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With the reduction of engine and road noise, wind has become an important source of interior noise when cruising at highway speed. The challenges of weight reduction, performance improvement and reduced development time call for stronger support of the development process by numerical methods. Computational Fluid Dynamics (CFD) and finite element (FE) vibroacoustic computations have reached a level of maturity that makes it possible and meaningful to combine these methods for wind noise prediction. This paper presents a method used for coupling time domain CFD computations with a finite element vibroacoustic model of a vehicle for the prediction of low-frequency wind noise below 500 Hz. The procedure is based on time segmentation of the excitation load and transformation into the frequency domain for the vibroacoustic computations. It requires simple signal processing and preserves the random character as well as the spatial correlation of the excitation signal.

Transient and steady-state kinetic data are herein presented to analyze the inhibiting effect of ammonia on the NH₃-SCR of NO at low temperatures over a Fe-zeolite commercial catalyst for vehicles. It is shown that in SCR converter models a rate expression accounting for NH₃ inhibition of the Standard SCR reaction is needed in order to predict the specific dynamics observed both in lab-scale and in engine test bench runs upon switching on and off the ammonia feed. Two redox, dual site kinetic models are developed which ascribe such inhibition to the spill-over of ammonia from its adsorption sites, associated with the zeolite, to the redox sites, associated with the Fe promoter. Better agreement both with lab-scale intrinsic kinetic runs and with engine test-bench data, particularly during transients associated with dosing of ammonia to the SCR catalyst, is obtained assuming slow migration of NH₃ between the two sites.

Mercedes-Benz BlueTEC passenger cars have been on the cutting edge of clean diesel technology since 2006. These BlueTEC vehicles furthermore passed millions of kilometers in the hands of customers. SCR-equipped passenger cars already meet the most stringent exhaust emissions standards in international markets such as the USA, Europe and Japan. Diesel engines with BlueTEC technology also reduce CO₂ emissions and provide the high torque and performance associated with the diesel engine in addition to keeping exhaust emissions at the lowest possible level. Nowadays the requirements for SCR emission concepts are increasing continuously. In fact the emission legislation is getting stricter with the LEVIII emission standards in 2015. Additionally the requirements and effort for on-board diagnosis are increasing year after year. In combination with ambitious CO₂ targets all these issues constitute the further challenges of BlueTEC SCR emission concepts for worldwide markets.