[Tomnavigator]

I have a new approach to the cause and elimination of carbon buildup. Here are my thoughts.

Anyone who has ever cooked knows that you cannot use a measuring cup for dry ingredients like flour after you put liquid in the measuring cup because the flour will mix with the liquid and coat the sides of the measuring cup with a thick layer of flour. You can repeatedly measure flour in a dry measuring cup without any buildup occurring as long as everything stays dry. Carbon buildup in your vehicle is like the buildup on a wet measuring cup. Wet plus dry equals buildup.

Carbon buildup in a car is a result of two components. Soot and oil. The two components combine and coat the intake system. The engine provides heat to cook the paste causing the buildup we all dread.

The soot comes with the exhaust gas recirculation (EGR) gases. Soot is not intentionally recirculated to the intake. It is just part of the exhaust gases. EGR is a relatively recent method of reducing emissions from diesel engines. EGR is done to reduce nitrogen oxide emissions in the exhaust by recirculating exhaust gases back to the intake. This lowers the combustion temperature in the cylinders. Nitrogen oxides (NOX) are created when the fuel burns at high temperatures with nitrogen. EGR reduces NOX created by lowering the combustion temperature. The diesel exhaust fluid (def) eliminates the remaining NOX. BMW intentionally made it almost impossible to remove the EGR without creating issues and causing service engine lights. Therefore, removing the soot is very difficult.

Oil enters the intake system as a mist with the positive crankcase ventilation (PCV) gases. The pcv gases are gas that squeeze (blow) by the piston rings when the engine fires and get into the crankcase with your oil. These gases must be removed from the crankcase to prevent the crankcase from building up pressure and causing oil to leak everywhere. For about fifty years these gases were vented to the atmosphere through a positive crankcase ventilation valve or vent. In the early 1960s these gases were routed to the air intake system on vehicles and burned to prevent the oil mists from polluting the atmosphere. The oil did not cause any significant problems to the car because it was sucked into the cylinder and burned. Carbon build up was not an issue because there was no exhaust gas recirculation to add soot. EGR was added to diesel engines a few years ago to reduce exhaust emissions. The EGR contains soot which mixes with the oil from the pcv causing the paste that we refer to as carbon buildup. Keep in mind that Carbon build up is caused by oil mixing with soot.

You can prevent carbon buildup by either eliminating the soot or eliminating the oil. The only way to eliminate the soot is to eliminate the EGR. Eliminating the EGR is difficult and will cause service engine soon (SES) lights and will increase you NOX emissions. BMW has done everything they could to prevent you from removing or eliminating EGR. However, it is not very difficult to eliminate the oil introduced with the pcv. Once the oil is eliminated, the intake system will be totally dry and no buildup should occur. You can eliminate the oil by rerouting the PCV (positive crankcase ventilation) to the atmosphere instead of the air intake like it was done prior to 1960. This can be done by running the oil vapors from the PCV to a coalescing filter such as a Provent 200. The provent will remove the oil mist from the blowby gases and the gases can then be safely vented to the air without creating significant pollution. The provent collects the oil from the mist and must be drained/emptied occasionally to keep it working properly.

This is the only easy way to eliminate the carbon buildup without causing service engine lights, bypassing the EGR, or increasing emissions significantly. Total cost is approximately $150 and total time to do this is 1 to 4 hours depending on where you mount the provent 200, the oil drain and the vent gas tubing.
Please note that I am not promoting the provent 200. I have nothing to do with the company that makes the Provent. The provent is the only filter I know of that is made specifically for oil removal from pcv blowby gases. Any similar filter will work.

[9mmkungfu]

And here is a ProVent 200 install:

http://www.e90post.com/forums/showthread.php?t=1070311

[Thecastle]

I think this is a good discussion, but I hate to rain a little on the solutions.... But there is no way to totally eliminate all sources petroleum that leads to carbon build up. There are some more sources of oil/carbon that would have to be addressed to really eliminate the issue that weren't covered above.

1) The valve stem seals all leak/weep oil and this is often a major source of oil build up on the intake valves that people see. This is a bigger source than most people realize and accounts for the majority generally of oil build up on intake valves.
2) The turbo's themselves leak oil into the intake tract.

So EGR re-route/catch cans/pcv vent to atmosphere/etc, will cut down on the build up but it won't eliminate the build up. Also if your PCV is actually working correctly the gas/oil separator should eliminate most of the oil coming through the PCV system. You also have to be careful of venting the PCV as sometimes the oil it introduces is vital to lubing components in the intake (ask supercharger folks) and folks with metal diverter valves.


Also people talk about water/meth, which can help however, at least on gasoline direct injection engines it has been show to make no difference in build up, to a slight reduction in build up. Problem is that meth/water aren't a good solvent for the type of carbon build up we get and can't do much to eliminate it.

Bottom line you can slow it down (maybe to the point where its not really an issue?), but you can't eliminate the problem. The only real solutions are coating which prevent carbon from adhering to surfaces (design flaw from BMW), or high enough temperatures to bake of the carbon (italian tune up) but it won't get everything hot enough.

I think an EGR block/filter would be a great idea and making sure your PCV is actually working right is a good idea. Catch cans/etc, come with their own downsides.

[torqueisking]

is a coalescing filter a viable solution in colder climates? isn't there a potential for the water&oil vapour to freeze in the filter?

[cschmelz]

So what IS the best solution to avoiding the CBU?

My car has just under 40k miles and just left warranty and, of course, 3 weeks after warranty has started throwing engine smoothness 6, 3 and 2 values out of range and runs awful, certainly CBU and is headed to shop next week for workup/cleanup.

I'd like to avoid spending $1,200-$2,500 for cleaning every 40k miles.

EGR block off seems like the best solution to avoid rapid CBU. Does the EGR block off still allow for DPF regen or does blocking it off mess up the DPF regeneration cycles? I would be fine with buying blocking plates and then buying a tune to get a little more performance AND coding out the EGR at the same time. Is DPF delete also a requirement with the EGR block?

Methanol is also an option for me, but it seems from all the pages of threads that methanol injection is not enough of a solvent to remove the CBU and may not really keep that gremlin at bay.

What IS the best solution without going hog wild with mods?

[Persian Whisperjet]

EGR block is probably the single most important mod you can perform to reduce CBU, and since you are getting a tune you can have the resultant CELs coded out. You still have the ticking time bombs of the SCR and DPF systems under the hood, but those can be dealt with at a later date e.g., when they fail.

[Thecastle]

Originally Posted by cschmelz

What IS the best solution without going hog wild with mods?

EGR block off will help a ton, along with ensuring the PCV is working correctly. This isssue isn't unique to the 335d, it happens to the 335i and VW's/Audi's, fords really nearly every direct injection gasoline of diesel engine. The design flaw is materials that allow carbon to adhere to them in the intake and no fuel washing over those surfaces to clean them of oil.

I think the real goal shouldn't be to eliminate CBU, but to slow it down enough that its only an issue once or twice during the serviceable life of the engine. Since its really not possible to eliminate all sources of material that contribute to the build up, oil is just gonna get in the intake from the turbos, valve stems, (k/n filters) and other leaks, heat up and carbonize as it sticks to surfaces.

As for actual solutions that aren't costly, besides EGR block, and ensuring your PCV hasn't failed.... The only real solution I've seen employed with a lot of success is adding an injector to the intake tract that injects a solvent for cleaning carbon/oil build up. Gasoline works really well as a carbon solvent, not sure I'd want to add a ton of that to a diesel's intake though :-)

[dixy2k]

Originally Posted by cschmelz

So what IS the best solution to avoiding the CBU?

My car has just under 40k miles and just left warranty and, of course, 3 weeks after warranty has started throwing engine smoothness 6, 3 and 2 values out of range and runs awful, certainly CBU and is headed to shop next week for workup/cleanup.

I'd like to avoid spending $1,200-$2,500 for cleaning every 40k miles.

EGR block off seems like the best solution to avoid rapid CBU. Does the EGR block off still allow for DPF regen or does blocking it off mess up the DPF regeneration cycles? I would be fine with buying blocking plates and then buying a tune to get a little more performance AND coding out the EGR at the same time. Is DPF delete also a requirement with the EGR block?

Methanol is also an option for me, but it seems from all the pages of threads that methanol injection is not enough of a solvent to remove the CBU and may not really keep that gremlin at bay.

What IS the best solution without going hog wild with mods?

regen is independent of EGR. It will work just fine.

[cschmelz]

So roughly EGR block off plus tunes about $800?

EGR/DPF/SCR plus tune is what? $2500?

[NC335d]

Originally Posted by cschmelz

So roughly EGR block off plus tunes about $800?

EGR/DPF/SCR plus tune is what? $2500?

Pretty much, maybe closer to $2,800. Alphabet delete parts, labor, shipping of ECU & tuning along w/ SCR flush.

[Thecastle]

Originally Posted by cschmelz

So roughly EGR block off plus tunes about $800?

EGR/DPF/SCR plus tune is what? $2500?

To slow not prevent

[Hoooper]

EGR block will prevent the cbu that everyone is having issues with on here. I don't think we really know at this point whether we will have the valve stem buildup that plagues other direct injection engines. It's kind of a question really, diesels have all been direct injection for a really long time and didn't really have cbu with the consistency that direct injection gas engines have. But with the amount of oil in the intake system it would be a bit hard to believe you would never have any. However, your intake won't be caked full of cbu if you have an EGR block

[dixy2k]

Originally Posted by Tomnavigator

EGR reduces NOX created by lowering the combustion temperature.

I'm having a tough time wrapping my mind around this.
You get post combustion gases (going through the EGR cooler) back into the intake.
How is that lowering the combustion temp?

Fine, I get the analogy with moisture and dry soot.

From what I've noticed, when the EGR valve is closed (0%) the EGT's are lower.

[floydarogers]

Originally Posted by dixy2k

I'm having a tough time wrapping my mind around this...

Here's the quote from the AdvancedDiesel....pdf document:
"Exhaust gas recirculation (EGR):
Exhaust gas recirculation is one of the
available options for reducing NOx emissions.
Adding exhaust gas to the intake air reduces
the oxygen in the combustion chamber, thus
resulting in a lower combustion temperature."

Less burning results in lower temp.

[BB_cuda]

Originally Posted by floydarogers

Here's the quote from the AdvancedDiesel....pdf document:
"Exhaust gas recirculation (EGR):
Exhaust gas recirculation is one of the
available options for reducing NOx emissions.
Adding exhaust gas to the intake air reduces
the oxygen in the combustion chamber, thus
resulting in a lower combustion temperature."

Less burning results in lower temp.

Tacking onto Floyd's point [which i agree with], the exhaust gases are cooled by liquid to gas HX via the EGR cooler.

Now that I think about it, its sort of interesting that BMW chose to inject the EGR gasses after the IAT in the charge pipe. This may not be a big deal but wouldn't they want to account for the mix to be hotter?

[DWR]

Originally Posted by BB_cuda

Tacking onto Floyd's point [which i agree with], the exhaust gases are cooled by liquid to gas HX via the EGR cooler.

Now that I think about it, its sort of interesting that BMW chose to inject the EGR gasses after the IAT in the charge pipe. This may not be a big deal but wouldn't they want to account for the mix to be hotter?

Probably the reason for the temperature sensor on the cooler.

[Pierre Louis]

Clearly none of the posters have presented any scientific data or molecular mechanisms of carbon buildup.

Here is an SAE paper that finds different substances found in the fuel contribute to fouling of injectors etc.

Here is another paper comparing different compositions of fuel and different rates of deposit formation.

This paper implies that lubricating oil is not found to any significant extent in deposits, but shows how different precursor molecular chains are common and in what scale.

This paper describes the almost definite association between deposits and fuel quality:

Most testing has been carried out with metal contaminated fuel. The data show that the level of deposit is fuel dependent for both base and additive treated fuel.

Finally, here is a paper that discovers that the level of fuel oxygenation may indeed affect the quality and quantity of soot formation:

Results show that increasing fuel oxygenation produces lower in-cylinder and engine-out soot levels, consistent with existing studies of the effects of fuel oxygenation on soot emissions from diesel engines. The intriguing new information is that increasing the level of fuel oxygenation produced soot with less graphitic structure and correspondingly higher reactivity. Hence, diesel fuel oxygenation may help curtail soot emissions by enhancing soot reactivity and oxidation rates as well as by preventing certain fuel carbon atoms from participating in reactions that form soot.

PL

[dixy2k]

EGR helps the engine get to the optimal operating temperature faster. Why would that be?
When EGR is closed, the EGT goes down.

Anyone can verify these two statements.

[Hoooper]

Pierre instead of posting links to a bunch of articles and then hopping out, why don't you at least summarize the articles or offer us your interpretation of the causes and maybe what you believe are the most effective preventative measures?

[Hoooper]

Originally Posted by dixy2k

EGR helps the engine get to the optimal operating temperature faster. Why would that be?
When EGR is closed, the EGT goes down.

Anyone can verify these two statements.

Egr causes lowered combustion chamber temps. Higher egt while the EGR is open can have a number of causes including the fuel continuing to burn in the manifold. Higher egr really doesn't matter though, safe egt is below the threshold for forming high concentrations of nox.

[Pierre Louis]

Yes.

Abstract
To meet stringent vehicular exhaust emission norms worldwide, several exhaust pre-treatment and post-treatment techniques have been employed in modern engines. Exhaust Gas Recirculation (EGR) is a pre-treatment technique, which is being used widely to reduce and control the oxides of nitrogen (NOx) emission from diesel engines. EGR controls the NOx because it lowers oxygen concentration and flame temperature of the working fluid in the combustion chamber. However, the use of EGR leads to a trade-off in terms of soot emissions. Higher soot generated by EGR leads to long-term usage problems inside the engines such as higher carbon deposits, lubricating oil degradation and enhanced engine wear. Present experimental study has been carried out to investigate the effect of EGR on soot deposits, and wear of vital engine parts, especially piston rings, apart from performance and emissions in a two cylinder, air cooled, constant speed direct injection diesel engine, which is typically used in agricultural farm machinery and decentralized captive power generation. Such engines are normally not operated with EGR. The experiments were carried out to experimentally evaluate the performance and emissions for different EGR rates of the engine. Emissions of hydrocarbons (HC), NOx, carbon monoxide (CO), exhaust gas temperature, and smoke opacity of the exhaust gas etc. were measured. Performance parameters such as thermal efficiency, brake specific fuel consumption (BSFC) were calculated. Reduction in NOx and exhaust gas temperature were observed but emissions of particulate matter (PM), HC, and CO were found to have increased with usage of EGR. The engine was operated for 96 h in normal running conditions and the deposits on vital engine parts were assessed. The engine was again operated for 96 h with EGR and similar observations were recorded. Higher carbon deposits were observed on the engine parts operating with EGR. Higher wear of piston rings was also observed for engine operated with EGR.

[Pierre Louis]

Originally Posted by Hoooper

Pierre instead of posting links to a bunch of articles and then hopping out, why don't you at least summarize the articles or offer us your interpretation of the causes and maybe what you believe are the most effective preventative measures?

The question I prefer is to explain why many, in fact the highest percentage of consumer diesels, don't get CBU problems while a certain unfortunate percentage do.

Certainly modifications to engine management systems will help, but not to any known extent has this been proven, since articles describing how changing the timing etc. can make more of a difference than basic engine component modification.

i.e. most still believe "diesel is diesel" and will put any brand into their car as long as its "from a busy station" while the same people, I wager, wouldn't hesitate to criticize a fast food chain for example for the quality and artery clogging effects of the food.

To my knowledge, there is no conclusive data on what actually causes CBU in a molecular sense, and those papers that do, imply that fuel composition is a major factor.

Its much more likely that in testing the 335d for the NA market, BMW didn't use crap fuel and drove the cars "like a BMW." But that would also be as much of a guess as what many posters believe. If CBU was such a pervasive problem, would you think that most of the cars would have been found, in testing, to have this problem?

I really don't know nor do I care to believe much of the opinion I read, including my own....

PL