Study of Internal EGR Control Using Variable Valve Timing

In marine diesel engines, NOx in exhaust gas emissions is regulated by the IMO (International Maritime Organization) . EGR (exhaust gas recirculation) is widely used for NOx reduction, but EGR aggravates fuel consumption. Research on intake and exhaust valve timing is necessary to make active use of internal EGR without increasing BSFC. In this study, internal EGR was effected by a variable valve timing mechanism using the hydraulic actuator. The NOx reduction consequences were investigated by two methods: an overlap change and late closure of the exhaust valve. The results demonstrated that the negative overlap and late closure of the exhaust valve, using the effect of the other cylinder, have a NOx reduction effect. Because the trade-off between NOx emission and BSFC is maintained with the same exhaust valve opening timing (EO), compatibility between NOx reduction and constant BSFC can be achieved by internal EGR and the delay in EO.