Philipp, S., Hoyer, R., Adam, F., Eckhoff, S. et al., "Exhaust Gas Aftertreatment for Lean Gasoline Direct Injection Engines - Potential for Future Applications," SAE Technical Paper 2013-01-1299, 2013, doi:10.4271/2013-01-1299.
Future emission standards will require further reduction of harmful gaseous emissions such as HC, CO and NOx as well as consideration for greenhouse gas emissions such as CO₂. Gasoline engines with lean combustion spray-guided direct fuel injection in conjunction with turbocharging have a very high potential for fuel savings. The main challenge for stratified lean GDI aftertreatment systems is the development of a catalyst system to fulfill the emission legislation requirements under low exhaust temperature operating conditions with efficient use of precious metals. In addition to the very stringent emission legislation another challenge for the introduction of lean gasoline engines in North America is the higher sulfur content of the fuel compared to Europe.In this paper exhaust gas aftertreatment requirements for stratified gasoline direct injection engines will be discussed and the latest advances in catalyst and system development will be shown. With a newly developed three-way nitrogen oxide storage catalyst (TWNSC) mounted close-coupled to the engine and an improved NOx storage catalyst in the underfloor of the vehicle, the operating range for lean combustion can be significantly increased and further potential for minimizing CO₂ emissions can be realized. This new concept provides the basis for exhaust gas aftertreatment with substantially improved efficiency in vehicles with gasoline engines operated with a lean fuel mixture.