[DWR]

Originally Posted by Pierre Louis

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.

I don't think the some total of knowledge comes from the academic community (having been a former member). We can discern cause and effect relationships, and in fact have. The fact is all common rail injected vehicles exhibit a higher level of deposit buildup - diesels just happen get it worse than gas engines. Also, let's separate the detection of CBU and its presence. CBU is not a problem in any engine until airflow restriction becomes measureable. For some owners, that could take quite a long time. And yes, maintenance, oil and fuel quality, driving style, and even local humidity can play role.

Originally Posted by Pierre Louis

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.

Not sure finding the answer on a "molecular level" is pertinent. The contention that it is fuel based maybe true, but likely irrelevant when it comes to an individual implementing a solution. Many of us have very few options when it comes to selecting the diesel we put in our vehicles. Therefore the countermeasure cannot be fuel based. There is conclusive evidence of what causes CBU on a macro level. So, why not deal with the problem on that level?

[Pierre Louis]

Originally Posted by DWR

I don't think the some total of knowledge comes from the academic community (having been a former member). We can discern cause and effect relationships, and in fact have. The fact is all common rail injected vehicles exhibit a higher level of deposit buildup - diesels just happen get it worse than gas engines. Also, let's separate the detection of CBU and its presence. CBU is not a problem in any engine until airflow restriction becomes measureable. For some owners, that could take quite a long time. And yes, maintenance, oil and fuel quality, driving style, and even local humidity can play role.

Not proving it on a molecular level, which should be easy if there is a cause found, will lead us to conjecture and hyperbole. Science is science, you cannot avoid it if you want truth.

Not sure finding the answer on a "molecular level" is pertinent. The contention that it is fuel based maybe true, but likely irrelevant when it comes to an individual implementing a solution. Many of us have very few options when it comes to selecting the diesel we put in our vehicles. Therefore the countermeasure cannot be fuel based. There is conclusive evidence of what causes CBU on a macro level. So, why not deal with the problem on that level?

If you read my statement carefully, I did not exclude "macro" solutions to CBU, and I did not discount CBU either. I did say that some of the "macro solutions" don't have data to support them. Realistically, the data on how many cars get CBU isn't there. A mechanic will tell you "all cars get it eventually" but they don't take apart every car on the road, just the ones that come in for problems.

Typically, posters will think anyone who disagrees with something by not belonging to the "status quo beliefs" on a discussion board will be opposed and thought to be against everything that is said. Just read threads on "lubricity" to find that once a belief occurs, many will see what they want to believe in the data and not have any doubts.

I've had two direct injection diesel cars go over 150,000 miles - one now with 240,000 miles and still no sign of CBU. How does one explain this rationally? I've expressed interest in knowing why.

PL

[Puerto Rican 335d]

Pierre amigo let me know when youre coming down here ok!!

[Pierre Louis]

Originally Posted by Puerto Rican 335d

Pierre amigo let me know when youre coming down here ok!!

Thanks I will!

Look me up if you are near Savannah or Jacksonville!

P

[DWR]

Originally Posted by Pierre Louis

Not proving it on a molecular level, which should be easy if there is a cause found, will lead us to conjecture and hyperbole. Science is science, you cannot avoid it if you want truth.

Yes, fortunately not all scientists have to be chemists.

[DWR]

Originally Posted by Pierre Louis

I've had two direct injection diesel cars go over 150,000 miles - one now with 240,000 miles and still no sign of CBU. How does one explain this rationally? I've expressed interest in knowing why.
PL

I appreciate your inquisitiveness. I too would like to know more. It was your insistence that the answer must come at a molecular level that seemed ... irrational. I see your follow up response and can now better understand your point of view. Thanks.

Sometimes knowledge is enough. Understanding, in light of history, is fluid, at best.

[Puerto Rican 335d]

Will do Pierre I will be in Orlando/Mt Dora in may for my daughters and granddaughters Bday

[Thecastle]

So I'm gonna have to add some more input on this thread after doing extensive research on another factor than can cause cbu. So we all know a major constituent of the carbon build up in the intake is from the soot recirculated into the intake by the egr.

So what causes soot on a diesel. There are some good papers written by chevron and others researching the phenomenon.http://www.chevron.com/documents/pdf...TechReview.pdf

Anyway suffice it to say it is made up primarily of unburnt fuel and oil in the cylinders. Why do we have unburied fuel?

Low cetane fuel is more likely to form soot, the lower the cetane the more likely the fuel isn't going to completely combust.
Clogged injectors that don't properly atomize the fuel which leads to fuel droplets in the cylinder not mixing with air and being converted into soot when exposed to combustion temps
Low engine temps
Oil in the engine that easily evaporates into the combustion chamber and possibly weak oil rings. Aka engines that drink oil will generate more soot.


So basically, keeping your injectors clean and using high centane fuel are the major factors we can contro, and yes fuel quality can make a difference in soot formation, and volume that gets sent through the egr.

Basically,
Low cetane fuel, egr, pcv sending lots of oil, turbos leaking, valve stem seals leaking, and materials that allow soot/oil/carbon accumulation to adhere to the surfaces are the problem areas. Eliminating egr will help to reduce the amount of soot in the intake. But it's not the only source of the problem.

[DWR]

Originally Posted by Thecastle

So I'm gonna have to add some more input on this thread after doing extensive research on another factor than can cause cbu. So we all know a major constituent of the carbon build up in the intake is from the soot recirculated into the intake by the egr.

So what causes soot on a diesel. There are some good papers written by chevron and others researching the phenomenon.http://www.chevron.com/documents/pdf...TechReview.pdf

Anyway suffice it to say it is made up primarily of unburnt fuel and oil in the cylinders. Why do we have unburied fuel?

Low cetane fuel is more likely to form soot, the lower the cetane the more likely the fuel isn't going to completely combust.
Clogged injectors that don't properly atomize the fuel which leads to fuel droplets in the cylinder not mixing with air and being converted into soot when exposed to combustion temps
Low engine temps
Oil in the engine that easily evaporates into the combustion chamber and possibly weak oil rings. Aka engines that drink oil will generate more soot.


So basically, keeping your injectors clean and using high centane fuel are the major factors we can contro, and yes fuel quality can make a difference in soot formation, and volume that gets sent through the egr.

Basically,
Low cetane fuel, egr, pcv sending lots of oil, turbos leaking, valve stem seals leaking, and materials that allow soot/oil/carbon accumulation to adhere to the surfaces are the problem areas. Eliminating egr will help to reduce the amount of soot in the intake. But it's not the only source of the problem.

You have done an excellent job listing the contributors that form soot in the exhaust. The analogy here is epoxy. You need both parts A & B to make it stick. It is obvious that Exhaust Gas Recirculation is how carbon gets into the intake. Your point is you need something for that soot (carbon) to stick to. And note, it can be the same contributors that make up parts A & B, just depends on whether it has made its way through the combustion process.

[merkis1024]

Originally Posted by Pierre Louis

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.

...

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.

As a soon-to-be 335d owner, I'm curious what resource you have to share on finding out different fuel compositions per gas station brand. It seems that you're suggesting each gas station (or gas brand) has some variation in fuel mixture that has a major role in CBU. However, the most crucial information - what gas composition is best and which brand offers this - has been left out.

[Pierre Louis]

Originally Posted by merkis1024

As a soon-to-be 335d owner, I'm curious what resource you have to share on finding out different fuel compositions per gas station brand. It seems that you're suggesting each gas station (or gas brand) has some variation in fuel mixture that has a major role in CBU. However, the most crucial information - what gas composition is best and which brand offers this - has been left out.

Many believe, after looking at the data, that CBU is a regional issue. This would imply that the base stock, which often comes from one or two refineries to all brands, may be at fault, or at least something else such as climate or driving style for each region.

Each brand of fuel, however, uses its own additive package and has its own terminals, although its not uncommon to get fuel from a different brand's terminal when its economically feasible.

I got the word straight from an engineer at Marathon (last month) that they use, at least in their gasoline, STP additive. He also verified that additives are put in at the terminal, not at the refinery. If you search through the ASTM/SAE literature, additives in diesel are not thought to be good while transporting through the pipeline or at the refinery. It apparently mixes with other types of fuel that use the pipeline and is not otherwise economically feasible.

I have no idea if brand name fuel is necessarily better than "off-brand" but can only use inductive reasoning to say that BMW, as a reputable company, would not put anything but brand name, top-tier fuel in their test vehicles.

PL

[brando1985]

Originally Posted by Pierre Louis

Many believe, after looking at the data, that CBU is a regional issue. This would imply that the base stock, which often comes from one or two refineries to all brands, may be at fault, or at least something else such as climate or driving style for each region.

Each brand of fuel, however, uses its own additive package and has its own terminals, although its not uncommon to get fuel from a different brand's terminal when its economically feasible.

I got the word straight from an engineer at Marathon (last month) that they use, at least in their gasoline, STP additive. He also verified that additives are put in at the terminal, not at the refinery. If you search through the ASTM/SAE literature, additives in diesel are not thought to be good while transporting through the pipeline or at the refinery. It apparently mixes with other types of fuel that use the pipeline and is not otherwise economically feasible.

I have no idea if brand name fuel is necessarily better than "off-brand" but can only use inductive reasoning to say that BMW, as a reputable company, would not put anything but brand name, top-tier fuel in their test vehicles.

PL

I appreciate your input, but question your hypothesis. I'm curious how the quality of diesel contributes to CBU in the intake / intake ports. The fuel never reaches those areas, unless it's implied that increased soot is the bi-product of lessor quality diesel, hence increasing the chances of CBU via EGR?

Further, as we all know, the N54 guys are battling CBU as well. Since those engines don't have to combat soot, one would suspect that while the prevention of EGR is good for our diesels, it's only half the equation. To completely eliminate the chances of CBU of any kind, one needs to eliminate the EGR, and take steps to reduce oil from finding its way into the intake manifold, correct?

Thanks,

Brando

[Pierre Louis]

Originally Posted by brando1985

I appreciate your input, but question your hypothesis. I'm curious how the quality of diesel contributes to CBU in the intake / intake ports. The fuel never reaches those areas, unless it's implied that increased soot is the bi-product of lessor quality diesel, hence increasing the chances of CBU via EGR?

Further, as we all know, the N54 guys are battling CBU as well. Since those engines don't have to combat soot, one would suspect that while the prevention of EGR is good for our diesels, it's only half the equation. To completely eliminate the chances of CBU of any kind, one needs to eliminate the EGR, and take steps to reduce oil from finding its way into the intake manifold, correct?

Thanks,

Brando

Understanding that the oil from different regions has different levels of paraffins and variations in types of hydrocarbon molecules, both gasoline and diesel will have different composition to a certain extent from different types of crude and refining/hydrocracking techniques. The chemical composition of the soot itself may also matter and be a function of the fuel composition, I don't know.

If you google direct injection and CBU, the scientific papers, mostly from SAE, imply fuel composition and/or additives in their conclusions as preventing or causing deposit formation is mentioned. Please see attached files.

ACEA Position on Metal Based Fuel Additives.pdf
IDID Quigley TAE Esslingen 2011 .pdf
The Use of Ferrocene Additives to Reduce Carbon Build Up in Diesel Based Internal Combustion Eng.pdf

The importance of diesel fuel cleanliness and contamination is also part of the discussion in this chapter:

Diesel fuels.pdf

But this doesn't refute the role, in general, of engine management and EGR design:

EGR Applied Energy August_2011.pdf

I'm sure the same can be said for gasoline direct injection. I don't have any studies on the gasoline side, being a diesel head since 1997.....

PL

[Pierre Louis]

Originally Posted by brando1985

I appreciate your input, but question your hypothesis. I'm curious how the quality of diesel contributes to CBU in the intake / intake ports. The fuel never reaches those areas, unless it's implied that increased soot is the bi-product of lessor quality diesel, hence increasing the chances of CBU via EGR?

Further, as we all know, the N54 guys are battling CBU as well. Since those engines don't have to combat soot, one would suspect that while the prevention of EGR is good for our diesels, it's only half the equation. To completely eliminate the chances of CBU of any kind, one needs to eliminate the EGR, and take steps to reduce oil from finding its way into the intake manifold, correct?

Thanks,

Brando

Direct injection gasoline engine design includes EGR.

See:

http://www.sciencedirect.com/science...89430498000071

Gasoline engines produce particulate matter, often in greater amounts compared to diesels:

See:

Particulate Emissions from a Pre-Emissions Control Era Spark-Ignition Vehicle: A Historical Benc.pdf

PL

[merkis1024]

Originally Posted by Pierre Louis

Many believe, after looking at the data, that CBU is a regional issue. This would imply that the base stock, which often comes from one or two refineries to all brands, may be at fault, or at least something else such as climate or driving style for each region.

Each brand of fuel, however, uses its own additive package and has its own terminals, although its not uncommon to get fuel from a different brand's terminal when its economically feasible.

I got the word straight from an engineer at Marathon (last month) that they use, at least in their gasoline, STP additive. He also verified that additives are put in at the terminal, not at the refinery. If you search through the ASTM/SAE literature, additives in diesel are not thought to be good while transporting through the pipeline or at the refinery. It apparently mixes with other types of fuel that use the pipeline and is not otherwise economically feasible.

I have no idea if brand name fuel is necessarily better than "off-brand" but can only use inductive reasoning to say that BMW, as a reputable company, would not put anything but brand name, top-tier fuel in their test vehicles.

PL

Very interesting. Thanks for sharing. I just did some more research on diesel and was wondering if it had to do with cetane rating or the composition of biodiesel (B5 vs B100 or pure petrodiesel), but your reply suggests that the additives are the dominant contributing factor here in CBU. I'll do some more research on STP additives myself. Again, thanks for sharing your knowledge!

FYI, some other diesel heads have shared that Chevron will have 49 cetane rating. Some regions with Chevron's Diesel Techron reportedly have 51.
The next best bet, at least in the west coast, is ConocoPhilips (76), which offers 47 cetane rating.
These numbers were provided by corporate employees, apparently.

[Pierre Louis]

Here is an article that describes conditions under which a direct injection gasoline engine creates soot:

Gasoline direct injection.pdf

Gasoline engines do not emit soot emission normally. Soot emission can occur at very rich mixtures. However, the GDI engines emit soot at stratified-charge operation, as in–cylinder can be areas with very rich mixtures. In addition, in GDI engine, if mixture formation do not realize at full loads due to rich mixture, the soot emission can increase.

EGR as part of the management system is also mentioned:

4.2 The Engine Management System
Engine management system consists of electronic control unit, sensors and actuators. The engine control unit continually chooses the one among operating modes depending on engine operating point and sensor’s data. The ECU controls the actuators to input signals sent by sensors. All actuators of the engine is controlled by the ECU, which regulates fuel injection functions and ignition timing, idle operating, EGR system, fuel-vapor retention system, electric fuel pump and operating of the other systems. Adding this function to the ECU requires significant enrichment of its processing and memory as the engine management system must have very precise algorithms for good performance and drive ability.

PL

[Pierre Louis]

Originally Posted by merkis1024

Very interesting. Thanks for sharing. I just did some more research on diesel and was wondering if it had to do with cetane rating or the composition of biodiesel (B5 vs B100 or pure petrodiesel), but your reply suggests that the additives are the dominant contributing factor here in CBU. I'll do some more research on STP additives myself. Again, thanks for sharing your knowledge!

FYI, some other diesel heads have shared that Chevron will have 49 cetane rating. Some regions with Chevron's Diesel Techron reportedly have 51.
The next best bet, at least in the west coast, is ConocoPhilips (76), which offers 47 cetane rating.
These numbers were provided by corporate employees, apparently.

Yes, cetane seems to matter, and more so in the 335d high revving high performance "light duty" diesel, as you know BMW specifies a cetane number of 51 for this engine in NA.

Cheers.

PL

[Pierre Louis]

Originally Posted by brando1985

I appreciate your input, but question your hypothesis. I'm curious how the quality of diesel contributes to CBU in the intake / intake ports. The fuel never reaches those areas, unless it's implied that increased soot is the bi-product of lessor quality diesel, hence increasing the chances of CBU via EGR?

Further, as we all know, the N54 guys are battling CBU as well. Since those engines don't have to combat soot, one would suspect that while the prevention of EGR is good for our diesels, it's only half the equation. To completely eliminate the chances of CBU of any kind, one needs to eliminate the EGR, and take steps to reduce oil from finding its way into the intake manifold, correct?

Thanks,

Brando

The question remains as to why the majority of 335d engines and other similar engines from VW and Mercedes don't seem to get into problems with CBU while a good but small percentage do. Some of us don't want to eliminate emissions equipment, so it would be nice to know under what conditions the system actually "works" or what to look for as to a mechanical/electronic problems such as excess cylinder blowby or leaky turbos etc.

Cheers,

PL

[CharlesCA]

Originally Posted by Pierre Louis

The question remains as to why the majority of 335d engines and other similar engines from VW and Mercedes don't seem to get into problems with CBU while a good but small percentage do. Some of us don't want to eliminate emissions equipment, so it would be nice to know under what conditions the system actually "works" or what to look for as to a mechanical/electronic problems such as excess cylinder blowby or leaky turbos etc.

Cheers,

PL

I'm sure other manufactures have this issue too. For example a VW motor:

. There are plenty more on youtube.

[Hoooper]

Wait I'm confused, who believes that cbu is a regional issue and why? Regional within the US or regional worldwide?

[Pierre Louis]

Originally Posted by CharlesCA

I'm sure other manufactures have this issue too. For example a VW motor:

. There are plenty more on youtube.

Yeah, just like on this board and with mechanics, only the ones that have the problem post... I'm fairly confident that BMW owners are more computer/forum savvy so we can estimate the number that actually get CBU problems. I don't believe there is an argument that its anywhere North of 10% - bad enough and inexcusable, but not catastrophic, and more likely related to some unknown factor(s) we have been guessing about. Sure, removing EGR should do the trick, but not everyone, as I said, wants to do this.

I'm still waiting for my VW's to get any CBU problems, one was sold at around 156,000 miles, the other has 105,000 miles. The Mercedes CDI is still going strong without CBU at 240,000 miles, as I know the person that bought it.

PL

[Pierre Louis]

Originally Posted by Hoooper

Wait I'm confused, who believes that cbu is a regional issue and why? Regional within the US or regional worldwide?

Yeah, its mentioned in passing by those interested in statistics - there seem to be clusters of CBU problems.

Its likely more in the US, but my French nephew mentioned Peugeot (or Renault?) diesels that are primarily driven in the city seem to get it - (he was captain of a large merchant ship and takes apart diesel motors for fun) so a good thrashing may be what it needs once in a while...

I'm fairly certain that anyone that gets CBU and reports it that uses primarily brand name diesel would have mentioned it, but most don't, so inductive reasoning reveals they most likely use "off brand" fuel - a common thing among diesel owners, many of whom believe that "diesel is diesel." I've read one conversation that brand name diesel has better filters at the stations, but its only a rumor. Additives, as the papers I mentioned imply, used at the terminal do seem to make a difference, sometimes causing problems of carbon deposits. Most of the posters don't report whether they use additives or not - to me, likely from a belief that additives can do no wrong, and that reporting them would not fit their mental picture of CBU.

PL