Estimation method to determine the concentration of recirculated exhaust gas present in a cylinder of an internal combustion engine

An estimation method to determine the concentration of recirculated exhaust gas present in a cylinder (2) of an internal combustion engine (1). The concentrations (%EGR) of recirculated exhaust gas ina gas mixture flowing through an intake duct (6) are periodically stored in a buffer (30). The method includes determining a first moment (T1), and programming following combustion in the cylinder (2) at the first moment (T1); determining advance time (Tpred) which elapses between the first moment (T1) and a second moment (T2) in the future, in which air will be taken into the cylinder (2) for the following combustion in the cylinder (2) at the second moment (T2); determining transport time (TTR); determining a third moment (T3) in the past by subtracting a difference between the transport time (TTR) and the advance time (Tpred) from the first moment (T1); estimating the concentration (%EGR) of recirculated exhaust gas present in the cylinder (2) at the second moment (T2) by utilizing theconcentration (%EGR) of r