What does the acronym DPF stand for in diesel engine exhaust systems?

In diesel engine exhaust systems, DPF stands for Diesel Particulate Filter.

A DPF is an emissions-control device that traps soot and other diesel particulate matter before the exhaust leaves the vehicle. Unlike a catalytic converter, which chemically changes gases as they flow through, a typical wall-flow DPF forces exhaust through porous ceramic channels. The particles collect on the channel walls while the gases pass onward.

The trapped soot cannot remain there indefinitely, so the filter periodically performs regeneration. During passive or active regeneration, exhaust temperatures rise high enough to oxidize much of the soot into gases. Ash from engine-oil additives does not burn away, however, and gradually accumulates; that is why a DPF may eventually need professional cleaning or replacement.

A common mix-up is treating DPF as another name for DEF, or diesel exhaust fluid. They are different: the DPF captures particulate matter, while DEF is used in a separate selective-catalytic-reduction system to reduce nitrogen oxides. DPFs became increasingly widespread as emissions rules tightened, and PSA Peugeot Citroën made particulate filters standard on passenger cars in 2000.