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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.

A low-temperature, premixed combustion concept, called Modulated Kinetics (MK) combustion, has been developed that reduces emissions of nitrogen oxide (NOx) and smoke simultaneously. This new combustion concept requires heavy exhaust gas recirculation (EGR) to reduce the NOx emission and combustion noise. However, there is an interaction between the effects of controlling exhaust gas recirculation (EGR) and the variable geometry turbocharger (VGT). This makes controlling both the EGR rate and air mass flow rate more difficult under transient operating conditions. Therefore, the authors investigated a cooperative control of EGR and VGT in an effort to control the accuracy of both the EGR rate and the air mass flow rate. This paper presents an approach through the application of a control system CAD program and rapid prototyping tools to improve transient operating states by referring to a model-based EGR and VGT control algorithm.