Hydrothermal ageing control of diesel engine urea selective catalytic reduction (SCR) based on adaptive time-step extended Kalman filter (ATS-EKF) and combination of open-loop feedforward and closed-loop feedback

Abstract

The gradual deactivation of SCR catalysts at high temperatures and under steam conditions leads to a reduction in their NOx reduction efficiency. In order to mitigate the adverse effects of hydrothermal aging on the SCR catalyst and ensure compliance with Euro VII diesel exhaust standards. Firstly, the concept of SCR hydrothermal aging and its corresponding model are constructed. The model is then transformed using the variable substitution method and Method of Lines, optimized by the Levenberg–Marquardt method, and solved with the backward differentiation formula method. Secondly, this paper designs the ATS-EKF hydrothermal aging factor observer, informed by the model’s solution characteristics, NH${}_3$ concentration, NOx concentration, and ammonia coverage within the SCR catalyst. Based on the observer’s monitoring, open-loop feedforward and closed-loop feedback control methods are formulated. The closed-loop feedback utilizes the effective set algorithm to address the SCR hydrothermal aging system’s nonlinearity, uncertainty, and time-varying nature. Finally, the SCR model is validated through testing cycles at the WHTC. Validation results reveal a high calculation accuracy. Observations of the ATS-EKF hydrothermal aging factor, in conjunction with control of upstream NH${}_3$ concentration, indicate mean downstream NH${}_3$ concentrations of 8.6 ppm, 8.18 ppm, and 7.87 ppm and NOx concentrations of 11.03 ppm, 10.59 ppm, and 10.14 ppm for hydrothermal aging factors of 1, 0.8, and 0.6, respectively, all meeting the Euro VII emission standards. The methodology in this paper accurately responds to the hydrothermal ageing of the SCR catalyst and controls the NH${}_3$ and NOx concentrations using the ATS-EKF monitoring and control strategy to ensure Euro VII compliant emissions with greater accuracy and stability than existing systems.