Exhaust gas recirculation (EGR) is an effective strategy to control NOx emissions from diesel engines. The EGR reduces NOx through the reduction of oxygen concentration in the combustion chamber as well as through the absorption of heat. Several configurations have been proposed, including high and low pressure loop EGR as well as hybrid systems. EGR is also used in gasoline engines, primarily in order to reduce pumping work and increase engine efficiency.
Exhaust Gas Recirculation (EGR) is an emission control technology that enables significant reductions in NOx emissions from most diesel engines: from light to medium to heavy engine applications Twin-engine marine two-stroke engines. While the application of EGR for NOx reduction is the most common reason to apply EGR to modern commercial diesel engines, its potential extension of the application also to other purposes. Some of these include: imparting shock resistance and reducing the need for high-load fuel enrichment in SI engines, assisting the vaporization of liquid fuels in SI engines [McAdams 1933], as a closed-loop diesel engine activator [Thwaites 1956] or to improve the ignition quality of fuels difficult to ignite in diesel engines [Mühlberg 1964]. While NOx reductions had been reported with EGR in 1940 [Berger 1940], early experiments with engines to investigate the NOx reduction potential of EGR appeared to be carried out in the late 1950s on SI engines [Kopa 1960 ]. In the 1970s, EGR was being seriously considered as a measure of NOx control for diesel engines [Teshirogi 1974] [Kern 1977].
From 1972/73 to the late 1980s, EGR was commonly used for NOx control in gasoline fueled gasoline engines and light truck engines in North America. After the early 1990s, some gasoline-powered applications were able to do without EGR. After the early application of gasoline, EGR was also introduced to diesel passenger cars and light trucks and then heavy duty diesel engines. Although there were heavy diesel applications dating back to the 1970s, it was not until the early 2000s that cooled EGR became very common in heavy duty diesel engines in North America [Hawley 1999]. It was this heavy duty application that attracted the most attention to EGR because of the more difficult technical challenges compared to earlier light applications. After 2010, the EGR application was extended to light gasoline engines, not for NOx control, but for fuel economy purposes. Using EGR in reduced direct injection gasoline engines can reduce pumping losses, improve combustion efficiency, improve shock tolerance, and reduce the need for fuel enrichment. A potential non-reducing application of NOx EGR for modern diesel engines is combined with other engine control measures to increase exhaust gas temperature and facilitate the regeneration of diesel particulate filters.