A Brief Overview of the Diesel Particulate Filter (DPF)

The diesel particulate filter (DPF) has been mandatory equipment since 2005, following the introduction of Euro 4 standards. As its English name suggests, it is installed in diesel vehicles to protect not the engine, but the environment from soot emissions. Although it is often integrated with the catalytic converter, it does not duplicate or replace it. The catalytic converter is more relevant in gasoline engines, where a DPF is essentially unnecessary.
Soot mainly forms in diesel engines, where fuel combustion is triggered not by a spark but by compression, resulting in lower combustion temperatures. Under these conditions, the hydrocarbons in petroleum products combust in stages, with hydrogen burning first, while carbon remains. The remaining carbon atoms bond to form soot, a solid substance. Although soot constitutes less than 1% of exhaust gases, it can turn emissions a radically black color and is a potent carcinogen.
A DPF is a unique component. It not only collects pollutants but also has the capability to destroy them by burning at high temperatures or through catalytic reactions. The car's electronic control unit (ECU) manages the routine cleaning of the DPF, usually during long highway drives. However, this well-designed regeneration process often fails in practice, leading to DPF clogging and engine issues such as:
• Reduced power
• Lower maximum speed
• Increased fuel consumption
A completely clogged filter can render the vehicle inoperable.

Ways to solve problems with the Diesel Particulate Filter

There are three main ways to address DPF failure:
1. Replacing the filter with a new one. This is costly, with prices reaching several thousand dollars, often exceeding half the vehicle’s residual value.
2. Removing and reprogramming to Euro 2 standards. This may result in issues with vehicle inspections or entry into EU countries.
3. Cleaning the DPF with chemical washing or other methods. This is generally the most practical and reasonable way to resolve the problem.
The outcome depends on the cleaning method used. The most affordable and therefore common method today is chemical washing. While not highly effective, it allows for temporary use of the vehicle. This method has several drawbacks: it’s highly toxic, the results can be unreliable, and the process is time-consuming, requiring 8–12 hours of soaking. However, it’s simple enough that DPF removal is often unnecessary. There are reagents available that can simply be poured in after removing a sensor, then blown out through the exhaust system.
It may seem straightforward, but automotive services are constantly evolving. A new range of services has emerged: hydrogen cleaning of engines and components. Advocates of this method claim it can (and should) be used to clean DPFs effectively, with one caveat: it works only if the DPF is "not too clogged," typically up to "80%." Moreover, the filter does not need to be removed.

Why Hydrogen Cleaning for DPFs is Impossible

It is difficult to understand how one can visually assess the percentage of clogging without removal. Even professional DPF cleaning equipment, such as the MS900 stand, only measures air resistance. The description of hydrogen technology, where available, is even more puzzling.
We are promised that a "hydrogen-oxygen mixture" will act on the carbon at the atomic level. This supposedly causes carbon deposits to break down into molecules (of what substance?) and exit through the exhaust. The promise is to clean not only the DPF but also the catalytic converter, pistons, rings, EGR valves, and anything else it reaches.
This sounds promising, especially for those who haven’t studied chemistry, or have forgotten it. On a positive note, it is theoretically possible to clean carbon deposits with hydrogen, such as oxidation products of hydrocarbons (resins, asphaltenes, etc.) mixed with metal impurities. Oil sludges, which are similar but appear as a viscous liquid, could also react with hydrogen, forming water and carbon dioxide.
However, soot is not a deposit but a formation. It is not a compound but nearly pure carbon (98%). Previously thought to be amorphous, recent X-ray studies show that soot has a low degree of crystallinity, resembling diamond or graphite, but with a different type of sp-hybridization (sp² rather than sp³). Affecting the crystalline structure of soot chemically is extremely difficult, as it is self-sufficient. Producing CO₂ from it requires oxidation, which involves oxygen, not hydrogen (which is a reducing agent, not an oxidizer). This can only be achieved at high temperatures (600-800°C) or with a catalyst. These methods are precisely what factory DPF cleaning systems use:
• Thermal for German systems (DPF)
• Catalytic for French systems (FAP)
No hydrogen is involved in either method.

Effective Equipment for Diesel Particulate Filter Washing

When discussing hydrogen in the context of DPF cleaning equipment, it’s worth remembering its simplest and most popular combination with oxygen—H₂O, or water. This application actually makes sense, albeit with a "minor" requirement: a DPF cleaning stand like the MS900.
This unique three-module system can clean a DPF thoroughly and quickly, within 2–3 hours, and diagnose it both before and after the procedure. DPFs of any design are cleaned using simple water and compressed air pulses that alternate flow directions for more thorough cleaning. After washing, the DPF is dried and fully ready for reinstallation. In this case, the lifespan and filtration efficiency of the DPF are generally comparable to a new part.

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