title: Ammonia concentration distribution measurements in the exhaust of a heavy duty diesel engine based on limited data absorption tomography.
abstract: A multichannel tunable diode laser absorption spectrometer is used to measure absolute ammonia concentrations and their distributions in exhaust gas applications with intense CO2and 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 ppmVwith a temporal resolution of 1 Hz whereas, while operated as a single-channel sensor, these characteristics improved to 10 ppmVand 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.
authors.forename: Felix
authors.initials: F
authors.lastname: Stritzke
authors.forename: Sani
authors.initials: S
authors.lastname: van der Kley
authors.forename: Alexander
authors.initials: A
authors.lastname: Feiling
authors.forename: Andreas
authors.initials: A
authors.lastname: Dreizler
authors.forename: Steven
authors.initials: S
authors.lastname: Wagner