Development of a methodology to monitor NOX emission of Urea-SCR system

In order to ensure the engine’s in-use emission performance, the heavy-duty On Board Diagnostics (OBD) are required by most of the regulations to be applied to all on-highway engines, whose key part is the NOX emissions monitoring with a defined NOX OBD threshold. In this paper, two different NOX emission prediction methods based on the tailpipe NOX sensor are proposed: Quasi-steady State Prediction method (QSP method) and Two-stage Integral Prediction method (TIP method), which were verified in the bench tests and field trial. And the test results show that the prediction errors of the two methods are within ± 0.5 g/kWh under high NH3 slip. Moreover, in addition to the high accuracy, QSP method can quickly spot the degradation of the SCR system, and thus can be adopted in the Adblue dosage control strategy to offer robustness.

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