NOx sensor ammonia-cross-sensitivity factor estimation in Diesel engine selective catalytic reduction systems

In this paper, the NO_x sensor ammonia-cross-sensitivity factor observer design problem is studied for the applications in Diesel engine selective catalyst reduction (SCR) systems. Since the NO_x sensor is cross-sensitive to gaseous ammonia, this phenomenon restricts the application of NO_x sensor in the SCR system. A practical and economic approach is to design an observer to estimate the cross-sensitivity factor and correct the NO_x sensor reading. Firstly, a three-state nonlinear model for the SCR system is adopted. It is assumed that the qth-order derivative of the temperature-dependent cross-sensitivity factor is zero. Then, based on the nonlinear model, a proportional-multiple-integral (PMI) observer of the factor is proposed and a nonlinear estimation error system is obtained. With the linear-parameter-varying (LPV) technique, the stability of the nonlinear estimation error system is investigated and the design method of the observer gains is developed. At the end, simulations and comparisons via an experimentally-validated full vehicle simulator are done to illustrate the efficacy and the advantages of the proposed approach over the existing methods.