DPF cleaning, DPF cleaning Australia, DPF cleaning Brisbane, DPF cleaning Gold Coast, DPF cleaning Sunshine Coast
Diesel Particulate Filter
Unlike the DOC, the diesel particulate filter (DPF) is a wall-flow filter consisting of a matrix of materials (a composite of cordierite, silicon carbide, or metal fibres) that traps any remaining soot that the DOC couldn’t oxidize. Wall-flow diesel particulate filters usually remove 85% or more of the soot, and under certain conditions can achieve soot removal efficiencies approaching 100%. Some filters are a single-use unit, intended for disposal and replacement once full of accumulated ash. The soot remains in the DPF until it is regenerated either passively, actively or forced.
Passive regeneration occurs during the vehicle’s normal operating temperatures when engine load and vehicle drive-cycle create temperatures that are high enough to regenerate the soot build up on the DPF walls. The DPF will oxidise the particulates anywhere between 275-360⁰ Celsius. Passive regeneration takes place automatically approximately every 400-800 km depending on the quantity of particulate inside the filter and the driving behaviour.
Active regeneration happens while the vehicle is in use, when low engine load and lower exhaust gas temperatures inhibit a passive regeneration. Sensors upstream and downstream of the DPF (or a pressure differential sensor) provide readings that initiate a measured addition of fuel into the exhaust stream. There are two methods to inject the extra fuel, either downstream injection directly into the exhaust stream, downstream of the turbo, or fuel injected into the engine cylinders on the exhaust stroke. This fuel and exhaust gas mixture passes through the Diesel Oxidising Catalyst (DOC) creating temperatures over 600 degrees Celsius to burn off the accumulated soot. Once the pressure drop across the DPF lowers to a calculated value, the process ends, until the soot accumulation builds up again.
This regeneration process occurs at road speeds higher than can generally be attained on city streets. Vehicles driven exclusively at low speeds in urban or peak hour traffic can require periodic trips at higher speeds to trigger an active regeneration to clean out the DPF. If you as a driver ignore the warning light and wait too long to operate the vehicle at about 100km/hr for a reasonable time frame the DPF may not regenerate properly and continued operation past that point may cause damage to the DPF filter resulting in the need for a complete replacement.
If the DPF develops too much pressure then the last type of regeneration must be used - a forced regeneration. This can be accomplished in two ways.
1. The Vehicle operator can initiate the regeneration via a dashboard mounted switch. Various signal interlocks, such as park brake applied, transmission in neutral, engine coolant temperature, and an absence of engine related fault codes are required (vary by OEM and application) for this process to initiate.
2. When the soot accumulation reaches a level that is potentially damaging to the engine or the exhaust system, the solution involves a qualified technician using a computer program to run a regeneration of the DPF manually.
Back pressure usually returns to normal after the soot is oxidised during an active, passive or forced regen, however don’t forget about the remaining ash! It builds up inside the DPF and does not burn or oxidize like soot and will remain in the DPF until removed.
Ash is made of minerals, metals and other trace elements from the breakdown of lubricants, additives and engine wear.
Ash builds up at a much slower rate than soot but if it’s ignored will eventually cause an increase in back pressure, fuel consumption and at worst DPF failure. As the ash builds up inside the DPF the number of active regenerations increase causing fuel economy to become poor, temperatures inside the DPF to become extreme which can severely damage the construction of the internal filter system and more constant back pressure that can be detrimental to the turbo itself.
The longer the ash is left inside the DPF the higher the chance of it hardening into a plug which closes off that portion of the filter.
Shorter intervals between regenerations is the first clue to ash build up and is a tell tale sign the DPF needs to be removed for cleaning. This can also be observed by logging the regen cycles in a workshop with diagnostic equipment. When the DPF is removed for cleaning it’s always a good practice to also remove the DOC and clean it as well if necessary.
Failure of fuel injectors or turbochargers resulting in contamination of the filter with raw diesel, engine oil or debris can also necessitate cleaning.
