EXHAUST GAS RECIRCULATION (EGR) SYSTEM

When the temperature of the combustion flame exceeds approximately 2,500F, the nitrogen that is present in the intake air begins to combine with oxygen to produce oxides of nitrogen (NO_x ). The exhaust gas recirculation (EGR) system (fig. 4-53) helps to control the formation of oxides of nitrogen by recirculating a portion of the exhaust gases back through the intake manifold, resulting in cooler combustion chamber temperatures.

Figure 4-53. - EGR system.