Detaillierte Frage: Audi A6 2.0 TDI + Biodiesel | Posts 16+

@Julian

'I certainly know more about how to treat the engine compared to someone who only drives extremely short distances. Also, my usage involves long distances, which means the engine gets properly warmed up and is definitely not operated in a low-load range. That last point, in particular, is crucial for achieving a clean and complete combustion.'

@Dirk_S
That's quite a strong statement you're making. But anyone who has a negative opinion about diesel engines has good reasons for it and the right to express them. The same goes for supporters. There have been a lot of threads here about people who have had problems with diesel engines. Go to a Porsche forum and ask about diesel engines. I bet you'll get more flak there than here. Ultimately, everyone has to know what they're doing and is responsible for their actions. It's also not appropriate to demand that someone publish internal, often confidential, documents. Have you ever thought that this could jeopardize the job of the person involved? Why are there relatively few reports of damage from PDE (Particulate Diesel Engine) in BD (Biodiesel) use? In my opinion, it's quite easy to explain: firstly, the vehicles don't have that many kilometers on the clock yet, so it's hard to say anything definitive about them. Secondly, the owners of these vehicles are sometimes warned by VP-TDI (Volkswagen Particulate Diesel Injection) about the warranty policy. The vehicles that have endless kilometers on the clock are usually fleet vehicles, which often have a BD tank ban anyway.
Counter-question: Why do you think DC lifted the BD approval for the CDIs, and why do you think BMW will likely follow suit? Is it out of sympathy for the VW Group? Hardly!

@joergs
There have been a damn lot of threads from people with damaged arms. Go to a Pöhler forum and ask about arms.
'I am familiar with the search function and the forum you mentioned. I politely inquired about problems with PD. I am not aware of any specific cases of damage caused by BD in this forum. I am also familiar with the Pöler forums. I have been researching the topic of BD for two years. The Pöler company seems to have enough of its own problems, judging by what is discussed in their forums.'

It is also not the fine English tradition for someone to demand the internal, often confidential, publication of documents.
Please read the thread more carefully. I have not asked anyone to release documents that would jeopardize their job. The poster did not make any statement that it was a document from their employer. As a member who is not constantly present in the forum, I cannot know the personal backgrounds of the members. Unfortunately, I am not a mind reader .


Counter-question: why do you think DC lifted the BD approval for the CDIs, and why is BMW likely to follow suit? Is it out of sympathy for the VW group? Hardly!
I can't say for sure. Perhaps it's because they are CR engines? As far as I know, DC still sells vehicles with the RME option. I think my father even has one (either a 200CDI or a 220CDI, I'm not sure now). What does this question have to do with the PD engines of the VW Group?

Why are there relatively few reported issues with PDE engines in BD (Border Patrol) vehicles? In my opinion, it's quite easy to explain: Firstly, the vehicles haven't accumulated that many miles yet, so it's difficult to draw definitive conclusions. Secondly, some owners of these vehicles have been warned by VP-TDI (presumably a company or organization) about potential warranty issues related to the PDE engines.
Since the introduction of PD (common rail diesel injection), it has been 4 years. To my knowledge, a requirement for the development of PD components was compatibility with BD (Biodiesel) fuel (as opposed to VEP). The first releases of VEP-TDI engines occurred in 1996. In 1999, there were already reports of defects, even though BD was still quite rare at that time. It's unlikely that the relatively short availability of PD engines is the cause. There are also reports of PD engines exceeding 100,000 km. If the theory that damage deters people is correct, then the biodiesel industry shouldn't be having record sales year after year. The same argument would apply to VEP-TDI engines.

That's quite a strong opinion you're expressing. However, anyone who has a negative attitude towards RME has good reasons for it and the right to express them, just like the supporters. } I don't think I've expressed that I deny the RME opponents or supporters the right to express their opinions. I'm also interested in the opinions. However, the claims regarding PD-TDI seem excessive to me. I'm also happy to change my opinion, but I need a little bit of arguments and examples for that. Unfortunately, the arguments so far are refutable and have no basis. This shouldn't be an attack on the forum. I highly value the professional knowledge of the participants in this forum.

Regards,
Dirk.

Hi Dirk,

Dirk_S wrote:

..... The poster did not state that the document belonged to their employer. As a member who is not always present in the forum, I cannot know the personal backgrounds of the members. Unfortunately, I am not a mind reader. ...

No one has ever asked you to demonstrate psychic abilities, not even me. I simply shared my perspective on the topic, and that's all I needed to do. I have no problem with it.
Even though this document doesn't belong to my employer and I came across it by chance, I would refrain from publishing it in a publicly accessible forum. The legal consequences of such a publication (regardless of whether it affects my job or not) are too uncertain for me.

But now, to answer your question:
Yes, I know of a case of BD damage in a PD vehicle. It was an AJM engine that Volkswagen had approved for use with BD fuel after the introduction of the PD system. The vehicle already had 180,000 km on the clock at the time, and the PD injectors were completely clogged. "Rusted" is no longer an adequate description. BD is, after all, a substance that promotes corrosion to an extreme degree. Unfortunately, it is also water-attracting, which further intensifies the corrosive effect (especially if the fuel remains in the tank for an extended period).

'for the sake of completeness:'

Bertil has already alluded to the lubricity and the actual relationships involved.


The main reason for the withdrawn approval is the emissions regulations. Considering the upcoming limits (and even those already in place), the injection system must be extremely precisely adapted to the fuel being used. Even the different viscosity of biodiesel (and other differing properties) is now causing problems with engine operation. While the engine doesn't fundamentally have any issues, it can no longer pass the emissions tests under worst-case scenarios. The 'biodiesel kit' mainly includes a fuel sensor that informs the EDC (Engine Control Unit) about the most basic properties of the fuel being used (e.g., viscosity). This allows the EDC to at least adjust its parameters to prevent things from going completely wrong (e.g., correcting injection timing and amount).

The now increasingly criticized issue of weak acceleration when starting a cold engine (especially with PD engines) also originates from this area. But please, no Russian modifications, and for heaven's sake, don't blow out any HC (hydrocarbons). However, if you don't inject anything into the intake, you won't get any torque.

CU Gremlin.

@Gremlin
The main reason for the withdrawn approval is the emission regulations. Considering the upcoming limits (and even those already in place), the injection system must be extremely precisely adapted to the fuel being used. Even the different viscosity of biodiesel (and there are many other differing properties) is now causing problems with the engine's operation. While the engine doesn't fundamentally have problems, it can no longer pass the emission tests under worst-case scenarios. The 'biodiesel kit' mainly includes a fuel sensor that informs the EDC about the most basic properties of the currently available fuel (viscosity, etc.). This gives the EDC at least the possibility to adjust its parameters so that nothing goes completely wrong (e.g., correction of injection timing and amount).

I completely agree with that, or that's my understanding as well. Unfortunately, in other contexts, it's often mentioned that the approval was withdrawn due to frequent defects. This is definitely not the case with VW, at least.

@Bertil
'That's perfectly fine with me, and I don't have any problems with it. What bothers me a bit is the fact that you even mention this document. For someone outside the loop, the content is completely incomprehensible and unverifiable. There are enough people on the internet who simply make claims. I think you're familiar with that too. This thread itself clearly shows that unfounded claims are being made. Please don't take the following personally: If I were to say that I possess an internal research paper stating that damage to the injection system due to the poor lubricating properties of regular diesel occurs in 3% of cases, that statement would be baseless and its truthfulness would be impossible to verify unless I released this document. The statement might not even be false. However, it always depends on the experimental conditions and other factors. In this case, those factors would simply remain hidden.'
Scientific papers are typically characterized by being made publicly available and usually undergoing a peer review process.

Thank you for your example. I understand it very well. I have a study from an Austrian institute that tested the effects of biodiesel with very low oxidation stability (far outside the norm) on engines and injection components. Among other things, two vehicles with common rail (PD) injection systems were included in the test. After approximately 1.5 years and about 50,000 km, oxidation traces were detected on the common rail injectors of one of the vehicles, although they were still minor. There was also a type of gel-like deposit.
The shortcoming of this study is that vehicles using biodiesel that met the standard specifications were not tested simultaneously. Therefore, in my opinion, the study's conclusion that the oxidation was caused by the substandard biodiesel is not particularly informative. The damage could potentially occur even when using biodiesel that meets the standard specifications. Otherwise, the scientific approach seemed sound to me.
If needed, I can make these available (however, they are only available in English).

For me, the question with your example is whether the problem was caused by the fuel filter itself or by a fuel filter that didn't meet the required standards. If it was a non-compliant fuel filter, the owner would have had to drive it for a very long time to reach this level of damage, which is relatively unlikely. Also, the fuel filter wouldn't have been in the tank for very long to accumulate enough water, given the high mileage and the relatively recent availability of the fuel pump.

Can you please answer a few more questions? What does 'baked on' mean in this context (referring to the high-pressure part, the nozzle, the solenoid valve, from the outside)? Did you disassemble the PD element? Did the 'customer' only use biodiesel? Or a mixture? Do you know where the 'customer' refueled? What does a PD element look like after 180,000 km with diesel?
Zumindest habe ich jetzt wieder Stoff zum nachdenken. Thank you very much.

Regards,

Dirk.

Dirk_S wrote:

@Bertil Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. Can you please answer a few more questions? What does "zugebacken" mean (in the high-pressure section, at the nozzle, at the solenoid valve, from the outside)? Have you disassembled the PD element? Did the "customer" only use BD (biodiesel)? Or did they alternate? Do you know where the "customer" refueled? What does a PD element look like after 180,000 km with diesel?

. . . and here are some questions from me:
-> What driving behavior symptoms (gradual or sudden) were caused by the deposits?
-> Were there any secondary damages (for example, a failure of the pump piston caused by deposits, leading to a fracture of the "delicate" ball valve)?

Bertil wrote:

Since when have the North Sea and Russia been in a war zone? D obtains 90% of its crude oil from these regions. [..Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. Unfortunately, that will still be the case, even if we use BD.

It's not just about Germany. I'm talking about the global use of oil for energy production. It can't be that everyone always just says "it doesn't concern me." Someone has to start somewhere! Now we have a practical alternative fuel (which I'll come back to), and no one uses it; partly justifiably due to technical reasons (which I'll also come back to), and partly unjustly due to completely unfounded prejudices, simply because it's new, unknown, "eco" (ugh), and so on. It's really frustrating.

Bertil wrote:

By the way, biodiesel is heavily subsidized. The national debt continues to grow with every liter of biodiesel sold.

This is also one of those strange lies of the petroleum industry. Biodiesel is not subsidized! Farmers receive a subsidy from the state if they leave their fields fallow or grow plants whose impact on the mineral and nutrient balance of the soil is comparable to that of a fallow period. This includes rapeseed. The subsidy for the fallow land is given to farmers regardless of whether they grow rapeseed or not. Therefore, the argument that the national debt increases with every liter of BD is completely unfounded. On the contrary: rapeseed cultivation creates jobs, while fallow land does not. The sale of biodiesel generates revenue, which in turn generates sales tax for the state's coffers. The sale of biodiesel generates profits for farmers, cooperatives, production facilities, and gas stations, and thus generates tax revenue for the state's coffers.

Bertil wrote:

The biodiesel (BD) consumption in Germany is significantly below the 2% quota required by the EU.

This will certainly change, at the latest now, when 5% BD is added to mineral diesel - whether you want it or not.

Bertil wrote:

I would not describe this fuel as suitable for practical use.

So, that's another statement that is full of prejudices. I certainly do consider a fuel to be suitable for practical use if...
- has a sufficient infrastructure (1500 gas stations in Germany) [unlike Pöl].
- is liquid at room temperature [unlike hydrogen].
- is liquid at atmospheric pressure [unlike LPG/autogas].
- can be burned in an engine without any modifications [unlike fuel oil/gas/hydrogen].
- releases more energy than was required for its production [unlike hydrogen].
- which, after two weeks of storage, did not diffuse out of the tank on its own [unlike hydrogen].
- does not cause an environmental disaster in the event of an accident, as it is biodegradable [unlike diesel/gasoline].
- does not cause a fire/explosion in the event of a leak or damage to the tank [unlike gas/hydrogen].

joergs wrote:

You say that you are concerned with ecology, etc. So why BD? The amount of energy required for the transesterification of petroleum is not insignificant. What do you think it comes from? Right! Probably not from biomass! So, there isn't much else left: nuclear, coal, natural gas, petroleum... and whether that is really that ecological...

The methanol for the transesterification, as well as the energy for biodiesel production, comes from conventional energy sources, which is correct. But what kind of argument is that? Diesel doesn't just flow out of the ground next to the gas station either. Crude oil must also be extracted, transported, and, above all, processed very energy-intensively to produce diesel or gasoline. With BD, we are talking about a relatively simple chemical reaction with methanol, which proceeds spontaneously at a temperature of 70 degrees thanks to a catalyst. In the refining of diesel, nothing happens spontaneously, and certainly not at 70°C.

"Biodiesel is not an option for me, as I don't have the time or desire to fill up from bottles at Aldi, or to set up a home fueling station for biodiesel in my basement. I need a fuel that is readily available when I'm on the road, and for which I don't have to install additional hardware costing 2000 EUR just to be able to refuel it easily."

joergs wrote:

Furthermore, I'm also interested in what motivates someone to buy a car costing over €30,000 and then forgo warranty coverage due to minor amounts? Those 20 cents/liter are just a smokescreen, and I don't think I've believed that for a long time, unlike what you're writing. I travel a lot and pay very close attention to the BD price. Currently, it's between 6 and a maximum of 11 cents. I'm very curious to hear your honest answers, even if it seems off-topic to you.

Who says that I'm concerned about those few cents of fuel costs? I think I've made it very clear in my statements what I'm talking about. It's a matter of attitude, nothing more, nothing less. If everyone always says "it's none of my business," "let others deal with it," or "everything new is bad," we won't get anywhere.

Und da komme ich zum nächsten Punkt: der Mineralöl-Lobby. Es kann mir doch niemand erzählen, dass die geringen Lösungsmitteleigenschaften und die um ein paar Prozent vom mineralischen Diesel differierenden sonstigen Eigenschaften von Biodiesel ein so großes technisches Problem darstellen, dass diese nicht zu lösen sind! Verdammt, wir führen Laugen und Säuren in resistenten Rohren (die auch Dichtungen benötigen), die so ätzend sind, dass allein die Dämpfe einen Menschen zu Matsch auflösen können. Für jedes noch so popelige Einsatzgebiet und Einsatzprofil gibt es ein passendes Material! Und es will mir ernsthaft jemand erzählen, dass ausgerechnet Biodiesel ein Problem ist, das nicht in den Griff zu kriegen ist? Hallo?? Biodiesel DARF nicht in den Griff zu bekommen sein, das ist der Punkt. Warum die Mineralöl-Industrie dagegen ist, leuchtet mir ein, die Automobil-Industrie vielleicht auch noch. Aber warum sich die Kunden (auch viele, die überhaupt keine eigenen Erfahrungen haben mit BD) von solch hirnrissigen Argumenten in den Bann ziehen lassen und hier wie dort immer wieder die selben (meist haltlosen) Anti-Parolen gegen BD herunterbeten, das ist mir völlig schleierhaft. Es läge am Druck des Kunden auf die Hersteller, endlich Dichtungen zu verbauen, die in der Herstellung 0,5 Ct teurer sind, aber endlich das unendlich komplizierte (ROFL) Lösungsmittelproblem von BD aus der Welt schaffen. But as you can see, many customers even help the manufacturers to avoid responsibility .

BTW: In my town, biodiesel costs 81 cents, while diesel costs 99 cents. That's actually not 20 cents of deception!!! Stone him!!!

Hello,

Nero24 wrote:

BTW: In my town, biodiesel costs 81 cents, while diesel costs 99 cents. That's actually not 20 cents of deception!!! Stone him!!!

Quite apart from the various political and technical arguments for and against it,
Why doesn't the industry itself ensure acceptance through appropriate pricing?
I have personally never seen a gas station that has the price difference between BD and D that you mentioned.

Simply set the price so that the undisputed increase in consumption and the equally undisputed higher risk of defects are more than offset.
Apparently, the industry can no longer sell BD (presumably referring to a product or service), otherwise they would have already convinced consumers through appropriate pricing strategies.

If biodiesel prices are, as they always have been, so strongly linked to the price of diesel, then there's no need for anyone to open their mouth and complain about the "evil" petroleum industry or the automotive manufacturers.

Best regards, Rainer.

Hi Dirk,

Dirk_S wrote:

.... For me, the question in your example is whether the issue was generally due to the building permit (BD) or due to a building permit that did not comply with regulations.

It is impossible to say with absolute certainty. The customer always refueled at the same gas station, which advertised fuel that met the standard (at that time, the DIN preliminary standard!). However, there were also several instances where diesel fuel was used.
However, a later test revealed that the fuel did not meet the required standards (at that time, it was the DIN Virnorm standard, which was later replaced by the EU standard). The viscosity was far outside the norm, at 8 mm²/s. Also, the water content could not be met according to the old DIN standard. I no longer remember the details of the other values mentioned in the report.
Unfortunately, this sample is just a snapshot. I am leaving completely open how the fuel quality was in the years prior, as I have no information on that.

Quote:

If the battery wasn't defective from the factory, the owner would have had to drive it for a very long time to reach this level of damage, which is relatively unlikely. Also, the battery couldn't have been in the tank for a long time to accumulate enough water, given the high mileage and the relatively short time the product has been available.

The AJM PD engine is quite old (1999).
The vehicle in question was operated with biodiesel for approximately 150,000 kilometers. Diesel operation was more of an exception.

Quote:

Can you please answer a few more questions? What does "baked on" mean (referring to the high-pressure part, the nozzle, the solenoid valve, from the outside)? Did you disassemble the PD element? Did the "customer" only use biodiesel? Or a mixture? Do you know where the "customer" refueled? What does a PD element look like after 180,000 km with diesel?

The PD elements could no longer be disassembled. The only option was to cut them apart. Unfortunately, this made it impossible to perform a functional test of the components. However, the deposits inside the PD elements were alarming.
Error description:
The engine started running progressively worse (gradually). Frequent "stuttering" (customer description) and jerking were the next symptoms. One day, the engine was only running on 3 cylinders. One common rail injector had completely failed. This injector was disassembled. The nozzle holes were almost completely clogged. No material fractures were visible.
The other PD elements were not further investigated, but some deposits were visible on the outside of the nozzle head.

I wouldn't completely rule out the possibility that a particulate filter element could become clogged with diesel, but I would definitely question it strongly.
After 180,000 km, the common rail injectors would have needed a revision anyway. Injectors in diesel engines are consumable parts (but that's my personal opinion).

Quote:

Zumindest habe ich jetzt wieder Stoff zum nachdenken. Thank you very much.

This engine also gave me something to think about. At that time, I still had my 1Z and was also (briefly) using BD. After that, I quickly switched back to DINO.
The savings I achieved with BD were simply too small.
Considering a roughly 5-10% increase in consumption (based on my own experience) and a cost saving of just under 10%, it's not worth taking the risk.
I also once tested my AXR, at the beginning (with the old PD element set), with BD fuel, just to see how it would perform. Even then, I noticed a significant increase in fuel consumption and some reluctance to start when the engine was cold. Since I don't want to unnecessarily stress my engine, I stopped using it. If I could save 20-30%, I would reconsider the idea. However, I would then set aside a portion of the money saved for new PD elements.


Furthermore, some statements about BD from the manufacturers are already giving me a severe headache (source http://www.ufop.de).

Quote:

Biodiesel can cause filter blockages. When vehicles that have been operating on mineral oil-based fuels are switched to biodiesel, there is a possibility that deposits of old mineral oil diesel fuel may detach and enter the fuel filter.

What kind of corrosive liquid must that be?
Will this damage my injection equipment?

Quote:

The use of biodiesel leads to a loss of performance and an increased fuel consumption of 10 to 15%. Due to the lower specific energy content of biodiesel, an increase in fuel consumption is to be expected. However, in practical operation, this increase is significantly lower than what the theoretical calculations suggest, as other favorable characteristics of biodiesel allow for more efficient engine operation. In fleet trials, fuel consumption increases of 0-5% were observed compared to the use of diesel fuel. Increases of 10% or more are not known and would not be technically justified.

That aligns with my own observations and is also understandable.

Quote:

In case of technical problems with the injection system, the customer often bears the cost of the damage. Unfortunately, the level of qualification regarding biodiesel among the local workshops varies greatly.

Why the workshops?
There is no diesel system manufacturer that approves its systems for use in battery-powered vehicles. Only the vehicle manufacturers do that. So, decisions are being made over the heads of the suppliers, which I find extremely concerning!

Hi,

Rainer K. wrote:

Hello, If BD prices, as has always been the case, are so heavily influenced by the price of diesel, then no one needs to open their mouth and complain about the evil petroleum lobby or the automotive manufacturers, but should first look in the mirror.

Sorry, I don't understand this sentence. BD prices, greedy, open your mouth, look in the mirror? Can you explain the logical sequence of this sentence again, even for a "stupid" environmental lobbyist? Why should I look in the mirror just because the BD price is based on the price of diesel, according to the laws of the free market?

Nero24 wrote:

.... It's not just about Germany. I'm concerned about the global use of crude oil for energy production. It can't be that everyone always just says "it doesn't concern me."

That's good and nice, but not with the risk I have to take.

Quote:

Bertil wrote: By the way, biodiesel is heavily subsidized. The national debt continues to grow with every liter of biodiesel sold. That's also one of those strange lies told by the petroleum industry.

Huh?
Please provide the text you would like me to translate from German to English.
However, the Arbeitsgemeinschaft Qualitätsmanagement Biodiesel e.V. ( http://www.agqm-biodiesel.de ) says something different:

"Since January 1, 2004, an amended Mineral Oil Tax Act has been in effect. Since that time, biofuels (including biodiesel) have been treated as taxable items with an effective mineral oil tax rate of 0%."

If BD is exempt from mineral oil tax, it logically follows that it is also subsidized.

Adding 5% biodiesel is not a problem for me. The manufacturers of the injection systems allow a maximum biodiesel mixture of 5% with diesel.

Regarding its suitability for practical use:
Your arguments are all correct, but regarding various other specifications, BD is far from being a practical fuel.
- No approval from system manufacturers.
- The water content may be extremely high.
- Unfortunately, the BD oxidizes after prolonged storage.
It can happen right at the gas station, at the pump. I have no control over that!
- I will leave the comparison with hydrogen open, as I don't see any practical feasibility in that either.

Quote:

BTW: In my town, biodiesel costs 81 cents, while diesel costs 99 cents. That's actually not 20 cents of deception!!! Stone him!!!

It varies from region to region.
It's great that the price is like that with you.
Just put it in and get happy.
I would also drive a BD (presumably a type of vehicle) if there was a 30% savings, and I would put back 50% of the savings. It's that simple .

As of today, the price for gasoline is 89 cents per liter, and for diesel it's 93 cents per liter. The difference of 4 cents is negligible because the increased fuel consumption outweighs the savings.

Bertil wrote:

So, if BD is exempt from mineral oil tax, it is consequently also subsidized!

Well, that's a matter of opinion. For me, a tax exemption is not a subsidy. A subsidy is when funds flow in the "opposite" direction; moreover, biodiesel is not a mineral oil, and a mineral oil tax on biodiesel is not logical from a basic definition. Incidentally, hardly any mineral oil tax is levied on heating oil (60 EUR instead of 480 EUR per ton), even though it is a mineral oil. Is that also subsidized?

Nero24 wrote:

By the way, hardly any mineral oil tax is levied on heating oil (60 EUR instead of 480 EUR per ton), even though it is a mineral oil. Is this also subsidized?

"Yes, that's also what it's called (at least, according to customs)."

I'm saying that only people who are clueless fill up with "regular" gasoline, thinking they're saving money, because you actually end up paying more due to the increased fuel consumption.
If you're also taking on additional risk, it should be worth it.

Bertil wrote:

I would definitely choose BD if there was a 30% savings, and I would put back 50% of the savings. It's that simple

.
Hmm, how long would the PDE with BD need to last before it would be worthwhile?

The 15% reserve would be offset by the increased consumption.
So, let's say the reserve, minus the extra consumption, would be 10 cents per liter.

At 6 liters per 100 kilometers, which is equivalent to 60 cents per 100 kilometers, or 60,000 cents for 100,000 kilometers, that's 600 euros for 100,000 kilometers.

If (as in your example) the PDEs are worn out after 150,000 km, then a reserve of 900 euros for a new set of PDEs is only sufficient if you have an unusually cheap source .

-> The average driver = someone who goes to a workshop (instead of being an "IhBäh" buyer or a DIY enthusiast) would still pay more, even with a 15% price difference and a 100% reserve .

As of today, the price is 89 cents for gasoline and 93 cents for diesel... The difference is 4 cents, which is not significant because the additional fuel consumption is much higher than the amount saved.
Current status with us:

BD: 84 Ct.
Diesel: 99 cents.
Difference: 15 cents.

I find the discussion interesting.
I have experience with VEP and BD, but that's all I can offer.

Best regards, Georg.