EGR

The abbreviation for Exhaust Gas Recirculation. A system used in modern diesel engines which recirculates a portion of the exhaust gases back into the intake system, via an electronically controlled valve to precisely control the quantity. The gases are usually passed through a cooler first to increase their density. EGR reduces the available oxygen in the charge air, thus reducing the peak combustion temperature since the burn is not as efficient. The system substantially reduces the level of NOx emissions, but at the cost of increasing particulate emissions.