In North America, Europe, Japan, and soon Brazil, heavy highway diesel engine particulate matter emissions regulations force the use of diesel particulate filters (DPFs) to trap and oxidize carbon soot in the exhaust. Installation of DPFs allowed diesel builders to retune engines (more specifically, to adjust fuel injection events) to achieve cooler combustion which reduces the formation of harmful nitrous oxides (NOx) but at the expense of boosting output of unburned carbon soot. The increased unburned carbon soot particulate emissions are handled by the DPF.

The porous ceramic filter element substrates in DPFs can be cordierite, silicon carbide, or aluminum titanate. Active regeneration is used in heavy diesel highway vehicles, wherein a periodic rich injection (late injection in combustion chambers or direct injection of fuel into the exhaust stream) lights off and combusts the accumulated fine (micron-size class) carbon soot. Exhaust backpressure sensors signal when regeneration is required, and the process is completed automatically with no driver intervention. Active DPFs are at least 99% effective in trapping carbon soot particulates. DPFs are commonly installed behind the truck cab and are similar in size and shape to a conventional truck muffler.

Starting in 2007, the US Environmental Protection Agency (EPA) made DPFs mandatory for highway diesels, as there is no other cost effective means to achieve the low soot emissions limits. Suppliers typically offer warranties for these filters for 500,000 miles. The filter element has reached the end of its life when holes or cracks appear that allow unfiltered exhaust to flow downstream. During its lifetime, the DPF are typically removed and cleaned 2-3 times. The range of DPF service intervals, according to diesel engine builders, is between 80,000 miles (in severe service) and 250,000 miles (under ideal conditions). The typical long haul heavy duty diesel truck travels more than 80,000 miles per year so depending on the severity of the duty cycle, off-truck cleaning of the DPF could take place between once a year and once every three years. That service interval has been steady, with no appreciable extension of service life, in recent years. Commercial off-truck DPF servicing costs between $100 and $150, and takes 30 minutes to process plus 30 minutes for removal and reinstallation. DPF cleaning machines made by Donaldson and others use pulsed shop air (around 100 psi [pounds per square inch]) to blow out and vacuum out accumulated ash particles, which are primarily oxides of metals. For extremely clogged DPFs, Donaldson?s process begins with a pulsed-air blasting, followed by extended (6-hour) thermal regeneration in separate apparatus to extract remaining carbon soot or hydrocarbons, and then a final pulsed-air cleaning to extract residual ash. Competing machines use steady, not pulsed, air blasts. Large diesel truck fleet operators usually have their own DPF cleaning machines. Air flow readings before and after cleaning verify that the DPF is ready for reinstallation.

The primary source of ash constituents that can build up in DPFs are chemical additives in engine lube oil, such as organometallic detergents which are needed in the engine oil to neutralize acids and to keep the internal parts of the engine clean. Other sources of the metallic derivatives that form ash can originate from engine wear (iron, copper, lead, silicon, etc.), diesel fuel (sodium, potassium), coolant leaks (sodium, potassium) and air contaminants (silicon). Lubricant borne ash deposits are based primarily on calcium and magnesium. Modern engine oils, such as API CJ-4, have been developed with limited ash content which helps extend the intervals between DPF cleaning. These lubricants not only meet stringent ash limits to allow the successful use of DPFs, but they also pass rigorous engine tests to ensure the lubricant will protect all aspects of engine performance even better than previous generations of oil. That makes these new oils mandatory for use in newer, DPF equipped, vehicles, but also recommended for older engines.