Effects of egr transient operation on emissions and performance of automotive engines during rde cycles

Resumen

The automotive emission regulations are getting more stringent these days. New methods of homologation are being considered other than standard cycles considering the real driving behavior on road. The EGR system is one of the proven and well tested strategies in steady state which can be used on those dynamic real driving conditions too. This dissertation focuses on implementation of different EGR systems during dynamic operations of turbocharged diesel engine. Firstly, a driving cycle analysis is carried out to identify the specific and frequent transient operations on dynamic cycles like WLTC and RDE. The results show that, the frequency of harsh load transients is higher than speed transients. Among them, the number of Tip-Out operations outnumber the Tip-Ins with higher density in 1250-2000 RPM range. Therefore, these harsh transients are repeated separately on the dynamic engine test bench equipped with high frequency gas analyzers to track the instantaneous CO2 and NOx concentration. A parametric study is carried out with EGR valve actuation during various severe load transients, quantifying the transportation delays, NOx concentration and particulate matter. The LPEGR is found to be more effective at the full load as well as during transient operations compared to HPEGR. The best suited LPEGR valve control is proposed, which can be helpful for transient calibration of a turbocharged diesel engine. Moreover, the trade-off between the performance and emission during EGR transients is also pointed out. The implementation of EGR all over the engine map minimizes the unexpected NOx peaks during transients. Specifically, LPEGR strategies manages to reduce around 20-60% of NOx in first few seconds with less than 5% of penalty in performance. Additionally, 1D model simulation results of load transient operations are presented in the document. The VGT control plays important role to calibrate the model for transient operations with EGR. Apart from this, the EGR split optimization on various steady points is carried out by simulations following the trade-off between performance and emissions. Furthermore, an algorithm to search the optimum split is proposed, reducing around 80% of the calculation time consumed by DOE or genetic algorithm method. Finally, a simple 3D quasi steady NOx model is created to predict the transient emissions in real driving conditions. EGR rate, as 3rd input in model shows significant improvement in prediction of transient NOx over the 2D model.