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4.3.2 DPF System
4.3.2.1 Diesel particulate filter (DPF) – Operating principle
Closed diesel particulate filter
The diesel particulate filter (DPF) is a wall-flow filter which cleanses particles of soot and ash from the ex-
haust gas created in the engine in the course of combustion. This involves routing the exhaust gas through a
finely-pored ceramic structure (substrate) inside the filter. The particles are separated from the gas flow and
accumulate on the duct walls as the cleansed exhaust gas flows through. This allows exceedingly high parti-
cle reduction rates of over 90 percent to be achieved.
Depending on the load and operating profile, soot and ash particles may accumulate in the DPF thereby in-
creasing the exhaust pressure. Such accumulations of particulate matter must be removed to avoid exces-
sively high exhaust pressures.
MTU deploys a passive and continuously regenerating diesel particulate filter which utilizes the so-called CRT
effect (Continuous Regeneration Trap). With this method, the prevailing exhaust temperatures experienced in
normal engine operation suffice to continuously reduce soot deposited in the DPF.
Thermal management to support the regeneration process is generally only necessary in unusual climatic
conditions or when operating continuously in the low-load range. The MTU engine management system in the
ECU (Engine Control Unit) calculates DPF load and, if necessary, temporarily increases the exhaust tempera-
ture, and hence soot burn-off, significantly by means in-engine thermal management.
Particles of ash in the filter cannot be eliminated by way of in-engine measures. The DPF has to be removed
and cleaned at regular intervals to do this (see maintenance table). Maintenance intervals have been pro-
longed by deploying generously dimensioned filters and further optimizing engine oil consumption to a signif-
icant degree.
72 | DPF System | MS15065/01E 2019-01
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