Exhaust Gas Recirculation: Description and Operation

Fig. 5 Exhaust gas recirculation system:

The EGR system, Fig. 5, helps lower the peak burning temperatures and pressures within the combustion chambers, limiting the formation of oxides of Nitrogen (NOx). This is accomplished by drawing a portion of the exhaust gasses into the intake manifold under certain engine operating conditions. These gasses mix with and dilute the incoming air-fuel mixture charge which results in lower combustion chamber temperatures and pressures.

Fig. 6 Exhaust gas recirculation system related components:

OPERATION

Exhaust gasses are picked up from the exhaust manifold. An EGR valve, Fig. 6, is placed in the circuit between the exhaust and intake manifolds to control the flow of exhaust gas. The valve is actuated by a ported vacuum signal. The vacuum signal is taken from a port above the throttle plate in the carburetor. The vacuum signal line is interrupted by a temperature vacuum valve which senses engine coolant temperature. With the engine cold, the temperature vacuum valve is closed. This blocks the vacuum signal to the EGR valve. The EGR valve remains closed preventing recirculation of exhaust gasses. With the engine warm, the temperature vacuum valve is opened. This applies a vacuum signal to the EGR valve. This signal will cause the EGR valve to open, allowing recirculation of the exhaust gasses.