Advanced thermal regulation of muffler

Abstract

Tighter legislation on emissions, such as the upcoming EURO-7, puts increased pressure on manufacturers to further decrease emissions from their vehicles. This study address Nitrogen Oxides (NOx) emission from heavy-duty trucks. For the selective catalytic reduction catalyst, an important component of the exhaust after-treatment system to properly react NOx into pure nitrogen and water, is that the temperature needs to be sufficiently high in the muffler. During extended periods of low engine load, such as downhills or idling, the muffler cools down as colder exhaust enters the muffler, as a result NOx emissions increases.

To address this, the study investigates a thermal property of the muffler’s dynamics that allows the use of time normalization, which simplifies the dynamics. Time normalization was then utilized in the design of the resulting model predictive controller. Furthermore, the impact of incorporating preview information was investigated to determine what benefits could be gained by using a model predictive controller with preview, compared to one without.

The results demonstrated that it was possible to utilize the structure of the dynamics to construct a controller in a linear time-invariant environment, to control the linear time-varying system. Additionally, incorporating preview information improved the performance in cases where the exhaust temperature drops fell outside the region of which the controller could compensate. In such cases the controller pre-heated the muffler to maintain a sufficient temperature, thus extending the duration of constraint satisfaction but at the cost of increased energy consumption. However, when the temperature drop was within the region of what the controller could supply, the controller without preview performed equally well.