EGR valve: Key to smog-free Saturn ride

Anthony Fontanelle
August 9, 2007

The exhaust system of the Saturn engine is typically optimized for emission reduction. From the manifold of the Saturn exhaust system, a valve-controlled network of pipes called exhaust gas recirculation (EGR) system connects to the inlet manifold and recirculates portions of the fumes that are going to be emitted. These gas are rerouted to the combustion chamber where the air and fuel mixture of the burn materials are held up and burned. Using the heat of the recirculated gas, the Saturn EGR valve enables the air and fuel mixture to burn easily. The process helps the engine burn the fuel and facilitates engine operation. With less work on the engine during combustion, the Saturn EGR valve lowers the amount of noxious gas produced in the burning of the fuel.

In normal Saturn engine combustion, the nitrogen and oxygen molecules in the air combine with the hydrocarbons in the fuel to form water and carbon dioxide, while leaving its nitrogen component unchanged. When they are released into the atmosphere via the Saturn tailpipe, the nitrogen reacts with the other two combustion byproducts and forms nitrogen oxide. The compound then picks up another oxygen and becomes nitrogen dioxide. In the presence of sunlight, it combines with other compounds like hydrocarbons and forms the noxious smog. By recirculating these exhaust materials into the intake manifold of the Saturn, the burn mixtures produce less materials that can turn into smog.

A Saturn EGR valve uses either the vacuum from the induction system or a signal from the computer to open the pipe network on the manifold and allow exhaust gas to reenter the burn fuel chamber. The valve is operationally opened by the vacuum to its control diaphragm. Some also require a certain amount of exhaust backpressure before they open. On newer Saturn makes, the EGR valve is electronically operated and uses one or more solenoids or a small stepper motor. The Saturn EGR valve remains open when the engine is warm and maintaining a constant speed. During exhaust emission, the valve closes the pipes to allow a metered amount of exhaust to flow back into the engine. The recirculated gas, which is hotter than the intake air, optimizes the fuel materials to lessen the combustion work of the engine, reducing underhood temperatures and curbing the formation of nitrogen oxides.

Source:  Amazines.com