Carbon Build Up in the 4.0 TFSI V8
06-02-2015, 01:52 PM
#1
Carbon Build Up in the 4.0 TFSI V8
After reading tons about direct injection motors all over the place and trying to understand the process, it seems that direct injection engines will be prone to this no matter what.
I read quite a bit and learned a lot about the new 4.0 TFSI from sites like this:
The new Audi 4.0-L V8 TFSI engine - Springer
I wanted to know why some people say that running the car harder may actually make carbon deposits worse in direct injection engines. I think I finally found out why this phenomenon takes place.
First, a direct injection engine has fuel injectors inside the combustion chamber, NOT, (emphasis here!) in the ports directly in front of the intake valves. I.e. there is a fuel injector inside where the piston goes up and down in every single cylinder.
Carbon build up happens on the INTAKE valves and the preceding areas in front of the intake valves.
How in the world does this carbon magically appear here? There aren't any carbon containing air, liquid or other things traversing here. Right? I mean all the combustion (i.e. carbon producing events) are happening down stream separated by closed intake valves. Right???
RIGHT????
Nope. There are 3 (at least) different sources of carbon (gases and liquids) that are traversing all the intake areas.
1. Atmospheric gases. 21% O2 and 70% N2 with less than 1% CO2
2. Evaporative fuel from the charcoal canister (plenty of carbon containing stuff here!)
3. Positive Crankcase pressure. All engines, especially, forcefully inducted engines have some "blow by".
Blow by is a phenomenon of escaped gases that escape around the pistons as the pistons enter the compression cycle. This escaped gas can't just get vented into the atmosphere. That is unwanted pollution.
From my reading, I couldn't find an EGR valve in the 4.0 TFSI. This would be another potential source of carbon that could crud up the intake side. But alas, it doesn't seem like our 4.0's have them.
So what happens with all the positive pressure "blow by"?
In short, it gets vented BACK into the intake side.
This "blow by" forms positive pressure inside the crankcase where there is TONS Of oil circulating with oil droplets galore!!! And the harder you drive the engine, the more "blow by" gets through and pressurizes the crankcase and hence more oil infused gases get circulated to the intake side.
This is where the misplaced notion that driving your car hard will "burn" off the carbon deposits. Yes, super heated elements in the engine can burn carbon deposits, but intake valves are rarely hot enough for long enough for that to happen.
On engines that are NOT direct port injected, this oil infused crankcase gas gets mixed and, more importantly, dissolved with fuel from the injectors before the intake valves and all the gunk goes back into the combustion chamber and it's all burned up and expelled.
Most engines have filtering mechanisms that help with eliminating the oil droplets in the crankcase gases. The 4.0 has a rather sophisticated version and hopefully this new Audi system will keep too many carbon deposits from forming.
Our 4.0's have large oil droplet accumulation and small oil droplet accumulation mechanisms.
The old 4.2L V8, in the RS4 e.g., was notorious for carbon deposits as early as 10,000 miles! Ack! In my readings the 4.2 also had an crankcase oil accumulator, but it seems less sophisticated than in the 4.0.
Has anyone heard, and confirmed, carbon deposits in the 4.0 TFSI?
I read quite a bit and learned a lot about the new 4.0 TFSI from sites like this:
The new Audi 4.0-L V8 TFSI engine - Springer
I wanted to know why some people say that running the car harder may actually make carbon deposits worse in direct injection engines. I think I finally found out why this phenomenon takes place.
First, a direct injection engine has fuel injectors inside the combustion chamber, NOT, (emphasis here!) in the ports directly in front of the intake valves. I.e. there is a fuel injector inside where the piston goes up and down in every single cylinder.
Carbon build up happens on the INTAKE valves and the preceding areas in front of the intake valves.
How in the world does this carbon magically appear here? There aren't any carbon containing air, liquid or other things traversing here. Right? I mean all the combustion (i.e. carbon producing events) are happening down stream separated by closed intake valves. Right???
RIGHT????
Nope. There are 3 (at least) different sources of carbon (gases and liquids) that are traversing all the intake areas.
1. Atmospheric gases. 21% O2 and 70% N2 with less than 1% CO2
2. Evaporative fuel from the charcoal canister (plenty of carbon containing stuff here!)
3. Positive Crankcase pressure. All engines, especially, forcefully inducted engines have some "blow by".
Blow by is a phenomenon of escaped gases that escape around the pistons as the pistons enter the compression cycle. This escaped gas can't just get vented into the atmosphere. That is unwanted pollution.
From my reading, I couldn't find an EGR valve in the 4.0 TFSI. This would be another potential source of carbon that could crud up the intake side. But alas, it doesn't seem like our 4.0's have them.
So what happens with all the positive pressure "blow by"?
In short, it gets vented BACK into the intake side.
This "blow by" forms positive pressure inside the crankcase where there is TONS Of oil circulating with oil droplets galore!!! And the harder you drive the engine, the more "blow by" gets through and pressurizes the crankcase and hence more oil infused gases get circulated to the intake side.
This is where the misplaced notion that driving your car hard will "burn" off the carbon deposits. Yes, super heated elements in the engine can burn carbon deposits, but intake valves are rarely hot enough for long enough for that to happen.
On engines that are NOT direct port injected, this oil infused crankcase gas gets mixed and, more importantly, dissolved with fuel from the injectors before the intake valves and all the gunk goes back into the combustion chamber and it's all burned up and expelled.
Most engines have filtering mechanisms that help with eliminating the oil droplets in the crankcase gases. The 4.0 has a rather sophisticated version and hopefully this new Audi system will keep too many carbon deposits from forming.
Our 4.0's have large oil droplet accumulation and small oil droplet accumulation mechanisms.
The old 4.2L V8, in the RS4 e.g., was notorious for carbon deposits as early as 10,000 miles! Ack! In my readings the 4.2 also had an crankcase oil accumulator, but it seems less sophisticated than in the 4.0.
Has anyone heard, and confirmed, carbon deposits in the 4.0 TFSI?
06-02-2015, 04:11 PM
#2
AudiWorld Senior Member
Great write-up. I agree with all of your points.
Do you think the specification and cleanliness of the oil has anything to do with it? Or is there any component already included, or that we can add to the oil to reduce this effect?
Also, a turbocharged engine has two pathways for the PCV system.
1. Naturally-aspirated mode when there is an intake manifold vacuum which draws the blow-by gases directly into the manifold.
2. Charged mode where the blow-by gases are drawn into the turbocharger. Perhaps when people use boost a lot, more of the blow-by gases will go down this pathway, and some of the oil will get caught in the intercooler?
Do you think the specification and cleanliness of the oil has anything to do with it? Or is there any component already included, or that we can add to the oil to reduce this effect?
Also, a turbocharged engine has two pathways for the PCV system.
1. Naturally-aspirated mode when there is an intake manifold vacuum which draws the blow-by gases directly into the manifold.
2. Charged mode where the blow-by gases are drawn into the turbocharger. Perhaps when people use boost a lot, more of the blow-by gases will go down this pathway, and some of the oil will get caught in the intercooler?
06-02-2015, 04:52 PM
#3
AudiWorld Member
Great write-up. I agree with all of your points.
Do you think the specification and cleanliness of the oil has anything to do with it? Or is there any component already included, or that we can add to the oil to reduce this effect?
Also, a turbocharged engine has two pathways for the PCV system.
1. Naturally-aspirated mode when there is an intake manifold vacuum which draws the blow-by gases directly into the manifold.
2. Charged mode where the blow-by gases are drawn into the turbocharger. Perhaps when people use boost a lot, more of the blow-by gases will go down this pathway, and some of the oil will get caught in the intercooler?
Do you think the specification and cleanliness of the oil has anything to do with it? Or is there any component already included, or that we can add to the oil to reduce this effect?
Also, a turbocharged engine has two pathways for the PCV system.
1. Naturally-aspirated mode when there is an intake manifold vacuum which draws the blow-by gases directly into the manifold.
2. Charged mode where the blow-by gases are drawn into the turbocharger. Perhaps when people use boost a lot, more of the blow-by gases will go down this pathway, and some of the oil will get caught in the intercooler?
Nothing you change in the crankcase with oil additives, or different brands of oil will have any effect on intake carbon. Fuel used to keep the intake clean, or cleaner when using fuels with cleaning additives added, but now there is no fuel upstream of the intake valves and ports for any cleaning effect.
NA engines put the crankcase breather right into the intake stream. Turbo engines also draws the blowby right into the intake. Intercoolers will always contain oil when taken apart. Its impossible to completely seal the oil in a turbo. Turbos contain a labyrinth seal and they will not totally seal the oil in. Therefore turbo engines always use a slight bit more oil than a NA engine. Also, Turbo engines when under boost also have more blowby past the piston rings than a NA engine.
More throttle = more cylinder pressure and more blowby, so more chance of oil mist in the blowby gasses and dirtier intake.
I'd like to see an intake line where we could have Seafoam added when under load going down the road to keep the intake clean. It would be great if we could run Seafoam thru the intake when under say more than 3/4 throttle. I may have to rig something up like that using a windshield washer pump designed to operate at WFO and inject into the intake, much like a meth injection system only using Seafoam instead. That would keep the intake clean!
06-02-2015, 07:41 PM
#4
If there was carbon issues with the new 4.0t engines, it would be talked about. There are no cases yet. The 3.0t engine is five years running now, and it also has no known cases.
The 4.2 was the killer carbon case, and the 2.0T from some years.
I know the S4 has a ten degree higher running temperature that was specifically there to combat carbon, and it had a newly designed oil separator on the vent to Intake.
The 4.2 was the killer carbon case, and the 2.0T from some years.
I know the S4 has a ten degree higher running temperature that was specifically there to combat carbon, and it had a newly designed oil separator on the vent to Intake.
06-03-2015, 06:28 AM
#5
AudiWorld Senior Member
Nothing you change in the crankcase with oil additives, or different brands of oil will have any effect on intake carbon. Fuel used to keep the intake clean, or cleaner when using fuels with cleaning additives added, but now there is no fuel upstream of the intake valves and ports for any cleaning effect.
NA engines put the crankcase breather right into the intake stream. Turbo engines also draws the blowby right into the intake. Intercoolers will always contain oil when taken apart. Its impossible to completely seal the oil in a turbo. Turbos contain a labyrinth seal and they will not totally seal the oil in. Therefore turbo engines always use a slight bit more oil than a NA engine. Also, Turbo engines when under boost also have more blowby past the piston rings than a NA engine.
More throttle = more cylinder pressure and more blowby, so more chance of oil mist in the blowby gasses and dirtier intake.
More throttle = more cylinder pressure and more blowby, so more chance of oil mist in the blowby gasses and dirtier intake.
But I need to correct myself because the 4.0 TFSI engine has an air-to-water intercooler placed directly ahead of the intake manifold. Under non-boost operation, the blow-by gases are injected into this intercooler. So my theory is probably incorrect that using boost more often would send more of the blow-by gases through the intercooler where some of the oil might get filtered out. In this engine, all of the blow-by gases will travel through the intercooler.
06-03-2015, 04:12 PM
#6
I read that exact same self study PDF and downloaded it. Great stuff!
From all my reading, it sure seems that there isn't really much we can do other than to hope that Audi's new crankcase filtering/accumulation system works as well as it can.
With the 4.0T getting up in mileage now, I'd have thought we'd hear something about it. Here's to continued success with our engines!
From all my reading, it sure seems that there isn't really much we can do other than to hope that Audi's new crankcase filtering/accumulation system works as well as it can.
With the 4.0T getting up in mileage now, I'd have thought we'd hear something about it. Here's to continued success with our engines!
06-03-2015, 05:09 PM
#7
AudiWorld Member
I'm not talking about putting something in the oil to directly clean the intake valves. I'm talking about some property of the oil to better keep contaminants from the blow-by gases dissolved in the oil, or maybe for the oil to form larger droplets so that it is easier to filter out of the crankcase ventilation system, or whatever. Basically so that the oil and carbon remains in the crankcase and does not flow up through the crankcase ventilation system where it might eventually get baked onto the intake valves.
Well do a Google search for "self study guide for the 4.0 twin turbo engine" and you will find a PDF of the Self-Study Program 920223 for this engine. The crankcase ventilation information starts on page 16. It shows the two pathways for blow-by gas reinjection. When there is boost pressure, you can't vent blow-by gases directly into the intake manifold because the boost pressure will cause the blow-by to flow back into the crankcase ventilation system. So there is a valve to route the blow-by gases with uncharged intake air to the turbocharger instead.
But I need to correct myself because the 4.0 TFSI engine has an air-to-water intercooler placed directly ahead of the intake manifold. Under non-boost operation, the blow-by gases are injected into this intercooler. So my theory is probably incorrect that using boost more often would send more of the blow-by gases through the intercooler where some of the oil might get filtered out. In this engine, all of the blow-by gases will travel through the intercooler.
Well do a Google search for "self study guide for the 4.0 twin turbo engine" and you will find a PDF of the Self-Study Program 920223 for this engine. The crankcase ventilation information starts on page 16. It shows the two pathways for blow-by gas reinjection. When there is boost pressure, you can't vent blow-by gases directly into the intake manifold because the boost pressure will cause the blow-by to flow back into the crankcase ventilation system. So there is a valve to route the blow-by gases with uncharged intake air to the turbocharger instead.
But I need to correct myself because the 4.0 TFSI engine has an air-to-water intercooler placed directly ahead of the intake manifold. Under non-boost operation, the blow-by gases are injected into this intercooler. So my theory is probably incorrect that using boost more often would send more of the blow-by gases through the intercooler where some of the oil might get filtered out. In this engine, all of the blow-by gases will travel through the intercooler.
Again, nothing that you add to the oil will keep it from coming out of the breather. Blowby is basically exhaust being pushed past the rings and the ring end gaps. It has, and always will contain oil vapor. This vapor will always contain oil mist with it as there is oil on the cylinder walls and pistons, as the exhaust/air is blown past the rings, it picks up tiny molecules of oil. You can use a oil seperator system, which I imagine Audi does just like everyone else, to try and capture some of the oil and put it back in the crankcase, but no seperator built to date has been able to capture 100% of the oil mist that I know of.
Whether its being put into the intercooler when not under boost, or before the turbo under the boost, the blowby is going thru the intake and hitting the intake ports and valves, where the heat and intake reversion cook it on the valves and intake ports in the head. Another good way to help with carbon on the intake valves and intake ports is with cam timing to prevent reversion back into the intake. Also, the intercooler does nothing to "filter" blowby. The intercooler cools the intake charge after the charge is compressed and heated from the turbo. I'm sure Audi is doing all they can to help this, but I doubt they can prevent intake deposits entirely in any direct injected engine. I won't go as far to say its impossible, but the technology is not there yet to totally prevent it. No manufacture has been able to keep the intakes clean with direct injection yet. They are improving on it, but it's not like port injection or carbs with fuel running thru the intake system.
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06-04-2015, 07:15 AM
#8
AudiWorld Senior Member
Again, nothing that you add to the oil will keep it from coming out of the breather. Blowby is basically exhaust being pushed past the rings and the ring end gaps. It has, and always will contain oil vapor. This vapor will always contain oil mist with it as there is oil on the cylinder walls and pistons, as the exhaust/air is blown past the rings, it picks up tiny molecules of oil. You can use a oil seperator system, which I imagine Audi does just like everyone else, to try and capture some of the oil and put it back in the crankcase, but no seperator built to date has been able to capture 100% of the oil mist that I know of.
Anyway, the oil separator system actually doesn't seem that sophisticated. The SSP says:
"The blow-by gas stream makes a 180° change of direction in the first, large-volume chamber. Because the larger drops of oil have greater inertia, they bounce off the chamber wall and run into the collector on the floor of the heavy oil separator. A drain opening is located there."
And there is a fine-oil separator as well. Perhaps they should put more effort into getting as close to 100% as possible? Especially now with direct injection engines that do not have fuel to wash away the oil in the intake.
Whether its being put into the intercooler when not under boost, or before the turbo under the boost, the blowby is going thru the intake and hitting the intake ports and valves, where the heat and intake reversion cook it on the valves and intake ports in the head. Another good way to help with carbon on the intake valves and intake ports is with cam timing to prevent reversion back into the intake. Also, the intercooler does nothing to "filter" blowby. The intercooler cools the intake charge after the charge is compressed and heated from the turbo.
In fact, oil buildup in the intercooler has always been an issue with turbocharged engines, even before direct injection, because there has never been any fuel in the intercooler to clean it up. Hence the popularity of the oil catch can, but these don't seem to be 100% effective either.
06-04-2015, 12:30 PM
#9
AudiWorld Member
Oil will fall out out suspension if there is no velocity to carry it out the escape tube. It takes a very small particle of oil mist to remain in suspension with the air its being carried with. Hence the reason it goes right thru the oil cooler and into the intake. There is oil in the intake and intercooler because the droplets have fallen out of suspension and clung to the ports and walls of the intercooler, but I can assure you that its still getting carried into the engine to the tune of over 99%
No matter what, It's impossible to keep the intake ports and vavles clean without fuel or another cleaning agent running thru the heads intake ports, but it doesn't really matter till the intake gets plugged enough to limit HP output, which over time, is hard to detect from the seat of your pants for the average guy. Only a dyno or 1/4 timeslip would show the power going away from the intakes getting plugged up. One thing is certain, when they start getting plugged the power will drop.
No matter what, It's impossible to keep the intake ports and vavles clean without fuel or another cleaning agent running thru the heads intake ports, but it doesn't really matter till the intake gets plugged enough to limit HP output, which over time, is hard to detect from the seat of your pants for the average guy. Only a dyno or 1/4 timeslip would show the power going away from the intakes getting plugged up. One thing is certain, when they start getting plugged the power will drop.
06-08-2015, 09:33 AM
#10
I wonder why the PCV has to be routed back into the intake? Why not just behind the exhaust valves?
If all of it is going into the combustion chamber anyways, why not put it just past the valves?
If all of it is going into the combustion chamber anyways, why not put it just past the valves?