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Numerical Simulation Study on Urea-SCR System of Diesel Engine
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DOI：10.1039/D5CY01120E.png)
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Abstract
En 中文
Nitrogen oxides (NOx) emitted by diesel engines represent a major category of atmospheric pollutants. As the most sophisticated and efficient technology for controlling NOx emissions from diesel engines; Urea-SCR (Urea-Selective Catalytic Reduction) technology necessitates complex engineering during its development and matching processes. Simulation calculations offer an effective approach to reduce the time and cost involved in Urea-SCR system development. Currently; commercial software dominates the computational research on Urea-SCR systems. Although commercial software boasts powerful capabilities; it poses challenges for users to understand and expand models; accompanied by high costs for usage and upgrades. This study aims to develop a one-dimensional flow model and simulation program for Urea-SCR systems; verifying their accuracy and effectiveness through experimental validation. An unsteady one-dimensional flow model for engine exhaust pipelines was established; solved using the finite volume method in conjunction with the Runge-Kutta method. The Rosin-Rammler empirical equation was employed to fit the droplet size distribution of injected urea aqueous solution; while the Lagrangian method was applied to calculate the state variations of droplets throughout their lifecycle. The program was utilized to compute urea decomposition efficiency; and the results showed favorable agreement when compared with the experimental data reported by Kim et al. A simplified one-dimensional flow model for the SCR reactor was constructed; solved via the SIMPLE algorithm; with the under-relaxation method adopted to enhance the convergence of implicit format iterative calculations. A one-dimensional Urea-SCR system simulation program was developed using C++. Leveraging an SCR small-scale performance evaluation test bench; the impacts of different operating conditions on NOx conversion efficiency were tested. The results indicate that the program's computational outcomes exhibit close consistency with experimental data. In the low-temperature range; a higher space velocity corresponds to a lower NOx conversion rate. The addition of NO₂ improves NOx conversion efficiency; with the optimal effect achieved when the NO₂/NO ratio is 1:1. An ammonia-nitrogen ratio below 1 imposes limitations on NOx conversion. D2 and E3 test cycle evaluations were conducted on a medium-speed diesel engine test bench; and simulations were performed using the developed program.
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