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Diesel Particulate Filter

Of late Kenyan Vehicle market has seen massive uptake of diesel vehicles with Diesel Particulate Filters and lack of proper knowledge of DPFs has cause some technicians and Mechanics / Kawayas have caused irreversible damage to vehicles with such devices.

On several auto groups on social media the issue of DPFs has been raised with some keyboard self-proclaimed mechs giving advices which are not helpful.

Diesel Particulate Filters, also known as DPFs, are exhaust aftertreatment devices that significantly reduce emissions from diesel fuelled vehicles and equipment. DPFs typically use a porous ceramic or cordierite substrate or metallic filter, to physically trap particulate matter (PM) and remove it from the exhaust stream. After it is trapped by the DPF, collected PM is reduced to ash during filter regeneration. Regeneration occurs when the filter element reaches the temperature required for combustion of the PM. “Passive” regeneration occurs when the exhaust gas temperatures are high enough to initiate combustion of the accumulated PM in the DPF, without added fuel, heat or driver action. “Active” regeneration may require driver action and/or other sources of fuel or heat to raise the DPF temperature sufficiently to combust accumulated PM.

The frequency of regeneration is determined by the engine’s duty cycle, PM emission rate, filter technology and other factors. When using an active filter, it is particularly important to follow the manufacturer’s instructions for regeneration. In addition to regeneration, the filter must be periodically cleaned to remove non-combustible materials and ash. It is important to avoid excessive PM and ash accumulation in a DPF, so proper maintenance and cleaning instructions should be followed closely.

Cleaning of DPFs is typically required every 6 to 12 months. The cleaning process involves manually removing the filter element from the vehicle and placing it in a cleaning station designed for this purpose. An engine emitting excessive PM or inadequate filter regeneration will cause a DPF to require more frequent cleaning. Diagnostics should be performed to identify the cause for more frequent cleaning intervals. A backpressure monitoring system should always be used with a DPF and periodic inspection of the monitoring system should be performed to confirm proper operation.

DPFs verified by typically effective at reducing emissions of PM by 85 to 90 percent or more. EPA’s Verified Technology List also shows that certain DPFs reduce emissions of hydrocarbons and CO by 70 to 90 percent. DPFs generally do not reduce oxides of nitrogen (NOx) emissions. DPFs can be combined with crankcase ventilation systems for additional emission reductions. There aware of concerns that catalysed DPFs may increase the nitrogen dioxide (NO2) fraction of total NOx emissions. Some DPFs generate NO2 as a means to help filter regeneration at lower temperatures. The NO2 produced by a DPF is dependent on the catalyst formulation.

Application Verified DPFs are available for nonroad and highway heavy-duty diesel engines including those on buses, trucks, construction equipment, auxiliary power units and stationary generators.

Each DPF is verified for use with specific engines and/or with specific configurations over a range of model years. In addition to vehicle and engine specifications, the intended application should be evaluated for exhaust temperature, duty cycle, fuel sulphur levels, lubrication oil consumption and engine-out PM emission levels. Exhaust temperature data logging should be performed with each installation over a range of vehicle duty cycles and, if possible, over a range of ambient temperatures

Fuel DPFs are verified for use with Ultra Low Sulphur Diesel fuel (ULSD), which contains up to 15 parts per million sulphur. Fuel additives should not be used unless explicitly approved by the DPF manufacturer. Active DPF systems are more expensive than passive DPF systems

Because a DPF is likely to be heavier than a muffler, it is likely that special mounting is necessary. Costs for cleaning stations or cleaning services should also be considered when purchasing DPFs. Longevity When properly installed and maintained, DPFs should remain effective for the life of the vehicle, generally five to ten years or 10,000 or more hours of operation.

Engine problems with fuel control or oil consumption may quickly deteriorate the performance of a DPF. Consequently, regular engine maintenance is essential to DPF performance.