Exhaust Gas Recirculation: Description and Operation

Fig. 46 EGR System:

Fig. 48 EGR Operations Chart:

The exhaust gas recirculation (EGR) system is used to dilute the incoming air/fuel mixture with recirculated exhaust gasses. Dilution of the incoming mixture lowers the peak flame temperatures and thus limits the formation of nitrous oxides (NOx). The EGR system is temperature activated by means of a bi-metal vacuum switching valve. An EGR vacuum modulator is used to control vacuum flow in relation to exhaust gas pressure. At periods of high exhaust pressure, a full flow of vacuum is supplied to the EGR valve. At periods of low exhaust pressure, air is bled into the vacuum circuit through the modulator, causing the EGR valve to close.