![]() ![]() By 1973, an EGR valve controlled by manifold vacuum opened or closed to admit exhaust to the intake tract only under certain conditions. Difficult starting, rough idling, reduced performance and lost fuel economy inevitably resulted. The first EGR systems were crude some were as simple as an orifice jet between the exhaust and intake tracts which admitted exhaust to the intake tract whenever the engine was running. For example methanol is more tolerant to EGR than gasoline. Chemical properties of different fuels limit how much EGR may be used. Gases re-introduced from EGR systems will also contain near equilibrium concentrations of NO x and CO the small fraction initially within the combustion chamber inhibits the total net production of these and other pollutants when sampled on a time average. Because NO x forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NO x that the combustion process generates. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture. In a gasoline engine, this inert exhaust displaces some amount of combustible charge in the cylinder, effectively reducing the quantity of charge available for combustion without affecting the air-fuel ratio. Mazda's turbocharged SkyActiv gasoline direct injection engine uses recirculated and cooled exhaust gases to reduce combustion chamber temperatures, thereby permitting the engine to run at higher boost levels before the air-fuel mixture must be enriched to prevent engine knocking. In a spark-ignition engine, an ancillary benefit of recirculating exhaust gases via an external EGR valve is an increase in efficiency, as charge dilution allows a larger throttle position and reduces associated pumping losses. In the combustion cylinder, NO x is produced by high-temperature mixtures of atmospheric nitrogen and oxygen, and this usually occurs at cylinder peak pressure. The actual amount of recirculated exhaust gas varies with the engine operating parameters. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The exhaust gas displaces atmospheric air and reduces O 2 in the combustion chamber. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. ![]() In internal combustion engines, exhaust gas recirculation ( EGR) is a nitrogen oxide ( NO x) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. ( Learn how and when to remove this template message)ĮGR valve the top of box on top of the inlet manifold of a Saab H engine in a 1987 Saab 90 JSTOR ( March 2009) ( Learn how and when to remove this template message). ![]() Unsourced material may be challenged and removed.įind sources: "Exhaust gas recirculation" – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification. ![]()
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