Open main menu Search Exhaust gas recirculation Language Edit This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed. Find sources: "Exhaust gas recirculation" – news · newspapers · books · scholar · JSTOR ( March 2009 ) ( Learn how and when to remove this template message ) EGR valve the top of box on top of the inlet manifold of a Saab H engine in a 1987 Saab 90 In internal combustion engines , exhaust gas recirculation ( EGR ) is a nitrogen oxide ( NO x ) emissions reduction technique used in petrol/gasoline and diesel engines . EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders . This dilutes the O 2 in the incoming air stream and provides gases inert to combustion to act as absorbents of combustion heat to reduce peak in-cylinder temperatures. NO x is produce