A method of reducing exhaust emissions by recirculating some of an engine's exhaust gas into its intake manifold. The inert exhaust gas absorbs heat during the combustion process and reduces the peak temperature reached during combustion, reducing emissions.

System to reduce automotive emission of nitrogen oxides (NOx). It routes exhaust gases into the carburetor or intake manifold where they dilute the air/fuel mixture and reduce peak combustion temperatures, thereby reducing the tendency for NOx to form.

Some engines are equipped with a device or system that recirculates a small amount of exhaust gas back through the combustion cycle under certain operating conditions. EGR systems cool the temperature of combustion, and result in reduced formation of NOx emissions. For more info on trouble-shooting EGR systems, see Exhaust Gas Recirculation System Testing.