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The Euro IV legislation for heavy-duty on-road vehicles enforces emissions limits on the tailpipe NOx levels during both transient and modal testing, typically paired with additional limitations on, for example, ammonia emissions. There are several possible strategies for complying with the legislation, including engine management measures as well as after-treatment in the form of catalytic removal of NOx with ammonia as the reducing agent. Based on experimental data, a range of important aspects are presented and discussed, with both overall system performance and the installation and operational costs in mind. Factors relevant for future legislations, in the form of EU V and beyond, are also discussed. Operating the engine with high levels of Exhaust Gas Recirculation (EGR) is a possible path to EU IV compliance with no or little catalytic NOx reducing after-treatment. Here, it is contrasted against an SCR-only solution based on a non-EGR engine calibration.

The Selective Catalytic Reduction (SCR) catalyst with ammonia as reducing agent plays a central role in today's exhaust after-treatment systems for heavy-duty vehicles and there is a wide selection of possible catalytic materials to use. In order to facilitate the design of future catalysts, several aspects of the materials must be evaluated both in steady-state and transient operation. To this end, this paper presents a methodology for comparing the dynamic properties of different catalysts using full-size engine testing. The studied characteristics include the ammonia storage capacity, the effect of starting with an empty catalyst, the transient response to temperature gradients and changes in the urea dosing level. The temperature response is of particular importance in transient operation, where temperature increases may lead to substantial ammonia slip. A vanadium catalyst is compared to a Cu-SAPO-34 catalyst, and they show significant differences in their dynamic response.

Emissions and in-cylinder pressure traces are used to compare the relative importance of soot formation and soot oxidation in a heavy-duty diesel engine. The equivalence ratio at the lift-off length is estimated with an empirical correlation and an idealized model of diesel spray. No correlation is found between the equivalence ratio at lift-off and the soot emissions. This confirms that trends in soot emissions cannot be directly understood by the soot formation process. The coupling between soot emission levels and late heat release after end of injection is also studied. A regression model describing soot emissions as function of global engine parameters influencing soot oxidation is proposed. Overall, the results of this analysis indicate that soot emissions can be understood in terms of the efficiency of the oxidation process.