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EXHAUST GAS AFTER TREATMENT
To meet the demands of Stage IIIB / Tier 4 Interim
Emission Legislation, the engine is equipped with an
exhaust aftertreatment module (EAM), consisting of an
exhaust gas recirculation system and a particulate filter.
The exhaust gas is fully automatically cleaned. The
process is monitored by the machine controller.
Step 1 Exhaust Gas Recirculation
With Exhaust Gas Recirculation (EGR), part of the
exhaust gases are cooled and then injected back into the
engine cylinders to reduce NOx.
Exhaust gas is cooled to allow the introduction of a greater
mass of recirculated gas.
The outcome is a lower peak combustion temperature.
Step 2 Diesel Particulate Filter + Diesel Oxidation
Catalyst
To remove excess particulate matter from the exhaust gas,
a Diesel Particulate Filter (DPF) is used. This system
consists of a Diesel Oxidation Catalyst (DOC) and a filter
module. The DOC reduces CO, HC and NO through
oxidation. It also produces NO2 to regenerate the DPF.
The filter system removes 99% of particulate matter.
Step 3 Active regeneration
Particulate matter left in the filter system is burned in a
process called regeneration. Extending the lifetime of a
filter, it converts particulate matter into CO2 and ash.
Atlas Copco engines use high temperature regeneration
that includes a fuel burner in the exhaust stream that
intermittently raises the temperature above 600º C / 1100°
F.
A separate High Pressure Fuel Pump (HPFP) supplies fuel
to the burner in the active regeneration system.
Active regeneration decreases in the higher load cycles of
the compressor.
Step 4 Ash removal
Additives in lube oil that do not combust during
regeneration, turn into ash. This reduces filter volume,
oxidation efficiency and backpressure. Ash must be
removed mechanically, according a service interval, either
by washing or blowing it out. This service interval can be
increased depending on duty cycle.
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