MPG's decrease with Oil viscosity decrease?
#61
06-09-2011, 11:27 PM
Join Date: Sep 2010
Location: Chicago, Illinois
Posts: 4,428
But again, you're ignoring the throttle.
edit: putting the straw analogy in perspective, imagine two straws of different diameters, both with a valve in them. Why would I expect the straw to be the largest blocker of air given there's a big valve in the way specifically there to block the flow of air.
edit: putting the straw analogy in perspective, imagine two straws of different diameters, both with a valve in them. Why would I expect the straw to be the largest blocker of air given there's a big valve in the way specifically there to block the flow of air.
I also tried to point out that it depends on how clogged the filter is.
#62
06-09-2011, 11:36 PM
try using two balloons of exact dimension with the same volume of air under the same conditions and evacuating them with different diameter straws of the same length.
Regardless, given that the two items are in series, why does it make a difference where the majority of the drop occurs? Why did neither Oak Ridge or Consumer Reports find any fuel efficiency loss?
#63
06-09-2011, 11:44 PM
These folks, whoever they are, say 6% is engine friction.
The Efficiency of The Internal Combustion Engine
A quick google search yielded the answer that it's really gonna take more than a quick google search to find more detailed data. But given that I can turn an engine, and I can't produce more than 1 hp... (although admittedly I don't know that I can produce enough force to turn an engine at 8000 rpm).
The Efficiency of The Internal Combustion Engine
A quick google search yielded the answer that it's really gonna take more than a quick google search to find more detailed data. But given that I can turn an engine, and I can't produce more than 1 hp... (although admittedly I don't know that I can produce enough force to turn an engine at 8000 rpm).
#64
06-10-2011, 12:10 AM
Join Date: Sep 2010
Location: Chicago, Illinois
Posts: 4,428
No that looks like you're ignoring the throttle plate. If you aren't, where is the throttle plate in your analogy.
Regardless, given that the two items are in series, why does it make a difference where the majority of the drop occurs? Why did neither Oak Ridge or Consumer Reports find any fuel efficiency loss?
Regardless, given that the two items are in series, why does it make a difference where the majority of the drop occurs? Why did neither Oak Ridge or Consumer Reports find any fuel efficiency loss?
I am not talking about a filter that just looks dirty. Particulate filters get better as they get dirty. This applies to oil filters as well.
This is why I state explicitly that this depends on how clogged the filter is and we never bothered to define what constitutes "clogged" in your mind.
In which case, even in whats called steady state testing there will be a drastic change for a carbureted car and roughly 1-3% drop in fuel economy on a modern (meaning OBD2) EFI engine which is why I made my comment on fuel trims earlier. That 1-3% is after the STFT's and LTFTs have tweaked things.
Without fuel trims this would be yet more significant for us EFI folks.
I find it hard to believe that under no circumstances what-so-ever there would zero effect on fuel economy, and if I have some time tonight I will read through the Oak Ridge report.
Almost all of us, since we drive a 1.5L, have to wind out the motor to merge with traffic or overtake, which is where a clogged filter will really hurt you.
Unless you are a real cheap skate or the laziest man in the world, there is no reason not to change or at the very least blow out the air filter every 30-40k miles.
Yes, I consider 1-3% statistically significant in a system that works on firing spark and injectors for periods measured in millionths of a second.
Last edited by DiamondStarMonsters; 06-10-2011 at 12:34 AM.
#65
06-10-2011, 12:14 AM
Join Date: Sep 2010
Location: Chicago, Illinois
Posts: 4,428
These folks, whoever they are, say 6% is engine friction.
The Efficiency of The Internal Combustion Engine
A quick google search yielded the answer that it's really gonna take more than a quick google search to find more detailed data. But given that I can turn an engine, and I can't produce more than 1 hp... (although admittedly I don't know that I can produce enough force to turn an engine at 8000 rpm).
The Efficiency of The Internal Combustion Engine
A quick google search yielded the answer that it's really gonna take more than a quick google search to find more detailed data. But given that I can turn an engine, and I can't produce more than 1 hp... (although admittedly I don't know that I can produce enough force to turn an engine at 8000 rpm).
If you could even physically move fast enough, you would never be able to turn the engine at a paltry ~750rpm idle speed, and frictional force increases with speed in this case.
You don't really seem to understand that turning the engine by hand even without having to fight compression at a couple dozen rpm is not even in the same ball park, not even the same league as turning at 8000rpm.
The starter motor has a much greater leverage advantage and puts out a ton of torque for its size, and to compete you would need a sizable lever and all your weight behind it.. then you would have to maintain that for several revolutions.
It just uses a tiny gear to work on the outside of the flywheel where it has a mechanical advantage.
Last edited by DiamondStarMonsters; 06-10-2011 at 12:17 AM.
#66
06-10-2011, 12:27 AM
Join Date: Sep 2010
Location: Chicago, Illinois
Posts: 4,428
Heres the conversation we had BC where you were making a lot of assumptions and commiting a ton of logical fallacies:
Hence my aggravated tone throughout in case you had forgotten.
I just redid the math for our Fits using some far more conservative numbers and stock redline and the figure comes out closer to 7HP per main bearing. Which is still a ton of energy. I am going to talk to a friend of mine who is an Engineer at a major oil company to see if I can get some better figures to re-do the math for the 0w20 full syn oil I currently use in my L15A1.
Then I'll redo the numbers after I am boosted. Should be interesting to say the least.
Some things cannot and should not be dumbed down for consumption by the lowest common denominator. Oil is one of them.
Fluid dynamics is not something you can just put in layman's terms and illustrate the mechanics of it in an accurate fashion.
You want an example of how a simple change in oil can create a significant difference in fuel economy and power (which are both related by the way, one often follows the other)
The following was originally intended for one of my boosted gas 2.0L's
There is something called Bearing Operating Condition(BOC) which can be one of 3 states, but you really only want it operating in the 3rd state, fully developed hydrodynamic lubrication. Which correlates to a BOC of 35+. The formula to find BOC is as follows:
BOC = Viscosity x RPM x Diameter x K / Unit Load
Viscosity is in units of absolute viscosity. "K" is a value to convert RPM and Diameter into surface speed. Unit Load is the applied force divided by the projected area of the bearing (the insert width times the journal diameter).
First, viscosity. I can't find absolute/dynamic viscosity numbers for various grades of motor oil, so I took the Kinematic Viscosity of 10w30 (dino) motor oil at 100*C and multiplied it by it's specific gravity. This should give me the Dynamic Viscosity.
Second is the value "K". To find surface speed you multiply circumference by RPM. So Diameter x Pi x RPM = Surface speed, therefore K = Pi Right?
Lastly, unit load. I used 12,000 lbs of force, but this is relative to motoGP/Formula1 type engines, not boosted 4cylinders. I know our engine's see a BMEP nearly twice that of a formula 1 car, so it is a conservative place to start.
I also had no bearings out of the motor to measure their width, so I just put a caliper on the main cap and eyeballed it. I came up with an area of 1.425, so a load value of 8421.
Put it all together, 8.4 x 9500 x 2.245 x 3.1415 / 8421 = 66
The optimal range between 35 and 50 so we are well out of that range.
From here we can use the Stribeck Curve to find our friction coefficient, which I found to be .0057
So with an applied load of 12,000lbs, that gives us a friction load of 68.4 lbs. The diameter of the journal used is 2.245, so 1.1225 x 68.4 = 76.7 in/lbs or 6.39 lb/ft.
At 9500 this equates to 11.56 hp per main bearing.
That is 8600 watts of energy wasted per bearing, and that is only for the 5 main bearings!
That is not accounting for all the rockers, cam journals, cylinder bore contact patches, rod journals or wrist pins. Or the oil pump its self.
So maybe you should bone up on the basics, BC.
What units are used for measuring viscosity?
How does temperature affect viscosity?
What are the real differences between weights of comparable group oils at a given temperature?
These all are key to understanding what the hell I am trying to tell you.
None of this is made up or conventional knowledge. When I tell you something, think about it don't just throw it back in my face or I won't bother explaining it further.
There is method to my madness and I wouldn't be sharing if it didn't have merit for Joe Commuter perusing this board.
If you actually give a damn about learning the science involved for oil go here and read everything two or three times and absorb it:
Deprecated Browser Error
Fluid dynamics is not something you can just put in layman's terms and illustrate the mechanics of it in an accurate fashion.
You want an example of how a simple change in oil can create a significant difference in fuel economy and power (which are both related by the way, one often follows the other)
The following was originally intended for one of my boosted gas 2.0L's
There is something called Bearing Operating Condition(BOC) which can be one of 3 states, but you really only want it operating in the 3rd state, fully developed hydrodynamic lubrication. Which correlates to a BOC of 35+. The formula to find BOC is as follows:
BOC = Viscosity x RPM x Diameter x K / Unit Load
Viscosity is in units of absolute viscosity. "K" is a value to convert RPM and Diameter into surface speed. Unit Load is the applied force divided by the projected area of the bearing (the insert width times the journal diameter).
First, viscosity. I can't find absolute/dynamic viscosity numbers for various grades of motor oil, so I took the Kinematic Viscosity of 10w30 (dino) motor oil at 100*C and multiplied it by it's specific gravity. This should give me the Dynamic Viscosity.
Second is the value "K". To find surface speed you multiply circumference by RPM. So Diameter x Pi x RPM = Surface speed, therefore K = Pi Right?
Lastly, unit load. I used 12,000 lbs of force, but this is relative to motoGP/Formula1 type engines, not boosted 4cylinders. I know our engine's see a BMEP nearly twice that of a formula 1 car, so it is a conservative place to start.
I also had no bearings out of the motor to measure their width, so I just put a caliper on the main cap and eyeballed it. I came up with an area of 1.425, so a load value of 8421.
Put it all together, 8.4 x 9500 x 2.245 x 3.1415 / 8421 = 66
The optimal range between 35 and 50 so we are well out of that range.
From here we can use the Stribeck Curve to find our friction coefficient, which I found to be .0057
So with an applied load of 12,000lbs, that gives us a friction load of 68.4 lbs. The diameter of the journal used is 2.245, so 1.1225 x 68.4 = 76.7 in/lbs or 6.39 lb/ft.
At 9500 this equates to 11.56 hp per main bearing.
That is 8600 watts of energy wasted per bearing, and that is only for the 5 main bearings!
That is not accounting for all the rockers, cam journals, cylinder bore contact patches, rod journals or wrist pins. Or the oil pump its self.
So maybe you should bone up on the basics, BC.
What units are used for measuring viscosity?
How does temperature affect viscosity?
What are the real differences between weights of comparable group oils at a given temperature?
These all are key to understanding what the hell I am trying to tell you.
None of this is made up or conventional knowledge. When I tell you something, think about it don't just throw it back in my face or I won't bother explaining it further.
There is method to my madness and I wouldn't be sharing if it didn't have merit for Joe Commuter perusing this board.
If you actually give a damn about learning the science involved for oil go here and read everything two or three times and absorb it:
Deprecated Browser Error
You're saying that at 9500 rpm in the particular engine you're using as an example there are frictional losses of almost 60 hp? This is a question, not throwing something back in your face.
When I was in HS an automotive engineer told me that at higher speeds it takes about a hp per mph just to overcome air resistance. Now that was before cars were more fluid so it's probably maybe 2/3 of that now. But still, that's where a lot of the engine's power goes at higher speeds- overcoming wind resistance.
When I was in HS an automotive engineer told me that at higher speeds it takes about a hp per mph just to overcome air resistance. Now that was before cars were more fluid so it's probably maybe 2/3 of that now. But still, that's where a lot of the engine's power goes at higher speeds- overcoming wind resistance.
Yes at WOT (full load) not accounting for all the other parasitic losses I am losing as much as 60HP at the crank on 10w30.
At cruise where load is much lower, at least on a modern car, I don't think it would even take 1 hp/mph. That will be dependent on gearing, rolling friction, drivetrain losses, and aero drag.
My cruising IDC's in my 2500lb, 0.29C/d Laser @ 75mph are usually less than 5% in 5th gear (very tall ratio), which would be about 290cc/min.
1450cc/min per injector times 4 injectors @ 5% IDCs = 290cc/min fuel delivered.
At stoich (which is what we see at cruise ~14.2-14.7:1AFRs depending on fuel) this is good for 5lbs/min worth of air flow, or about 50whp
So that may be about accurate. Seems a little high to me, but I can do some more math on that later.
At cruise where load is much lower, at least on a modern car, I don't think it would even take 1 hp/mph. That will be dependent on gearing, rolling friction, drivetrain losses, and aero drag.
My cruising IDC's in my 2500lb, 0.29C/d Laser @ 75mph are usually less than 5% in 5th gear (very tall ratio), which would be about 290cc/min.
1450cc/min per injector times 4 injectors @ 5% IDCs = 290cc/min fuel delivered.
At stoich (which is what we see at cruise ~14.2-14.7:1AFRs depending on fuel) this is good for 5lbs/min worth of air flow, or about 50whp
So that may be about accurate. Seems a little high to me, but I can do some more math on that later.
I had a diesel VW Rabbit that produced (net) 48 hp.
Now of course that 48 is after internal friction losses.
Top speed was over 70 mph and the car weighed, if I remember right, just about 2000 lbs.
That's without people in it. I once had 7 and wow was it sluggish! Where I live there are some steep hills and even with just me in it (<150 lbs at the time) I couldn't get it over about 20 mph.
Now of course that 48 is after internal friction losses.
Top speed was over 70 mph and the car weighed, if I remember right, just about 2000 lbs.
That's without people in it. I once had 7 and wow was it sluggish! Where I live there are some steep hills and even with just me in it (<150 lbs at the time) I couldn't get it over about 20 mph.
I just redid the math for our Fits using some far more conservative numbers and stock redline and the figure comes out closer to 7HP per main bearing. Which is still a ton of energy. I am going to talk to a friend of mine who is an Engineer at a major oil company to see if I can get some better figures to re-do the math for the 0w20 full syn oil I currently use in my L15A1.
Then I'll redo the numbers after I am boosted. Should be interesting to say the least.
Last edited by DiamondStarMonsters; 06-10-2011 at 12:39 AM.
#67
06-10-2011, 09:59 AM
Did a little more googling:
Car & Driver Magazine says that a rear wheel drive car with a manual trans. can lose 15% to internal friction (the article's about a more powerful car but they're speaking in generalizations). This is for "drivetrain components—transmission, driveshafts, bearings, differential."
What is the GT-R
That's 15% of the gross, not the net. In other words, if the gross is 100, the net is 85, it's not 15% of 85 it's 15% of 100.
Other places on the web say "Up to 25%" but I think it's people quoting the same generalization over and over, since I don't see a citation and most of the places quoting that are selling something they claim will reduce internal friction so they have a vested interest in quoting the biggest number they can get away with.
As far as a clogged air filter goes- if the filters now last such a long time without needing replacement, would they get so clogged as to actually impede air flow significantly even in 150,000 miles?
Car & Driver Magazine says that a rear wheel drive car with a manual trans. can lose 15% to internal friction (the article's about a more powerful car but they're speaking in generalizations). This is for "drivetrain components—transmission, driveshafts, bearings, differential."
What is the GT-R
That's 15% of the gross, not the net. In other words, if the gross is 100, the net is 85, it's not 15% of 85 it's 15% of 100.
Other places on the web say "Up to 25%" but I think it's people quoting the same generalization over and over, since I don't see a citation and most of the places quoting that are selling something they claim will reduce internal friction so they have a vested interest in quoting the biggest number they can get away with.
As far as a clogged air filter goes- if the filters now last such a long time without needing replacement, would they get so clogged as to actually impede air flow significantly even in 150,000 miles?
#68
06-10-2011, 10:11 AM
Join Date: Sep 2010
Location: Chicago, Illinois
Posts: 4,428
SAE Gross output is still measured at the flywheel and is not accounting for internal engine friction. Which is what I am talking about.
What you are talking about is how much of the power that makes it to the flywheel is then lost to the transmission. That number actually changes between steady state and accelerating. There are different kinds of parasitic losses. Until you understand what you are discussing don't expect to find anything conclusive, because right now you are flying blind.
15% is about right for a healthy FWD manual transmission. 20% or worse is about right for automatic transmissions, especially AWD.
Anyone who is familiar with putting their car on a chassis dynamometer (DynoJet/Mustang/etc) already knows this.
AS far as the airfilters.. anyone who lives in a desert or a very dusty area knows that you can jam up a filter in less than 30,000 miles. That depends on your environment.
What you are talking about is how much of the power that makes it to the flywheel is then lost to the transmission. That number actually changes between steady state and accelerating. There are different kinds of parasitic losses. Until you understand what you are discussing don't expect to find anything conclusive, because right now you are flying blind.
15% is about right for a healthy FWD manual transmission. 20% or worse is about right for automatic transmissions, especially AWD.
Anyone who is familiar with putting their car on a chassis dynamometer (DynoJet/Mustang/etc) already knows this.
AS far as the airfilters.. anyone who lives in a desert or a very dusty area knows that you can jam up a filter in less than 30,000 miles. That depends on your environment.
#69
06-10-2011, 11:25 AM
The study has to do with a partially clogged filter. A completely clogged filter would cause a malfunction. If the study is correct and there would be no change in mpg just a decrease in performance...then my question is at what point would the ecu not be able to handle the level of being clogged. I would have liked this study more if they would have taken it to the breaking point.
As the pressure drop increases from specified 10 inches of water to more than 1 psig the engine will have work harder to suck the air thru the filter, costing power and mpg.
Its not how clogged the filter, its how much pressure drop occurs sucking the air thru. Once the pressure drop exceeds 1 psig (pounds per square inch gauge, or psi above atmospheric) you begin losing power and mpg. It happens before too but it usually takes statistical analysis to see it.
For competition engines we specify at least 5 square inches of loose filter opening per cfm of engine flow at maximum rpm. For a 1500 cc Fit engine sucking 175 cfm at 6500 rpm we want 860 square inches of filter showing 10 inches of water pressure drop at 6500 rpm. The standard Fit filter is about 80 square inches if memory serves. If the filter is very low pressure drop media we cut back on the area accordingly. Now you know why NASCAR 5 liter engines turning 9000 rpm have those enormous 24" diamter x 6 inch high filters with very open media. Street engines naturally don't have that problem.
Last edited by mahout; 06-10-2011 at 11:29 AM.
#70
06-10-2011, 02:49 PM
Just 'cause my eyes were closed doesn't mean I was flying blind... this is what happens when I try to think, half asleep... good thing the stock market wasn't open yet.
You're right, the C&D article talks about everything past the engine- I saw the word 'bearings' and thought they included internal friction.
That said, here's what I'd do to get a rough estimate of how much energy it takes to turn the engine- look at how fast the starter turns the engine and how much energy it uses. If they don't give HP or torque info for the starter, well, it's an electric engine and they're pretty efficient so worst case see how much power it draws and assume all, or almost all, of that goes into turning the engine. Turning the engine is essentially overcoming internal engine friction (although the starter needs not only to overcome friction but also to get the engine up to speed, and getting that momentum takes more power than just turning things).
And then, since that's what, 1000 rpm? Multiply that by whatever speeds we're talking about.
Although I don't know for sure if friction increases linearly with rpm.
That said, engines are only about 25-35% efficient but I think most of the losses are heat losses, and not the heat from friction but the heat from, well, pretty much your engine's on fire, right? Burning gas produces a lot of heat.
You're right, the C&D article talks about everything past the engine- I saw the word 'bearings' and thought they included internal friction.
That said, here's what I'd do to get a rough estimate of how much energy it takes to turn the engine- look at how fast the starter turns the engine and how much energy it uses. If they don't give HP or torque info for the starter, well, it's an electric engine and they're pretty efficient so worst case see how much power it draws and assume all, or almost all, of that goes into turning the engine. Turning the engine is essentially overcoming internal engine friction (although the starter needs not only to overcome friction but also to get the engine up to speed, and getting that momentum takes more power than just turning things).
And then, since that's what, 1000 rpm? Multiply that by whatever speeds we're talking about.
Although I don't know for sure if friction increases linearly with rpm.
That said, engines are only about 25-35% efficient but I think most of the losses are heat losses, and not the heat from friction but the heat from, well, pretty much your engine's on fire, right? Burning gas produces a lot of heat.
#71
06-10-2011, 02:51 PM
Just 'cause my eyes were closed doesn't mean I was flying blind... this is what happens when I try to think, half asleep... good thing the stock market wasn't open yet.
You're right, the C&D article talks about everything past the engine- I saw the word 'bearings' and thought they included internal friction.
That said, here's what I'd do to get a rough estimate of how much energy it takes to turn the engine- look at how fast the starter turns the engine and how much energy it uses. If they don't give HP or torque info for the starter, well, it's an electric engine and they're pretty efficient so worst case see how much power it draws and assume all, or almost all, of that goes into turning the engine. Turning the engine is essentially overcoming internal engine friction (although the starter needs not only to overcome friction but also to get the engine up to speed, and getting that momentum takes more power than just turning things).
And then, since that's what, 1000 rpm? Multiply that by whatever speeds we're talking about.
Although I don't know for sure if friction increases linearly with rpm.
That said, engines are only about 25-35% efficient but I think most of the losses are heat losses, and not the heat from friction but the heat from, well, pretty much your engine's on fire, right? Burning gas produces a lot of heat.
You're right, the C&D article talks about everything past the engine- I saw the word 'bearings' and thought they included internal friction.
That said, here's what I'd do to get a rough estimate of how much energy it takes to turn the engine- look at how fast the starter turns the engine and how much energy it uses. If they don't give HP or torque info for the starter, well, it's an electric engine and they're pretty efficient so worst case see how much power it draws and assume all, or almost all, of that goes into turning the engine. Turning the engine is essentially overcoming internal engine friction (although the starter needs not only to overcome friction but also to get the engine up to speed, and getting that momentum takes more power than just turning things).
And then, since that's what, 1000 rpm? Multiply that by whatever speeds we're talking about.
Although I don't know for sure if friction increases linearly with rpm.
That said, engines are only about 25-35% efficient but I think most of the losses are heat losses, and not the heat from friction but the heat from, well, pretty much your engine's on fire, right? Burning gas produces a lot of heat.
#72
06-10-2011, 02:57 PM
Then just tell me the size of the friggin' starter fuse, because I don't see that in the manual. I'll do the math, for example:
(if your brain's still hurting, stop reading here)
If it's a 30 amp fuse, at 12 volts that's 360 watts. 1 hp= 750 watts (roughly) so the starter produces half a hp.
Now multiply that by ten because the starter doesn't turn the engine very fast. That's 5 hp, assuming it's a linear relationship between friction and rotation speed.
(if your brain's still hurting, stop reading here)
If it's a 30 amp fuse, at 12 volts that's 360 watts. 1 hp= 750 watts (roughly) so the starter produces half a hp.
Now multiply that by ten because the starter doesn't turn the engine very fast. That's 5 hp, assuming it's a linear relationship between friction and rotation speed.
#73
06-10-2011, 03:07 PM
Then just tell me the size of the friggin' starter fuse, because I don't see that in the manual. I'll do the math, for example:
(if your brain's still hurting, stop reading here)
If it's a 30 amp fuse, at 12 volts that's 360 watts. 1 hp= 750 watts (roughly) so the starter produces half a hp.
Now multiply that by ten because the starter doesn't turn the engine very fast. That's 5 hp, assuming it's a linear relationship between friction and rotation speed.
(if your brain's still hurting, stop reading here)
If it's a 30 amp fuse, at 12 volts that's 360 watts. 1 hp= 750 watts (roughly) so the starter produces half a hp.
Now multiply that by ten because the starter doesn't turn the engine very fast. That's 5 hp, assuming it's a linear relationship between friction and rotation speed.
Lest see, the fuse isn't a great way to judge total energy used, its typically much less, because electrical motors draw infinite current when first started.
Friction in fluids is non-linear, its typically at least second order dominate (that is, frictional forces are a function of speed squared).
The starter is typically acting on a cold engine rather than hot.
#74
06-10-2011, 03:19 PM
I tried to find the actual power used by the starter, and gave it at least five minutes before I gave up.
If friction is second-order then to go from 800 to 8000 rpm means 100-fold increase in wasted hp. But on the positive side, most of our driving is what, 2000-3000 rpm? So on average the frictional losses when actually driving are maybe 10-20 X high idle.
If friction is second-order then to go from 800 to 8000 rpm means 100-fold increase in wasted hp. But on the positive side, most of our driving is what, 2000-3000 rpm? So on average the frictional losses when actually driving are maybe 10-20 X high idle.
#75
06-10-2011, 04:27 PM
Just 'cause my eyes were closed doesn't mean I was flying blind... this is what happens when I try to think, half asleep... good thing the stock market wasn't open yet.
You're right, the C&D article talks about everything past the engine- I saw the word 'bearings' and thought they included internal friction.
That said, here's what I'd do to get a rough estimate of how much energy it takes to turn the engine- look at how fast the starter turns the engine and how much energy it uses. If they don't give HP or torque info for the starter, well, it's an electric engine and they're pretty efficient so worst case see how much power it draws and assume all, or almost all, of that goes into turning the engine. Turning the engine is essentially overcoming internal engine friction (although the starter needs not only to overcome friction but also to get the engine up to speed, and getting that momentum takes more power than just turning things).
And then, since that's what, 1000 rpm? Multiply that by whatever speeds we're talking about.
Although I don't know for sure if friction increases linearly with rpm.
That said, engines are only about 25-35% efficient but I think most of the losses are heat losses, and not the heat from friction but the heat from, well, pretty much your engine's on fire, right? Burning gas produces a lot of heat.
You're right, the C&D article talks about everything past the engine- I saw the word 'bearings' and thought they included internal friction.
That said, here's what I'd do to get a rough estimate of how much energy it takes to turn the engine- look at how fast the starter turns the engine and how much energy it uses. If they don't give HP or torque info for the starter, well, it's an electric engine and they're pretty efficient so worst case see how much power it draws and assume all, or almost all, of that goes into turning the engine. Turning the engine is essentially overcoming internal engine friction (although the starter needs not only to overcome friction but also to get the engine up to speed, and getting that momentum takes more power than just turning things).
And then, since that's what, 1000 rpm? Multiply that by whatever speeds we're talking about.
Although I don't know for sure if friction increases linearly with rpm.
That said, engines are only about 25-35% efficient but I think most of the losses are heat losses, and not the heat from friction but the heat from, well, pretty much your engine's on fire, right? Burning gas produces a lot of heat.
Most heat loss is exhaust gases, which is fortunate. If that wasn't the cooling system would not keep the engine from melting down.
If you want to find internal friction loss find the cooling capacity of an external oiil cooler. Few street engines really need oil coolers so you know its fairly low. I'd be surprised if that 5-15% power loss is valid for anything less than 2/3 max throttle.
#76
06-10-2011, 04:32 PM
Originally Posted by
That said, here's what I'd do to get a [B
That said, here's what I'd do to get a [B
rough[/B] estimate of how much energy it takes to turn the engine- look at how fast the starter turns the engine and how much energy it uses.
That said, engines are only about 25-35% efficient but I think most of the losses are heat losses, and not the heat from friction but the heat from, well, pretty much your engine's on fire, right? Burning gas produces a lot of heat.
That said, engines are only about 25-35% efficient but I think most of the losses are heat losses, and not the heat from friction but the heat from, well, pretty much your engine's on fire, right? Burning gas produces a lot of heat.
It only takes a torque wrench to turn the engine at low speed, say 12 rpm. Just by guess I'd say 10-12 lbft. I suspect the power to turn the engine over will decrease up to a thousand or two rpm and then increase to a maximum at red line. Starters only turn an engine at 300 rpm or so and most are less than 1 hp.
#77
06-11-2011, 12:00 AM
There is a lot of talk about HP,mpg and its about the fuel,and oil but its not constant. You can drive with the cruise control on at 60 mph at 2000 rpm for example. Each combustion cycle is going to be different up to +-10 percent and then you multiply it by four. I am not talking HP but timing and total combustion pressure produced. You can have miss fires and knock too. There are so many variables that if you can keep your mpg within 5 percent from tank to tank you are doing excellent. Good fuel helps smooth the variables.
Thinner oil flows better and lubricates the piston rings better. There is more friction from the piston ring then the bearings except at WOT. The oil is becoming thinner so that it reaches the top compression ring and that means less friction.
Thinner oil flows better and lubricates the piston rings better. There is more friction from the piston ring then the bearings except at WOT. The oil is becoming thinner so that it reaches the top compression ring and that means less friction.
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MikeNSX
2nd Generation (GE 08-13)
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11-01-2011 04:05 PM
