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Numerical evaluation of urea-mixing devices for close-coupled selective catalytic reduction systems

Kaźmierski Bartosz Grzegorz, Kapusta Łukasz Jan

Combustion Engines

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2023

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R. 62, nr 2

84--93

EN

The following research presents a numerical evaluation of existing and conceptual urea-mixing devices used in close-coupled (to the engine) selective catalytic reduction (SCR) systems. The analysis was aimed at the assessment of urea-mixing devices that could considerably enhance the reduction of nitrogen oxides from the diesel-engine combustion process under a wide range of operating conditions, including cold starts. The analysis showed that replacing blade-equipped static mixers with perforated stationary mixing devices may provide a more uniform spatial distribution of ammonia at the inlet to the SCR catalyst and reduce pressure drops generated by mixing devices. Moreover, the conceptual mixing devices, based on combinations of the blade and perforated mixers to develop intensive turbulence, enabled the increase of the mixing length leading to effective decomposition of the urea-water solution (UWS), and provided uniform spatial distribution of ammonia, even for the small-sized mixing systems. However, the intensive mixing was often associated with a significant rise in the pressure drop.

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Numerical investigation of the back pressure influence on urea-water-solution mixing performance in close coupled SCR system

Rogóż R., Bachanek J., Boruc Ł., Teodorczyk A.

Journal of KONES

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2018

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Vol. 25, No. 3

377--383

EN

The upcoming Euro 6d emission standard puts more even stringent requirements for diesel engine cars, especially in the case of nitrogen oxides (NOx) emission. The most widely used technique to meet tight standards is Selective Catalytic Reduction (SCR) with urea-water-solution (UWS) injection. One of the crucial factors is even ammonia distribution at the catalyst inlet; hence, very often product development is focused around this issue. The product development is supported by both experimental and numerical work. The common approach to measure cross section ammonia distribution on the SCR is using sampling system at catalyst outlet. Very often exhaust layout is opened just after the SCR catalyst, cutting off the rest part for instance tailpipe or Clean-up Catalyst. Therefore, a backpressure at SCR outlet resulting from the downstream part is also eliminated. This could significantly affect flow parameters as the density changes, thus ammonia distribution and wall film deposition may vary as well. Within this work, the influence of the backpressure at SCR outlet on the ammonia distribution and wall wetting was numerically investigated. The simulations were run under various boundary conditions for the Close Coupled SCR architecture. It was shown that depending on the operating point the boundary pressure affects both factors on the different level.

3

The influence of the injection frequency on the urea selective catalytic reduction systems performance

Rogóż R., Jaworski P., Kapusta Ł. J., Teodorczyk A.

Combustion Engines

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2017

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R. 56, nr 3

73--77

EN

This study presents the influence of the UWS injection frequency on a close coupled SCR systems performance. The investigation was performed with the CFD tool AVL Fire. In the paper the analysis of four different UWS injection frequencies in the three different operating points of diesel engine was shown. The assessments of the system performance was referred to the ammonia distribution at catalyst intake and wall film formation inside the investigated geometry, as these are considered as crucial in such a configuration. The results showed that injection frequency affects both factors on different level depending from the flow conditions. In addition, the wall film crystallization risk was discussed basing on the obtained wall film characteristics.