Effects of Dual Loop EGR and Variable Geometry Turbocharger on Performance and Emissions of a Diesel Engine

An experimental study is carried out to investigate the coupling between dual loop EGR (DL-EGR) and variable geometry turbocharger (VGT) on a heavy-duty commercial diesel engine under different operating conditions and inlet conditions. The effects of VGT rack position and high-pressure (HP) proportion in DL-EGR on engine performance and emissions are studied. The boosting system is a series 2-stage turbocharger with a VGT as the HP-stage. The HP-Proportion in DL-EGR is swept from 0% to 100% while several intake pressure values and EGR rates are fixed by adjusting the VGT position. Results demonstrate that the VGT and HP EGR both have great influence on the exhaust enthalpy and turbocharger efficiency. The exhaust enthalpy and the intake demand have great influence on the DL-EGR split strategy. For the ESC operating point C25with sufficient exhaust enthalpy, the high pressure loop EGR (HPL-EGR) performs better than VGT in decreasing the pumping losses (PL) and facilitates elevating the compressor efficiency. So the DL-EGR with the HP EGR valve fully opened combined with optimized VGT position can achieve superior fuel economy. For the A100 and B50 with insufficient exhaust enthalpy, pure HPL-EGR and pure low pressure loop EGR (LPL-EGR) both have potentials in achieving satisfactory fuel efficiency. But as to higher demand of intake pressure and EGR rate, the LPL-EGR and DL-EGR with low HP-Proportion can reach better boosting efficiency and fuel efficiency. The exhaust enthalpy distribution between VGT and HP EGR is critical in achieving an optimum trade-off in PL and gross indicated thermal efficiency (ITEg).