drive very hard, so my car will generate more heat than those who drive normally. Thus, the burnt clutch smell I had earlier noted. Burnt clutch smell does not mean slippage is occuring. It means that the condition for slippage is ripe, that is if you ride your clutch or engage or disengage your clutch improperly.
It should also be noted that the temperature differences we are talking about maybe as small as 1 degree celsius or less. However, that is enough to make a difference in the linear expansivity of the clutch since it has a lower thermal conductivity than the flywheel.
If you have any questions regarding this information, please let me know.
First of all, when a clutch is clamped to a flywheel, they are both considered a single walled solid. At this point, you technically have only 2 surfaces (two outer surfacs). While the thermal conductivity of the clutch and the flywheel are slightly different because of the porous nature of the clutch material and the solid metal of the flywheel, and also there thicknesses, in engineering terms, when clamped together, they are considered a single piece of material wall, since both materials are expected to spin at the same RPM. However, both materials are technically different but expected to function as a single unit.
However, the heat from the engine heats up both materials. Thus, when both materials are clamped together, the flywheel will accumulate slightly more heat than the clutch because the thermal conductivity of the flywheel is usually higher than that of the clutch. This is why your clutch is made of a material that naturally does not conduct as much heat as the flywheel, while some level of grip is sacrificed, thus leading to potentially to slipping. There are better materials than the materials used in making your clutch. But the engineers have to consider how much heat that material can absorb and dissipate before the clutch starts to fail. This is why your clutch is made of an asbstos type material that is less prone ot heat absorption and quick to heat dissipation. Ceramic materials are even better, but they are expensive. Ceramic means clay. Clay is a good conductor and dissipator of heat.
In the process of the clutch and flywheel spinning, the linear expansivity of the flywheel will be greater than that of the clutch, thus increasing its surface area for more heat accumulation, while the surface area of your clutch isn't as affected because of the relatively lower thermal conductivity of the clutch material. Your flywheel does expand as a result of heat absorption, but your clutch does so only in smaller amounts.
When the flywheel and the clutch are clamped together, on either side of the flywheel and the clutch system walls, you have a thin wall of air on both sides. That thin wall of air is called a thermal boundary layer.
The rate of heat transfer per unit area, called the heat flux on the side of the flywheel is usually slower and less than the heat flux on the side of the clutch. And according to Fourier's law, which is dq/da = -k dt/dn, heat will move from a region of a hotter surface to a region of a colder surface. Assume the surface of the flywheel to be isothermal regardless of the heat it is absorbing from the engine, for ease of understanding.
Thus, the heat flux on the side of the clutch system, as a result of the heat transfer from the flywheel to the clutch system, based on Fouriers law, increases the temperature gradient of the air at the thermal boundaries on either side of the clutch and the flywheel.
This heat gradient in addition to the heat continuously generated by the engine, causes expansion of the surface area of the flywheel and the clutch, thus reducing grip and clutch reliability---this is what partly leads to slipping of the clutch. Slipping is accelerated under these conditions if the clutch is not fully depressed or fully engaged. Clutches don't slip by themselves, they do so slip as a result of improper engagement or disengagement in addition to the effects of temperature on the flywheel and the clutch material itself. During this phenomenon, the porous material of your clutch will tend to disintegrate, which is what causes the burnt clutch smell. Slippage may not have occured at that time. However, this process is a precursor to slippage.
Thus, in order to reduce slippage or the potential for slippage, a third thermal boundary has to be introduced. That thermal boundary is in between the clutch system and the flywheel when they are disengaged. It is a small area for the air. Air will fill up any area if a vacum does not exist. However, what is important is that the small area contributes another area for further heat transfer away from either the cluth material or flywheel, from a region of cold to a region of warmth, according to Fouriers law.
During this period, the air inside and close to the walls of the bell housing which covers the flywheel and the clutch system, are touching the bell housing metal, and consequently loosing heat by conduction to the bell housing, while air on the outside and close to the bell housing, is absorbing the heat being conducted by the bell housing. All this is happening as the engine continues to generate more heat.
Thus, the air in side and close to the bell housing gets cooler and returns to the clutch system and flywheel by convection to absorb more heat to be transferred outwards through the bell housing. This is why the bell housing is made of a material which has a higher thermal conductivity than the cast iron used in making many flywheels. This material has to be able to dissipate heat very fast. Cast iron is also cheaper to make.
The more a thermal boundary is introduced close to the gripping surfaces of the flywheel and clutch system, the better heat can be transferred from the clutch, and the less damage you do to your clutch, assuming the clutch is operated porperly.
The clutch is subject to heat impact. And because a clutch is made up of a porous material, the dust form the clutch in an enclosed chamber can actually ignite on its own. When you have an enclosed space with powdery substances, explosions are common, especially if you don't have an efffective ventilator. This is what led to the recent explosion of a sugar factory in Savannah Georgia. Thus, among one of many reasons why clutches can ignite on their own, without explanation and forewarning. Much of the heat from a clutch does not come from its spining with the flywheel. Much of its heat comes from the engine. And to reduce this heat, you will have to increase the surface area for cooler air to come in contact with the clutch and flywheel, no matter how small the area. Thus, the reason to disenage the clutch from the flywheel for a few seconds.
When a clutch is clamped to a flywheel you effectively have only two surface (outer surfaces) areas for heat to be effectively dissipated by the air. When you disengage the clutch from the flywheel, you increase the surface area for heat dissipation to four (two inner surfaces and two outer surfaces), and your Fouriers law holds in this case because, the heated surfaces of the clutch and flywheel automatically is absorbed by the air in between the two surfaces, thus reducing the possibility of slip from heated surfaces.
As you will recall, I drive very hard, so my car will generate more heat than those who drive normally. Thus, the burnt clutch smell I had earlier noted. Burnt clutch smell does not mean slippage is occuring. It means that the condition for slippage is ripe, that is if you ride your clutch or engage or disengage your clutch improperly.
It should also be noted that the temperature differences we are talking about maybe as small as 1 degree celsius or less. However, that is enough to make a difference in the linear expansivity of the clutch since it has a lower thermal conductivity than the flywheel.
If you have any questions regarding this information, please let me know.
Re: Just a reminder... (adren77)
I'll clarify more. Higher octane has a higher activation energy for combustion. That means it takes more heat and pressure to initiate combustion combustion with a higher octane fuel than with a lower octane fuel. Its "resistance to burn" and "resistance to self ignition" stem from that.adren77 wrote:
I figured I'd clarify this a bit. Higher octane is not more resistant to burn, but rather more "resistant" to self ignition.
Everything else you said was spot on, imo.
Re: Just a reminder... (Jacko3)
Sentientbydesign:
In addition, the flow of heat out of both material is governed by the equation:
Rate = temperature drop/resisitance to heat flow. The thickker the material, the higher the resistance to heat flow.
Thus the resistance to heat flow outwards from the clutch and the flywheel clamped together is the total resistances form either material. Again, this is under a steady state conduction.
The equation for an unsteady state heat flow outwarss is a lot more complex.
I hope this helps.
In addition, the flow of heat out of both material is governed by the equation:
Rate = temperature drop/resisitance to heat flow. The thickker the material, the higher the resistance to heat flow.
Thus the resistance to heat flow outwards from the clutch and the flywheel clamped together is the total resistances form either material. Again, this is under a steady state conduction.
The equation for an unsteady state heat flow outwarss is a lot more complex.
I hope this helps.
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smockers83
- Posts: 3889
- Joined: Sat Oct 28, 2006 12:07 pm
- Car: 2006 G35 Coupe
Re: Just a reminder... (Jacko3)
PARTY!!! We did it! We finally have an intelligent conversation happening.
Thanks a lot Jacko...good info in one spot, so much easier to understand. Now I finally feel like I know what you've been trying to say all along.
So does this mean we can delete the last 5 pages or so and just start over with this and C-Kwik's stuff--do a little clean up on aisle 5? Know what I sayin?
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!979TransAm
- Posts: 47
- Joined: Tue Jan 22, 2008 9:07 am
Re: Just a reminder... (smockers83)
we did get a better explained answer. Unfortunately I still disagree with it. But oh well you tried. The whole clutch not properly being engaged thing is what many of us screamed here. I also have to question the amount of heat actually generated. I mean hot enough to ignite aspestos replacement materials?? I've taken oxygen-acetelyne torches to such substances with no more than blackening. Specially considering the water in our vehicles peaks at 220 degrees.
A PROPERLY ADJUSTED CLUTCH AT HIGHER SPEEDS WILL NOT SLIP (unless coaxed to by hard driving), THERE IS NO WAY THE EXPANSION IS GREAT ENOUGH OR FREQUENT ENOUGH TO GENERATE ENOUGH HEAT TO BURN A CLUTCH.
The thermal conductivity of a metal flywheel and ceramic clutch are not close. metal quickly conducts heat where as the ceramic material absorbs heat slowly and disperse heat. The differences in their surfaces are what allows them to stick. Try putting a metal flywheel against a metal clutch, the force needed to stick the two together and not slip would be ridiculous. The porus surface of a clutch allows it to bite, and clutches as they wear have a consistent porus surface throughout.
you also say the lower thermal conductive clutch material expands over the very conductive metal flywheel???
What school did you go to and what major?? honestly curious
A PROPERLY ADJUSTED CLUTCH AT HIGHER SPEEDS WILL NOT SLIP (unless coaxed to by hard driving), THERE IS NO WAY THE EXPANSION IS GREAT ENOUGH OR FREQUENT ENOUGH TO GENERATE ENOUGH HEAT TO BURN A CLUTCH.
The thermal conductivity of a metal flywheel and ceramic clutch are not close. metal quickly conducts heat where as the ceramic material absorbs heat slowly and disperse heat. The differences in their surfaces are what allows them to stick. Try putting a metal flywheel against a metal clutch, the force needed to stick the two together and not slip would be ridiculous. The porus surface of a clutch allows it to bite, and clutches as they wear have a consistent porus surface throughout.
you also say the lower thermal conductive clutch material expands over the very conductive metal flywheel???
What school did you go to and what major?? honestly curious
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W661335PF
- Posts: 247
- Joined: Sat Dec 08, 2007 5:29 pm
- Car: 2004 G35 sport sedan-- Mod money goes to 401K
Re: Just a reminder... (!979TransAm)
This all reminds of the question asked by the 6 year old boy:
Boy: "Mommy.... where do babies come from?"
Parent: "Well son, the ovary is an oval shaped, egg producing organ in females. It measures approximately 3 cm x 1.5 cm x 1.5 cm. The ovary (for a given side) is located in the lateral wall of the pelvis in a region called the ovarian fossa. The fossa usually lies beneath the external iliac artery and in front of the ureter and the internal iliac artery........."
DAVGREG-- you still with us????? Just use the recommended 91 from the manual and don't play with the grade until you're very comfortable in what you're doing. Good Luck my friend!
Boy: "Mommy.... where do babies come from?"
Parent: "Well son, the ovary is an oval shaped, egg producing organ in females. It measures approximately 3 cm x 1.5 cm x 1.5 cm. The ovary (for a given side) is located in the lateral wall of the pelvis in a region called the ovarian fossa. The fossa usually lies beneath the external iliac artery and in front of the ureter and the internal iliac artery........."
DAVGREG-- you still with us????? Just use the recommended 91 from the manual and don't play with the grade until you're very comfortable in what you're doing. Good Luck my friend!
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SVTCOBRA
- Posts: 6046
- Joined: Wed Sep 03, 2003 2:26 am
- Car: 2018 Q60 AWD 2023 F150 4x4 5.0 FX4
- Location: LKN NC
Re: Just a reminder... (G_whizz)
Then, blue it is!!!G_whizz wrote:Yes... red is recommended... the blue one may make you happy in the pants!!
seven pages.....is this what my engineering room mate went thru back in college??? If so, I'm glad I stuck with math & computer science.
Lot of information, unfortunately, I would not begin to know what to believe. But, it might inspire me to do a little research........or not.
Continue on...
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SVTCOBRA
- Posts: 6046
- Joined: Wed Sep 03, 2003 2:26 am
- Car: 2018 Q60 AWD 2023 F150 4x4 5.0 FX4
- Location: LKN NC
Re: Just a reminder... (W661335PF)
yes,yes I agree! (actually, I use the 93 here)W661335PF wrote:DAVGREG-- you still with us????? Just use the recommended 91 from the manual and don't play with the grade until you're very comfortable in what you're doing. Good Luck my friend!
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W661335PF
- Posts: 247
- Joined: Sat Dec 08, 2007 5:29 pm
- Car: 2004 G35 sport sedan-- Mod money goes to 401K
Re: Just a reminder... (SVTCOBRA)
SVTCOBRA: No....No.... NO-- don't take the blue pill (it's generic name is BenzoClozafloraform HCL4), it's for folks with a psychotic disorder NOS!!! The side effect profile includes an increasing fondness for sheep! Take it from me, I'm a psychiatrist!SVTCOBRA wrote:
Then, blue it is!!!
seven pages.....is this what my engineering room mate went thru back in college??? If so, I'm glad I stuck with math & computer science.
Lot of information, unfortunately, I would not begin to know what to believe. But, it might inspire me to do a little research........or not.
Continue on...
Modified by W661335PF at 4:40 AM 2/13/2008
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telcoman
- Posts: 5762
- Joined: Sat Jul 08, 2006 11:30 am
- Car: Tesla 2022 Model Y, 2016 Q70 Bye 2012 G37S 6 MT w Nav 94444 mi bye 2006 Infiniti G35 Sedan 6 MT @171796 mi.
- Location: Central NJ
Re: Just a reminder... (Jacko3)
Jacko3
I enjoy reading your posts but I'm with some of the others here.Can you please provide:1- Citations as to where you are obtaining your information on heat transfer?2- Where you attended school?3- The degrees that you presently hold?
Physics was not one of my strengths when I was in school so I find your posts interesting. However, I have my doubts because of the way you present your arguments.
I base my argument on using regular unleaded gasoline based solely on my many years of driving experience, consumer reports, Tom & Ray on Car Talk, etc. For normal everyday driving, commuting etc and not pushing the vehicle I believe regular is fine. Others do not and I respect their opinions. Many find modifing their G's and spending all that money to obtain a few extra HP satisfying and I respect that & read those posts also even though I disagree and feel it is a waste of money. I am not going to argue with them but I have previously mentioned that money spent on mods would be better placed in a 401k for someone in their twenties that will grow substantially whether used for retirement, purchase of a first home, college education etc. Most young single people do not think of these things. I didn't when I was at that age.Back to the G.. sorryI have almost 50k miles on my G & it hasn't blown up yet from using regular 87 octane. Since many dealers seem to be filling the G's with regular, I haven't heard of any warranty issues cropping up over its use.
So Jacko3 let us know your sources on heat transfer?
Telcoman
I enjoy reading your posts but I'm with some of the others here.Can you please provide:1- Citations as to where you are obtaining your information on heat transfer?2- Where you attended school?3- The degrees that you presently hold?
Physics was not one of my strengths when I was in school so I find your posts interesting. However, I have my doubts because of the way you present your arguments.
I base my argument on using regular unleaded gasoline based solely on my many years of driving experience, consumer reports, Tom & Ray on Car Talk, etc. For normal everyday driving, commuting etc and not pushing the vehicle I believe regular is fine. Others do not and I respect their opinions. Many find modifing their G's and spending all that money to obtain a few extra HP satisfying and I respect that & read those posts also even though I disagree and feel it is a waste of money. I am not going to argue with them but I have previously mentioned that money spent on mods would be better placed in a 401k for someone in their twenties that will grow substantially whether used for retirement, purchase of a first home, college education etc. Most young single people do not think of these things. I didn't when I was at that age.Back to the G.. sorryI have almost 50k miles on my G & it hasn't blown up yet from using regular 87 octane. Since many dealers seem to be filling the G's with regular, I haven't heard of any warranty issues cropping up over its use.
So Jacko3 let us know your sources on heat transfer?
Telcoman
Re: Just a reminder... (telcoman)
Ok, since I have learned quite a bit here concerning heat transfer and conductivity, can someone now please explain how gravity works? I mean, if gravity is a force emitting from the earth, how can that force simultaneously "pull" an object back to earth? Seems to me the two actions (pushing/pulling) cannot happen at the same time....ah, I digress.
I'm glad I have an auto these days.
I'm glad I have an auto these days.
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W661335PF
- Posts: 247
- Joined: Sat Dec 08, 2007 5:29 pm
- Car: 2004 G35 sport sedan-- Mod money goes to 401K
Re: Just a reminder... (Beezer)
Consider this: did you know that the speed with which gravity propogates is equivalent to the speed of light? This is the latest gravity model that is now constraining so called string theory and the idea of multiple universes.Beezer wrote:Ok, since I have learned quite a bit here concerning heat transfer and conductivity, can someone now please explain how gravity works? I mean, if gravity is a force emitting from the earth, how can that force simultaneously "pull" an object back to earth? Seems to me the two actions (pushing/pulling) cannot happen at the same time....ah, I digress.
I'm glad I have an auto these days.
Now look at what you've done--- added one more tangent to this already confused thread.
Re: Just a reminder... (!979TransAm)
1979Transam:
You said, "A PROPERLY ADJUSTED CLUTCH AT HIGHER SPEEDS WILL NOT SLIP (unless coaxed to by hard driving), THERE IS NO WAY THE EXPANSION IS GREAT ENOUGH OR FREQUENT ENOUGH TO GENERATE ENOUGH HEAT TO BURN A CLUTCH.
The thermal conductivity of a metal flywheel and ceramic clutch are not close. metal quickly conducts heat where as the ceramic material absorbs heat slowly and disperse heat. The differences in their surfaces are what allows them to stick. Try putting a metal flywheel against a metal clutch, the force needed to stick the two together and not slip would be ridiculous. The porus surface of a clutch allows it to bite, and clutches as they wear have a consistent porus surface throughout.
you also say the lower thermal conductive clutch material expands over the very conductive metal flywheel???
1. I never said a clutch will slip at higher speeds. You have chosen to discover your own meaning in my words. Certainly, at higher speeds, a clutch will not slip. I don't know where you got that interpretation form my comments.
2. The exapnsion of heat related materials in moving objects were not designed to be significant enough for your eyes to see---you are looking at microscopic behaviors here. It is natural for humans to want to see expansion with the naked eyes, but in reality, that is not the case. A case in point is an aircraft fuselage, which does expand during flight as a result of the dynamic friction of the sheer forces of the air and the aluminum material used in making the aircraft fuselage. In flight, I doubt you will notice this expansion phenomenon occuring, but yet it is.
3. Expansion does not generate heat. Rather it is heat that generates expansion. Materials that expand temporarily loose some of their qualities by their nature. For example, meat cooked wil become tender. Add stress to that process, and it becomes obvious why deteriororation will occur. For example, pulverized cooked meat. In this case, it begins with a burning smell in a clutch. Heat not only produces a heat transfer process but it also transforms the property of substances. However, some substances, after cooling return to their original state. The bahvior is almost thermoplastic, eventhough the materials are not thermoplastic in nature.
4. I never said the thermal conductivity of a cermic clutch and the flywheel are the same. Again, you have choosen to read what you want from my comments. Of course, their thermal conductivities cannot be the same for two reasons (1) they are different materials (2) engineers would prefer to have one material dissipate heat faster than the other so that excess heat is not stored in both materials wne mated.
5. Yes, clutches have a constant porous surface. I did not say otherwise. Again, you have chosen to read what you may, from my comments.
6. Every type of material of clutch in the market expands with the flywheel while mated to the flywheel. The nature of materials is that they expand, especially when they absorb some heat form the engine. Engineers, thus, have to find that material that will expand wothout loosing its core charcteristics to a significant degree, and while taking costs into account. The better the heat transfer quality of a material, the more expensive it becomes.
I hope this helps. I never intedned to go into engineering terms here. But as most of you feel more explanantions are warranted. There you are. Read to your hearts delight. Don't confuse everyday mechanical knowledge with engineering concepts. Engineers are not mechanics, and mechanics are not engineers. I am not an engineer in practice. I also once said that I did not want to go into these complex explanations because most would not understand. And when people do not understand stuff, they default to what they are comfortable with.
Don't worry about the school I went to. I wish you would be fair enough to ask others the same question before you asked me. I don't remember reading any of your comments asking anyone else about their education and degrees. Why?
You said, "A PROPERLY ADJUSTED CLUTCH AT HIGHER SPEEDS WILL NOT SLIP (unless coaxed to by hard driving), THERE IS NO WAY THE EXPANSION IS GREAT ENOUGH OR FREQUENT ENOUGH TO GENERATE ENOUGH HEAT TO BURN A CLUTCH.
The thermal conductivity of a metal flywheel and ceramic clutch are not close. metal quickly conducts heat where as the ceramic material absorbs heat slowly and disperse heat. The differences in their surfaces are what allows them to stick. Try putting a metal flywheel against a metal clutch, the force needed to stick the two together and not slip would be ridiculous. The porus surface of a clutch allows it to bite, and clutches as they wear have a consistent porus surface throughout.
you also say the lower thermal conductive clutch material expands over the very conductive metal flywheel???
1. I never said a clutch will slip at higher speeds. You have chosen to discover your own meaning in my words. Certainly, at higher speeds, a clutch will not slip. I don't know where you got that interpretation form my comments.
2. The exapnsion of heat related materials in moving objects were not designed to be significant enough for your eyes to see---you are looking at microscopic behaviors here. It is natural for humans to want to see expansion with the naked eyes, but in reality, that is not the case. A case in point is an aircraft fuselage, which does expand during flight as a result of the dynamic friction of the sheer forces of the air and the aluminum material used in making the aircraft fuselage. In flight, I doubt you will notice this expansion phenomenon occuring, but yet it is.
3. Expansion does not generate heat. Rather it is heat that generates expansion. Materials that expand temporarily loose some of their qualities by their nature. For example, meat cooked wil become tender. Add stress to that process, and it becomes obvious why deteriororation will occur. For example, pulverized cooked meat. In this case, it begins with a burning smell in a clutch. Heat not only produces a heat transfer process but it also transforms the property of substances. However, some substances, after cooling return to their original state. The bahvior is almost thermoplastic, eventhough the materials are not thermoplastic in nature.
4. I never said the thermal conductivity of a cermic clutch and the flywheel are the same. Again, you have choosen to read what you want from my comments. Of course, their thermal conductivities cannot be the same for two reasons (1) they are different materials (2) engineers would prefer to have one material dissipate heat faster than the other so that excess heat is not stored in both materials wne mated.
5. Yes, clutches have a constant porous surface. I did not say otherwise. Again, you have chosen to read what you may, from my comments.
6. Every type of material of clutch in the market expands with the flywheel while mated to the flywheel. The nature of materials is that they expand, especially when they absorb some heat form the engine. Engineers, thus, have to find that material that will expand wothout loosing its core charcteristics to a significant degree, and while taking costs into account. The better the heat transfer quality of a material, the more expensive it becomes.
I hope this helps. I never intedned to go into engineering terms here. But as most of you feel more explanantions are warranted. There you are. Read to your hearts delight. Don't confuse everyday mechanical knowledge with engineering concepts. Engineers are not mechanics, and mechanics are not engineers. I am not an engineer in practice. I also once said that I did not want to go into these complex explanations because most would not understand. And when people do not understand stuff, they default to what they are comfortable with.
Don't worry about the school I went to. I wish you would be fair enough to ask others the same question before you asked me. I don't remember reading any of your comments asking anyone else about their education and degrees. Why?
Re: Just a reminder... (W661335PF)
haha....I figured I'd try and remove some of the monotony.
Re: Just a reminder... (telcoman)
Telcoman:
You said, "1- Citations as to where you are obtaining your information on heat transfer?2- Where you attended school?3- The degrees that you presently hold?
Physics was not one of my strengths when I was in school so I find your posts interesting. However, I have my doubts because of the way you present your arguments.
I base my argument on using regular unleaded gasoline based solely on my many years of driving experience, consumer reports, Tom & Ray on Car Talk, etc. For normal everyday driving, commuting etc and not pushing the vehicle I believe regular is fine. Others do not and I respect their opinions. Many find modifing their G's and spending all that money to obtain a few extra HP satisfying and I respect that & read those posts also even though I disagree and feel it is a waste of money. I am not going to argue with them but I have previously mentioned that money spent on mods would be better placed in a 401k for someone in their twenties that will grow substantially whether used for retirement, purchase of a first home, college education etc. Most young single people do not think of these things. I didn't when I was at that age.Back to the G.. sorryI have almost 50k miles on my G & it hasn't blown up yet from using regular 87 octane. Since many dealers seem to be filling the G's with regular, I haven't heard of any warranty issues cropping up over its use.
So Jacko3 let us know your sources on heat transfer?
___________________________________________________________
If you go back to read my previous comments, I agree with you that regular is just fine and it would not hurt anything. So, I am unsure what you are asking about. In that discussion, SentientbyDesign assisted me by pointing out that my argument was the other way around, and this wa because I was typing too fast, as you can observe form the many typos I have in my comments. Nonetheless, I came to the conclusion that 87 octane gas will not hurt your car at all, and that it is okay to use. Go back and read my comments again.
In addition, don't worry about the school I went to. I doubt it is relevant in this matter. I wish you had ask others this same question. I shall not revel my sources. Any good book on heat transfer will do justice to the explanations i provide. Mind you, these books are complex and hard to read. I hope this helps.
You said, "1- Citations as to where you are obtaining your information on heat transfer?2- Where you attended school?3- The degrees that you presently hold?
Physics was not one of my strengths when I was in school so I find your posts interesting. However, I have my doubts because of the way you present your arguments.
I base my argument on using regular unleaded gasoline based solely on my many years of driving experience, consumer reports, Tom & Ray on Car Talk, etc. For normal everyday driving, commuting etc and not pushing the vehicle I believe regular is fine. Others do not and I respect their opinions. Many find modifing their G's and spending all that money to obtain a few extra HP satisfying and I respect that & read those posts also even though I disagree and feel it is a waste of money. I am not going to argue with them but I have previously mentioned that money spent on mods would be better placed in a 401k for someone in their twenties that will grow substantially whether used for retirement, purchase of a first home, college education etc. Most young single people do not think of these things. I didn't when I was at that age.Back to the G.. sorryI have almost 50k miles on my G & it hasn't blown up yet from using regular 87 octane. Since many dealers seem to be filling the G's with regular, I haven't heard of any warranty issues cropping up over its use.
So Jacko3 let us know your sources on heat transfer?
___________________________________________________________
If you go back to read my previous comments, I agree with you that regular is just fine and it would not hurt anything. So, I am unsure what you are asking about. In that discussion, SentientbyDesign assisted me by pointing out that my argument was the other way around, and this wa because I was typing too fast, as you can observe form the many typos I have in my comments. Nonetheless, I came to the conclusion that 87 octane gas will not hurt your car at all, and that it is okay to use. Go back and read my comments again.
In addition, don't worry about the school I went to. I doubt it is relevant in this matter. I wish you had ask others this same question. I shall not revel my sources. Any good book on heat transfer will do justice to the explanations i provide. Mind you, these books are complex and hard to read. I hope this helps.
Re: Just a reminder... (telcoman)
Telcoman:
Let me add that so far, I am amazed at the speed and lack of judgement posed by many on this forum, as they quickly take sides with knowledge they are comfortable with, rather than knowledge that they perceive as unusual?
Because it takes two to tango, it would seem fair to suggest that either the reader did not understand my previous comments or that the writer did not do a great job of explaining themselves well. Well, to my dismay, many have chosen to beleive that I may not have explained myself properly, when in fact, all I am saying is rehatching the same thing in a different light.
There was no need for me to go this in depth to explain a phenomenon. It was totally pointless. So, how many people truely understand the phenomenon I have explained? How many people will remember these engineering behaviors while they drive? I just wanted to have a simple discussion simply because i did not want to go that in depth with advanced epxlanations. Thius forum ahs awoken my senses a greta deal, and i will be less forgiving of anyone who explains trashy science on this forum.
But I still thank you for enjoying my comments. They are unusuaul, as it is with many engineering concepts. So, i don't expect many to understand them at all, at least not now.
Let me add that so far, I am amazed at the speed and lack of judgement posed by many on this forum, as they quickly take sides with knowledge they are comfortable with, rather than knowledge that they perceive as unusual?
Because it takes two to tango, it would seem fair to suggest that either the reader did not understand my previous comments or that the writer did not do a great job of explaining themselves well. Well, to my dismay, many have chosen to beleive that I may not have explained myself properly, when in fact, all I am saying is rehatching the same thing in a different light.
There was no need for me to go this in depth to explain a phenomenon. It was totally pointless. So, how many people truely understand the phenomenon I have explained? How many people will remember these engineering behaviors while they drive? I just wanted to have a simple discussion simply because i did not want to go that in depth with advanced epxlanations. Thius forum ahs awoken my senses a greta deal, and i will be less forgiving of anyone who explains trashy science on this forum.
But I still thank you for enjoying my comments. They are unusuaul, as it is with many engineering concepts. So, i don't expect many to understand them at all, at least not now.
Re: Just a reminder... (smockers83)
Smocker83 and Adren77:
I was fairly disappointed with your earlier comments. I cannot but believe that you both took sides at the slightest opportunity. What is one to read from your comments--fairness and objectivity or bias? No one's explanation should ever make anyone take sides at any time or at any moment. I cannot stop you both from taking sides but I can observe with great interest and intent, in this forum at this type of behavior.
I was fairly disappointed with your earlier comments. I cannot but believe that you both took sides at the slightest opportunity. What is one to read from your comments--fairness and objectivity or bias? No one's explanation should ever make anyone take sides at any time or at any moment. I cannot stop you both from taking sides but I can observe with great interest and intent, in this forum at this type of behavior.
Re: Just a reminder... (Jacko3)
C-Kwik,
i want to congratulate you for avoiding the personal attacks. it seems others can only resort to them (attacks) when they repeatedly fail to backup their claims. good work!
troy
Modified by redhed at 7:02 AM 2/13/2008
i want to congratulate you for avoiding the personal attacks. it seems others can only resort to them (attacks) when they repeatedly fail to backup their claims. good work!
troy
Modified by redhed at 7:02 AM 2/13/2008
Re: Just a reminder... (redhed)
C-Kwik is good people! He is HIGHLY respected among the admins and users alike. He used to own a G35, until he bought a titan...so even as a non-G35 owner, he visits this forum to offer advice. Believe me, if the attacks were to get too personal (over the line comments), I would have locked this thread and issued vacations...redhed wrote:C-Kwik,
i want to congratulate you for avoiding the personal attacks. it seems others can only resort to them (attacks) when they repeatedly fail to backup their claims. good work!
troy
Modified by redhed at 7:02 AM 2/13/2008
I too have enjoyed this thread as cars, physics, and engineering are interesting to me.
Re: Just a reminder... (Beezer)
I thought it was a reference to the Matrix.Beezer wrote:haha....I figured I'd try and remove some of the monotony.
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Sentientbydesign
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Re: Just a reminder... (SVTCOBRA)
Jacko:
Excellent presentation. I agree with all of it up to the point at which you say that engine heat will overheat the clutch material and cause slippage while the clutch is engaged.
The situation you presented is definately possible, I just question how realistic the situation is. It is common for theoretical models to have significant deviation from their physical counterparts.
I also, have never heard of spotaneous combustion of clutch dust, but since the basis for my belief is directly dependent upon my exposure to car fires, I'll concede that portion of my disbelief.
Excellent presentation. I agree with all of it up to the point at which you say that engine heat will overheat the clutch material and cause slippage while the clutch is engaged.
The situation you presented is definately possible, I just question how realistic the situation is. It is common for theoretical models to have significant deviation from their physical counterparts.
I also, have never heard of spotaneous combustion of clutch dust, but since the basis for my belief is directly dependent upon my exposure to car fires, I'll concede that portion of my disbelief.
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!979TransAm
- Posts: 47
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Re: Just a reminder... (rn79870)
Jacko don't be offended that i asked you where you attended school. I was actually just curious. I have no reason to ask anyone else because they are not posting complex theories on heat expansion.
I didnt twist your words at all, you said, "While the thermal conductivity of the clutch and the flywheel are SLIGHTLY different because of the porous nature of the clutch material and the solid metal of the flywheel" Slightly is a far cry from right. The thermal conductivity of clutch material and a metal flywheel are closer to oppisite, point being heat either one, which one conduct heat throughout?
Your point on the airplane is pretty irrelavant. Expansion on the fuselage is seen from pressure difference on the inside and the outside, nothing to do with heat. If heat were involved you would more likely see contraction becuase of cold tempatures at high altitudes. Unless your air plane was made of water which would expand as it became ice
"This heat gradient in addition to the heat continuously generated by the engine, causes expansion of the surface area of the flywheel and the clutch, thus reducing grip and clutch reliability---this is what partly leads to slipping of the clutch" Jacko said. The way you presented this lead me to believe you were contributing the "slipping/burning" clutch at high speeds because of your increased heat gradient idea.
The clutch material would take some very high tempatures to ignite, very high. So high i have to question if those tempatures could even be generated, if they could it would be during severe slipping, not from microscopic heating and expanding.
"All this is happening as the engine continues to generate more heat. " jacko said. The engine hits an operating tempature that is controled by the cooling system and lingers around that tempature, it doesnt continue to constantly increase.
I agree a little air will have an effect on cooling the clutch, but one so miniscule it is more likely just the fact disengaging the clutch that makes it cool.
I mentioned the porus surface of the clutch because it is very good at preventing slip and doesnt conduct heat quickly like metal. I didnt want people to think the clutch magically became like the metal flywheel beacuse of your intial statement "A single piece material wall"
I didnt twist your words at all, you said, "While the thermal conductivity of the clutch and the flywheel are SLIGHTLY different because of the porous nature of the clutch material and the solid metal of the flywheel" Slightly is a far cry from right. The thermal conductivity of clutch material and a metal flywheel are closer to oppisite, point being heat either one, which one conduct heat throughout?
Your point on the airplane is pretty irrelavant. Expansion on the fuselage is seen from pressure difference on the inside and the outside, nothing to do with heat. If heat were involved you would more likely see contraction becuase of cold tempatures at high altitudes. Unless your air plane was made of water which would expand as it became ice
"This heat gradient in addition to the heat continuously generated by the engine, causes expansion of the surface area of the flywheel and the clutch, thus reducing grip and clutch reliability---this is what partly leads to slipping of the clutch" Jacko said. The way you presented this lead me to believe you were contributing the "slipping/burning" clutch at high speeds because of your increased heat gradient idea.
The clutch material would take some very high tempatures to ignite, very high. So high i have to question if those tempatures could even be generated, if they could it would be during severe slipping, not from microscopic heating and expanding.
"All this is happening as the engine continues to generate more heat. " jacko said. The engine hits an operating tempature that is controled by the cooling system and lingers around that tempature, it doesnt continue to constantly increase.
I agree a little air will have an effect on cooling the clutch, but one so miniscule it is more likely just the fact disengaging the clutch that makes it cool.
I mentioned the porus surface of the clutch because it is very good at preventing slip and doesnt conduct heat quickly like metal. I didnt want people to think the clutch magically became like the metal flywheel beacuse of your intial statement "A single piece material wall"
Re: Just a reminder... (Sentientbydesign)
Sentient bydesign:
I should have said it a little differently. The engine does not overheat the clutch. Rather, the heat through linear expansion, expands the surface area and diameter of the clutch, much less than the expansion of the flywheel.
What happens in this situation is that the material on the clutch itself, which remains constant, is slightly stretch, so that it begins to reduce its grip in small amounts when in contact with tyhe flywheel.
A clutches grip design depends partly on the ratio of the diameter of the clutch to the diameter of the flywheel. Because both materials have different thermal conductivites and linear expansivities, both materials will expand in a non-linear ratio becuse of the different rate of heat absorption of their materials, thus, changing the ratio of the clutch diameter to the flywheel diameter. This is what ultimately causes slipping, in addition to poor clutch use.
Thanks for pointing this out and I hope this explanation is better.
I should have said it a little differently. The engine does not overheat the clutch. Rather, the heat through linear expansion, expands the surface area and diameter of the clutch, much less than the expansion of the flywheel.
What happens in this situation is that the material on the clutch itself, which remains constant, is slightly stretch, so that it begins to reduce its grip in small amounts when in contact with tyhe flywheel.
A clutches grip design depends partly on the ratio of the diameter of the clutch to the diameter of the flywheel. Because both materials have different thermal conductivites and linear expansivities, both materials will expand in a non-linear ratio becuse of the different rate of heat absorption of their materials, thus, changing the ratio of the clutch diameter to the flywheel diameter. This is what ultimately causes slipping, in addition to poor clutch use.
Thanks for pointing this out and I hope this explanation is better.
Re: Just a reminder... (rn79870)
you got it!!rn79870 wrote:
I thought it was a reference to the Matrix.
Re: Just a reminder... (!979TransAm)
1979transam: You said,
"Jacko don't be offended that i asked you where you attended school. I was actually just curious. I have no reason to ask anyone else because they are not posting complex theories on heat expansion.I didnt twist your words at all, you said, "While the thermal conductivity of the clutch and the flywheel are SLIGHTLY different because of the porous nature of the clutch material and the solid metal of the flywheel" Slightly is a far cry from right. The thermal conductivity of clutch material and a metal flywheel are closer to oppisite, point being heat either one, which one conduct heat throughout?
Your point on the airplane is pretty irrelavant. Expansion on the fuselage is seen from pressure difference on the inside and the outside, nothing to do with heat. If heat were involved you would more likely see contraction becuase of cold tempatures at high altitudes. Unless your air plane was made of water which would expand as it became ice
"This heat gradient in addition to the heat continuously generated by the engine, causes expansion of the surface area of the flywheel and the clutch, thus reducing grip and clutch reliability---this is what partly leads to slipping of the clutch" Jacko said. The way you presented this lead me to believe you were contributing the "slipping/burning" clutch at high speeds because of your increased heat gradient idea.
The clutch material would take some very high tempatures to ignite, very high. So high i have to question if those tempatures could even be generated, if they could it would be during severe slipping, not from microscopic heating and expanding.
"All this is happening as the engine continues to generate more heat. " jacko said. The engine hits an operating tempature that is controled by the cooling system and lingers around that tempature, it doesnt continue to constantly increase.
I agree a little air will have an effect on cooling the clutch, but one so miniscule it is more likely just the fact disengaging the clutch that makes it cool.
I mentioned the porus surface of the clutch because it is very good at preventing slip and doesnt conduct heat quickly like metal. I didnt want people to think the clutch magically became like the metal flywheel beacuse of your intial statement "A single piece material wall"
------------------------------------------------------------------------------------------------
1. I am not offended because, at least, you recognized I could be offended. So, i think that is a good trait. I appreciate this!
2. I used the word "slightly" because I was trying to show the difference between pulverized material that has been put together by a bonding agent (clutch) and a piece of metal (fly wheel) which is a product of processed Iron III Oxide. A clutch surface is simply dusty material bonded together under pressure and heat treated, to keep it together, while cast iron is simply cooled liquid metal. Yes, their conductivities are way apart than I had suggested.
3. I was once worked on aircrafts and every cable and screw on an aircraft is temperature sensitive. When working on aircrafts, we use tons of temperature related charts to determine adjustments to be made to flight surfaces. Pilots use similar information to determine how much to extend flight surfaces with changing temperature. Pressure is only a secondary force a plane may experience. In fact, in flight, an aircraft absorbs heat by conduction through the air molecules friction with the aircraft fuselage and through radiation form the sun. The higher you are, the more radiation you wil absorb. try touching an aircrafts fuselage immediately after landing---you will notice it is slightly warm. The pressure difference between the interior and exterior of an aircraft, is only as effective as the exapansion that has already occured outside of the eye's visibility. Thus, aircraft inspectors have to thoroughly inspect aircrafts for cracks. I don't remember seeing the inspectors inspect an aircraft for pressure effects on the fuselage. I used the aircraft analogy to demonstrate how haet conduction and convection can occur at any heigth in the atmosphere.
4. You said, ".....i have to question if those tempatures could even be generated, if they could it would be during severe slipping, not from microscopic heating and expanding." You are right to the extent that the vehicle is properly maintained. A vehicle that is not well maintained as a result of a lack of changing the oil religiously, or a fouling of the inner engine wall cooling heat exchange surfaces as a result of not changing your cooling fluids as specified, will cause the engine to generate more heat than it was designed for. Every engine can tolerate more heat than the cooling sytem is designed for. However, it degrades the life span of your engine, and sends more heat than is necessary to parts that have been designed to wear out with time such as the clutch system.
This is enough heat to aid in the process of an explosion of small microscopic matter. Microscopic matter does not explode from the heat. They explode from their creation of electric charges within the atmosphere of their creation inside the bell housing. The excess heat only aids in the creation of more microscopic matter by detioriorating the clutch more rapidly than normal. The explosion in the suger factory in Georgia from small particles, occured at night when it was actually cooler. This is another reason why auto manufacturers have to design clutches to erode slowly rather than quickly.
I hope this helps.
"Jacko don't be offended that i asked you where you attended school. I was actually just curious. I have no reason to ask anyone else because they are not posting complex theories on heat expansion.I didnt twist your words at all, you said, "While the thermal conductivity of the clutch and the flywheel are SLIGHTLY different because of the porous nature of the clutch material and the solid metal of the flywheel" Slightly is a far cry from right. The thermal conductivity of clutch material and a metal flywheel are closer to oppisite, point being heat either one, which one conduct heat throughout?
Your point on the airplane is pretty irrelavant. Expansion on the fuselage is seen from pressure difference on the inside and the outside, nothing to do with heat. If heat were involved you would more likely see contraction becuase of cold tempatures at high altitudes. Unless your air plane was made of water which would expand as it became ice
"This heat gradient in addition to the heat continuously generated by the engine, causes expansion of the surface area of the flywheel and the clutch, thus reducing grip and clutch reliability---this is what partly leads to slipping of the clutch" Jacko said. The way you presented this lead me to believe you were contributing the "slipping/burning" clutch at high speeds because of your increased heat gradient idea.
The clutch material would take some very high tempatures to ignite, very high. So high i have to question if those tempatures could even be generated, if they could it would be during severe slipping, not from microscopic heating and expanding.
"All this is happening as the engine continues to generate more heat. " jacko said. The engine hits an operating tempature that is controled by the cooling system and lingers around that tempature, it doesnt continue to constantly increase.
I agree a little air will have an effect on cooling the clutch, but one so miniscule it is more likely just the fact disengaging the clutch that makes it cool.
I mentioned the porus surface of the clutch because it is very good at preventing slip and doesnt conduct heat quickly like metal. I didnt want people to think the clutch magically became like the metal flywheel beacuse of your intial statement "A single piece material wall"
------------------------------------------------------------------------------------------------
1. I am not offended because, at least, you recognized I could be offended. So, i think that is a good trait. I appreciate this!
2. I used the word "slightly" because I was trying to show the difference between pulverized material that has been put together by a bonding agent (clutch) and a piece of metal (fly wheel) which is a product of processed Iron III Oxide. A clutch surface is simply dusty material bonded together under pressure and heat treated, to keep it together, while cast iron is simply cooled liquid metal. Yes, their conductivities are way apart than I had suggested.
3. I was once worked on aircrafts and every cable and screw on an aircraft is temperature sensitive. When working on aircrafts, we use tons of temperature related charts to determine adjustments to be made to flight surfaces. Pilots use similar information to determine how much to extend flight surfaces with changing temperature. Pressure is only a secondary force a plane may experience. In fact, in flight, an aircraft absorbs heat by conduction through the air molecules friction with the aircraft fuselage and through radiation form the sun. The higher you are, the more radiation you wil absorb. try touching an aircrafts fuselage immediately after landing---you will notice it is slightly warm. The pressure difference between the interior and exterior of an aircraft, is only as effective as the exapansion that has already occured outside of the eye's visibility. Thus, aircraft inspectors have to thoroughly inspect aircrafts for cracks. I don't remember seeing the inspectors inspect an aircraft for pressure effects on the fuselage. I used the aircraft analogy to demonstrate how haet conduction and convection can occur at any heigth in the atmosphere.
4. You said, ".....i have to question if those tempatures could even be generated, if they could it would be during severe slipping, not from microscopic heating and expanding." You are right to the extent that the vehicle is properly maintained. A vehicle that is not well maintained as a result of a lack of changing the oil religiously, or a fouling of the inner engine wall cooling heat exchange surfaces as a result of not changing your cooling fluids as specified, will cause the engine to generate more heat than it was designed for. Every engine can tolerate more heat than the cooling sytem is designed for. However, it degrades the life span of your engine, and sends more heat than is necessary to parts that have been designed to wear out with time such as the clutch system.
This is enough heat to aid in the process of an explosion of small microscopic matter. Microscopic matter does not explode from the heat. They explode from their creation of electric charges within the atmosphere of their creation inside the bell housing. The excess heat only aids in the creation of more microscopic matter by detioriorating the clutch more rapidly than normal. The explosion in the suger factory in Georgia from small particles, occured at night when it was actually cooler. This is another reason why auto manufacturers have to design clutches to erode slowly rather than quickly.
I hope this helps.
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C-Kwik
- Moderator
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Re: Just a reminder... (Jacko3)
Heat that originates in the engine is going to have little significant effect on the flywheel or clutch. Lets assume for a moment that the engine is a big block of metal. It's temperature will remain within a relatively small range as it is regulated by the cooling system. As a result, the temperature of the flywheel can only get as high as the temperature of the engine.Jacko3 wrote:However, the heat from the engine heats up both materials. Thus, when both materials are clamped together, the flywheel will accumulate slightly more heat than the clutch because the thermal conductivity of the flywheel is usually higher than that of the clutch. This is why your clutch is made of a material that naturally does not conduct as much heat as the flywheel, while some level of grip is sacrificed, thus leading to potentially to slipping. There are better materials than the materials used in making your clutch. But the engineers have to consider how much heat that material can absorb and dissipate before the clutch starts to fail. This is why your clutch is made of an asbstos type material that is less prone ot heat absorption and quick to heat dissipation. Ceramic materials are even better, but they are expensive. Ceramic means clay. Clay is a good conductor and dissipator of heat.
It gets even better. The primary source of heat transfer to the flywheel would be through conduction which would occur at the point at which the flywheel is connected to the end of the crankshaft. This point is maybe 4 inches in diameter at most. This is effectively a heat dam. It reduces the amount of heat transfer that can occur. Imagine you are freezing cold and find a very warm wall that you can press against to absorb some its heat. If you press only the tip of your finger against it, you'll probably never warm up. But if you press your entire body against it, you'll probably be warm in no time. Ultimately, between these two factors alone, the flywheel should be cooler than the engine, and by mechanical standards, is already fairly cool.
Better materials for a clutch is relative to what one considers to be better. Are there materials that have higher coefficients of friction and better ability to handle heat and abuse? Absolutely. Are there drawbacks? Most certainly. Higher coeffecients of friction can be one cause of clutch chatter. While you might be okay with it, most average consumers will not. In severe cases (which I have experienced), it is down right uncomfortable. And better heat load capacity may come in the form of more mass (perhaps copper ceramic pucks). Keep in mind that extra weight on the clutch disc can affect the operation of your transmission's syncros as it adds additional inertial loads that the syncros must overcome.
Last I checked, ceramics were insulators. They are poor conductors of heat. Try holding a tin cup filled with a hot cup of coffee and a ceramic cup of hot coffee. While eventually, the temperatures will be the same at the surface, you'll notice that with the metal cup, it will feel hotter. when you pick up either cup, your hands start to absorb heat from it. The surface of the cup where you are holding it will drop in temperature, so the heat from the coffee will begin transferring to the surface again. In the metal cup, this will happen pretty quickly. With the ceramic cup, it will occur at a slower rate so the surface temperature of the ceramic cup will be lower.
In order for any clutch to slip, the lateral load across the friction surfaces would have to overcome the pressure the pressure plate exerts on clutch disc coupled with the coefficient of friction of the materials. Thermal expansion is not what you need to look at here. Perhaps it may have an effect on the coefficient of friction, which it might (brake pads coefficient of friction vary with temperature), but ultimately, the coefficient of friction and pressure plate clamping force determines the load at which the clutch would slip.Jacko3 wrote:In the process of the clutch and flywheel spinning, the linear expansivity of the flywheel will be greater than that of the clutch, thus increasing its surface area for more heat accumulation, while the surface area of your clutch isn't as affected because of the relatively lower thermal conductivity of the clutch material. Your flywheel does expand as a result of heat absorption, but your clutch does so only in smaller amounts.
When the flywheel and the clutch are clamped together, on either side of the flywheel and the clutch system walls, you have a thin wall of air on both sides. That thin wall of air is called a thermal boundary layer.
The rate of heat transfer per unit area, called the heat flux on the side of the flywheel is usually slower and less than the heat flux on the side of the clutch. And according to Fourier's law, which is dq/da = -k dt/dn, heat will move from a region of a hotter surface to a region of a colder surface. Assume the surface of the flywheel to be isothermal regardless of the heat it is absorbing from the engine, for ease of understanding.
Thus, the heat flux on the side of the clutch system, as a result of the heat transfer from the flywheel to the clutch system, based on Fouriers law, increases the temperature gradient of the air at the thermal boundaries on either side of the clutch and the flywheel.
This heat gradient in addition to the heat continuously generated by the engine, causes expansion of the surface area of the flywheel and the clutch, thus reducing grip and clutch reliability---this is what partly leads to slipping of the clutch. Slipping is accelerated under these conditions if the clutch is not fully depressed or fully engaged. Clutches don't slip by themselves, they do so slip as a result of improper engagement or disengagement in addition to the effects of temperature on the flywheel and the clutch material itself. During this phenomenon, the porous material of your clutch will tend to disintegrate, which is what causes the burnt clutch smell. Slippage may not have occured at that time. However, this process is a precursor to slippage.
I'm not quite sure if you are referring to the thermal expansion as a phenomenom, or clutch slip as the phenomenom. In any case, while thermal expansion will occur, it's going to be a relatively small amount. Both materials will expand to some extent as well (if we assume both are at the same temperature), so regardless of which one expands more, the actual difference in size change between them will still be smaller than the distance the material with the higher expansion rate expands to.
But then how exactly would this accelerate clutch slippage. The pressure plate still exerts the same pressure on the disc. The load from the engine is not changed. The only thing left to change then is the coefficient of friction. My thought is that this would perhaps go up slightly with temperature, but even if we entertained the idea that it went down, wouldn't you think that the engineers would not have thought about this already? Since most cars spends most of it's mileage in a warmed up state, do you not think that engineers would make sure that the materiels used would provide a reasonably adequate amount of friction at the temperatures it will operate at while even leaving a bit of headroom?
What you describe is a very general process about how heat naturally dissapates from the clutch system. And it's true. But the difference here is that you are assuming that the heat that exists in the flywheel once everything has warmed up is actually enough to cause the clutch to burn. If cooling the clutch system were actually a big enough concern to engineers, then a more effective method than the one you describe would be to allow air from outside the transmission into the bell housing. It would reduce any thermal loading on the transmission and bellhousing casing and be much more effective as air outside the case would be cooler. And engineers have done very little to allow outside air in. While it's certainly not air tight, there are few gaps that air can flow in and out of in the bellhousing of a transmission.Jacko3 wrote:Thus, in order to reduce slippage or the potential for slippage, a third thermal boundary has to be introduced. That thermal boundary is in between the clutch system and the flywheel when they are disengaged. It is a small area for the air. Air will fill up any area if a vacum does not exist. However, what is important is that the small area contributes another area for further heat transfer away from either the cluth material or flywheel, from a region of cold to a region of warmth, according to Fouriers law.
During this period, the air inside and close to the walls of the bell housing which covers the flywheel and the clutch system, are touching the bell housing metal, and consequently loosing heat by conduction to the bell housing, while air on the outside and close to the bell housing, is absorbing the heat being conducted by the bell housing. All this is happening as the engine continues to generate more heat.
Thus, the air in side and close to the bell housing gets cooler and returns to the clutch system and flywheel by convection to absorb more heat to be transferred outwards through the bell housing. This is why the bell housing is made of a material which has a higher thermal conductivity than the cast iron used in making many flywheels. This material has to be able to dissipate heat very fast. Cast iron is also cheaper to make.
You don't need a thermal boundaray if your clutch isn't above it's intended operating temperature in the first place.Jacko3 wrote:The more a thermal boundary is introduced close to the gripping surfaces of the flywheel and clutch system, the better heat can be transferred from the clutch, and the less damage you do to your clutch, assuming the clutch is operated porperly.
While I doubt there is much material in a clutch disc that can actually catch fire, even if it could, it would probably be at extreme temperatures. One which an engine's heat ouside of the combustion chambers would ever actually reach.Jacko3 wrote:The clutch is subject to heat impact. And because a clutch is made up of a porous material, the dust form the clutch in an enclosed chamber can actually ignite on its own. When you have an enclosed space with powdery substances, explosions are common, especially if you don't have an efffective ventilator. This is what led to the recent explosion of a sugar factory in Savannah Georgia. Thus, among one of many reasons why clutches can ignite on their own, without explanation and forewarning. Much of the heat from a clutch does not come from its spining with the flywheel. Much of its heat comes from the engine. And to reduce this heat, you will have to increase the surface area for cooler air to come in contact with the clutch and flywheel, no matter how small the area. Thus, the reason to disenage the clutch from the flywheel for a few seconds.
My argument was and still is that any cooling effects that any air between and even flowing between the friction surfaces provides will be slower than that of conduction into the flywheel and pressure plate masses. Both will provide a heat sink effect that allows for more immediate temperature reductions at the frictiion surfaces, but naturally they will radiate and convect heat to eventually shed this heat. In order for convection between the friction surfaces to be more effective than conduction is if the temperature of the flywheel and pressure plates are the same as the disc. This is because if they are at the same temperature, there would essentially be no conduction. But to reach such a point where this would be the case and the clutch disc material were burning would mean that a lot more heat than the engine could provide through conduction, convection or radiation could possiblty provide. Meaning the only other soource for the amount of heat necessary for this condition would be by causing an unreasonable amount of clutch slippage.Jacko3 wrote:When a clutch is clamped to a flywheel you effectively have only two surface (outer surfaces) areas for heat to be effectively dissipated by the air. When you disengage the clutch from the flywheel, you increase the surface area for heat dissipation to four (two inner surfaces and two outer surfaces), and your Fouriers law holds in this case because, the heated surfaces of the clutch and flywheel automatically is absorbed by the air in between the two surfaces, thus reducing the possibility of slip from heated surfaces.
Driving hard and abusing a car are not the same thing. There is no condition that your car could probably see as harsh as a road race rack. If you drive like you do on a track, it's likely that you'll be way behind every other driver on the course and/or you'll be replacing the clutch the next day. Driving fast is about being smooth and deliberate. Harsh movements and transitions only result in wasted movement and energy.Jacko3 wrote:As you will recall, I drive very hard, so my car will generate more heat than those who drive normally. Thus, the burnt clutch smell I had earlier noted. Burnt clutch smell does not mean slippage is occuring. It means that the condition for slippage is ripe, that is if you ride your clutch or engage or disengage your clutch improperly.
Thermal expansion occurs with even the slightest changes in temperature. But a clutch disc doesn't burn because of a 1 degree Celsius change in temperature.Jacko3 wrote:It should also be noted that the temperature differences we are talking about maybe as small as 1 degree celsius or less. However, that is enough to make a difference in the linear expansivity of the clutch since it has a lower thermal conductivity than the flywheel.
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C-Kwik
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Re: Just a reminder... (Jacko3)
Meat cooking is not a temporary change. Unlike phase changes of molecules that only change their physical change, cooking a meat causes chemical changes. Which are not directly reversible.Jacko3 wrote:3. Expansion does not generate heat. Rather it is heat that generates expansion. Materials that expand temporarily loose some of their qualities by their nature. For example, meat cooked wil become tender. Add stress to that process, and it becomes obvious why deteriororation will occur. For example, pulverized cooked meat. In this case, it begins with a burning smell in a clutch. Heat not only produces a heat transfer process but it also transforms the property of substances. However, some substances, after cooling return to their original state. The bahvior is almost thermoplastic, eventhough the materials are not thermoplastic in nature.
Regardless, engineers are going take precaution in the materials that are chosen for such a task. As I mentioned before, temperature can affect the coeffcicient of friction, but the materials chosen for an OE application are going to have pretty good consistency in their normal operating heat ranges (which likely covers a much wider range than a single car will actually see).
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!979TransAm
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Re: Just a reminder... (Jacko3)
good write ups guys. Glad to see us getting somewhere.
Jacko I definately understand the idea of the plane being heated by the air molecules it passes through, same concept of the space shuttle on re-entry. On a 197ft supersonic jet expasion is seen as almost one foot total. That is a .005076 inches per foot, give or take a little. Pretty minimal but still there i guess. The wings see the most on the underside where air is accelerated. Most modern planes have ventilation systems within the fuselage to cool the outer skin with cabin exhaust air. We of course are only talking 10-13 degrees celsius on a good day in temp difference from take off. Pressure and stress are pretty big forces on a plane, normally the cause for the cracks they worried about when inspecting them. Don't get me wrong heat and expansion can also help, but more or less the least of the worries. Especially when talking about the stresses of 910000lbs (average take off weight of passenger plane) on a wingspan.
Jacko I definately understand the idea of the plane being heated by the air molecules it passes through, same concept of the space shuttle on re-entry. On a 197ft supersonic jet expasion is seen as almost one foot total. That is a .005076 inches per foot, give or take a little. Pretty minimal but still there i guess. The wings see the most on the underside where air is accelerated. Most modern planes have ventilation systems within the fuselage to cool the outer skin with cabin exhaust air. We of course are only talking 10-13 degrees celsius on a good day in temp difference from take off. Pressure and stress are pretty big forces on a plane, normally the cause for the cracks they worried about when inspecting them. Don't get me wrong heat and expansion can also help, but more or less the least of the worries. Especially when talking about the stresses of 910000lbs (average take off weight of passenger plane) on a wingspan.