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This paper offers a two-zone NOx model suitable for vehicle on-board, on-line implementation. Similar NOx modeling attempts have previously been undertaken. The hereby suggested method does however offer clear and important benefits over the previously methods, utilizing a significantly different method to handle temperature calculations within the (two) different zones avoiding iterative computation. The new method significantly improves calculation speed and, most important of all, reduces implementation complexity while still maintaining reasonable accuracy and the physical interpretation of earlier suggested methods. The equations commonly used to compute NOx emissions is also rewritten in order to suit a two-zone NOx model. An algorithm which can be used to compute NOx emissions is presented and the intended contribution of the paper is a NOx model, implementation feasible for an embedded system, e.g. embedded processor or embedded electronic hardware (FPGA).

For trucks today, the diesel particulate filter (DPF) and SCR catalysts are combined in this sequential order in diesel exhaust systems with the drawback of insufficient temperature for the SCR catalyst during cold start and large volume. The problems can potentially be solved by integrating the SCR catalyst into the particulate filter as one multifunctional unit. For off-road and heavy-duty vehicles applications with fully managed passive NO2-soot regenerations, integration of V-based SCR formulations on the DPF (V-SCRonDPF) represents an attractive solution due to high sulfur resistance accompanied by low-temperature NOx conversion and improved fuel economy. Engine bench tests together with an NO2-active DOC show that it is possible to manage the NO2/NOx ratio so both a high NOx conversion and still a low soot balance point temperature is obtained. The soot balance point is almost unaffected by the fast SCR reaction when urea is introduced.

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.