Louis Ott's full valve cover video now on youtube
05-28-2010, 11:37 AM
#76
Rennlist Member
Thats why you need to leave the system stock, and use a good, non foaming, viscosity stable oil like Amsoil or Redline. 
plus, bernoulli doesnt apply with his venturis as they dont act like gasses do
plus, bernoulli doesnt apply with his venturis as they dont act like gasses do
The following files are snapshot images taken from the video. They show that it is very possible with careful observation to judge both the areas that the violent surging air and oil come from as well as the distinctive foam that is ejected by the cam bearings and flung by the cam lobe. This distinctive fine foam appears after a delay that can vary in length of time. This is typical of aerated oil being ingested by a pump.
http://www.crank-scrapers.com/A-928.jpg
http://www.crank-scrapers.com/B-928.jpg
http://www.crank-scrapers.com/C-928.jpg
We can see that the engineers knew a lot of aerated oil was making its way back to the sump. The screening over the early sumps is an attempt to release trapped air from the oil. The clover-leaf fitting that sits next to the sump floor is an attempt to stop foamed oil from being directly ingested by the pickup for as long as possible. We know that the Porsche engineers would be aware of the quick benefit of adding a perimeter ledge around the sump well. It would trap a substantial portion of the oil that easily spills out during a turn producing only a 30 degree angle of repose.
We now know that the gerotor pump in at least some of the 928 engines was not a positive displacement pump with a certain amount of oil being pushed into the oil galleys or even out the relief valve with every revolution of the pump. In at least some of the pumps a deaerator relief passage was also provided.
What seems most likely is that for levels of lateral acceleration up to perhaps 1.5 Gs that the thrashed oil and air does return to the sump in sufficient quantities to keep the pickup covered. I think somewhere between sustained 1.5 Gs and 2 Gs the pickup does start to become uncovered. At 2 Gs it seems reasonable to assume that the pickup is more uncovered than not.
At some point even the deaerator in the pump (at least some of them) is overwhelmed by the sheer volume of entrained air. At that point the hope must be that the multiple bars of pressure that can be generated by the pump is sufficient to push the air into solution at the rate of 9% per bar.
If that pressure was maintained throughout the circuit at all times the 2/6 bearing could hold out longer but there are a series of cross sectional decreases from the exit at the pump to the various arms of the circuit. In a dynamic hydraulic circuit this leads to pressure drops and that in turn leads to a supersatured solution releasing dissolved air to come into equilibrium with the new pressure.
There is a lot of debate over why the 2/6 circuit in particular gives so much trouble. It could be because it is the first to get a good dose of highly aerated oil. It could be as Mike Simard thinks, that there is some sort of Bernoulli effect happening at the entrance to the circuit. At some point it doesn't matter because fixing it will simply transfer the problem to another branch, ultimately. And there is no guarantee that with the 2/6 bearing protected that another bearing will not fail EVEN MORE QUICKLY than the 2/6 bearing did. I really think this is the sort of demonic situation the Porsche engineers were faced with.
Assuredly this is a highly complex problem. It is very understandable that people want to bypass it by installing a dry sump. Just be careful there too. Some new Vettes pop the engines despite having OEM dry sumps. Proper design is critical.
http://www.crank-scrapers.com/A-928.jpg
http://www.crank-scrapers.com/B-928.jpg
http://www.crank-scrapers.com/C-928.jpg
We can see that the engineers knew a lot of aerated oil was making its way back to the sump. The screening over the early sumps is an attempt to release trapped air from the oil. The clover-leaf fitting that sits next to the sump floor is an attempt to stop foamed oil from being directly ingested by the pickup for as long as possible. We know that the Porsche engineers would be aware of the quick benefit of adding a perimeter ledge around the sump well. It would trap a substantial portion of the oil that easily spills out during a turn producing only a 30 degree angle of repose.
We now know that the gerotor pump in at least some of the 928 engines was not a positive displacement pump with a certain amount of oil being pushed into the oil galleys or even out the relief valve with every revolution of the pump. In at least some of the pumps a deaerator relief passage was also provided.
What seems most likely is that for levels of lateral acceleration up to perhaps 1.5 Gs that the thrashed oil and air does return to the sump in sufficient quantities to keep the pickup covered. I think somewhere between sustained 1.5 Gs and 2 Gs the pickup does start to become uncovered. At 2 Gs it seems reasonable to assume that the pickup is more uncovered than not.
At some point even the deaerator in the pump (at least some of them) is overwhelmed by the sheer volume of entrained air. At that point the hope must be that the multiple bars of pressure that can be generated by the pump is sufficient to push the air into solution at the rate of 9% per bar.
If that pressure was maintained throughout the circuit at all times the 2/6 bearing could hold out longer but there are a series of cross sectional decreases from the exit at the pump to the various arms of the circuit. In a dynamic hydraulic circuit this leads to pressure drops and that in turn leads to a supersatured solution releasing dissolved air to come into equilibrium with the new pressure.
There is a lot of debate over why the 2/6 circuit in particular gives so much trouble. It could be because it is the first to get a good dose of highly aerated oil. It could be as Mike Simard thinks, that there is some sort of Bernoulli effect happening at the entrance to the circuit. At some point it doesn't matter because fixing it will simply transfer the problem to another branch, ultimately. And there is no guarantee that with the 2/6 bearing protected that another bearing will not fail EVEN MORE QUICKLY than the 2/6 bearing did. I really think this is the sort of demonic situation the Porsche engineers were faced with.
Assuredly this is a highly complex problem. It is very understandable that people want to bypass it by installing a dry sump. Just be careful there too. Some new Vettes pop the engines despite having OEM dry sumps. Proper design is critical.
05-28-2010, 12:10 PM
#77
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I think you have amply demonstrated that technique in driving the car and adjusting rpm is very important for a stock system to survive. I do not think that Porsche intended for the engines to require this treatment.
Note carefully that the foaming or non-foaming tendency of an oil is not necessarily correlated with the tendency to entrain air bubbles. The siloxane anti-foam surfactants are a good example of an anti-foam tending to increase air entrainment.
Bernoulli can be applied. Think flow differential. A venturi is simply one way of accomplishing that.
05-28-2010, 02:19 PM
#78
Rennlist Member
Hi Mark,
I think you have amply demonstrated that technique in driving the car and adjusting rpm is very important for a stock system to survive. I do not think that Porsche intended for the engines to require this treatment.
Note carefully that the foaming or non-foaming tendency of an oil is not necessarily correlated with the tendency to entrain air bubbles. The siloxane anti-foam surfactants are a good example of an anti-foam tending to increase air entrainment.
Bernoulli can be applied. Think flow differential. A venturi is simply one way of accomplishing that.
I think you have amply demonstrated that technique in driving the car and adjusting rpm is very important for a stock system to survive. I do not think that Porsche intended for the engines to require this treatment.
Note carefully that the foaming or non-foaming tendency of an oil is not necessarily correlated with the tendency to entrain air bubbles. The siloxane anti-foam surfactants are a good example of an anti-foam tending to increase air entrainment.
Bernoulli can be applied. Think flow differential. A venturi is simply one way of accomplishing that.
You mentioned venturi to Mark K. I don't recall all the details but it's similar to discussing horsepower and torque with him.
06-04-2010, 03:03 PM
#79
Three Wheelin'
Kevin,
I think your observations/conclusions on the oil aerating situation is right on target. There is aerated oil being pumped even when going down the straight. It does diminish near the end of the straight, but sure isn't gone. That indicates to me that after going through corners, the sump oil is thoroughly aerated and it takes a while for the air to get out of it. The first time down the straight there is no air in the oil. It is only after going through corners at high RPM.
One other point I'd like to comment on is that of oil flow volume and just how much oil volume must be handled by the sump cover and drain back system. Some calculations were done in earlier posts that showed the volume could be up to 21 gpm. The pump has losses and the already mentioned aeration bypass ports internal to the pump would reduce that volume by some amount. I was driving my GT a few days ago and took note of the oil pressure vs RPM. It isn't hot weather here now so the oil temp only got to 202F to 210F. The oil was Amsoil 20W 50. Idle RPM of 800 gave me 35 psi. The max oil pressure goes to 100 psi with hot oil then the pressure relief valve maintains that pressure. I get to 100 psi at 2400 to 2700 rpm. 2400 with oil temp 202 and 2700 at 210F oil temp. Oil that the pump supplies is bypassed at RPM above that. This tells me that the oil volume, at 100 psi, the engine uses is what the oil pump supplies at 2200 to 2700 RPM. With hotter oil the RPM for 100 psi would higher, depending on the oil. The engine uses, and the sump drain back system needs to handle, the oil volume the pump supplies at around 3000 RPM max. The remainder is merely bypassed and doesn't go through the engine. The engine use volume is nowhere near 21 gpm. Maybe 8-9 gpm.
I think your observations/conclusions on the oil aerating situation is right on target. There is aerated oil being pumped even when going down the straight. It does diminish near the end of the straight, but sure isn't gone. That indicates to me that after going through corners, the sump oil is thoroughly aerated and it takes a while for the air to get out of it. The first time down the straight there is no air in the oil. It is only after going through corners at high RPM.
One other point I'd like to comment on is that of oil flow volume and just how much oil volume must be handled by the sump cover and drain back system. Some calculations were done in earlier posts that showed the volume could be up to 21 gpm. The pump has losses and the already mentioned aeration bypass ports internal to the pump would reduce that volume by some amount. I was driving my GT a few days ago and took note of the oil pressure vs RPM. It isn't hot weather here now so the oil temp only got to 202F to 210F. The oil was Amsoil 20W 50. Idle RPM of 800 gave me 35 psi. The max oil pressure goes to 100 psi with hot oil then the pressure relief valve maintains that pressure. I get to 100 psi at 2400 to 2700 rpm. 2400 with oil temp 202 and 2700 at 210F oil temp. Oil that the pump supplies is bypassed at RPM above that. This tells me that the oil volume, at 100 psi, the engine uses is what the oil pump supplies at 2200 to 2700 RPM. With hotter oil the RPM for 100 psi would higher, depending on the oil. The engine uses, and the sump drain back system needs to handle, the oil volume the pump supplies at around 3000 RPM max. The remainder is merely bypassed and doesn't go through the engine. The engine use volume is nowhere near 21 gpm. Maybe 8-9 gpm.
The following files are snapshot images taken from the video. They show that it is very possible with careful observation to judge both the areas that the violent surging air and oil come from as well as the distinctive foam that is ejected by the cam bearings and flung by the cam lobe. This distinctive fine foam appears after a delay that can vary in length of time. This is typical of aerated oil being ingested by a pump.
http://www.crank-scrapers.com/A-928.jpg
http://www.crank-scrapers.com/B-928.jpg
http://www.crank-scrapers.com/C-928.jpg
We can see that the engineers knew a lot of aerated oil was making its way back to the sump. The screening over the early sumps is an attempt to release trapped air from the oil. The clover-leaf fitting that sits next to the sump floor is an attempt to stop foamed oil from being directly ingested by the pickup for as long as possible. We know that the Porsche engineers would be aware of the quick benefit of adding a perimeter ledge around the sump well. It would trap a substantial portion of the oil that easily spills out during a turn producing only a 30 degree angle of repose.
We now know that the gerotor pump in at least some of the 928 engines was not a positive displacement pump with a certain amount of oil being pushed into the oil galleys or even out the relief valve with every revolution of the pump. In at least some of the pumps a deaerator relief passage was also provided.
What seems most likely is that for levels of lateral acceleration up to perhaps 1.5 Gs that the thrashed oil and air does return to the sump in sufficient quantities to keep the pickup covered. I think somewhere between sustained 1.5 Gs and 2 Gs the pickup does start to become uncovered. At 2 Gs it seems reasonable to assume that the pickup is more uncovered than not.
At some point even the deaerator in the pump (at least some of them) is overwhelmed by the sheer volume of entrained air. At that point the hope must be that the multiple bars of pressure that can be generated by the pump is sufficient to push the air into solution at the rate of 9% per bar.
If that pressure was maintained throughout the circuit at all times the 2/6 bearing could hold out longer but there are a series of cross sectional decreases from the exit at the pump to the various arms of the circuit. In a dynamic hydraulic circuit this leads to pressure drops and that in turn leads to a supersatured solution releasing dissolved air to come into equilibrium with the new pressure.
There is a lot of debate over why the 2/6 circuit in particular gives so much trouble. It could be because it is the first to get a good dose of highly aerated oil. It could be as Mike Simard thinks, that there is some sort of Bernoulli effect happening at the entrance to the circuit. At some point it doesn't matter because fixing it will simply transfer the problem to another branch, ultimately. And there is no guarantee that with the 2/6 bearing protected that another bearing will not fail EVEN MORE QUICKLY than the 2/6 bearing did. I really think this is the sort of demonic situation the Porsche engineers were faced with.
Assuredly this is a highly complex problem. It is very understandable that people want to bypass it by installing a dry sump. Just be careful there too. Some new Vettes pop the engines despite having OEM dry sumps. Proper design is critical.
http://www.crank-scrapers.com/A-928.jpg
http://www.crank-scrapers.com/B-928.jpg
http://www.crank-scrapers.com/C-928.jpg
We can see that the engineers knew a lot of aerated oil was making its way back to the sump. The screening over the early sumps is an attempt to release trapped air from the oil. The clover-leaf fitting that sits next to the sump floor is an attempt to stop foamed oil from being directly ingested by the pickup for as long as possible. We know that the Porsche engineers would be aware of the quick benefit of adding a perimeter ledge around the sump well. It would trap a substantial portion of the oil that easily spills out during a turn producing only a 30 degree angle of repose.
We now know that the gerotor pump in at least some of the 928 engines was not a positive displacement pump with a certain amount of oil being pushed into the oil galleys or even out the relief valve with every revolution of the pump. In at least some of the pumps a deaerator relief passage was also provided.
What seems most likely is that for levels of lateral acceleration up to perhaps 1.5 Gs that the thrashed oil and air does return to the sump in sufficient quantities to keep the pickup covered. I think somewhere between sustained 1.5 Gs and 2 Gs the pickup does start to become uncovered. At 2 Gs it seems reasonable to assume that the pickup is more uncovered than not.
At some point even the deaerator in the pump (at least some of them) is overwhelmed by the sheer volume of entrained air. At that point the hope must be that the multiple bars of pressure that can be generated by the pump is sufficient to push the air into solution at the rate of 9% per bar.
If that pressure was maintained throughout the circuit at all times the 2/6 bearing could hold out longer but there are a series of cross sectional decreases from the exit at the pump to the various arms of the circuit. In a dynamic hydraulic circuit this leads to pressure drops and that in turn leads to a supersatured solution releasing dissolved air to come into equilibrium with the new pressure.
There is a lot of debate over why the 2/6 circuit in particular gives so much trouble. It could be because it is the first to get a good dose of highly aerated oil. It could be as Mike Simard thinks, that there is some sort of Bernoulli effect happening at the entrance to the circuit. At some point it doesn't matter because fixing it will simply transfer the problem to another branch, ultimately. And there is no guarantee that with the 2/6 bearing protected that another bearing will not fail EVEN MORE QUICKLY than the 2/6 bearing did. I really think this is the sort of demonic situation the Porsche engineers were faced with.
Assuredly this is a highly complex problem. It is very understandable that people want to bypass it by installing a dry sump. Just be careful there too. Some new Vettes pop the engines despite having OEM dry sumps. Proper design is critical.
06-04-2010, 07:10 PM
#80
Nordschleife Master
Thread Starter
One other point I'd like to comment on is that of oil flow volume and just how much oil volume must be handled by the sump cover and drain back system. Some calculations were done in earlier posts that showed the volume could be up to 21 gpm. The pump has losses and the already mentioned aeration bypass ports internal to the pump would reduce that volume by some amount. I was driving my GT a few days ago and took note of the oil pressure vs RPM. It isn't hot weather here now so the oil temp only got to 202F to 210F. The oil was Amsoil 20W 50. Idle RPM of 800 gave me 35 psi. The max oil pressure goes to 100 psi with hot oil then the pressure relief valve maintains that pressure. I get to 100 psi at 2400 to 2700 rpm. 2400 with oil temp 202 and 2700 at 210F oil temp. Oil that the pump supplies is bypassed at RPM above that. This tells me that the oil volume, at 100 psi, the engine uses is what the oil pump supplies at 2200 to 2700 RPM. With hotter oil the RPM for 100 psi would higher, depending on the oil. The engine uses, and the sump drain back system needs to handle, the oil volume the pump supplies at around 3000 RPM max. The remainder is merely bypassed and doesn't go through the engine. The engine use volume is nowhere near 21 gpm. Maybe 8-9 gpm.
If these calculations are correct then I think we can rule out oil aeration as a reason for the intermittent oil pressure drops on track. Here's why. A really badly aerated oil contains say 50% air by volume. At say 6000 rpm, the oil pump has enough capacity to completely compress these bubbles to zero volume (17 gallons of air oil mixture in per minute, 8.5 gallons of oil and completely compressed air out) and the pump will still have to return 4 gallons per minute thru the relief valve. Therefore, it seems to me that oil aeration can't be the reason for intermittent oil pressure drops on track.
06-04-2010, 07:22 PM
#81
Three Wheelin'
If these calculations are correct then I think we can rule out oil aeration as a reason for the intermittent oil pressure drops on track. Here's why. A really badly aerated oil contains say 50% air by volume. At say 6000 rpm, the oil pump has enough capacity to completely compress these bubbles to zero volume (17 gallons of air oil mixture in per minute, 8.5 gallons of oil and completely compressed air out) and the pump will still have to return 4 gallons per minute thru the relief valve. Therefore, it seems to me that oil aeration can't be the reason for intermittent oil pressure drops on track.
06-04-2010, 07:28 PM
#82
Nordschleife Master
Thread Starter
One other point I'd like to comment on is that of oil flow volume and just how much oil volume must be handled by the sump cover and drain back system. Some calculations were done in earlier posts that showed the volume could be up to 21 gpm. ... The remainder is merely bypassed and doesn't go through the engine. The engine use volume is nowhere near 21 gpm. Maybe 8-9 gpm.
If these calculations are correct then I think we can rule out oil aeration as a reason for the intermittent oil pressure drops on track. Here's why. A really badly aerated oil contains say 50% air by volume. At say 6000 rpm, the oil pump has enough capacity to completely compress these bubbles to zero volume (17 gallons of air oil mixture in per minute, 8.5 gallons of oil and completely compressed air out) and the pump will still have to return 4 gallons per minute thru the relief valve. Therefore, it seems to me that oil aeration can't be the reason for intermittent oil pressure drops on track.
06-15-2010, 09:06 PM
#83
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Hi,
I apologize for not replying earlier. I read the comment by Rick but did not log on and so was not notified of the subsequent posts.
On to the topic.
Ok, I am looking at a diagram of what I believe is the 928 oil pump and pressure circuit that I snagged somewhere online perhaps now years gone by.
So, first, the question, as Louie points out, of how much oil is really passing through the pump into the circuits and out through the "controlled leaks" is still very much open. I think his estimate is overly high given the information above.
Second, you must be clear on what you mean by aeration percentage level. Cosworth Technology defined it in SAE 2003-01-1994 as [Total air volume (i.e. free and dissolved)] divided by [oil volume] times 100%. In the SAE paper by Hyundai, 932785, the aeration percentage is defined as the [Volume of entrained air (i.e. small compressible bubbles of free air)] divided by [the total volume]. Why is this important? Well, Hyundai was using aeration levels of ~70% in a ~5.7bar capable system (relief valve setting) at 4500 rpms to generate ~2.5bar of pressure in the main oil galley. At 50% aeration level the generated pressure at 4500 rpm was ~4.2bar. At no point were the bubbles compressed to zero volume. I think what you meant was that the air would completely dissolve into solution -- but this is obviously not neccessarily the case at the pump outlet itself and certainly not neccessarily the case further into the oil circuit by point three below.
Third, you appear to be assuming that the pressure gradient in the lubrication circuit is a constant at the pressure developed by the pump ergo the compressed volume of the air-oil mix is constant. The paper by Cosworth makes very clear that this assumption is incorrect in a dynamic circuit such as found in an engine.
By no means whatsoever has oil aeration been ruled out as the method by which intermittent oil pressure drops are observed on the track. As the lateral and longitudinal Gs rise higher and higher then, of course, the pump pickup will be uncovered and a move to a dry sump system required (or an active wetsump).
I apologize for not replying earlier. I read the comment by Rick but did not log on and so was not notified of the subsequent posts.
On to the topic.
If these calculations are correct then I think we can rule out oil aeration as a reason for the intermittent oil pressure drops on track. Here's why. A really badly aerated oil contains say 50% air by volume. At say 6000 rpm, the oil pump has enough capacity to completely compress these bubbles to zero volume (17 gallons of air oil mixture in per minute, 8.5 gallons of oil and completely compressed air out) and the pump will still have to return 4 gallons per minute thru the relief valve. Therefore, it seems to me that oil aeration can't be the reason for intermittent oil pressure drops on track.
Ok, I am looking at a diagram of what I believe is the 928 oil pump and pressure circuit that I snagged somewhere online perhaps now years gone by.
The oil delivered by the oil pump goes first to the pressure relief valve. The pressure relief valve will open when a pressure of 8 bar is reached. The excessive oil will return into the suction side of the pump. The oil required for lubrication continues to the thermostat on which the oil pressure sending unit is located.
Second, you must be clear on what you mean by aeration percentage level. Cosworth Technology defined it in SAE 2003-01-1994 as [Total air volume (i.e. free and dissolved)] divided by [oil volume] times 100%. In the SAE paper by Hyundai, 932785, the aeration percentage is defined as the [Volume of entrained air (i.e. small compressible bubbles of free air)] divided by [the total volume]. Why is this important? Well, Hyundai was using aeration levels of ~70% in a ~5.7bar capable system (relief valve setting) at 4500 rpms to generate ~2.5bar of pressure in the main oil galley. At 50% aeration level the generated pressure at 4500 rpm was ~4.2bar. At no point were the bubbles compressed to zero volume. I think what you meant was that the air would completely dissolve into solution -- but this is obviously not neccessarily the case at the pump outlet itself and certainly not neccessarily the case further into the oil circuit by point three below.
Third, you appear to be assuming that the pressure gradient in the lubrication circuit is a constant at the pressure developed by the pump ergo the compressed volume of the air-oil mix is constant. The paper by Cosworth makes very clear that this assumption is incorrect in a dynamic circuit such as found in an engine.
By no means whatsoever has oil aeration been ruled out as the method by which intermittent oil pressure drops are observed on the track. As the lateral and longitudinal Gs rise higher and higher then, of course, the pump pickup will be uncovered and a move to a dry sump system required (or an active wetsump).
Last edited by Kevin Johnson; 06-15-2010 at 09:11 PM. Reason: gradiant to gradient
06-15-2010, 10:06 PM
#84
Nordschleife Master
Thread Starter
If these calculations are correct then I think we can rule out oil aeration as a reason for the intermittent oil pressure drops on track. Here's why. A really badly aerated oil contains say 50% air by volume. At say 6000 rpm, the oil pump has enough capacity to completely compress these bubbles to zero volume (17 gallons of air oil mixture in per minute, 8.5 gallons of oil and completely compressed air out) and the pump will still have to return 4 gallons per minute thru the relief valve. Therefore, it seems to me that oil aeration can't be the reason for intermittent oil pressure drops on track.
Second, you must be clear on what you mean by aeration percentage level. Cosworth Technology defined it in SAE 2003-01-1994 as [Total air volume (i.e. free and dissolved)] divided by [oil volume] times 100%. In the SAE paper by Hyundai, 932785, the aeration percentage is defined as the [Volume of entrained air (i.e. small compressible bubbles of free air)] divided by [the total volume]. Why is this important? Well, Hyundai was using aeration levels of ~70% in a ~5.7bar capable system (relief valve setting) at 4500 rpms to generate ~2.5bar of pressure in the main oil galley. At 50% aeration level the generated pressure at 4500 rpm was ~4.2bar. At no point were the bubbles compressed to zero volume. I think what you meant was that the air would completely dissolve into solution -- but this is obviously not neccessarily the case at the pump outlet itself and certainly not neccessarily the case further into the oil circuit by point three below.
The aerated air-oil mixture sucked by the pump will have to be 1/3 oil + 2/3 air by volume before the lower bound is attained. Air bubbles in the oil, aeration, whatever, are/is not going to lead to 1/3 oil + 2/3 air mixture being fed to the pump.
The extreme 70% aeration level you defined is 10/17 oil + 7/17 air. The pump could compress all the air and deliver full pressure to the sender with that.
Also, the oil pressure sender is really close to the pump outlet, so it's not any of the downstream effects that you describe. Sure, by the time the oil is in the rod journal, a lot of things can happen. Who knows what the pressure is there. However, we know that the pressure already drops right outside the pump outlet. This rules out the aeration (unless you define aeration as the pickup sucking wind intermittently.)
06-16-2010, 12:28 AM
#85
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I am running the numbers for the Hyundai formula and am getting the following sorts of figures:
Figure 7 liters of motor oil aerated to 70% at 1 bar in the sump.
.7 = (Vair)/(7l^3 + Vair)
= 16.333 liters of air mixed into the oil = 23.333 liters (volume) of air-oil mix or about 24.65 quarts or about 6.16 gallons (again, the later two by volume at 1 bar).
I am not sure why you don't feel this could account for the observed oil pressure fluctuations without any need for the pickup to be uncovered. Mind you, by the principal phase by volume being air the effect is similar.
Figure 7 liters of motor oil aerated to 70% at 1 bar in the sump.
.7 = (Vair)/(7l^3 + Vair)
= 16.333 liters of air mixed into the oil = 23.333 liters (volume) of air-oil mix or about 24.65 quarts or about 6.16 gallons (again, the later two by volume at 1 bar).
I am not sure why you don't feel this could account for the observed oil pressure fluctuations without any need for the pickup to be uncovered. Mind you, by the principal phase by volume being air the effect is similar.
06-16-2010, 12:58 AM
#86
Nordschleife Master
Thread Starter
Misread your definition, sorry about that.
Now it would be interesting to see some evidence of that 70% level (by your definition) actually being observable in the vicinity of the 928 engine.
There are further inconsistencies with the aeration theory. Higher the engine rpm (and thus the pump rpm and gross volume), bigger the observed pressure drop problem. That's the evidence. Aeration in oil is persistent. The aeration hypothesis would predict that the pressure drops would go away temporarily when the rpm and the gross pump flow increases. This is however the exact opposite of what we see.
The likely explanation for why the oil pressure drops at higher rpms is that the crankshaft is throwing oil to the heads and the top of the crankcase. The oil can't return to the sump and the pickup sucks wind. The higher the rpm, the more work the crankshaft does, the worse this problem.
Oil aeration has nothing to do with the 928 oil pressure drop problem in the high speed cornering at high rpm.
Now it would be interesting to see some evidence of that 70% level (by your definition) actually being observable in the vicinity of the 928 engine.
There are further inconsistencies with the aeration theory. Higher the engine rpm (and thus the pump rpm and gross volume), bigger the observed pressure drop problem. That's the evidence. Aeration in oil is persistent. The aeration hypothesis would predict that the pressure drops would go away temporarily when the rpm and the gross pump flow increases. This is however the exact opposite of what we see.
The likely explanation for why the oil pressure drops at higher rpms is that the crankshaft is throwing oil to the heads and the top of the crankcase. The oil can't return to the sump and the pickup sucks wind. The higher the rpm, the more work the crankshaft does, the worse this problem.
Oil aeration has nothing to do with the 928 oil pressure drop problem in the high speed cornering at high rpm.
I am running the numbers for the Hyundai formula and am getting the following sorts of figures:
Figure 7 liters of motor oil aerated to 70% at 1 bar in the sump.
.7 = (Vair)/(7l^3 + Vair)
= 16.333 liters of air mixed into the oil = 23.333 liters (volume) of air-oil mix or about 24.65 quarts or about 6.16 gallons (again, the later two by volume at 1 bar).
I am not sure why you don't feel this could account for the observed oil pressure fluctuations without any need for the pickup to be uncovered. Mind you, by the principal phase by volume being air the effect is similar.
Figure 7 liters of motor oil aerated to 70% at 1 bar in the sump.
.7 = (Vair)/(7l^3 + Vair)
= 16.333 liters of air mixed into the oil = 23.333 liters (volume) of air-oil mix or about 24.65 quarts or about 6.16 gallons (again, the later two by volume at 1 bar).
I am not sure why you don't feel this could account for the observed oil pressure fluctuations without any need for the pickup to be uncovered. Mind you, by the principal phase by volume being air the effect is similar.
06-16-2010, 01:52 AM
#87
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It is not my definition -- it is the definition used by Hyundai in their peer reviewed research paper.
To bring up the video ist leider nicht gestattet. Actually there is a large amount of inferential data that the 928 is doing just this. I was going to write that the characteristically large amounts of ejected oil could be easily explained by this phenomenon (but NOT so by the pickup merely being uncovered -- so the former has greater predictive value than the latter).
I think we simply need to pony up a few million and run oil with isotope tracers in some sort of real time X-ray scanner.
Maybe a little transfinite analysis can strip us this paltry sum from the economy at large. Go Georg ! There are further inconsistencies with the aeration theory. Higher the engine rpm (and thus the pump rpm and gross volume), bigger the observed pressure drop problem. That's the evidence. Aeration in oil is persistent. The aeration hypothesis would predict that the pressure drops would go away temporarily when the rpm and the gross pump flow increases. This is however the exact opposite of what we see.
The likely explanation for why the oil pressure drops at higher rpms is that the crankshaft is throwing oil to the heads and the top of the crankcase. The oil can't return to the sump and the pickup sucks wind. The higher the rpm, the more work the crankshaft does, the worse this problem.
Oil aeration has nothing to do with the 928 oil pressure drop problem in the high speed cornering at high rpm.
Oil aeration has nothing to do with the 928 oil pressure drop problem in the high speed cornering at high rpm.
I think the 928 engine is THE poster child for wetsump aeration at the intended racing rpms (7000 plus, btw). I think the engineers did the best they could to solve it given their constraints at the time.
Last edited by Kevin Johnson; 06-16-2010 at 01:55 AM. Reason: could could
06-16-2010, 08:12 AM
#88
Nordschleife Master
Thread Starter
Unrelated peer reviewed ergo sum aus dem Vaterland SAE CERN FBI aeration gradient paracompact Hausdorff space papers aside, the issue is in my opinion fairly simple at this point.
We observe intermittent low pressure spikes in corners at high rpm.
Because of the very large gross pump capacity, these low pressure spikes are unlikely to be caused by aeration. Pump would compress the air at most plausible aeration levels. Strike one.
If aeration were the cause of low pressure spikes, we wouldn't only observe those spikes in corners, because air bubbles in oil are persistent. Strike two.
If aeration would be the cause, the negative pressure spikes would be less likely appear at high rpm, because the gross pump capacity increases with rpm. We observe the opposite of what is predicted by the aeration hypothesis, the negative pressure spikes appear at high rpm. Strike three.
Three strikes and the aeration hypothesis is out.
In my opinion, it's not surprising that the a priori most likely explanation for intermittent low pressure spikes in corners, the pickup being uncovered, turns out to be true.
We observe intermittent low pressure spikes in corners at high rpm.
Because of the very large gross pump capacity, these low pressure spikes are unlikely to be caused by aeration. Pump would compress the air at most plausible aeration levels. Strike one.
If aeration were the cause of low pressure spikes, we wouldn't only observe those spikes in corners, because air bubbles in oil are persistent. Strike two.
If aeration would be the cause, the negative pressure spikes would be less likely appear at high rpm, because the gross pump capacity increases with rpm. We observe the opposite of what is predicted by the aeration hypothesis, the negative pressure spikes appear at high rpm. Strike three.
Three strikes and the aeration hypothesis is out.
In my opinion, it's not surprising that the a priori most likely explanation for intermittent low pressure spikes in corners, the pickup being uncovered, turns out to be true.
Well, SAE 940792 aus dem Vaterland shows an example of an engine spiking in aeration levels (see figure 4). The Porsche designed V6 at MIT studied over three SAE papers generated enough foam to obscure a camera placed above the sump. This is probably the genesis of the need to study it.
It is not my definition -- it is the definition used by Hyundai in their peer reviewed research paper.
To bring up the video ist leider nicht gestattet. Actually there is a large amount of inferential data that the 928 is doing just this. I was going to write that the characteristically large amounts of ejected oil could be easily explained by this phenomenon (but NOT so by the pickup merely being uncovered -- so the former has greater predictive value than the latter).
I think we simply need to pony up a few million and run oil with isotope tracers in some sort of real time X-ray scanner. Maybe a little transfinite analysis can strip us this paltry sum from the economy at large. Go Georg !
Higher rpms cause more/continued aeration. You somehow see this as reflexive evidence against aeration? I think all the papers I mentioned discuss this as an effect of high rpms. You have to give the oil time to release the air which is why the air release rate is so important and why it is important that some antifoams actually encourage air entrainment.
I think Porsche explored this hypothesis when they played around with the configuration of the oil return passages in the heads themselves. Ford did it too with the modular engine and the unfortunate location of the oil drains. I think the theory was properly rejected though. Foamed oil pouring forth from the cam bearings does flow more slowly back to the sump. However, this is an effect of the underlying problem and not a cause.
I think the 928 engine is THE poster child for wetsump aeration at the intended racing rpms (7000 plus, btw). I think the engineers did the best they could to solve it given their constraints at the time.
It is not my definition -- it is the definition used by Hyundai in their peer reviewed research paper.
To bring up the video ist leider nicht gestattet. Actually there is a large amount of inferential data that the 928 is doing just this. I was going to write that the characteristically large amounts of ejected oil could be easily explained by this phenomenon (but NOT so by the pickup merely being uncovered -- so the former has greater predictive value than the latter).
I think we simply need to pony up a few million and run oil with isotope tracers in some sort of real time X-ray scanner.
Maybe a little transfinite analysis can strip us this paltry sum from the economy at large. Go Georg ! Higher rpms cause more/continued aeration. You somehow see this as reflexive evidence against aeration? I think all the papers I mentioned discuss this as an effect of high rpms. You have to give the oil time to release the air which is why the air release rate is so important and why it is important that some antifoams actually encourage air entrainment.
I think Porsche explored this hypothesis when they played around with the configuration of the oil return passages in the heads themselves. Ford did it too with the modular engine and the unfortunate location of the oil drains. I think the theory was properly rejected though. Foamed oil pouring forth from the cam bearings does flow more slowly back to the sump. However, this is an effect of the underlying problem and not a cause.
I think the 928 engine is THE poster child for wetsump aeration at the intended racing rpms (7000 plus, btw). I think the engineers did the best they could to solve it given their constraints at the time.
06-16-2010, 09:26 AM
#89
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Oil Aeration in High Speed Combustion Engines
Product Code: 940792 Date Published: 1994-03-01
Author(s):
A. Haas - FEV Motorentechnik GmbH & Co.
F. MaaBen - FEV Motorentechnik GmbH & Co.
U. Geiger - FEV Motorentechnik GmbH & Co.
Abstract
Modern passenger car engines are designed to operate at increasingly higher rated engine speeds with more internal parts (multi-valve engines) requiring lubrication. There is a higher probability for the oil quality to deteriorate due to an unfavorabily high level of oil aeration. The high oil aeration can cause hydraulic lash adjuster misfunction and connecting rod bearing failure.
This paper presents results of recent research and development work concerning the occurrence of oil aeration within the lubricant system of modern combustion engines. In particular, the work has concentrated on the following: How oil aeration affects engine operation; How cavitation occurs in the supply bore to the connecting rod bearings; and What causes air entrainment in lubricants.
~~~~~~~~~~~~~~
Amazingly, you completely gloss over WHY?? the pump is so oversized and WHY?? would it have a deaeration circuit engineered into it and WHY?? would it feed the bypassed oil back into the pump.
Ay caramba.
If you took the time to READ the paper above you can also see how the engine design violates a number of considerations which lead to excessive aeration of the oil. If you look at the extant technology you can easily see how, say, BMW used the design suggestions when it revamped the M20. Or Toyota when it revamped the M series into the JZ. And on and on.
If you took the time to READ the citations I put up you might just find that these questions are addressed. Look at figure 7. in the paper below.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A New Technique for Dynamic Oil Aeration Monitoring
Product Code: 2003-01-1994 Date Published: 2003-05-19
Author(s):
Nigel McComb - Cosworth Technology
Adrian Cooper - Cosworth Technology
Abstract
Current trends in passenger cars are towards higher engine speeds, reduced oil fill volumes, and higher cornering forces, all of which tend to increase levels of oil aeration under dynamic cornering conditions.
For many years CT have been developing the oil aeration and oil handling performance of passenger car engines on a tilt rig under stabilized conditions, followed by validation in vehicle under dynamic conditions. There are currently several devices on the market for on- or off-line aeration measurements on the testbed, but in our experience none of these devices are particularly suitable for in-vehicle measurements. The vehicle validation has historically been a subjective assessment, predominantly based on observation of sudden drops in oil pressure. Although an effective Pass/Fail test, little useful information for development of the oil handling is gained.
CT have therefore developed a simple, real-time measure of oil aeration in vehicle, based on an accurate correlation of oil aeration level to oil pressure level.
~~~~~~~~~~~~~~~~~~~~~~~~
If aeration would be the cause, the negative pressure spikes would be less likely appear at high rpm, because the gross pump capacity increases with rpm. We observe the opposite of what is predicted by the aeration hypothesis, the negative pressure spikes appear at high rpm. Strike three.
Three strikes and the aeration hypothesis is out.
Three strikes and the aeration hypothesis is out.
I suggest more intensive study of the subject matter.
06-16-2010, 09:50 AM
#90
Nordschleife Master
Thread Starter
Kevin --
Are you into your usual tricks of mind reading and seeing thru camshafts with your full-color x-ray vision?
For example, you say say that I "completely gloss over WHY?? the pump is so oversized." Then you effectively propose we read the minds of the designers and ignore what they actually say. May I remind you that the stated reason by Porsche for increasing the pump capacity was increasing oil pressure at idle? Are your mind reading instruments indicating that this was not the true reason and further more pinpointing ths true reason? I couldn't make up this stuff you write, my imagination is too limited.
Your chain of logic about air bubbles in oil causing the intermittent oil pressure drops at high-rpm in fast corners is invalidated by the persistence of those air bubbles in oil. If aeration would be the problem then the low pressure wouldn't just show up temporarily in corners and at high rpm. Instead, the problem would persist much longer than that.
You can quote as many papers as you want. In the past, I've read maybe 5-10 SAE papers based on your recommendations. They turned out to be basically irrelevant to the problem at hand. Fool me once, shame on you, fool me ten times...?
In summary, I've concluded that you're full of it.
Best, Tuomo
Are you into your usual tricks of mind reading and seeing thru camshafts with your full-color x-ray vision?
For example, you say say that I "completely gloss over WHY?? the pump is so oversized." Then you effectively propose we read the minds of the designers and ignore what they actually say. May I remind you that the stated reason by Porsche for increasing the pump capacity was increasing oil pressure at idle? Are your mind reading instruments indicating that this was not the true reason and further more pinpointing ths true reason? I couldn't make up this stuff you write, my imagination is too limited.
Your chain of logic about air bubbles in oil causing the intermittent oil pressure drops at high-rpm in fast corners is invalidated by the persistence of those air bubbles in oil. If aeration would be the problem then the low pressure wouldn't just show up temporarily in corners and at high rpm. Instead, the problem would persist much longer than that.
You can quote as many papers as you want. In the past, I've read maybe 5-10 SAE papers based on your recommendations. They turned out to be basically irrelevant to the problem at hand. Fool me once, shame on you, fool me ten times...?
In summary, I've concluded that you're full of it.
Best, Tuomo
Aha... This could be part of the difficulty. Try looking at the references cited.
Oil Aeration in High Speed Combustion Engines
Product Code: 940792 Date Published: 1994-03-01
Author(s):
A. Haas - FEV Motorentechnik GmbH & Co.
F. MaaBen - FEV Motorentechnik GmbH & Co.
U. Geiger - FEV Motorentechnik GmbH & Co.
Abstract
Modern passenger car engines are designed to operate at increasingly higher rated engine speeds with more internal parts (multi-valve engines) requiring lubrication. There is a higher probability for the oil quality to deteriorate due to an unfavorabily high level of oil aeration. The high oil aeration can cause hydraulic lash adjuster misfunction and connecting rod bearing failure.
This paper presents results of recent research and development work concerning the occurrence of oil aeration within the lubricant system of modern combustion engines. In particular, the work has concentrated on the following: How oil aeration affects engine operation; How cavitation occurs in the supply bore to the connecting rod bearings; and What causes air entrainment in lubricants.
~~~~~~~~~~~~~~
Yes -- a swing and a miss.
Amazingly, you completely gloss over WHY?? the pump is so oversized and WHY?? would it have a deaeration circuit engineered into it and WHY?? would it feed the bypassed oil back into the pump.
Ay caramba.
If you took the time to READ the paper above you can also see how the engine design violates a number of considerations which lead to excessive aeration of the oil. If you look at the extant technology you can easily see how, say, BMW used the design suggestions when it revamped the M20. Or Toyota when it revamped the M series into the JZ. And on and on.
Yes, your second swing and a miss.
If you took the time to READ the citations I put up you might just find that these questions are addressed. Look at figure 7. in the paper below.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A New Technique for Dynamic Oil Aeration Monitoring
Product Code: 2003-01-1994 Date Published: 2003-05-19
Author(s):
Nigel McComb - Cosworth Technology
Adrian Cooper - Cosworth Technology
Abstract
Current trends in passenger cars are towards higher engine speeds, reduced oil fill volumes, and higher cornering forces, all of which tend to increase levels of oil aeration under dynamic cornering conditions.
For many years CT have been developing the oil aeration and oil handling performance of passenger car engines on a tilt rig under stabilized conditions, followed by validation in vehicle under dynamic conditions. There are currently several devices on the market for on- or off-line aeration measurements on the testbed, but in our experience none of these devices are particularly suitable for in-vehicle measurements. The vehicle validation has historically been a subjective assessment, predominantly based on observation of sudden drops in oil pressure. Although an effective Pass/Fail test, little useful information for development of the oil handling is gained.
CT have therefore developed a simple, real-time measure of oil aeration in vehicle, based on an accurate correlation of oil aeration level to oil pressure level.
~~~~~~~~~~~~~~~~~~~~~~~~
No, we observe exactly what is predicted by the aeration hypothesis and what is observed empirically and extensively reported across the subject matter. The problem is simply so severe in the 928 that the pump cannot control it.
I suggest more intensive study of the subject matter.
Oil Aeration in High Speed Combustion Engines
Product Code: 940792 Date Published: 1994-03-01
Author(s):
A. Haas - FEV Motorentechnik GmbH & Co.
F. MaaBen - FEV Motorentechnik GmbH & Co.
U. Geiger - FEV Motorentechnik GmbH & Co.
Abstract
Modern passenger car engines are designed to operate at increasingly higher rated engine speeds with more internal parts (multi-valve engines) requiring lubrication. There is a higher probability for the oil quality to deteriorate due to an unfavorabily high level of oil aeration. The high oil aeration can cause hydraulic lash adjuster misfunction and connecting rod bearing failure.
This paper presents results of recent research and development work concerning the occurrence of oil aeration within the lubricant system of modern combustion engines. In particular, the work has concentrated on the following: How oil aeration affects engine operation; How cavitation occurs in the supply bore to the connecting rod bearings; and What causes air entrainment in lubricants.
~~~~~~~~~~~~~~
Yes -- a swing and a miss.
Amazingly, you completely gloss over WHY?? the pump is so oversized and WHY?? would it have a deaeration circuit engineered into it and WHY?? would it feed the bypassed oil back into the pump.
Ay caramba.
If you took the time to READ the paper above you can also see how the engine design violates a number of considerations which lead to excessive aeration of the oil. If you look at the extant technology you can easily see how, say, BMW used the design suggestions when it revamped the M20. Or Toyota when it revamped the M series into the JZ. And on and on.
Yes, your second swing and a miss.
If you took the time to READ the citations I put up you might just find that these questions are addressed. Look at figure 7. in the paper below.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A New Technique for Dynamic Oil Aeration Monitoring
Product Code: 2003-01-1994 Date Published: 2003-05-19
Author(s):
Nigel McComb - Cosworth Technology
Adrian Cooper - Cosworth Technology
Abstract
Current trends in passenger cars are towards higher engine speeds, reduced oil fill volumes, and higher cornering forces, all of which tend to increase levels of oil aeration under dynamic cornering conditions.
For many years CT have been developing the oil aeration and oil handling performance of passenger car engines on a tilt rig under stabilized conditions, followed by validation in vehicle under dynamic conditions. There are currently several devices on the market for on- or off-line aeration measurements on the testbed, but in our experience none of these devices are particularly suitable for in-vehicle measurements. The vehicle validation has historically been a subjective assessment, predominantly based on observation of sudden drops in oil pressure. Although an effective Pass/Fail test, little useful information for development of the oil handling is gained.
CT have therefore developed a simple, real-time measure of oil aeration in vehicle, based on an accurate correlation of oil aeration level to oil pressure level.
~~~~~~~~~~~~~~~~~~~~~~~~
No, we observe exactly what is predicted by the aeration hypothesis and what is observed empirically and extensively reported across the subject matter. The problem is simply so severe in the 928 that the pump cannot control it.
I suggest more intensive study of the subject matter.