Onboard Emissions Monitoring on a HD Truck with an SCR System Using Nox Sensors

Abstract

<div class="htmlview paragraph">SCR technology has proven its ability to significantly reduce NO<sub>x</sub> emissions. Hence it has become an outstanding solution to be used to meet future emission limits in Europe, Japan and North America. To add even more confidence towards the introduction of SCR technology, the implementation of NO<sub>x</sub> sensors will become mandatory for on-board emission control systems.</div> <div class="htmlview paragraph">To demonstrate the usefulness of NOx sensors, a typical North American On-Highway Truck was chosen as a demonstration vehicle. It was equipped with vertically mounted, extruded SCR catalysts, a urea dosing system, and NO<sub>x</sub>-sensors.</div> <div class="htmlview paragraph">In order to achieve EURO 5 or even lower emission limits in NO<sub>x</sub> and PM, attempts were made to equip the system with oxidation catalysts upstream of the SCR catalyst as well as upstream of the turbine. Some changes had to be made to the model year 2000 engine calibration to reduce PM emissions to EURO 4 and 5 levels.</div> <div class="htmlview paragraph">The system was calibrated and then tested according to different HD test procedures on a transient test bench. NO<sub>x</sub> emissions were determined by CLD and NDIR analyzers and by state of the art NO<sub>x</sub> sensors.</div> <div class="htmlview paragraph">After completion of the test bench work, the catalyst system was transferred to the test truck and the final system calibration was copied from the test bench ECU to the vehicle ECU. On-road NO<sub>x</sub> measurements were gathered by using NDIR-analyzers and NO<sub>x</sub> sensors.</div> <div class="htmlview paragraph">Based on our previous experience with HD trucks, it can be stated that the introduction of NO<sub>x</sub> sensors is an appropriate method to monitor NO<sub>x</sub> conversion performance of SCR systems and also to adapt the system to compensate for various disturbances.</div> <div class="htmlview paragraph">Ongoing evaluation of the test truck in the future will include NO<sub>x</sub> sensor performance, implementation of the NO<sub>x</sub> signal into the dosing control algorithms, as well as on-road durability testing.</div>