I had a tutor who called EGR pi**ing on the fire. Nox forms under high combustion temps, on a petrol engine that is lean cruise, on a diesel it's a bit more complicated. One day I'll go for a drive with the scanner and watch EGR cycling on a late model diesel, see when it's open and shut...and stay on my side of the road.
High Noack Oils and Dirty EGR Valves...
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NOx is annoying, in that it's a reaction (as you say temperature dependent), that's a "fast forward" and slow backward reaction. Get the temperatures right, and you react heaps of nitrogen and oxygen really quickly, and in order to make it go away have to slowly drop the temperatures for comparatively ages to get the compounds to dissociate again...it's all about the equilibrium species that occur at what temperatures and pressures...was a really interesting part of the IC engines study.
In the power station boilers, combustion is slowed down and staged....partial combustion in the initial reaction zone produces lots of CO, and residual HC...introduce air to it a few seconds later, and the process continues, without the high peak temperatures....make it too slow and the carbon doesn't burn out of the ash particles...unreacted soot.
The peeing on the fire analogy works...water injection works better than EGR...but you lose the phase change latent heat in evaporating it.
In the power station boilers, combustion is slowed down and staged....partial combustion in the initial reaction zone produces lots of CO, and residual HC...introduce air to it a few seconds later, and the process continues, without the high peak temperatures....make it too slow and the carbon doesn't burn out of the ash particles...unreacted soot.
The peeing on the fire analogy works...water injection works better than EGR...but you lose the phase change latent heat in evaporating it.
Originally Posted By: Shannow
Originally Posted By: Silk
Having cleaned both GDI and diesel manifolds - it's the same stuff.
Re the same stuff....
https://energy.gov/sites/prod/files/2014/03/f10/pm009_lance_2012_o.pdf
Basically hydrocarbon molecules that have been partially pyrolised during low temperature combustion and haven't lost all of the hydrogen to become soot...so it stays tarry and sticky.
Could be the stuff boiling off the upper ring lands and bores, or fuel related bottom ends in the quench crevices...note that hot they created it intentionally was to operate at idle, with HIGH EGR, and retarded timing.
Good find! The lacquer-like deposit composition data contained in this report was very interesting...
First they show the deposit to contain poly nuclear aromatics, or 'proto-soot' as they call it. Yes, this is exactly what you would get from poor combustion of diesel (particularly the heaviest part of diesel), but equally it's what you might expect from burning oil. In fact I'd say that there's a degree of boiling range overlap between the heaviest 1% of diesel and the lightest 1% of engine oil.
The deposit was ash-free. This is significant. If, just for the sake of argument, you presume that some of the deposit originated from engine oil (as opposed to diesel fuel), if this stuff was coming from neat engine oil being sucked through worn valve seals or low speed top ring 'throw-off', one might expect to find some ash there; but there is none. On the other hand, if it was light oil strip-out, migrating through the PCV system, this oil would be ash-free (detergents are relatively heavy and stay in the sump) so partial burning of this stuff would yield an ash-free deposit.
I also noted that they found -OH radicals in the deposit. Obviously that's consistent with something being burnt. However one of the things that occurs to me is light-oil strip out not only won't contain detergent (which stays in the sump), but won't contain antioxidant either, so it will be far more prone to oxidative attack once it reaches the combustion chamber.
The target of my original post was gasoline engines fitted with EGR, not diesels, and there's only so much you can stretch a study like this. However I take heart that the analysis done suggest that EGR deposits are consistent with the partial combustion of something relatively heavy. In a gasoline engine, that might be something like oil or gasoline additives!
Originally Posted By: Silk
Having cleaned both GDI and diesel manifolds - it's the same stuff.
Re the same stuff....
https://energy.gov/sites/prod/files/2014/03/f10/pm009_lance_2012_o.pdf
Basically hydrocarbon molecules that have been partially pyrolised during low temperature combustion and haven't lost all of the hydrogen to become soot...so it stays tarry and sticky.
Could be the stuff boiling off the upper ring lands and bores, or fuel related bottom ends in the quench crevices...note that hot they created it intentionally was to operate at idle, with HIGH EGR, and retarded timing.
Good find! The lacquer-like deposit composition data contained in this report was very interesting...
First they show the deposit to contain poly nuclear aromatics, or 'proto-soot' as they call it. Yes, this is exactly what you would get from poor combustion of diesel (particularly the heaviest part of diesel), but equally it's what you might expect from burning oil. In fact I'd say that there's a degree of boiling range overlap between the heaviest 1% of diesel and the lightest 1% of engine oil.
The deposit was ash-free. This is significant. If, just for the sake of argument, you presume that some of the deposit originated from engine oil (as opposed to diesel fuel), if this stuff was coming from neat engine oil being sucked through worn valve seals or low speed top ring 'throw-off', one might expect to find some ash there; but there is none. On the other hand, if it was light oil strip-out, migrating through the PCV system, this oil would be ash-free (detergents are relatively heavy and stay in the sump) so partial burning of this stuff would yield an ash-free deposit.
I also noted that they found -OH radicals in the deposit. Obviously that's consistent with something being burnt. However one of the things that occurs to me is light-oil strip out not only won't contain detergent (which stays in the sump), but won't contain antioxidant either, so it will be far more prone to oxidative attack once it reaches the combustion chamber.
The target of my original post was gasoline engines fitted with EGR, not diesels, and there's only so much you can stretch a study like this. However I take heart that the analysis done suggest that EGR deposits are consistent with the partial combustion of something relatively heavy. In a gasoline engine, that might be something like oil or gasoline additives!
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http://papers.sae.org/2017-01-0806/
Quote:
Exhaust Gas Recirculation (EGR) systems reduce exhaust emissions and improve fuel efficiency. Recently, the number of EGR system installed vehicles has been increasing, especially for gasoline engine systems. One of the major causes of decreasing EGR function is deposit accumulation on a gas passage. The deposit consists mainly of hydrocarbons which are degradation products of fuel, thus the amount of deposit seems to be strongly affected by fuel compositions. Unfortunately there are not as many studies on EGR deposits with gasoline fuel as there are with diesel fuel. In this study, the influence of gasoline fuel compositions, especially aromatics which are major components of EGR gas, on chemical structures of the deposit were investigated. To clarify the accumulation mechanism of EGR deposits, a thermal oxidative degradation test with an autoclave unit and an actual gasoline engine test were employed. Different composition fuels to control the carbon number of the aromatic were prepared as test fuels. The result of the thermal oxidative degradation test showed that the higher carbon number of the aromatics in a fuel increases the accumulation of deposit. The result of the engine test indicated that the test fuel, containing higher amount of C10 and C10+ aromatics, caused higher accumulation rate of deposit. These results suggested that the accumulation of EGR deposit was affected by the carbon number of the aromatic.
Quote:
Exhaust Gas Recirculation (EGR) systems reduce exhaust emissions and improve fuel efficiency. Recently, the number of EGR system installed vehicles has been increasing, especially for gasoline engine systems. One of the major causes of decreasing EGR function is deposit accumulation on a gas passage. The deposit consists mainly of hydrocarbons which are degradation products of fuel, thus the amount of deposit seems to be strongly affected by fuel compositions. Unfortunately there are not as many studies on EGR deposits with gasoline fuel as there are with diesel fuel. In this study, the influence of gasoline fuel compositions, especially aromatics which are major components of EGR gas, on chemical structures of the deposit were investigated. To clarify the accumulation mechanism of EGR deposits, a thermal oxidative degradation test with an autoclave unit and an actual gasoline engine test were employed. Different composition fuels to control the carbon number of the aromatic were prepared as test fuels. The result of the thermal oxidative degradation test showed that the higher carbon number of the aromatics in a fuel increases the accumulation of deposit. The result of the engine test indicated that the test fuel, containing higher amount of C10 and C10+ aromatics, caused higher accumulation rate of deposit. These results suggested that the accumulation of EGR deposit was affected by the carbon number of the aromatic.
Originally Posted By: CR94
For what it's worth, I keep seeing reports of Prii with 2-3X the mileage of mine suffering from severely clogged EGR coolers.
Sounds like this is a part you will want to have "on hand" well ahead of time, and probably should change preventatively.
For what it's worth, I keep seeing reports of Prii with 2-3X the mileage of mine suffering from severely clogged EGR coolers.
Sounds like this is a part you will want to have "on hand" well ahead of time, and probably should change preventatively.
Oddly enough, my GDI 2.0L turbo has no EGR valve or system. They use the VVT (intake/exhaust) system to get whatever effect is needed to reduce emissions from it. What GDI intake valve deposits that have been seen in these engines is due to the PCV pathway.
Originally Posted By: Shannow
http://papers.sae.org/2017-01-0806/
Quote:
Exhaust Gas Recirculation (EGR) systems reduce exhaust emissions and improve fuel efficiency. Recently, the number of EGR system installed vehicles has been increasing, especially for gasoline engine systems. One of the major causes of decreasing EGR function is deposit accumulation on a gas passage. The deposit consists mainly of hydrocarbons which are degradation products of fuel, thus the amount of deposit seems to be strongly affected by fuel compositions. Unfortunately there are not as many studies on EGR deposits with gasoline fuel as there are with diesel fuel. In this study, the influence of gasoline fuel compositions, especially aromatics which are major components of EGR gas, on chemical structures of the deposit were investigated. To clarify the accumulation mechanism of EGR deposits, a thermal oxidative degradation test with an autoclave unit and an actual gasoline engine test were employed. Different composition fuels to control the carbon number of the aromatic were prepared as test fuels. The result of the thermal oxidative degradation test showed that the higher carbon number of the aromatics in a fuel increases the accumulation of deposit. The result of the engine test indicated that the test fuel, containing higher amount of C10 and C10+ aromatics, caused higher accumulation rate of deposit. These results suggested that the accumulation of EGR deposit was affected by the carbon number of the aromatic.
This is an interesting one...
If you take gasoline and batter it hard enough in an autoclave, I'm sure you can get it to decompose and yield a black, sticky deposit that has stuff in common with gasoline EGR crud. However, for me, that might not be enough to convince me that gasoline itself is actually the primary source of EGR deposits.
I only say this because so many times I've seen engine oils subjected to extreme, destabilising conditions and the resultant deposit formed deemed to 'correlate' with some aspect of oil performance, when in fact it doesn't.
The TEOST MHT-4, is one such test. It runs oil at 285°C over a steel tube for 24 hours and the weight of the gunk that has accumulated on the tube is supposed to 'represent' ring pack & under-crown deposits. This is such utter rubbish! In fact the test is so flaky (literally as flakes of deposit often fall off in transferring the steel tube to the weigh scale) that the test hardly correlates with itself, never mind with engine deposits!
In a way, the Japanese study reminds me of the old joke about the man walking home in the dark one night, who stumbles upon a drunk, on all fours, under a street light. 'What are you doing?' asks the man. 'I'm looking for my car keys' the drunk slurs back. 'Where did you lose them?' asks the man. The drunk points over to a dark back alley. 'Well why don't you look over there then?' asks the man, to which the drunk replies 'But I can see here!'.
http://papers.sae.org/2017-01-0806/
Quote:
Exhaust Gas Recirculation (EGR) systems reduce exhaust emissions and improve fuel efficiency. Recently, the number of EGR system installed vehicles has been increasing, especially for gasoline engine systems. One of the major causes of decreasing EGR function is deposit accumulation on a gas passage. The deposit consists mainly of hydrocarbons which are degradation products of fuel, thus the amount of deposit seems to be strongly affected by fuel compositions. Unfortunately there are not as many studies on EGR deposits with gasoline fuel as there are with diesel fuel. In this study, the influence of gasoline fuel compositions, especially aromatics which are major components of EGR gas, on chemical structures of the deposit were investigated. To clarify the accumulation mechanism of EGR deposits, a thermal oxidative degradation test with an autoclave unit and an actual gasoline engine test were employed. Different composition fuels to control the carbon number of the aromatic were prepared as test fuels. The result of the thermal oxidative degradation test showed that the higher carbon number of the aromatics in a fuel increases the accumulation of deposit. The result of the engine test indicated that the test fuel, containing higher amount of C10 and C10+ aromatics, caused higher accumulation rate of deposit. These results suggested that the accumulation of EGR deposit was affected by the carbon number of the aromatic.
This is an interesting one...
If you take gasoline and batter it hard enough in an autoclave, I'm sure you can get it to decompose and yield a black, sticky deposit that has stuff in common with gasoline EGR crud. However, for me, that might not be enough to convince me that gasoline itself is actually the primary source of EGR deposits.
I only say this because so many times I've seen engine oils subjected to extreme, destabilising conditions and the resultant deposit formed deemed to 'correlate' with some aspect of oil performance, when in fact it doesn't.
The TEOST MHT-4, is one such test. It runs oil at 285°C over a steel tube for 24 hours and the weight of the gunk that has accumulated on the tube is supposed to 'represent' ring pack & under-crown deposits. This is such utter rubbish! In fact the test is so flaky (literally as flakes of deposit often fall off in transferring the steel tube to the weigh scale) that the test hardly correlates with itself, never mind with engine deposits!
In a way, the Japanese study reminds me of the old joke about the man walking home in the dark one night, who stumbles upon a drunk, on all fours, under a street light. 'What are you doing?' asks the man. 'I'm looking for my car keys' the drunk slurs back. 'Where did you lose them?' asks the man. The drunk points over to a dark back alley. 'Well why don't you look over there then?' asks the man, to which the drunk replies 'But I can see here!'.
I now have a fair understanding of what's going, and after I read the Oak Ridge paper (not about EGR valves but EGR coolers), it confirmed that I was right about the EGR-valve fouling being caused by the EGR port running too cold.
Therefore, most EGR-valve fouling cases seem to be analogous to spark-plug fouling when plugs running too cold (plugs with too low heat range installed) and unable to self-clean themselves by heat.
If you inspect the fouled EGR systems, you find that fouling occurs at the EGR port of the valve, not the exhaust pipe that leads to it. This is the part of the valve that runs coldest. The HC in the exhaust likes to deposit on cold surfaces. In addition you don't get the thermal and chemical cleaning effects (such as spallation [ejection] caused by temperature and hot, fast-moving gas) with cold surfaces. Since the rate of heat transferred is proportional to the flow rate of the EGR gas, with lower flow rates, the EGR-valve port will run colder and be more prone to deposit accumulation.
In my 1985 Toyota Corolla, when the EGR vacuum modulator was failing, EGR valve started operating in a limited manner, and the port was running too cold. This lead to catastrophic deposit formation in a short amount of time. When more deposits were formed, less exhaust gas was able to pass, and the port starting running even colder due to less EGR-gas flow. Therefore, it was an avalanche effect that kept speeding up and resulted in full clogging quickly.
The same thing happened with the Volkswagen standard. They deliberately tampered with the EGR system and they allowed the EGR valve to run in a limited manner. When they did this, the EGR-valve port was running too cold and it resulted in quick fouling. When they wanted to operate the EGR valve in a normal manner after they got caught, they realized that they were already clogged shut or almost clogged shut.
So, if you have EGR-valve fouling, chances are that there is something else in the EGR system that has failed and was causing the EGR valve not to self-clean itself by heat, which is the actual reason for the fouling.
Note that the EGR coolers have a natural tendency to clog as they run cold. If you have an EGR cooler, you can only hope that a good design will extend its life.
EGR-valve clogging seems to be relatively rare, indicating that fuel and oil have a small effect only. It's interesting that HC coming from the gasoline is the main contributor to the deposits according to the SAE paper posted here. That's what I had thought all along before I saw the original post here. When you actually work on your own car and encounter and fix these problems, you have a better intuition of what's going on.
Therefore, most EGR-valve fouling cases seem to be analogous to spark-plug fouling when plugs running too cold (plugs with too low heat range installed) and unable to self-clean themselves by heat.
If you inspect the fouled EGR systems, you find that fouling occurs at the EGR port of the valve, not the exhaust pipe that leads to it. This is the part of the valve that runs coldest. The HC in the exhaust likes to deposit on cold surfaces. In addition you don't get the thermal and chemical cleaning effects (such as spallation [ejection] caused by temperature and hot, fast-moving gas) with cold surfaces. Since the rate of heat transferred is proportional to the flow rate of the EGR gas, with lower flow rates, the EGR-valve port will run colder and be more prone to deposit accumulation.
In my 1985 Toyota Corolla, when the EGR vacuum modulator was failing, EGR valve started operating in a limited manner, and the port was running too cold. This lead to catastrophic deposit formation in a short amount of time. When more deposits were formed, less exhaust gas was able to pass, and the port starting running even colder due to less EGR-gas flow. Therefore, it was an avalanche effect that kept speeding up and resulted in full clogging quickly.
The same thing happened with the Volkswagen standard. They deliberately tampered with the EGR system and they allowed the EGR valve to run in a limited manner. When they did this, the EGR-valve port was running too cold and it resulted in quick fouling. When they wanted to operate the EGR valve in a normal manner after they got caught, they realized that they were already clogged shut or almost clogged shut.
So, if you have EGR-valve fouling, chances are that there is something else in the EGR system that has failed and was causing the EGR valve not to self-clean itself by heat, which is the actual reason for the fouling.
Note that the EGR coolers have a natural tendency to clog as they run cold. If you have an EGR cooler, you can only hope that a good design will extend its life.
EGR-valve clogging seems to be relatively rare, indicating that fuel and oil have a small effect only. It's interesting that HC coming from the gasoline is the main contributor to the deposits according to the SAE paper posted here. That's what I had thought all along before I saw the original post here. When you actually work on your own car and encounter and fix these problems, you have a better intuition of what's going on.
Originally Posted By: Shannow
.
? What happened ?
.
? What happened ?
Yep, sometimes it's better to just let stuff go.
Originally Posted By: Linctex
Originally Posted By: CR94
For what it's worth, I keep seeing reports of Prii with 2-3X the mileage of mine suffering from severely clogged EGR coolers.
Sounds like this is a part you will want to have "on hand" well ahead of time, and probably should change preventatively.
Perhaps so, but they're expensive, at least new ones are. One guy (on Priuschat.com) reported success digging the gunk out using #20 AWG bare copper wire in a drill. (Copper because steel would puncture the heat exchanger tubes, I gather.) EGR passages in the intake manifold also reportedly clog up, but aren't as difficult to clean.
Meanwhile, so far (at ~76K miles), mine has no such problem yet, and consumes remarkably little oil.
Originally Posted By: CR94
For what it's worth, I keep seeing reports of Prii with 2-3X the mileage of mine suffering from severely clogged EGR coolers.
Sounds like this is a part you will want to have "on hand" well ahead of time, and probably should change preventatively.
Perhaps so, but they're expensive, at least new ones are. One guy (on Priuschat.com) reported success digging the gunk out using #20 AWG bare copper wire in a drill. (Copper because steel would puncture the heat exchanger tubes, I gather.) EGR passages in the intake manifold also reportedly clog up, but aren't as difficult to clean.
Meanwhile, so far (at ~76K miles), mine has no such problem yet, and consumes remarkably little oil.
Originally Posted By: Shannow
I still remember having the handbrake cable pulled up through the drain bung in the rear seat floor (remember cars having drain bungs ???)
My car had drain bungs, but I think I've lost them.
(Why) don't modern cars have drain bungs?
I still remember having the handbrake cable pulled up through the drain bung in the rear seat floor (remember cars having drain bungs ???)
My car had drain bungs, but I think I've lost them.
(Why) don't modern cars have drain bungs?
Google Books Link on Chemistry of Engine Combustion Deposits
Has specific mention of EGR deposits, and finds them to have significant (6%) ash from oils, and Polyisobutenes, potentially as a "binder" derived from fuels and lubes...
With regard to the "adiabatic cooling" theory, note that the article has volume loss with temperature, and this is thermal decomposition/residual fraction, not "dew point" and cold wall effects.
When it comes to deposit formation, one of the ones observable in industry is the "splat" effect, where sudden changes in acceleration and direction cause sticky stuff that was entirely capable of following the flow path impact and stick where it changed direction and ran into stuff.
Has specific mention of EGR deposits, and finds them to have significant (6%) ash from oils, and Polyisobutenes, potentially as a "binder" derived from fuels and lubes...
With regard to the "adiabatic cooling" theory, note that the article has volume loss with temperature, and this is thermal decomposition/residual fraction, not "dew point" and cold wall effects.
When it comes to deposit formation, one of the ones observable in industry is the "splat" effect, where sudden changes in acceleration and direction cause sticky stuff that was entirely capable of following the flow path impact and stick where it changed direction and ran into stuff.
Originally Posted By: Shannow
Google Books Link on Chemistry of Engine Combustion Deposits
Has specific mention of EGR deposits, and finds them to have significant (6%) ash from oils, and Polyisobutenes, potentially as a "binder" derived from fuels and lubes...
With regard to the "adiabatic cooling" theory, note that the article has volume loss with temperature, and this is thermal decomposition/residual fraction, not "dew point" and cold wall effects.
When it comes to deposit formation, one of the ones observable in industry is the "splat" effect, where sudden changes in acceleration and direction cause sticky stuff that was entirely capable of following the flow path impact and stick where it changed direction and ran into stuff.
I don't know what I find more amazing?
That here at last is some solid evidence that EGR deposits have a link to both engine oil and fuel/oil additives (contrary to what He Who Thinks He Knows Everything says)...
...or that somewhere out there is an individual who's sad life is so bereft of joy that he feels the need to write an entire book about The Chemistry Of Engine Combustion Deposits!!!
Google Books Link on Chemistry of Engine Combustion Deposits
Has specific mention of EGR deposits, and finds them to have significant (6%) ash from oils, and Polyisobutenes, potentially as a "binder" derived from fuels and lubes...
With regard to the "adiabatic cooling" theory, note that the article has volume loss with temperature, and this is thermal decomposition/residual fraction, not "dew point" and cold wall effects.
When it comes to deposit formation, one of the ones observable in industry is the "splat" effect, where sudden changes in acceleration and direction cause sticky stuff that was entirely capable of following the flow path impact and stick where it changed direction and ran into stuff.
I don't know what I find more amazing?
That here at last is some solid evidence that EGR deposits have a link to both engine oil and fuel/oil additives (contrary to what He Who Thinks He Knows Everything says)...
...or that somewhere out there is an individual who's sad life is so bereft of joy that he feels the need to write an entire book about The Chemistry Of Engine Combustion Deposits!!!
Last edited:
Originally Posted By: SonofJoe
...or that somewhere out there is an individual who's sad life is so bereft of joy that he feels the need to write an entire book about The Chemistry Of Engine Combustion Deposits!!!
....or that there's somebody who goes out and looks in every direction to find those things....only to share "other people's work"...
...or that somewhere out there is an individual who's sad life is so bereft of joy that he feels the need to write an entire book about The Chemistry Of Engine Combustion Deposits!!!
....or that there's somebody who goes out and looks in every direction to find those things....only to share "other people's work"...
Originally Posted By: Shannow
When it comes to deposit formation, one of the ones observable in industry is the "splat" effect, where sudden changes in acceleration and direction cause sticky stuff that was entirely capable of following the flow path impact and stick where it changed direction and ran into stuff.
Sounds like how "cyclonic" air filters work. In this context, one could perhaps put a "cyclonic" catch-can gizmo in the EGR path.
When it comes to deposit formation, one of the ones observable in industry is the "splat" effect, where sudden changes in acceleration and direction cause sticky stuff that was entirely capable of following the flow path impact and stick where it changed direction and ran into stuff.
Sounds like how "cyclonic" air filters work. In this context, one could perhaps put a "cyclonic" catch-can gizmo in the EGR path.
With Shannow's photo in his first post on this thread, I don't think crankcase blowby oil is a factor in these manifold deposits, and SonofJoe is looking at fuel.
Having stripped heads on these late model diesel engines, and had to clean them up, I noticed the inlet valves also coated with a thick but soft carbon - chip it off with another valve before cleaning up on the wire brush.
This set me thinking back 30 years, when some engines (carburettored and no PCV or EGR) got thick soft carbon deposits on the back of inlet valves. We used to chip it off with another valve and then clean up on the wire brush. And what I remember is the thick sweet taste in the back of my throat - lead. So they must've been fuel deposits.
Having stripped heads on these late model diesel engines, and had to clean them up, I noticed the inlet valves also coated with a thick but soft carbon - chip it off with another valve before cleaning up on the wire brush.
This set me thinking back 30 years, when some engines (carburettored and no PCV or EGR) got thick soft carbon deposits on the back of inlet valves. We used to chip it off with another valve and then clean up on the wire brush. And what I remember is the thick sweet taste in the back of my throat - lead. So they must've been fuel deposits.
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