Sensor Reduction in Diesel Engine Two-Cell Selective Catalytic Reduction (SCR) Systems for Automotive Applications

In this paper, we have studied the sensor reduction problem for two-cell selective catalytic reduction (SCR) systems with applications to Diesel-engine-powered automotive systems. For the purpose of constructing feedback control loops, three NOx sensors and three ammonia sensors are necessary for the ideal case. However, a large set of physical sensors will not only increase the system integration cost, but also the burden of fault diagnosis. Therefore, we aim to reduce the number of physical sensors for the system. The proposed strategy consists of three physical sensors and two observers. The three physical sensors include two NOx sensors and one ammonia sensor among which one NOx sensor is placed at the tailpipe and the other two are located between the two SCR cells. For the first SCR catalyst cell, the available measurements are the NOx and ammonia concentrations. The function of the observer for the first cell is to estimate the engine-out NOx concentration, the ammonia injection input, and ammonia coverage ratio. Two observers are designed for the first cell to estimate the inputs and states simultaneously. One observer is used to estimate inlet ammonia concentration and the other one is based on the assumption that the urea solution is completely converted into gaseous ammonia before the cells. Both observers show good performances on the input and state simultaneous estimation in terms of experimental results. For the second SCR catalyst cell, the inputs are available. The output is the reading of the NOx sensor at the tailpipe. A Luenberger observer is designed for the second cell to estimate the ammonia coverage ratio and the NOx concentration. The designed observers are validated with experimental data. It infers from the results that the number of physical sensors has been successfully reduced. All the states and inputs of a two-cell SCR system can be made available by the three physical sensors and designed observers.