EXHAUST SYSTEM FOR LEAN-BURN ENGINES

摘要

A lean-burn gasoline engine including an exhaust system, which system has a first oxidation catalyst for oxidizing engine-derived, unburned hydrocarbons during lambda>1 conditions, and a NOx-trap downstream of the oxidation catalyst. Also included in one embodiment is by-pass means arranged between an upstream end and a downstream end of the oxidation catalyst and means for switching at least some exhaust gas flowing in the exhaust system to flow in the bypass during rich or stoichiometric running conditions, thereby substantially to prevent bypassed exhaust gas from contacting the oxidation catalyst. Included in the invention are methods of treating the exhaust gas streams with the apparati defined above.