An Extensive Optimization Methodology to Validate the Exhaust After-Treatment System of a BS VI Compliant Modern Diesel Engine

The Indian automotive industry has migrated from BS IV (Bharat stage IV) to BS VI (Bharat Stage VI) emission norms from 1^st April 2020. This two-step migration of the emission regulations from BS IV to BS VI demands significant engineering efforts to design and integrate highly complex exhaust after-treatment system (EATS). In the present work, the methodology used to evaluate the EATS of a high power-density 1.5-liter diesel engine is discussed in detail. The EATS assembly of the engine consists of a diesel oxidation catalyst (DOC), a diesel particulate filter with selective catalytic reduction coating (sDPF), urea dosing module and urea mixer. Typically, all these components that are needed for emission control are integrated into a single canning of shell thickness ~1.5mm. Moreover, the complete EATS is directly mounted onto the engine with suitable mounting brackets on the cylinder block and cylinder head. The mounting brackets of the after-treatment system should be stiff enough to withstand the high cycle fatigue vibration loads coming from the engine. On the other hand, the brackets should allow the system to expand freely under high temperatures to avoid any low cycle fatigue issues created due to thermal loads at 800 deg.C. Hence, a robust methodology is followed to ensure the robustness of the entire system. The methodology included the prediction of metal temperature using a conjugate heat transfer analysis, high-temperature modal analysis, stress-strain analysis and high-cycle vibration fatigue analysis. In order to evaluate the system from the thermal compliance point of view, a high-temperature stress-strain analysis is carried out in a thermal shock test cycle. The simulation results have shown that the brackets positioned at the near-zero thermal expansion zone could have a much lesser plastic strain due to reduced thermal stress. Taking advantage of this, the stiffness of the brackets could be increased to improve the modal frequency values and robustness against high-cycle vibration fatigue. The paper gives a detailed insight on optimizing the bracket design of the EATS to ensure that a robust design solution is finalized.