DPF Materials: Differences & New Diesel Particulate Filters

There are various filter materials used in diesel particulate filters.

- Mullite
- Cordierite
- Silicon carbide
- Aluminum titanate

I cannot say whether there are other filter materials available. However, during my search for a new DPF (Diesel Particulate Filter), I have repeatedly come across silicon carbide and cordierite. It is now known from various sources that silicon carbide has a higher melting point of approximately 2730°C, while cordierite has a melting point of 1200°C.
Cordierite is therefore likely more suitable for long-distance vehicles. And that's the key point.

"Why? - When I've driven my TDI with regeneration enabled, I've never seen temperatures above 700°C after the DPF (as far as I can remember). Is the combustion temperature actually higher *inside* the DPF?"

2. For example, if you drive a month of short distances, followed by a week of very long distances, could that be a problem for the cordierite material?

Because: What is the difference in pressure drop between cordierite and silicon carbide when the DPF becomes full? Or is this negligible, since both materials have approximately the same airflow when they are saturated with ash?


Price-wise, a DPF with cordierite as the filter material would be more interesting for me, but well... I want to be able to use it for as long as possible.


Why am I looking for a new DPF? - I have a differential pressure of 325 mbar on my BLS engine, even after a regeneration cycle. And if I look at the thread with the standard values, I should take action! The differential pressure sensor is only 12 months old (original VW).

I read that cordierite was used previously, but now silicon carbide is more common.

Hello,

I can't really understand your considerations regarding the filter material. The structure of the filter itself is probably the most important factor, and the material of the filter ceramic is just one parameter among many. A forced regeneration should never be necessary during normal operation.

Either rinse the old filter or install a new, identical filter, and don't make it a complicated process.

A DPF (Diesel Particulate Filter) from the manufacturer typically lasts for around 250,000 km. It's generally not worthwhile to use a vehicle for much more than 500,000 km, but this can be achieved with proper DPF cleaning or replacement. Of course, exceptions exist, such as damage to the engine or turbocharger, which can affect the DPF.

Regarding your questions 1 and 2: Volkswagen has a self-study program called 336 (search the web for "SSP336 PDF").

Best regards, Rainer.

I don't really understand your approach either.
The reasons for changes in material selection over time are likely numerous. In the automotive industry, a key factor is probably that certain materials are more readily available and cost-effective in large quantities.

Melting points of ceramic materials under laboratory conditions are completely irrelevant to you as a user. Much worse things happen significantly earlier, believe me...

Your vehicle has two thermocouples, one before the filter and one after it. Both measure the exhaust gas flow at specific points and provide information. The hottest zone is where the oxidizing front passes, and there are many images of this online, and likely also in the aforementioned SSP (Service Information). The temperature at which the "soot" to be combusted undergoes thermal conversion depends on the oxygen supply and the "local amount of soot."

It's more important to figure out *why* you're having to do "emergency regenerations" than to focus on which material is the problem. I've driven cars with DPFs for almost 500,000 km and never had this issue. So, find the root cause and fix it. If a full filter is one of the causes, stop doing emergency regenerations and instead, after the "next" one, remove the filter, have it cleaned (or have it professionally cleaned), use the search function here to find out what to consider during installation and coding, and then enjoy another 200,000 km.
Then, after 200,000 km, carefully consider whether the vehicle is still worth the effort and either go back to the beginning or find a replacement. If you perform the cleaning yourself, you will have a very good feeling about what it is worth to you personally.

Good morning!

I actually wanted to give a reply after I received the book that Rainer recommended!

Perhaps I had simply gotten too worked up about the issue, because at the Walker company's website, you can find information on which of the two materials mentioned is better suited for each specific application. However, I'm not entirely clear on the exact reasons why and where the line is drawn.

But there's some news! Yesterday, I wanted to remove the filter and rinse it with water. After I finished the regeneration process, I did another test run with a differential pressure measurement. Suddenly, the pressure was much lower. Now it's at about 120 mbar... Of course, I didn't remove the filter!

Since I now have a new engine, and the old one had oily channels on the exhaust, it's possible that the filter was clogged, preventing it from opening properly during the first regeneration due to the oil mist?
My regeneration cycle always involves a slight uphill gradient, and the temperature inside the filter consistently ranges from 620 to 670 degrees Celsius.

It's difficult for anyone to accurately assess a situation while sitting at their computer, especially when they don't have all the information.

But Rainer was right to say that, if the problems persist, you might have damage to the engine or transmission. That seems to be confirmed, and it appears a new engine was installed, so the investigation into the cause is probably over.

If a large amount of oil enters the DPF, the material it's made of is irrelevant, as it's not designed to handle that.

Since the engine was replaced (as I understand it), I would have had the DPF cleaned at the same time, because it's not going to be any easier to remove it now than it would have been then.

Whether you're driving downhill or uphill during regeneration is almost irrelevant. The fuel needs to be initially ignited, and then it needs air. Ideally, this works perfectly well when rolling. In practice, however, it's unfortunately necessary to add more fuel, and your car does this automatically.

Since the author of the text contacted me privately to point out what he perceives as my incorrect behavior in his case, here are his comments, significantly shortened.
He refers to:

Ich kann den Inhalt dieser URL nicht abrufen, da ich keinen Zugriff auf externe Websites habe. Bitte gib mir den Text, den du übersetzt haben möchtest.

I didn't know that, or I don't remember every name and the corresponding vehicle. However, I think we also understood the problem in isolation, even without it being explicitly described.

He wants to achieve the following:

Quote:

ACTUALLY, I just wanted to find out why there are different types of particulate filter materials with this thread

"However, I believe this has already been mentioned. He refers to the company Walker, which presents a poor translation from English on its EU homepage and promotes various materials. His points and figures seem to originate from the homepage. While everything might be correct there, it doesn't appear very reliable or credible when read on the website, at least to me. Now, we could certainly discuss for a long time whether a melting point of over 2000 °C is necessary for materials used in a car's exhaust system. My opinion on the matter: No. There are significantly other, much more important requirements for the materials used."
However, it ultimately comes down to the same thing as here: it's simply a matter of price; the best quality materials are not always used.

My opinion: If you have different requests for generating and distributing information, simply write them to each other. For me (and apparently others), it seemed like the original problem might be coming from the DPF and could be a material issue. Then there was something about emergency regeneration (multiple times), which seemed to point to an acute problem rather than a fundamental discussion.

I've already stated my opinion. Now I know that there was a lot of oil in the DPF. The material itself isn't the deciding factor; it doesn't really matter which material you use. Airflow rates and loading coefficients, as well as channel lengths, can't really be changed by simply swapping materials, because the engine control unit (ECU) only measures differential pressure and temperature. All other values, such as ash content and soot content, are calculated by the ECU. However, the ECU doesn't know anything about different materials. If a material has a lower pressure drop (higher airflow) than another, that could also lead to confusion for your ECU. Also, the available space is certainly a factor, as is the engine size and power output. Whether the catalytic converter is located close to or far from the engine (as was the case with the earlier models), whether it's integrated into the DPF or separate, etc., all play a role.

Your wish that others might also learn something from this contribution:

1. First, identify the cause of the problem and, ideally, fix it.
2. Examine the consequences. For example, if oil has seeped into the DPF, a significant amount needs to be checked to determine if it can be salvaged. If so, it should be cleaned, either by yourself or by a professional (which is often the better option). Why? We have a forum here that doesn't justify its existence solely through large-scale component replacements, but rather aims to make arising problems financially manageable and to keep things simple through targeted repairs and maintenance.
3. Only replace what absolutely needs to be replaced, such as worn tires, worn brakes, bearings, belts, filters, and fluids. Often, many other parts can be repaired instead... of course, not always.

In that regard, I believe I have addressed all of your points. Furthermore, I would appreciate it if you could write your points here, rather than sending them to me privately.

I have observed temperatures up to 950°C in the DPF during our transit.
Wood starts to burn at approximately 550°F (288°C).
Regenerates normally at approximately 90% load, around 650°C.