Potential Technical Approaches for Improving Low‐Temperature NO_x Conversion of Exhaust Aftertreatment Systems

Abstract

Lean‐burn engines, such as diesel engines, are widely used in mobile and stationary applications. Operation of lean‐burn engines leads to formation of distinct amounts of nitrogen oxides (NO and NO2). Efficient aftertreatment is mandatory to meet legal requirements, especially at low exhaust temperatures, as for the future a decline of the exhaust temperature level can be predicted due to improved engine efficiencies. Within this review, potential technical solutions to enhance the DeNOx‐aftertreatment efficiency at low exhaust temperatures are presented.

Tracking AdBlue properties during tests of selective catalytic reduction (SCR) systems ‐ the suitability of various analytical methods for urea content determination

“…The standard working solution (2 000 mg/L) was prepared in a glass volumetric flask (5 mL) by diluting standard stock solutions with acetonitrile. Standard calibration solutions (2,10,20,50,100,200, 500, 1000 mg/L) were prepared by adding appropriate volumes of standard working solution and acetonitrile to obtain final volume 1000 μl. Calibration standard solutions were prepared in amber glass HPLC vials (1.8 mL) covered with PTFE/silicone septa.…”

“…In the SCR process reducing agents are injected into flue gases to convert the harmful compounds (nitrogen oxides) into nitrogen and water and thus reducing hazardous substances in exhaust gases. Therefore substantial research, testing and development of SCR systems and technologies have recently been performed . Braun et al provided an overview of the technical solutions to eliminate nitrogen oxides in exhaust gases.…”

Investigations on the Liquid‐Phase Decomposition of AdBlue Urea for the Selective Catalytic Reduction Process

“…In case of stoichiometrically operated engines such as gasoline engines, nitrogen oxides can be eliminated effectively by the three‐way catalyst. The high share of oxygen in lean burn engines, such as diesel engines, makes chemical reduction of NO x via exhaust aftertreatment much more complex , . For passenger car applications, two technologies for reduction of NO x have evolved over the last years: lean NO x trap (also: NO x storage catalyst) and selective catalytic reduction (SCR) .…”

“…In contrast, SCR systems with the external reducing agent AdBlue, also called diesel exhaust fluid (DEF), can be operated without influencing the engine operating point . Because of that, SCR systems are considered the method of choice for NO x reduction at lowest CO 2 emissions in future, not only in the field of heavy‐duty applications, but also in case of passenger cars , .…”

“…The SCR principle involves two fundamental steps. After injecting the external operating material AdBlue, an aqueous solution of 32.5 % urea, into the exhaust tract, in the first step, the urea contained in AdBlue gets decomposed by the exhaust‐water vapor in a two‐step thermo‐hydrolysis reaction , , : …”