Exhaust gas recirculation is the process of feeding exhaust gas back into the combustion chamber in a carefully regulated way. The recirculation is an effective method of reducing the nitrogen oxide levels at the combustion stage.
When the fuel/air mixture burns, the formation of nitrogen oxides increases at a disproportionately high rate as the temperature rises. Recirculating a portion of the exhaust gas back to the chamber lowers the combustion temperature inside the cylinder, reducing the rate of NOx formation. The exhaust gas is directed through a system of pipes back into the intake tract by means of a valve controlled electronically by the engine management unit. From the intake tract, the exhaust gas is drawn back into the combustion chamber.