| 摘要 |
<p>Theoretical absorption of NOx during weak running, is computer-integrated over time. Temperature-dependent storage capacity of fresh catalyst, and quantity of nitrogen oxide emitted at each engine operational point are taken into account. The capacity- and emission functions, are stored in the engine electronics. Having reached a target absorption value modified by a correction factor (K), rich running is initiated to desorb and convert NOx. Desorption duration (Td) is calculated from the target, and the oxygen stored in the exhaust purification system. Reaction stoichiometry, exhaust gas flow rate, temperature and content of reductant exhaust gas components are all taken into account. During desorption, the stoichiometry of the exhaust is monitored, after the storage catalyst. A duration (T) is measured, following descent of the monitored stoichometry below a given limiting value. Weak running is then reinitiated, all is repeated cyclically. The cited correction factor is the ratio of expected desorption duration (TD) and its measured duration (T), i.e. K=TD/T. Preferred features: Once the correction factor exceeds a set limit, the storage catalyst is deemed defective and replacement is signaled. The target storage value is below nominal storage capacity and/or is related to the engine operational point. On exceeding the correction factor, sulfur compounds are thermally desorbed in rich running (0.95 - 1) at over 600 degrees C for a given interval. A storage catalyst replacement is signaled, when thermal desorption of sulfur no longer reduces the correction factor. The target NOx storage is a value set below its capacity. It is alternatively related to the engine operational point. During desorption, air to fuel ratio is 0.6 - 1 ahead of the storage catalyst. Exhaust composition is measured by a rapid-response lambda sensor. On stopping the engine, the K value is stored in its electronics for the next operation. Exhaust gas composition after the catalyst, is measured using a hydrocarbon or carbon monoxide sensor.</p> |
