Sustina 0W-20, 6,003 kms, Caterham
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I didn't say that at all. I stated that having minimal load on the engine at a certain RPM gave me a much lower engine temperature than did the same revolutions with a substantial load.
Originally Posted By: CATERHAM
For example, the Subie BRZ/Scion FR-S twins can easily generate oil temp's higher than 230F but these cars were engineered from the get go with the 0W-20 grade as the specified lube.
Originally Posted By: Garak
I didn't say that at all. I stated that having minimal load on the engine at a certain RPM gave me a much lower engine temperature than did the same revolutions with a substantial load.
My air compressors don't have coolant, and most engines I have experienced with coolant are thermostatically regulated, so you don't tend to have coolant temperatures run away under load. So, in my examples, it's physical temperature on the head and the oil. And, there's no combustion whatsoever.
Garak, the main point which you've determined yourself, is that the principle source of heat is not from the bearings but rather released from the process of compressing air in an air compressor.
In an IC engine not only are you generating heat by compressing air (heck, in a diesel you'll get spontaneous combustion if you add a bit of fuel) but the considerable additional heat through combustion itself.
So you and turtlevette are in agreement; friction in the bearings, cylinder bores etc contributes little to total heat production, as if anyone had any doubts.
I still have no answer as to what percentage of heat is generated by work being done versus combustion occurring. 
Originally Posted By: bluesubie
Originally Posted By: CATERHAM
For example, the Subie BRZ/Scion FR-S twins can easily generate oil temp's higher than 230F but these cars were engineered from the get go with the 0W-20 grade as the specified lube.
Originally Posted By: CATERHAM
Garak, the main point which you've determined yourself, is that the principle source of heat is not from the bearings but rather released from the process of compressing air in an air compressor.
In an IC engine not only are you generating heat by compressing air (heck, in a diesel you'll get spontaneous combustion if you add a bit of fuel) but the considerable additional heat through combustion itself.
So you and turtlevette are in agreement; friction in the bearings, cylinder bores etc contributes little to total heat production, as if anyone had any doubts.
Hint...
Here's a chart from a motored engine test (not fire, no heat of compression) on a 1.5L 4 cylinder. You can see in the left of the curves the operation in boundary lubrication (which you don't believe in), moving to the predominance of hydrodynamic to the right.
As you well know, power is torque times revs per second (times 2Xpi).
So taking the blue line (ILSAC 5W30), the frictional power losses that go into creating heat in the oil (and coolant, as main bearings flow heat INTO the coolant at high revs) are 1.2KW at 1,600RPM, and a massive 4.2KW at 3,200RPM.
Science matches my observation surprisingly.
Then look at the blue line at 3,200RPM, versus the dashed red line, with is a 20 grade, high VI, with advanced friction modifiers...it's frictional losses are 3.6KW...less frcitional losses means better economy, and a slightly longer warmup.
All this BEFORE you even light a fire over the top of it...and it all exists at RPM, regardless of actual engine load.
As you well know, power is torque times revs per second (times 2Xpi).
So taking the blue line (ILSAC 5W30), the frictional power losses that go into creating heat in the oil (and coolant, as main bearings flow heat INTO the coolant at high revs) are 1.2KW at 1,600RPM, and a massive 4.2KW at 3,200RPM.
Science matches my observation surprisingly.
Then look at the blue line at 3,200RPM, versus the dashed red line, with is a 20 grade, high VI, with advanced friction modifiers...it's frictional losses are 3.6KW...less frcitional losses means better economy, and a slightly longer warmup.
All this BEFORE you even light a fire over the top of it...and it all exists at RPM, regardless of actual engine load.And here's big end BEARING temperature, that which can't be seen either by oil pressure or bulk oil temperature...again, an issue that you've failed to answer.
The temperature on the right is the bulk oil temperature, and the temperature on the left is the big end bearing temperature.
Not how:
a) there's 30C rise from bulk oil temperatures (a fact that you deny exists)
b) the main contributing variable is RPM, NOT load.
c) even at a low bulk oil temerature of 80C, the big ends were operating well over 100C, with whatever the viscosity happened to be at 125C.
The temperature on the right is the bulk oil temperature, and the temperature on the left is the big end bearing temperature.
Not how:
a) there's 30C rise from bulk oil temperatures (a fact that you deny exists)
b) the main contributing variable is RPM, NOT load.
c) even at a low bulk oil temerature of 80C, the big ends were operating well over 100C, with whatever the viscosity happened to be at 125C.Note the direction of the heat flow arrows in this example, and the values of the energy transfer...to the coolant, and to the conrod from the heat generated within the bearings.
Crank temperature was around 150C, which clearly has no contact with combustion, or products...the big end generated heat and transfers it INTO the conrod, rather than the popular misconception that heat from the piston travels down the conrod into the bearing to be "flowed away" by oil.
Agian, 4 big ends and 5 mains would give
4*97W, +5*148W = 1.13KW of heating, due ONLY to the viscous friction in the mains and big ends.
Same engine at 6,000 RPM
Crank temperature was around 150C, which clearly has no contact with combustion, or products...the big end generated heat and transfers it INTO the conrod, rather than the popular misconception that heat from the piston travels down the conrod into the bearing to be "flowed away" by oil.
Agian, 4 big ends and 5 mains would give
4*97W, +5*148W = 1.13KW of heating, due ONLY to the viscous friction in the mains and big ends.
Same engine at 6,000 RPM
Well there's a lot more to this. Did they remove the plugs? Did they motor the engine until the bulk oil came up to temp or did they preheat the oil? If they didn't preheat, how long did it take for the bulk oil to come up to temp. How much volume of oil? The heat of compression may be responsible for the bulk oil temp rise.
I'd rather see a rig that spins a shaft in a fixed bearing. There's too many variables when turning an engine. We aren't sure where the heat is coming from.
Originally Posted By: turtlevette
Well there's a lot more to this. Did they remove the plugs? Did they motor the engine until the bulk oil came up to temp or did they preheat the oil? If they didn't preheat, how long did it take for the bulk oil to come up to temp. How much volume of oil? The heat of compression may be responsible for the bulk oil temp rise.
I'd rather see a rig that spins a shaft in a fixed bearing. There's too many variables when turning an engine. We aren't sure where the heat is coming from.
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Here's a journal in a test rig, with caluculated and measured temperatures.
Supply temperature is controlled to the temperature "T oil supply". T sim oil out is the scientifically modelled temp, and T Exp oil out is the actual measurement.
Bearing has a 70MPa applied load.
SAE40 was full film (hydrodynamic) in both RPM cases, while the 20 at 2,000 was bordering on mixed.
The science is there, it has always been there, and known for more than a century...I don't know why people try so hard to deny it, and posit blarney.
Bearing has a 70MPa applied load.
SAE40 was full film (hydrodynamic) in both RPM cases, while the 20 at 2,000 was bordering on mixed.
The science is there, it has always been there, and known for more than a century...I don't know why people try so hard to deny it, and posit blarney.Originally Posted By: CATERHAM
The point is that there is no lubrication benefit in running an oil grade heavier than what's recommended, that's what the engineers have designed the final product released for sale to use. All the fail safe systems designed into the car are based on that grade.
It's clear that work performed by an engine causes sump temperatures to increase - and this is causal. Any claim otherwise in this thread, or anywhere else, simply demonstrates a lack of understanding of the equivalence of work and energy. Of course, the "fire" contributes, but you can get scalding oil temperatures in sumps in engines that have nothing to do with combustion.
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