Abstract
Exhaust gas recirculation (EGR) is an emission control technology for significant NOx emission reductions from light-and heavy-duty diesel engines. The key effects of EGR are lowering the flame temperature and the oxygen concentration of the working fluid in the combustion chamber. A high pressure loop (HPL) EGR is only applicable when the turbine upstream pressure is sufficiently higher than the boost pressure. In case the pressure difference cannot be met with the original matching between the turbocharger and the engine, remedies must be made by either increasing the turbine upstream pressure or reducing the boost pressure. However, HPL EGR have fast responses, especially at low speed range. In the contrary, a low pressure loop(LPL) EGR is relatively easy to achieve because a positive differential pressure between the turbine outlet and compressor inlet is generally available. However, LPL EGR have slow responses, especially at low and middle speed range. In this study, as one of the future EGR types, the dual loop EGR system which has combined features of high pressure loop EGR and low pressure loop EGR was developed and optimized at the selected operating conditions by using a commercial engine simulation program(GT-POWER) and DoE. Rack position of Variable Geometry Turbine (VGT), VGT performance (especially RPM), flap valve at the exhaust tailpipe, and EGR valve are selected as main variables to control dual loop EGR system. Then, HPL and LPL EGR portions were investigated at the given operating conditions. Finally, significant improvements in engine-out emission and performance were obtained by adjusting several major variables.
Keywords: Exhaust gas recirculation, Dual-loop EGR, Light-duty diesel engine, Design of experiments, 1D simulation