One of the most vital factors in combustion control is air-to-fuel ratio (AFR) control and estimation. It results from various inputs such as intake air mass flow arte, fuel injected quantity and EGR rate. In this work a detailed mathematical, nonlinear and control oriented model of dynamic processes of turbocharged diesel engines is presented for this purpose. This is an attempt to describe the two main subsystems of compression ignition (CI) engines called intake manifold and fuel injection.
Intake model itself consists of compressor, intercooler, intake manifold, EGR circuit, valve section and cylinder subsystems. This model has been developed for studying the air intake system in a turbocharged diesel engine, using physical equations. Experimental data has also been used to adjust the model. The output variable of this model (air mass flow) is a significant parameter in calculations of power performance, emission and AFR control. Of the methods of assisted aspiration, the exhaust gas driven turbocharger is by far the most widely used. Varying the rate of gas flow through the turbine by means of Variable Geometry Turbine (VGT) is a method by which the exhaust gas flow through turbine can be limited at high engine speeds. So turbo compound in this model is equipped with VGT.
Common Rail Injection (CRI) that is a fully flexible fuel injection system in which quantity, timing and pressure of injection are controllable (based on electronic control) separately is chosen for this purpose. Fuel injection system is comprised of solenoid, working chamber and needle subsystems. A one dimensional, transient and compressible flow model of CRI is derived.
AFR control of diesel engine is performed make use of fuzzy logic methodology. This method improves the control and simplifies the development process. The fuzzy logic controller achieves this by considerably reduced complexity and lack of tedious mathematical derivation associated with modern control theory methods.
All above-mentioned models are programmed in Matlab/Simulink software environment. The simulation results are compared with available data to check the accuracy of the model.