Exhaust Gas Recirculation: Description and Operation

The Exhaust Gas Recirculation (EGR) System is used to reduce the levels of oxides of nitrogen (NOx) entering the atmosphere. The tremendous heat encountered during the combustion process enables nitrogen to combine with oxygen to form oxides of nitrogen. In order to reduce levels of NOx, combustion temperatures must be lowered. The EGR system lowers combustion temperatures by introducing small amounts of exhaust gases into the intake manifold, where they are reburned. This recirculation of exhaust can lower combustion temperatures as much as 500~F.
The EGR system consists of an EGR valve mounted on a special intake manifold. The exhaust gas intake port of the EGR valve is connected to the intake manifold exhaust crossover channels where it can pick up exhaust gases.