Temperature control of nitrogen oxides storage catalyst used with diesel- and lean burn engines

摘要

Thermal flows (W1, W2) are extracted from the exhaust stream. To avoid damage, excessive temperatures at the NOx storage unit (7) are kept within a preset operational temperature band. They are extracted ahead of the unit, in accordance with the engine (1) state. An Independent claim is included for corresponding equipment carrying out the method. Preferred features: Thermal energy is extracted from the exhaust flow, before and/or after the first catalyst (2). The heat is extracted from the exhaust stream in two stages, especially before and after the catalyst. The storage unit stores NOx, acting as an oxidation catalyst. Heat flows abstracted amount to 5 kW-50 kW. Air blown by the engine turbocharger (9) applies forced convective cooling to the exhaust gas line (5) ahead of the storage unit. Hot exhaust gas flows may be abstracted under control. The control magnitude is a function of engine loading and the temperature of the NOx storage unit. The selected, set temperature band of the storage unit lies between the limits 150 deg C-700 deg C, and is preferably below 500 deg C. The engine is run rich until the storage unit minimum operational temperature of 150 deg C is reached. A closely related variant procedure is also described.