Abstract: One of the most vital factors in combustion control is air-to-fuel ratio (AFR) estimation and control. It results from inputs such as intake air mass, fuel injected quantity and EGR mass. In this work a detailed mathematical, nonlinear and control oriented model of dynamic processes of turbocharged diesel engines is presented. Intake model consists of compressor, intercooler, intake manifold, EGR circuit, valve section and cylinder subsystems. This model has been developed using physical equations and also experimental data. Common Rail Injection (CRI) that is a flexible fuel injection system in which quantity, timing and pressure of injection are controllable separately is chosen for this purpose. Fuel injection system is comprised of solenoid, working chamber and needle subsystems. AFR control is performed make use of fuzzy logic methodology. All above-mentioned models are programmed in Matlab/Simulink software. The simulation results are compared with available experimental data to check the accuracy of the model