Engine exhaust system routes exhaust gas from the engine and exhausts it into the environment, while providing noise attenuation and aftertreatment of the exhaust gas to reduce emissions. Engine exhaust system consists of Diesel Particulate Filter (DPF) & Catalytic Convertor which reduce the emissions of pollutant. It is very important to maintain the uniform flow at all catalyst inlets, keep pressure drop (back pressure) across exhaust system within critical limit and maintain temperature at catalysts within required temperature range. This can be achieved using CFD & it further helps in determining various flow parameters within exhaust system and modification of exhaust system for its improved performance.

• Appropriate consideration of catalyst resistance in various directions.
• Modelling of insulation around the catalysts by capturing the small gap properly for thermal simulation.

Flow and thermal analysis of exhaust system is quite challenging due to involvement of multiple high resistance flow zones (catalysts) and various solid zones like insulation, mat and pipe wall thickness. Mesh was manually controlled to keep the mesh count within limits and at the same time capture the critical regions under consideration. Due to sudden turning, expansion & contraction of the flow there were flow non-uniformity at catalyst inlets which caused reduction in performance & increase in back pressure of exhaust system. Using CFD, exact locations of non-uniformity + flow separation regions and their reasons were identified. Also temperature at catalysts, on outer skin & at various probe locations were checked. Further CFD analysis was carried out to make the exhaust system more efficient. This was achieved by making design modifications in exhaust system flanges and various perforation parameters which reduced flow separation regions, improved flow uniformity at catalysts inlets and maintained back pressure within critical limit.

• Quick turnaround time to fix existing problem of flow non-uniformity at catalysts inlet.
• Cost effective solution for reduced number of trials with improved Exhaust system performance.