METHOD AND APPARATUS FOR MONITORING RECIRCULATED EXHAUST GAS IN AN INTERNAL COMBUSTION ENGINE

A method for controlling EGR gas flow in an internal combustion engine during ongoing operation includes determining an engine operating point and a preferred EGR fraction for a cylinder charge based upon the engine operating point. A feed-forward command for controlling an external EGR gas flowrate to an engine intake manifold based upon the preferred EGR fraction for the cylinder charge is determined. An EGR ratio in the intake manifold is determined. And, the external EGR gas flowrate is controlled based upon the estimated EGR ratio in the intake manifold and the feed-forward command for controlling the external EGR gas flowrate.