Vehicle engine exhaust treatment process for engines designed for poor mixtures using discontinuous operation with poor/rich mixtures to improve lifetime consumption

摘要

The NOx storage catalyst has an upper temperature limit of at least 520 deg.C and a minimum NOx conversion rate of 80% at the operating temperatures. Desulphurisation is initiated when the minimum NOx conversion rate is passed and this uses an enriched exhaust gas at a catalyst temperature of at least 680 deg.C corresponding to the minimum desulphurisation temperature. The engine is operated in a discontinuous manner with intervals lambda with poor-rich mixtures where (a) the NOx storage catalyst has an upper temperature limit (TH) at the level of the operating temperatures at least equal to 520 deg.C (preferably 560 or even 600 deg. C), a minimum NOx conversion rate (KR min) of 80% at the operating temperatures, when fed with a poor mixture during the discontinuous operating time. The engine is run at the upper temperature limit without passing any load and/or regime thresholds or requiring desulphurisation using a stoiometric or enriched mixture. (b) the need for desulphurisation is identified when the mean minimum NOx conversion rate is passed during discontinuous operation with a poor mixture. (c) desulphurisation of the catalyst is carried out at a catalyst temperature (TKAT) of at least 680 deg. C (preferably 700 or even 720 deg.C) corresponding to the minimum desulphurisation temperature (T min) and with an enriched exhaust gas, where the catalyst has a sulphur rejection rate of at least 0.005g/s at the minimum desulphurisation temperature and with an exhaust gas supply with lambda = 0.99. The vehicle runs using discontinuous operation with a poor mixture when the vehicle speed reaches 80 km/h, preferably 100 km/h or even 120 km/h. Desulphurisation is carried out at a temperature at least 20K above the minimum desulphurisation temperature, with lambda =0.9 and for at least 200s per litre of catalyst. During its life, the catalyst undergoes at least 30 and possibly at least 100 desulphurisations without passing the 80% limit. The catalyst can store at least 0.5g of sulphur per litre of catalyst at the point of passing the 80% limit, and the need for desulphurisation is identified after 100l or 150l of fuel has been used in a poor mixture. The engine operates with a fuel sulphur content of at most 30pm, preferably 20ppm or even 10ppm. The catalyst contains components from the alkali and/or alkali-earth groups, preferably in oxide and/or carbonate forms, in particular potassium, rubidium, strontium and caesium. The temperature of the catalyst is increased for active desulphurisation by targeted measures, such as retarded ignition; secondary injection, injection of fuel into the exhaust or using a richer mixture and/or an injection of air upstream of the catalyst.