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To meet the 2010 diesel engine emission regulations, an aftertreatment system was developed to reduce HC, CO, NOx and soot. In NOx reduction, a baseline SCR module was designed to include urea injector, mixing decomposition tube and SCR catalysts. However, it was found that the baseline decomposition tube had unacceptable urea mixing performance and severe deposit issues largely because of poor hardware design. The purpose of this article is to describe necessary development work to improve the baseline system to achieve desired mixing targets. To this end, an emissions Flow Lab and computational fluid dynamics were used as the main tools to evaluate urea mixing solutions. Given the complicated urea spray transport and limited packaging space, intensive efforts were taken to develop pre-injector pipe geometry, post-injector cone geometry, single mixer design modifications, and dual mixer design options.

Vehicle cool down noises are receiving more attention as the NVH quality standards rise. The typical observer describes these noises as ping/ting, tick/tink and crinkle/crackle. A new test procedure is presented that measures audible metallic type noises during vehicle cool down (after the engine has been shut off). Vehicle run conditions are recommended for noise replication in the field and for measurement standardization. An objective measurement system is described using sound pressure level. In the past, a measurement has been very difficult to quantify. A recommended report format concisely communicates this critical vehicle quality characteristic. It is a valuable tool for vehicle NVH comparison, ranking and benchmarking.

Passive valves are common acoustic tuning devices for auto exhaust systems. A new mathematical algorithm based on fundamental physics is presented for simulating an exhaust flapper valve. It is programmed into the popular GT Power simulation software as a model component. Algorithm performance is evaluated for predicting pressure drop of an exhaust flapper valve. The model and software predict pressure and flow for steady state flow through the valve at elevated temperatures. Flow bench simulations and experiments are done. Hot flow results are compared to determine performance. The algorithm model is also compared to a reed valve component available in the standard GT library. A comparison of predictions and measurements show, 1. The error of an “Off the shelf” software component is on the order of 10%. 2. The new algorithm's error is on the order of 2%.