EGR Theory of Operation

The purpose of the EGR system is to precisely regulate EGR flow under different operating conditions, and to override flow under conditions which would compromise good engine performance. The precise amount of exhaust gas which must be metered into the intake manifold varies significantly as engine load changes. This results in the EGR system operating on a very fine line between good NOx control and good engine performance.

If too much exhaust gas is metered, engine performance will suffer. If too little EGR flows, the engine may knock and will not meet strict emissions standards. The theoretical volume of recirculated exhaust gas is referred to as EGR ratio. As the accompanying graph shows, the EGR ratio increases as engine load increases.

Relationship Between EGR Ratio and Load si

The theoretical volume of "S EGR gas is referred to as CC EGR ratio. As shown on the CC graph, EGR ratio increases [2 as engine load increases.

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Light -Load -► Heavy

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