Abstract
The upcoming more stringent automotive emission legislations and current developments have promoted new technologies for more precise and reliable catalyst control. For this purpose, radio-frequency-based (RF) catalyst state determination offers the only approach for directly measuring the NH3 loading on selective catalytic reduction (SCR) catalysts and the state of other catalysts and filter systems. Recently, the ability of this technique to directly control the urea dosing on a current NH3 storing zeolite catalyst has been demonstrated on an engine dynamometer for the first time and this paper continues that work. Therefore, a well-known serial-type and zeolite-based SCR catalyst (Cu-SSZ-13) was investigated under deliberately chosen high space velocities. At first, the full functionality of the RF system with Cu-SSZ-13 as sample was tested successfully. By direct RF-based NH3 storage control, the influence of the storage degree on the catalyst performance, i.e., on NOx conversion and NH3 slip, was investigated in a temperature range between 250 and 400 °C. For each operation point, an ideal and a critical NH3 storage degree was found and analyzed in the whole temperature range. Based on the data of all experimental runs, temperature dependent calibration functions were developed as a basis for upcoming tests under transient conditions. Additionally, the influence of exhaust humidity was observed with special focus on cold start water and its effects to the RF signals.
Highlights
Tightening vehicle emission legislations are the main driving factor for improvements in engine and exhaust gas aftertreatment technologies among automotive manufacturers worldwide [1]
Relying on current schemes of the selective catalytic reduction (SCR) reaction mechanism for several SCR catalysts, the prior NH3 adsorption is an essential precondition for all SCR reactions [5,6,7,8]
RF-based catalyst state monitoring has been a focus of research and development as the only direct measure of the current NH3 storage on SCR catalysts
Summary
Tightening vehicle emission legislations are the main driving factor for improvements in engine and exhaust gas aftertreatment technologies among automotive manufacturers worldwide [1]. The current DEF dosing control is completely model-based and relies on gas sensor signals, i.e., from NOx and/or NH3 sensors [10]. In these approaches, the whole ad- and desorption equilibrium and all reactions occurring on the catalyst surface are simulated and the necessary amount of DEF is calculated [11,16,17]. Storage-controlled SCR catalyst to operate the whole SCR system at its optimal NOx conversion point and to avoid NH3 slip This might lead to increased system efficiency and more robust catalyst control systems for future applications and emission limits
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