Effect of NO <sub>2</sub> on Gas-Phase Reactions in Lean NO <sub>x</sub> /NH <sub>3</sub> /O <sub>2</sub> /H <sub>2</sub> O Mixtures at Conditions Relevant for Exhaust Gas Aftertreatment



Automotive Technical Papers
Authors Abstract
This combined numerical simulation and experimental study focuses on the effect of nitrogen dioxide (NO2) in strong diluted oxygen-rich NOx/NH3/O2/H2O gas mixtures representative at exhaust gas aftertreatment in diesel engines. Conversion of nitrogen oxides (NOx) and ammonia (NH3) and the change of the NO/NO2 and NH3/NOx ratios were analyzed by means of comparison between experimental measurements and kinetic simulations. Homogeneous gas-phase experiments have been carried out in a special countercurrent continuous flow reactor at intermediate temperature (473-923 K) and elevated pressure up to 5 bar. In the simulation with an ideal plug-flow model, the occurring reactions in the gas mixture were calculated. To explain the observations, a reactions flow analysis was also performed. The experimental and modeling results revealed that despite a high NH3 conversion, the NOx concentration stays nearly constant in the presence of NO2. The NO2 reduction by amino (NH2) radicals producing NO was found to be the temperature-dependent chain-branching step between the competitive NO and NO2 reduction reactions. The kinetic modeling results show that the experimentally observed higher NH3 conversion at elevated pressure is a superposition of the direct effect of the elevated pressure and the effect of the pressure-caused longer residence time at a constant mass flow rate. The NO/NO2 and NH3/NOx ratios are significantly changing with temperature increase by the elevated pressure. The observed changes of the gas mixture composition, especially of the NO/NO2 and NH3/NOx ratios due to homogeneous gas-phase reactions, will consequently influence the efficiency of NOx conversion catalysts in the exhaust gas aftertreatment systems. Therefore, a numerical prediction of the gas-phase reactions between the injection point of the urea-water solution and the inlet of the selective catalytic reduction (SCR) catalyst could contribute to the further development of the dosage strategy of the urea-water solution in SCR systems, when operated close to the engine or even upstream the turbocharger.
Meta TagsDetails
Bertótiné Abai, A., Zengel, D., Janzer, C., Maier, L. et al., "Effect of NO 2 on Gas-Phase Reactions in Lean NO x /NH 3 /O 2 /H 2 O Mixtures at Conditions Relevant for Exhaust Gas Aftertreatment," SAE Technical Paper 2021-01-5005, 2021, https://doi.org/10.4271/2021-01-5005.
Additional Details
Feb 15, 2021
Product Code
Content Type
Technical Paper