Model Based Design Procedure of After Treatment Systems for Non-Road Diesel Engines 2011-24-0186

In 2011-2013, regulations will be tightened for non-road vehicles, via the application of Stage III-B standards in Europe. With state-of-the-art technology (high pressure common rail, cooled EGR), non-road diesel engines will require DPFs to control PM, as 90% reduction is requested with respect to STAGE III-A standards. Additional challenges may also foresee the obtainment of STAGE III-B standards with STAGE III-A engine technology, by means of retrofit systems for PM control. In that case, retrofit systems must furthermore guarantee simple control systems, and must be robust especially in terms of limited back pressure increase during normal operation. Moreover, retrofit systems must offer flexibility from the design point of view, in order to be correctly operated with several engines of same class, possibly characterized by totally different PM flow rates, temperature, NO_x and O₂ availability. The design process of such systems appears challenging itself, as experimental testing cannot be massively used to limit costs otherwise leading the product out of any feasibility. The design of OEM exhaust systems appears instead different, as the implementation of more effective regeneration strategies appears feasible, but time to market is limited and then efficient design procedures are required to save time and costs.

In the provided background, a model-based design tool, specifically developed for non-road diesel engines at the University of Rome Tor Vergata, is presented in this paper. This tool is partially based on the use of GT-Power, properly coupled to user-defined models to increase its flexibility as well as to improve computational efficiency. Moreover, an original clustering procedure has been specifically developed to understand the impact of key engine parameters (such as injection timing, EGR, etc.) on exhaust operating conditions (in terms of mass flow rate, species concentration and temperature), and in turn on exhaust system behavior. Special care has been given to analyze the whole engine/exhaust-system performance on a transient basis, and properly estimate performance on the NRTC (Non-Road Transient Cycle).

The design procedure was applied to characterize a DOC+DPF after-treatment system, where the DOC/DPF volume and DOC noble metal loading have been assumed the main design parameters. Obtained results finally led to the selection of two layouts, respectively for after-market (retrofit) and OEM applications.