| 摘要 |
A method of controlling an internal combustion engine and exhaust system having an SCR, and engine and exhaust system including an SCR, described herein, monitors, in real time, NOx conversion efficiency of an exhaust flow output by the internal combustion engine through the SCR. A determination is made as to whether the monitored NOx conversion efficiency exceeds a predetermined target conversion efficiency, such as a target based on a predetermined allowable amount of NOx emission. While the monitored NOx conversion efficiency exceeds the predetermined amount, the NOx concentration level in the exhaust flow is increased by an amount based on the difference in the monitored conversion efficiency and the predetermined target conversion efficiency. Another method and engine and exhaust system provided herein tracks an amount of ammonia stored on a catalyst of the SCR based on a feed-forward calculation of injected urea based on engine out NOx mass flow and reduction efficiency of the SCR catalyst based on a temperature of the SCR catalyst, and operates the engine and exhaust system in a NOx-rich mode in which an EGR fraction command is adjusted, based on the tracked amount of stored ammonia, to decrease an amount of EGR gas entering an intake of the internal combustion engine and thereby reduce ammonia stored on the SCR catalyst.
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