What Is Exhaust Gas Recirculation?


The future of exhaust gas recirculation is under close scrutiny by many, including the automotive industry. While this is an important topic that can affect us globally, most consumers don't know what exhaust gas recirculation even means. A closer look at how this system works will provide insight as to why so much emphasis is being placed on recirculating exhaust gas.


  • The world was first acquainted with an exhaust gas recirculation system (EGR) in the early 1970s. The existing smog controls at that time were not effectively cleaning exhaust emissions. The major problem was oxides of nitrogen (NOx) forming in heated combustion chambers whenever the heat exceeded 2,500 degrees Fahrenheit. When NOx combines with other elements, including sunlight, the result is the disgusting haze that we refer to as smog. Smog created a need for more effective methods of reducing toxic fumes from the air.


  • Researchers found that they needed a way to eliminate the reoccurrence of NOx formation. Learning to do this successfully would be the key to decreasing heavy smog levels. Various ways to do this were considered, but the disadvantages outweighed the advantages. The exhaust gas recirculation system was used because it enabled researchers to reduce the NOx levels, thereby cutting down on the most important variable to creating smog.


  • According to one research study by Caterpillar, Inc., a leading manufacturer of engines, the strategy of the EGR system involves reducing the emissions by creating a new environment in the engine. This is accomplished by recirculating exhaust that has already been combusted into an intake stream. Since the gases have already been combusted, they cannot burn again. The slowing and cooling process the exhaust goes through results in a reduction of NOx formation.


  • While reducing harmful emissions is a lofty and important goal, the U.S. Department of Energy also has another objective in mind. This department is responsible for a General Motors study that was launched in September 2007. In addition to minimizing emissions, the research that is scheduled to culminate in October 2010 focuses on optimizing fuel economy. Both objectives are important to the nation's future health and welfare.


  • The EGR technique is one that warrants further study and attention, especially since this system is the one most used in petroleum gasoline and diesel engines today. Extensive testing involves monitoring and documenting research findings. To do this accurately may require changes in research timelines and adjustments to any predicted research project dates.

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  • Photo Credit Image by Flickr.com, courtesy of Kevin Dooley
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