Development of a dosing strategy for a heavy-duty diesel exhaust cleaning system based on NOX storage and reduction technology by Design of Experiments

A dosing strategy for the transient control of an exhaust after-treatment system using the NOX storage and reduction approach was developed on a heavy-duty diesel engine rig equipped with an 11 l diesel engine. The catalysts were oxidation catalysts of 8.4 l and NOX storage and reduction catalysts of 16.8 l total volume. The dosing strategy has been tested in a European Transient Cycle (ETC) resulting in a NOX reduction of 60% (by 4.5 g/kWh) with a fuel penalty of 6.6% when the catalysts were preconditioned to 450 °C. The reducing agent was diesel fuel. To keep the fuel penalty low, a bypass system was used which bypassed approximately 90% of the exhaust flow under the regeneration periods. The parameters for the dosing strategy were obtained from steady-state optimization experiments (constant speed and torque) using Design of Experiments (DoE) to obtain much information from few experiments. The system was optimized for a high degree of NOX reduction with a low fuel penalty. The period when the flow through the catalyst is reduced (bypass time), the cycle time, the injection time and rate are important parameters to achieve an improved NOX reduction. The optimal values of these parameters varied with the load points used. The steady-state NOX conversion was approximately 60% (3.3–4.1 g/kWh) at catalyst temperatures between 330 and 530 °C. The most promising parameters for a large NOX reduction and a low fuel penalty have been applied in the dosing strategy and tested in an ETC.