Abstract
This paper describes an attempt made to test the parameters of fuel injection systems of turbocharged and naturally aspirated diesel engines, equipped with electronically controlled common rail type fuel injection system, to find the characteristics of it. As a result, it became clear that exhaust emissions could be reduced by optimizing the fuel injection timing and pressure, and that pilot injection was effective for reduction of not only noise emission but also exhaust emissions. It was confirmed that NOx-PM trade-off could be improved by combining the EGR and high pressure fuel injection.