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Modeling the effect of SCR denox unit on diesel engine performance

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2020
Pelen, Pelsu
The design of the internal combustion engines and the aftertreatment systems cannot be considered independently since imposing an aftertreatment equipment into the exhaust system brings extra backpressure which in turn decreases the engine efficiency and increases the fuel consumption and CO2 emission. In the present study, the existing 3D monolith reactor model in COMSOL Multiphysics® applications is modified to account for an SCR deNOx unit having 600 cpsi cell density by using exhaust mass flow rate and temperature data of a SCANIA 9-liter off-road Diesel engine. The model is verified against a published experimental work. While performing analyses, 98% NOx conversion is aimed. Results showed that when the engine operates at 2100 rpm, 29.1 kPa backpressure is observed in the SCR deNOx unit having 600 cpsi cell density and 20 cm diameter. It is seen that backpressure decreased down to 4.9 kPa by increasing the SCR deNOx unit diameter to 25 cm. Furthermore, it is observed that 50% more backpressure is formed to obtain only 1% more NOx conversion in the examined SCR deNOx unit conditions. When the engine efficiency is considered, backpressure caused by SCR unit reduces the net work that can be obtained from the engine. If the engine compression ratio is increased to enhance the net work, the efficiency increases however higher NOx emission is observed due to higher temperatures arising from higher compression ratios.