Model-based simulation and optimization of an scr system for a heavy-duty diesel engine

Abstract

This study aims to develop and optimize a simulation model of a Selective Catalytic Reduction (SCR) system for a 12.7-liter heavy-duty diesel engine that complies with Euro VI emission standards under transient operating conditions. Euro VI regulations have significantly tightened nitrogen oxide (NOₓ) emission limits for heavy-duty engines. Achieving such high NOₓ conversion efficiency under real driving conditions poses a considerable engineering challenge. Therefore, it is critically important to carefully design advanced aftertreatment solutions like SCR. In this context, modeling the performance of the SCR system under dynamic operating conditions, such as the World Harmonized Transient Cycle (WHTC), provides valuable insights into system behavior and optimization possibilities. In this study, the SCR system was modeled in MATLAB/Simulink, including both its physical components and control algorithms. The developed comprehensive simulation model covers the NOₓ emission source at the engine outlet, the AdBlue injection system, and the behavior of the SCR catalyst. Data obtained from WHTC test cycles were used for model calibration and validation. This ensured that the model could accurately reflect the emission behavior of the engine and the catalyst conversion performance under transient conditions. Model validation was carried out by comparing simulation results with experimental data. During this process, key performance indicators such as NOₓ concentration at the exhaust outlet and AdBlue consumption were evaluated. The simulation results largely aligned with the experimental data obtained at different engine load and speed conditions throughout the transient cycle. The model successfully predicted NOₓ reduction efficiency and urea consumption with near-realistic accuracy. This confirms that the model effectively captures the dynamic behavior of the SCR system and its control under real-world driving conditions. Following validation, a series of parametric studies was conducted to examine how different design and operating parameters affect SCR performance. Parameters such as catalyst volume, injector (AdBlue) capacity, catalyst aging, and dosing control strategy were systematically varied. The effects of each variable on NOₓ conversion efficiency and AdBlue consumption were analyzed. The analyses investigated the impacts of catalyst size, injector capacity, and catalyst aging on NOₓ emissions and the required AdBlue dosing amounts. The results highlight the benefits of the Model-Based Development (MBD) approach in designing and developing SCR systems. By using the simulation model, design optimizations and control improvements can be rapidly evaluated without the need for comprehensive physical prototypes. This allows a wide range of scenarios to be analyzed cost-effectively in a virtual environment. Through this approach, engineers can determine optimal system configurations and control strategies that ensure maximum NOₓ reduction while minimizing excessive AdBlue consumption and preventing ammonia slip. Thus, strict emission regulations can be met with significant time and resource savings. In conclusion, this thesis presents a comprehensive SCR system model and demonstrates its capability to effectively guide the design and optimization of exhaust systems for heavy-duty engines. The developed model serves as a powerful tool for predicting system behavior under transient operating conditions and guiding design decisions in an informed manner. Overall, this study contributes to the development of effective SCR system solutions for Euro VI compliance and emphasizes the role of simulation and model-based methods in modern automotive engineering.