Particulate filter

A DPF (Diesel Particulate Filter) traps solid soot particles in the exhaust system. A clogged or damaged DPF causes increased exhaust back pressure, regeneration faults or inadequate particulate filtration. For MAN and Mercedes trucks, buses and vans, a lasting repair therefore requires more than just Filter replacement: engine combustion, sensor readings and operating conditions must also be checked.

Always identify parts using the vehicle's chassis number. Visual comparison or selection based solely on the model name is never sufficient. Also check the engine variant, emissions class, part number and exhaust aftertreatment configuration. For example, different filter modules are used in MAN TGX models with D26 engines and Mercedes Actros models with OM 471 engines. For Lion's City, Citaro, TGE and Sprinter, the year of manufacture and emissions specification also determine the configuration fitted.

Many DPFs use a ceramic wall-flow substrate with alternately plugged channels. Exhaust gases flow through porous channel walls, while soot is retained. Cordierite and silicon carbide are common substrate materials; their thermal properties differ. Filter volume, porosity, wall thickness and catalytic coating all influence pressure drop and regeneration characteristics. Both separately replaceable filter elements and integrated aftertreatment modules are available.

Check connection diameters, flange fit, seal seats, mounting position and sensor ports. Permissible exhaust back pressure and differential pressure depend on exhaust gas flow rate and temperature: use vehicle-specific test conditions and limit values, not a universal pressure limit.

Frequent short journeys, idling and interrupted regenerations cause soot build-up. Engine oil consumption and lubricating oil additives also produce non-combustible ash. Regeneration removes soot, but not ash. Recurring warnings, power derating and rising fuel consumption can also be caused by faulty differential pressure sensors, blocked pressure sensing lines or incorrect exhaust gas temperatures. A cracked filter, on the other hand, may show a low pressure drop despite inadequate filtration.

1. Read the engine management system's diagnostic data. Record fault codes, fault conditions, calculated soot and ash loading, regeneration history and reasons for regeneration inhibition. Compare calculated loading with measured values.
2. Check pressure readings. Inspect pressure sensing lines for cracks, condensation, blockages and reversed connections. With the engine stopped, the differential pressure should be approximately zero, within the manufacturer's tolerance. Compare the sensor signal with a calibrated differential pressure gauge at the specified engine speed and load.
3. Assess temperature data. With the engine cold, compare sensor readings with the ambient temperature and record how they change during warm-up. Active regeneration typically requires around 550–650 °C at the filter; the exact control strategy varies by system. If the temperature is insufficient, also check the oxidation catalyst and regeneration fuel dosing system, where fitted.
4. Find the cause of excessive soot formation. Check the injectors in accordance with the engine diagnostic procedure, and check for charge-air leaks and faults in boost pressure control and exhaust gas recirculation. If engine oil consumption is excessive, also inspect the turbocharger and assess engine condition. Confirm suspected filter damage by inspection and, where specified, a particle number measurement.

Only carry out forced regeneration under the manufacturer's specified conditions and within the permissible soot loading limit. If the filter is overloaded, the temperature can rise uncontrollably and melt the substrate. Use a suitable, fire-safe work area with provisions for hot exhaust gases; keep combustible materials well away.

Have an ash-loaded but intact filter professionally cleaned using a suitable, approved procedure, with flow and integrity checks before and after treatment. Replace elements with cracks, melting damage or contamination that cannot be removed. Only remove the filter once it has cooled down, and prevent soot and ash dust from spreading.

Install using the specified seals and tightening torques, ensuring all connections are free from mechanical stress. Only carry out the specified relearn procedures and loading resets after the corresponding work has been completed. Then check for leaks, pressure drop under load and correct regeneration operation. Use engine oil with the correct manufacturer approval and minimise recurring interruptions to regeneration to prevent repeated downtime.

Braem has the equipment required to regenerate or clean a DPF off the vehicle, after it has been removed. When a DPF is severely blocked with non-combustible ash left behind after countless in-vehicle regenerations, the vehicle can no longer clear the filter through regeneration alone. The filter must then be removed and treated off the vehicle. Two methods are used: thermal regeneration (baking) for the remaining soot and hydrodynamic cleaning (washing) to remove the residual ash.

For this treatment, Braem has a DPF cleaning machine with hydrodynamic flushing equipment and a thermal DPF oven, complemented by supporting equipment:

1. Hydrodynamic / "Flash" flushing machine. Inside an enclosed washing cabinet, a mixture of warm water, compressed air and special additives is pumped through the filter in powerful pulses. This wave-surge or air-explosion technology flushes residual ash out of the microscopic channels.
2. Thermal DPF oven. The oven heats the filter to high temperatures in a controlled manner, causing stubborn residual soot to oxidise and burn off. Any remaining ash must then be removed from the filter.
3. DPF drying drum / drying function. After wet flushing, the filter is thoroughly dried using a high-temperature drying function before being refitted. This prevents residual moisture from causing new soot to clump together immediately.
4. Back pressure tester. An air pressure test is performed before and after cleaning. The measured air resistance in mbar quantifies the restored flow and allows comparison with the flow capacity of a new filter.
5. Dedicated DPF adapters and flanges. Universal and make-specific adapters ensure an airtight connection between various exhaust pipes and flanges and the cleaning machine.
6. Precision Soot Scale. The filter is weighed before and after the process. The weight difference in grams shows how much ash and soot has been removed during treatment.

This equipment enables Braem to treat removed DPFs, verify the cleaning results and sell DPFs on an exchange basis.