Exhaust Gas Recirculation: Description and Operation

Fig. 171 Exhaust Gas Recirculation System:

Fig. 174 EGR System Operations Chart:

SYSTEM DESCRIPTION

This system is used to dilute the incoming air/fuel mixture with recirculated exhaust gases. Dilution of the incoming mixture lowers the peak flame temperature and thus limits the formation of nitrous oxides (NOx).

EGR VALVE

This is a vacuum operated valve which opens and closes a passage from the exhaust manifold to the intake manifold. This allows flame temperature in the combustion chamber to be lowered by diluting the incoming mixture with exhaust gases. The EGR valve is controlled by the vacuum modulator.

VACUUM MODULATOR

This valve controls the amount of exhaust gases that are allowed into the intake manifold by sensing load conditions.

BI-METAL VACUUM SWITCHING VALVE

The bi-metal vacuum switching valve (BVSV) is a temperature sensative valve that controls the vacuum that is used to operate the EGR valve. It opens when the engine is warm (151° F) and closes when the coolant temperature is below 113° F.