In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in most modern petrol and diesel engines.
EGR works by recirculating a portion of an engine’s exhaust gas back to the engine cylinders. In a petrol engine, this inert exhaust displaces the amount of combustible matter in the cylinder. This means the heat of combustion is less, and the combustion generates the same pressure against the piston at a lower temperature. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture.
Autodata have produced a Tech Talk document called ‘Combustion and EGR’ in 3 parts as detailed below. You will need Adobe Reader to view these :-