Transient EGR in a Long-Route and Short-Route EGR-System

The use of EGR to lower NO_X-emissions from Diesel engines is a well-documented method. Recently, more and more research is done on alternative EGR routing systems such as long-route EGR. To reach future emission legislation goals it is not sufficient to focus on steady-state driving. The emission peaks during the transient parts of driving cycles are gaining importance. It is therefore interesting to analyze the EGR-flow in transients for different configurations of the EGR system. In this work, a 1-D simulation is performed in GT-Power for a Euro 4 passenger car diesel engine equipped with cooled short-route EGR and a variable geometry turbine. For calibration of the simulation, load transients were measured including the measurement of transient EGR-rates using a fast CO₂-analyzer and cylinder pressure to obtain heat-release data. While the transient heat-release rates are used as an input for the combustion-simulation, the EGR response measurements are used as a reference for calibration of the EGR-system and its components. A long route EGR system and a short-route EGR system are then simulated and compared, focusing on transient response, availability of EGR during the transient and the fuel consumption in steady state. It is shown that the long-route system has advantages in both steady-state and transient driving conditions. In steady state it can decrease fuel consumption, in transient it can provide EGR without negative effect on the transient response.