EGR Cooler.
EGR means “Exhaust Gas Recirculation”. The equipment returns part of the exhaust to the engine and decreases the maximum temperature of air-fuel burning mixture to lower the quantity of NOx.
When used with particulate matter (PM) reducing products, like highly efficient fuel injection or NOx reducing intercoolers, it shows more effects. EGR is placed between the exhaust and the intake of the engine and the purpose of the EGR is to return lowed temperature exhaust to the engine.