Exhaust gas after-treatment method for a gasoline internal combustion engine

摘要

During the phase of rising catalyst (26) temperature (PmT), the mixture richness (Er) is adjusted to increase the rate of temperature rise. The fuel mixture is varied from one cylinder (C1-4) to the next. At the same time, the mean richness is held close to stoichiometric. The procedure is carried out in such a way that carbon monoxide and molecular oxygen emissions are enhanced in the engine (12) exhaust gases (G). This promotes exothermic reactions in the catalyst (26). Richness variations are caused by weighting the duration (Di) of fuel injection into each cylinder, using a selected coefficient (ki). Selective richness distribution between the cylinders is initiated on reaching a catalyst temperature (Tmin) of minimal carbon monoxide treatment efficiency. Richness distribution is started when the hydrocarbon trap (24) has reached an initiation temperature (Ta) for hydrocarbon treatment. Richness distribution is continued until the catalyst (26) treats the hydrocarbons at about 90% efficiency.