Numerical Analysis of Urea to Ammonia Conversion in Automotive Selective Catalytic Reduction Realistic Conditions

Abstract

The selective catalytic reduction (SCR) is a technology employed for NO x reduction purposes which is based on the injection of an Urea Water Solution (UWS) into the exhaust line. Conversion of this injected urea into ammonia is a key step to ensure high SCR efficiency. In order to study this phenomenon, a three-dimensional model of the urea–water injection process has been created to recreate realistic conditions. A Lagrangian–Eulerian approach has been followed to model liquid and gas phases, respectively. Droplet evaporation as well as relevant chemical processes have been included to recreate the thermolysis and hydrolysis phenomena, and the results have been validated against literature data. Then, the validated model has been applied to recreate an in-house experimental facility that measured spray macroscopic and microscopic characteristics by means of diffused back illumination (DBI) visualization. Probability density functions of the UWS droplet sizes as well as the velocity distributions have been obtained at three different regions of interest to be compared with the experimental data set. Contours of isocyanic acid and ammonia mass fractions have been included to show the chemical transformation from urea into its products. The model accurately replicates the experimental results, and it stands as a good methodology to predict the main spray characteristics as well as the chemical processes that take place in actual SCR systems.

Estimation of Entropy Generation in a SCR-DeNOx System with AdBlue Spray Dynamic Using Large Eddy Simulation

“…Therefore, the respective models validation and verification are carried out in an individual test bench. The integrated numerical approach is then utilized to carry out more detailed numerical investigation in more realistic SCR configuration [ 8 ]. However, in this study the individual numerical modules (e.g., AdBlue injection, spray–wall–interaction/film formation, wall–film/spray evaporation, species transport, reactions etc.)…”

“…Focusing on computational fluid dynamics (CFD) based numerical analysis and design optimization of EGAS, the Reynolds-averaged Navier–Stokes (RANS)-based methods were the most adopted approach as it can provide a macroscopic understanding of the relevant processes with relatively less computational expenses and time [ 6 , 7 , 8 ]. However, the process inside a SCR system features a highly unsteadiness starting from the hot turbulent exhaust gas from the engine manifold, AdBlue injection, AdBlue film development, deposit formation and ammonia conversion to the NO X reduction.…”

“…The lack of comprehensive reference or experimental data to validate the adopted numerical methods for a given SCR system presents additional challenges to the modelling communities. Therefore, Payri et al [ 8 ] firstly, validated the adopted atomization model by using the in-house data. Subsequently, the available data for NH 3 conversion in another realistic SCR duct [ 9 ] was utilized to evaluate the used reacting kinetics of urea decomposition and NH 3 conversion for the RANS simulation.…”

Commentary on Earth Day and the Relationship to Historical Developments in Air Pollution Control and Scientific Next Steps

“…We as scientists should and will continue to work on new methods and materials for pollution reduction. Among areas of importance, diesel particulate filters and SCR catalysis need additional understanding and improvement as they are key enablers of pollution abatement during the transition period of heavy-duty vehicles from petrochemical fuels to electric transportation. ,, A key consideration in our transition to a low carbon economy is the value of our installed infrastructure/capital base and the expected lifetime of that equipment, which typically stretches well past 2030…”

“…Among areas of importance, diesel particulate filters and SCR catalysis need additional understanding and improvement as they are key enablers of pollution abatement during the transition period of heavy-duty vehicles from petrochemical fuels to electric transportation. 48,55,56 A key consideration in our transition to a low carbon economy is the value of our installed infrastructure/capital base and the expected lifetime of that equipment, which typically stretches well past 2030. 57 New technology solutions are also needed to address pollution within difficult to decarbonize sectors such as marine shipping.…”