| 摘要 |
<p>A spark ignition internal combustion engine 10 is described having an exhaust gas after-treatment system that includes a three-way catalyst 18 and an NOX trap 20. The NOX trap 20 stores NOX when the exhaust contains excess oxygen and is regenerated by releasing the NOX gases for reduction by the catalytic converter to N2 when the exhaust gases contain an excess of hydrocarbons (HC) and/or carbon monoxide (CO) in the absence of oxygen. The engine 10 is operated with an overall lean air/fuel ratio, during which the NOX gases contained in the exhaust gases are stored in the trap. The trap is regenerated by briefly injecting fuel from tank 14 - or vapour canister 16 - at regular intervals to a point upstream of the trap, thus supplying a reducing atmosphere to it, and enabling the catalyst within the trap to reduce the NOX. During this regeneration the engine is run with a stoichiometric air/fuel ratio.</p> |
