DPF Cleaning – Diesel Particle Filter Cleaning
All Diesel Particulate Filters (DPF) need to be cleaned with regular intervals as a small amount of inert debris (mainly ash and other debris from lubricating oil, engine wear metals and air-induced dust) will remain in the filter substrate. Soot and other organic compounds are removed during operation by oxidation. To ensure that the optimum level of performance is maintained, the filter must be cleaned regularly. The cleaning intervals vary depending on the condition of the vehicle and the duty cycle. Despite service intervals, always clean your filter when a backpressure alarm appears on the panel. Higher temperatures may cause the filter can to split. Comments to clean the filter completely of ash and soot, it is necessary to heat up the filter in a kiln. If the filter is not heated, some soot and ash may remain in the filter causing shorter cleaning intervals. The heating must be carried out gradually and well-controlled to avoid an uncontrolled regeneration causing the filter substrate to exothermic (burn through of filter channels) or the filter canning to split.
If the cleaning intervals of the filter are very short, check the opacity of the engine and if necessary clean injection nozzles etc.
Filters require more maintenance than catalytic converters. Ash, a byproduct of oil consumption from normal engine operation, builds up in the filter as it cannot be converted into a gas and pass through the walls of the filter. This increases the pressure before the filter. Warnings are given to the driver before filter restriction causes an issue with drive-ability or damage to the engine or filter develop. Regular filter maintenance is a necessity
Regeneration is the process of removing the accumulated soot from the filter. This is done either passively (from the engine’s exhaust heat in normal operation or by adding a catalyst to the filter) or actively introducing very high heat into the exhaust system.
On-board active filter management can use a variety of strategies:
1. Engine management to increase exhaust temperature through late fuel injection or injection during the exhaust stroke
2. Use of a fuel borne catalyst to reduce soot burn-out temperature
3. A catalytic oxidizer to increase the exhaust temperature, with after injection (HC-Doser)
All on-board active systems use extra fuel, whether through burning to heat the DPF, or providing extra power to the DPF’s electrical system, although the use of a fuel borne catalyst reduces the energy required very significantly. Typically a computer monitors one or more sensors that measure back pressure and/or temperature, and based on pre-programmed set points the computer makes decisions on when to activate the regeneration cycle. The additional fuel can be supplied by a metering pump. Running the cycle too often while keeping the back pressure in the exhaust system low will result in high fuel consumption. Not running the regeneration cycle soon enough increases the risk of engine damage and/or uncontrolled regeneration (thermal runaway) and possible DPF failure.
Diesel particulate matter burns when temperatures above 600 degrees Celsius are attained. This temperature can be reduced to somewhere in the range of 350 to 450 degrees Celsius by use of a fuel borne catalyst. The actual temperature of soot burn-out will depend on the chemistry employed. The start of combustion causes a further increase in temperature. In some cases, in the absence of a fuel borne catalyst, the combustion of the particulate matter can raise temperatures above the structural integrity threshold of the filter material, which can cause catastrophic failure of the substrate. Various strategies have been developed to limit this possibility. Note that unlike a spark-ignited engine, which typically has less than 0.5% oxygen in the exhaust gas stream before the emission control device(s), diesel engines have a very high ratio of oxygen available. While the amount of available oxygen makes fast regeneration of a filter possible, it also contributes to runaway regeneration problems.
Some applications use off-board regeneration. Off-board regeneration requires operator intervention. Off-board regeneration is not suitable for on-road vehicles, except in situations where the vehicles are parked in a central depot when not in use. Coal mines (with the attendant explosion risk from coal damp) use off-board regeneration if non-disposable filters are installed, with the regeneration stations sited in an area where non-permissible machinery is allowed.
Many forklifts may use disposable filters – machinery that spend their operational lives in one location, which makes having a disposable system practical. EHC HT filter cannot be cleaned, it shall be replaced with a new replacement filter.