Influence of high and low pressure EGR and VGT control on in-cylinder pressure diagrams and rate of heat release in an automotive turbocharged diesel engine

An experimental study was developed to compare high and low pressure exhaust gas recirculation systems (HP and LP EGR) fitted on an automotive turbocharged diesel engine, analysing the effects of their control on fuel consumption, pollutant emissions and combustion process. An extensive range of operating modes was considered at different engine part-load conditions, starting from the reference one without EGR, then considering the simple activation of the HP or LP EGR circuit, followed by the simultaneous application of high and low pressure recirculation and the addition of variable geometry turbine (VGT) control. The paper focused on different goals: firstly, to highlight the change of selected operating parameters (intake pressure and mass flow rate, EGR fraction) in the different configurations affecting the development of in-cylinder pressure curves, ignition delay and combustion process. Secondly, to analyse how rate of heat release is affected by the different EGR and VGT control strategies. Finally, to justify the observed trends of fuel consumption, NOx and soot emissions according to the pressure diagrams and heat release curves, as LP EGR and a different VGT position allowed reductions of 2.1, 50 and 22.8% of these parameters referring to the standard operating mode in the presented experimental point.