DPF-FAP-GPF-SCR-CAT

Genesis and application.

The history of exhaust gases aftertreatment systems in automobiles is a long one, linked to increasing environmental awareness and regulations that aimed to reduce air pollution.

In the 1960s, the problem of air pollution caused by cars began to receive attention in the United States. California, especially Los Angeles, had serious smog problems. In 1966, California introduced the first regulations to control car emissions. This was followed in 1970 by federal emission regulations under the Clean Air Act.

The first trifunctional catalytic converters appeared in the 1970s, mainly in response to stricter emission regulations in the USA. Three-way catalytic converters were able to reduce three main pollutants: nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC).

The 1980s saw the introduction of more advanced emission control systems, such as exhaust gas recirculation (EGR), fuel injection and oxygen sensors (lambda sensors), which improved the efficiency of catalytic converters. European countries also began to introduce their emission regulations, such as Euro 1 in 1992.

The 1990s were a period of further tightening of emission standards in both the US and Europe. Euro 2 (1996), Euro 3 (2000) and Euro 4 (2005) standards were introduced, which required increasingly advanced exhaust aftertreatment technologies, including the use of oxidation catalysts and diesel particulate filters (DPF/FAP) in cars with diesel engine.

The increase in popularity of diesel cars has necessitated the introduction of new exhaust aftertreatment technologies such as selective catalytic reduction (SCR) systems, which use AdBlue® (aqueous urea solution) to reduce NOx. GPF particulate filters have also been introduced for use in petrol engine cars. Today's regulations, such as the Euro 6d standards in Europe, require the use of even more advanced exhaust aftertreatment technologies, including a combination of SCR catalysts, DPF/FAP filters and ammonia (NH3) neutralisation systems.

Construction and principle of operation.

Three-way catalytic converter and oxidation catalytic converter.

The three-function catalytic converter (also known as a three-way catalytic converter or catalytic reactor) is one of the most important components in the exhaust aftertreatment system of modern petrol-engined cars. Its task is to convert the three main harmful substances produced during fuel combustion into less harmful compounds:

1. Nitrogen monoxide (NOx) - reduction to nitrogen (N2) and oxygen (O2)
2. Carbon monoxide (CO) - oxidation to carbon dioxide (CO2)
3. Hydrocarbons (HC) - oxidation to carbon dioxide (CO2) and water (H2O) 

The trifunctional catalytic converter consists of:

1. The core, made of ceramic or metal, has a honeycomb structure that provides a large contact surface for chemical reactions.
2. An active layer covering the core, consisting of precious metals such as platinum (Pt), palladium (Pd) and rhodium (Rh).
3. The housing - usually metal, which protects the catalytic converter and holds it in the correct position in the exhaust system.

For a trifunctional catalytic converter to work effectively, it must operate under certain conditions:

1. Temperature - the catalyst reaches its full efficiency at temperatures between approximately 250°C and 900°C. If the temperature is too low, the chemical reactions do not proceed fast enough.
2. Air/Fuel mixture composition - the optimum mixture composition (air/fuel ratio) is approximately 14.7:1 (stoichiometric ratio). Too rich a mixture (too much fuel) or too poor a mixture (too much air) can reduce the efficiency of the catalytic converter.
3. Oxygen sensors (lambda probes) - Located upstream and downstream of the catalytic converter, it monitors the oxygen levels in the exhaust gas, allowing the engine management system (ECU) to fine-tune the composition of the fuel-air mixture.

While a three-way catalytic converter is used in the exhaust system of petrol engines, diesel engines usually have an oxidation catalytic converter. This oxidises carbon oxides and hydrocarbons, but lacks the ability to reduce NOx due to the fact that diesel engines run on lean mixtures.

Diesel Particulate Filters (DPF/FAP) and Gasoline Particulate Filter (GPF).

The Diesel Particulate Filter (DPF) is a key component used in diesel cars to reduce particulate emissions, which are one of the main sources of air pollution. 

The DPF is usually made of materials with a porous structure, such as silicon carbide (SiC) or cordierite. The structure of the filter resembles a honeycomb with the inlet and outlet channels closed alternately, forcing the exhaust gases to pass through the porous walls of the filter. Particulate matter (soot, ash) is trapped on the porous walls and the rest of the exhaust gas escapes from the filter. As particulates build up inside the filter, the resistance to exhaust flow increases, leading to a decrease in engine performance. The engine controller monitors how full the particulate filter is by, among other things, a differential pressure sensor, comparing the exhaust gas pressure upstream and downstream of the filter. As soon as the programmed values are exceeded, it initiates procedures to help clean (regenerate) the particulate filter. Frequent short-distance driving prevents effective DPF filter regeneration, which may result in the filter becoming overfilled and engine malfunctioning.

Vehicle manufacturers use two main diesel particulate filter solutions:

• "dry" filters
• "wet" filters

Systems with a 'dry' filter do not use any chemical additives, and the increased exhaust gas temperature needed to regenerate and empty the particulate filter of accumulated soot particles is achieved by such measures as increasing the dose of injected fuel, delaying injection, disabling the exhaust gas recirculation system, etc. Some manufacturers have also used solutions in the form of an additional injector mounted in the exhaust system, which feeds fuel directly into the exhaust stream upstream of the particulate filter during its regeneration phase.

'Wet' filter systems use a special additive that, when added to the fuel, reduces the combustion temperature of the soot, allowing the regeneration process of the DPF to take place at a lower temperature. Soot accumulated in a DPF normally requires a high temperature (around 600°C) to burn. The additive lowers this temperature to around 450°C, making the regeneration process easier and faster, especially at lower engine speeds and temperatures. The fluid is stored in a special tank or reservoir in the car and automatically dosed into the fuel tank in small quantities. The engine management system (ECU) controls the dosage of the additive to ensure the correct amount in the fuel. When the fuel is burned in the engine, the cerium contained in the additive remains as particles, which are captured by the DPF along with the soot. When the cerium particles accumulate in the DPF, they reduce the temperature at which the soot starts to burn. This allows the filter regeneration process to take place efficiently even during normal city driving.

Nowadays, vehicle manufacturers strive to provide the most efficient and compact exhaust gas treatment system possible. The result is SCR-equipped particulate filter designs that combine the functions of two components - a DPF and an SCR catalytic converter.

The particulate filter (GPF) is also used in petrol engine cars, especially those with direct injection. This is because these engines emit higher levels of particulate matter compared to traditional indirect-injection engines. Many countries, especially in the European Union, have increasingly stringent emission standards, such as Euro 6. These standards require vehicles to emit less particulate matter, forcing manufacturers to use technology such as GPF to meet these standards. The GPF is designed to effectively capture these particles, reducing PM emissions from the exhaust system. Similar to a DPF, exhaust gases flow through the filter and particles are trapped on its porous walls. Unlike DPF filters, GPF creates fewer problems because exhaust gas temperatures in petrol engines are typically higher. The regeneration process involves combustion of the accumulated soot particles, which takes place automatically during normal engine operation, especially at higher loads and temperatures.

SCR catalytic converters.

It is a key component of the Selective Catalytic Reduction (SCR) system, in which chemical reactions take place that convert NOx into nitrogen (N2) and water (H2O). This is made possible by dosing a special reducing agent, an aqueous urea solution (AdBlue®), into the exhaust gases upstream of the SCR catalytic converter. Often there is a special mixer in the exhaust system upstream of the SCR catalytic converter, used to mix the injected additive thoroughly and evenly into the exhaust gas.

Its structure is similar to that of a three-way catalytic converter or oxidation catalytic converter. The SCR catalytic converter has a core of ceramic or metal honeycomb material coated with a catalytic coating. It contains compounds such as metal oxides (e.g. aluminium oxide, titanium oxide) and precious metals (e.g. platinum, palladium).

Remanufacturing process.

Our service consists of the chemical cleaning of particulate filters and catalytic converters using a safe, fast and effective method. The filter, which has been removed from the vehicle, is subjected to a cleaning process using chemicals and a water jet at the appropriate temperature and pressure. This removes all PM10 particles, oil and cerium deposits (in the case of 'wet' filters). This is a very effective method, which does not pose the risk of damaging the filter cartridge (as can happen with cleaning methods based on high temperature). The method used guarantees that the filter performance is restored to as high as 98% without any interference with the filter structure. The device allows the level of flow through the filter to be measured before and after the cleaning cycle and the results of these tests to be printed out, allowing the effectiveness of the process to be clearly assessed.

This method of cleaning the particulate filter has many advantages over so-called service regeneration:

• no increased mechanical load on the engine due to high speed operation during the service regeneration process
• no increased heat load on components in the exhaust system (turbocharger, catalytic converter, particulate filter core)
• no need to change the engine oil, which is required after service regeneration

The only condition for the filter cleaning process is that there is no mechanical damage, especially to the filter core. Each received filter undergoes a thorough technical condition check and inspection of the filter element using an endoscopic camera. If mechanical damage is detected inside the filter or catalytic converter, we are often able to propose its regeneration, which involves replacing the filter insert.

Causes and types of damage

Symptoms of a damaged or clogged particulate filter/catalytic converter:

1. Decrease in engine performance
2. Uneven engine running at low revs
3. Increased fuel consumption
4. Engine ("check engine") or filter (DPF/SCR) light on
5. Smoke from the exhaust system

The most common particulate filter/catalytic converter failures:

1. Contamination - leakage of engine oil, coolant, overfilling the particulate filter with soot or ash
2. Overheating - abnormal fuel combustion process, fault in injection system, exhaust gas recirculation, engine tuning, etc.
3. Mechanical damage to the core - heat, thermal shock, impact, vibration.