Model-based Analysis and Control of SCR Using NOx Sensor Measurements

Model-based closed-loop SCR controls are critical for urea-based SCR system to meet stringent NOx emission standards. Lack of full understanding of limit of SCR NOx reduction capability can lead to too conservative or too aggressive reference design. In this study, a model-based approach was proposed to analyze the maximum modified NOx conversion efficiency that can potentially be achieved by a SCR system for a given exhaust condition. In addition, a model-based approach was proposed to evaluate the performance of production SCR system based on the NOxsensor measurement and the maximum modified NOxconversion efficiency. A sliding mode controller was developed for tracking the desired reference. The performance of sliding mode control was assessed in a real-time manner using the proposed approach. Simulation results over US06 cycle demonstrate that the proposed approach can be utilized to appropriately interpret the tracking error between the actual control variable and reference. In addition, with the full understanding of limit of SCR DeNOx capability, this proposed approach can be applied to improve control reference design and thus improve the SCR performance.

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