Reduction of Transient Engine-Out NOx-Emissions by Advanced Digital Combustion Rate Shaping

Modern diesel passenger cars already fulfill high demands regarding the reduction in NOx emissions through complex exhaust aftertreatment systems. With the consideration of real driving emissions, the reduction in NOx emissions in high transient engine operation becomes even more challenging. Apart from increasing the complexity of exhaust aftertreatment systems, internal engine measures play a major role. The approach to reducing NOx emissions described in this paper uses the precise control of the combustion. For this purpose, the method of digital combustion rate shaping control is applied, which allows the realization of a predefined combustion by automatically adapting the injection profile during operation. Within this work, this controller is extended in order to control the predefined combustion trace based on target NOx values. First, the working principal of the state-of-the-art digital combusting rate shaping controller is explained. In the next step, the design and strategy of the extended control approach are explained and validated. Finally, its potential to reduce engine-out NOx emissions during transient driving situations is evaluated based on simulations of the WLTC. It is shown that the control concept fulfills the requirements and is able to effectively reduce high NOx peaks during transient operation.