SPRING 5481589 - Caterpillar

Engine Operation and the Aftertreatment System
The exhaust gases and hydrocarbon particles from the engine first pass through Diesel Oxidation Catalyst (DOC). Some of the gasses and matter are oxidized as they pass through the DOC. The gasses then pass through the Diesel Particulate Filter (DPF). The DPF collects the soot and any ash that is produced by the combustion in the engine. During regeneration, the soot is converted into a gas and the ash remains in the DPF. The gasses finally pass through the Selective Catalytic Reduction (SCR). Before the gasses pass through the SCR, Diesel Exhaust Fluid (DEF) is injected into the gas stream. The DEF is stored and controlled by the Pump Electronic Tank Unit (PETU). The mixtures of DEF and the exhaust gas pass through the SCR reducing the NOx in the exhaust emissions.The DPF may require the exhaust gas temperature to rise in order to remove the soot. If necessary, the back pressure valve operates in order to create the rise in temperature. In some applications, the operation of the back pressure valve will make the engine tone different.The engine software will control the amount of DEF that will be required in order to keep the exhaust emission compliant.This design of DPF will not require a service maintenance interval. The DPF can be expected to function properly for the useful life of the engine (emissions durability period), as defined by regulation, subject to prescribed maintenance requirements being followed.