A Study of an EGR Control System for Diesel Engines Based on an Intake/Exhaust System Model

An exhaust gas recirculation (EGR) system that recirculates a portion of the exhaust gas back to the intake system is effective in reducing nitrogen oxide (NOx) emissions from diesel engines. However, improved control accuracy over the EGR flow rate is required, because an excessively large flow rate causes emissions of particulate matter (PM) to increase. In recent years, direct injection (DI) diesel engines have also been used on ordinary passenger cars, because their fuel economy is superior to that of indirect injection (IDI) diesel engines. Since DI engines are more sensitive to the EGR flow rate than their IDI counterparts, improving the accuracy of EGR flow rate control has become even more significant.

This study concerned an EGR control algorithm based on the results of calculations performed with an engine model capable of representing the dynamic states of the intake and exhaust systems. The aim of this research was to find a method for improving the control accuracy of the EGR flow rate under both steady-state and transient operating conditions. Based on analyses of actual engine data and through the use of a control system CAD program, an algorithm was found for estimating the intake and exhaust pressures accurately, which are important parameters for EGR flow rate control. As a result, useful knowledge was obtained for controlling the EGR flow rate more accurately.