Emission-Optimized Diesel Engine

The ever increasing demand on the purity of vehicle exhaust gases has sparked the further development of Diesel engine systems among manufacturers. Most passenger car diesel engines use in-engine measures to minimize pollutant formation, i.e. exhaust gas recirculation and injection timing, as well as a chain of exhaust gas after-treatment systems to clean tailpipe exhaust gases. The minimization of pollutant formation requires the careful tuning of the in-engine actuators, which is a delicate task that is difficult to automate. Currently, manufacturers are required to freeze this in-engine actuation strategy, which means that the raw emission characteristic of the engine cannot be changed, once the engine leaves production.

In this project, we investigate the opportunities offered by a variable in-engine actuation strategy. Such a strategy could be used to influence the raw emission characteristic of the engine during operation. In a real-driving scenario, such as required for the so-called real driving emission (RDE) test, the engine emission characteristic could be adjusted during operation according to the needs of the exhaust gas after-treatment systems. For example, shortly after a cold start, when the after-treatment system is not fully capable yet, the engine could be operated with a low-emission strategy. As soon as the SCR system warms up to its nominal operating temperature and is capable of removing a larger amount of nitrogen oxides from the exhaust gases, the engine could adopt a more fuel efficient mode of combustion. Of course, legislation may have to be adjusted in order to allow for such an integrated emission management, nevertheless, this article aims at investigating the potential benefits.

The figure below shows the Pareto-optimal results, when driving the NEDC using a number of different emission strategy.

Once the engine is calibrated according to the procedure shown above, the newly obtained degree of freedom may be utilized to influence the emission characteristic of the full engine-and-aftertreatment system. The figure below indicates, that in the case where only a nominal operating strategy (red) of the engine is used, the tailpipe emissions are too high when driving on a highway. With the proposed calibration, an adaptive emission controller that adjusts the engine raw-emission characteristic in order to keep track of the emission limits during driving (blue). Such a procedure may be crucial in order to fullfill emission limits not only during governmental test procedures, but also during real driving.