Optically accessible generic exhaust gas test bench for the investigation of fundamental SCR-relevant processes.

In this work, a generic exhaust gas test bench is introduced on which reproducible experiments can be performed to gain a deeper understanding of processes during exhaust gas aftertreatment of internal combustion engines. We present the design and initial flow characterization as well as tomographic measurement results of gaseous water distributions. The aim of the development was to provide a generic geometry as well as highly reproducible process boundary conditions for numerical simulation of exhaust aftertreatment phenomena. The presented initial measurements are intended to demonstrate the qualification of the test bench for extensive experimental characterization ranging from measurements of the spray injection, film evaporation, and reaction kinetics to the highly complex multiphase flow conditions during selective catalytic reduction (SCR) processes, which are characterized by high mass flows and temperatures, pronounced transients, and a corrosive atmosphere.

Ammonia concentration distribution measurements in the exhaust of a heavy duty diesel engine based on limited data absorption tomography.

A multichannel tunable diode laser absorption spectrometer is used to measure absolute ammonia concentrations and their distributions in exhaust gas applications with intense CO2 and H2O background. Designed for in situ diagnostics in SCR after treatment systems with temperatures up to 800 K, the system employs a fiber coupled near-infrared distributed feedback diode laser. With the laser split into eight coplanar beams crossing the exhaust pipe, the sensor provides eight concentration measurements simultaneously. Three ammonia ro-vibrational transitions coinciding near 2200.5 nm with rather weak temperature dependency and negligible CO2/H2O interference were probed during the measurements. The line-of-sight averaged channel concentrations are transformed into 2-D ammonia distributions using limited data IR species tomography based on Tikhonov regularization. This spectrometer was successfully applied in the exhaust system of a 340 kW heavy duty diesel engine operated without oxidation catalyst or particulate filter. In this harsh environment the multi-channel sensor achieved single path ammonia detection limits of 25 to 80 ppmV with a temporal resolution of 1 Hz whereas, while operated as a single-channel sensor, these characteristics improved to 10 ppmV and 100 Hz. Spatial averaging of the reconstructed 2-D ammonia distributions shows good agreement to cross-sectional extractive measurements. In contrast to extractive methods more information about spatial inhomogeneities and transient operating conditions can be derived from the new spectrometer.