Suppressing knocking by using CleanEGR–better fuel economy and lower raw emissions simultaneously

The use of external Exhaust Gas Recirculation (EGR) is a common technology available for the reduction of nitrogen oxides (NOx) emitted by internal combustion engines. With regard to gasoline engines, the addition of EGR at higher loads reduces knock tendency and improves fuel economy by reducing the necessity for fuel enrichment. To further maximize these benefits, the recirculated exhaust gases are cooled down that improves engine efficiency by enabling an advanced center of combustion (MFB50). Hereby gasoline engines can be operated at EGR rates up to 20%, which is enabling stoichiometric operation in the entire engine map. On the other hand, cooled EGR is leading to well-known low-temperature issues such as fouling, corrosion and condensation. In response to that challenge, in this work the use of cooled LP- and HP-EGR is analyzed by engine testing for different engine intake temperatures. For dedicated tests a higher compression ratio for improved fuel economy and a coated Gasoline Particulate Filter (CleanEGR^TM) for cleaning the EGR gas is investigated as well. As a conclusion, external cooled and cleaned EGR is measure to meet future RDE requirements (stoichiometric operation in entire map) by achieving improvements in engine efficiency and engine out emissions (PN, NOx) simultaneously.