New fuel economy standards intensify the power train development
for more fuel efficient vehicles worldwide. Different approaches
are utilized to improve the fuel efficiency of gasoline engines. Of
all concepts, including downsizing plus turbocharging, stratified
operation of spray-guided gasoline direct injection (GDI) engines
show the greatest fuel savings benefit. A significant challenge for
stratified GDI aftertreatment systems is to develop both catalysts
and systems that can reduce the high amount and cost of precious
metals currently needed to meet performance standards under low
exhaust temperature operating conditions. Furthermore, tighter
emission standards will exceedingly require high conversion rates
for HC, CO and NOx. In this paper the most recently developed
catalyst and systems for lean GDI aftertreatment will be compared
with serial production EURO 5 systems against future legislated
targets. One development focus is on improvement of three-way
catalysts specifically for lean GDI applications needing advanced
light-off behavior with regard to different gas atmospheres (lean,
rich and λ==1).
An overview on the recent development improvements of NOx
storage catalyst systems is given with regard to cost, performance
and durability. New NOx storage catalyst systems show improved
performance in the low temperature region which allows for
enlarging the usable engine-map range of stratified gasoline
injection to the lower speed/load points without additional heating
measures used by calibrators to rapidly heat the exhaust catalysts.
By further optimization of the aftertreatment system with regard to
system integration (catalyst volume, precious metal distribution) a
considerable reduction in precious metal is realized with improved
over-all performance when compared to the current series
applications. An outlook is given for the requirements of the
aftertreatment for lean GDI in the US.