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Explain the EGR Valve

The first EGR valves were installed in engines in 1973, and these valves are still a staple in nearly all engines in 2010. The EGR valve is one of the many components used to control emissions. EGR is an acronym for "Exhaust Gas Recirculation."

Function

The main function of the EGR valve is to reduce the amount of nitrogen oxides (NOx) released into the air. The EGR valve prevents the release of NOx by recirculating cooled exhaust gases into the combustion chamber.

Effects

The EGRs cooling effect keeps the combustion chamber below 2800 degrees Fahrenheit. This temperature reduction limits the chemical reaction between nitrogen and oxygen, thus reducing NOx emissions.

Mechanics

Pre-electronic vehicles had vacuum-controlled EGR valves, while cars from 1996 and later use an electronic EGR. The mechanics of either valve are exactly the same. At idle, the EGR is fully closed and remains closed until warm-up. After warm-up, the EGR slowly opens as the engine speed increases, providing a cooling effect as the stress on the engine builds.