Abstract

Despite the development in NOx after-treatment for Diesel engines, EGR remains a cost-effective solution to fulfill current and future emissions regulations. With the widespread application of Diesel Particulate Filters, the traditional drawbacks of the Low Pressure EGR systems, i.e. compressor and charge air cooler reliability, have been reduced. In addition, the Low Pressure EGR routing has aroused technical interest since high EGR rates can be achieved while maintaining low intake temperatures.
 
There is a wide bibliography discussing the effects of EGR on combustion and emissions. However, little has been published about the effects of EGR on gas exchange processes and turbocharging, especially when Low Pressure EGR is applied. The effects of both EGR concepts on the gas exchange processes and the turbocharger operation are examined and discussed in this work. Regarding the impact of the EGR configuration on gas exchange processes three main factors are taken into account: the capability of both systems to introduce mass into the cylinder assessed by the air mass flow and the EGR rate, the efficiency of the gas exchange processes determined by the pumping work, and finally, the ability of both EGR circuits to distribute the EGR between cylinders homogeneously. Concerning the effects of the EGR configuration on turbocharging, this paper evaluates the effect of the different mass flow through the turbine and the compressor, the coupling between EGR and VGT, and some strategies to control the EGR and turbocharger are discussed. Since condensation is one of the most challenging problems of the Low Pressure EGR routing a specific study concerning this matter is performed. To conclude, the effects of the EGR architecture on engine emissions are discussed in a final section, where after studying the impact of intake temperature and charge dispersion on emissions, the overall effect of the EGR system on engine emissions is evaluated by means of a NEDC transient test.

To cope with the objectives of the study several modelling and experimental techniques have been combined. In this sense, some new models, measuring techniques and methodologies are proposed in the course of this work.