Exhaust Gas Recirculation: Description and Operation

EXHAUST GAS RECIRCULATION (EGR)

A proportion of the exhaust gases is recirculated to the intake manifold to reduce emissions of nitrogen oxides (NOx), which are produced by combustion at high temperature and at high engine loads.

Recirculation of a proportion of the exhaust gases at high loads lowers the combustion temperature and, as a result, reduces the NOx level.

The system is not operative when the engine is cold or idling, to avoid interference with idle running.

The recirculation flow is regulated by the vacuum-actuated EGR valve which, in turn, is controlled by the EGR controller. The ICM supplies the controller with a signal based on a combination of engine speed, load and temperature. The ICM, ambient air pressure and intake manifold pressure signals are converted to a vacuum control signal, which operates the EGR valve through a vacuum hose.

The EGR system is equipped with an NTC (Negative Temperature Coefficient) temperature sensor.