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 ppm_V with a temporal resolution of 1 Hz whereas, while operated as a single-channel sensor, these characteristics improved to 10 ppm_V 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.

No abstract

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.

Chemical species tomography enables non-invasive measurements of temperatures andconcentrations in gas phase processes. In this work, we demonstrate the recently introducedlinear hyperspectral absorption tomography (LHAT) on an axisymmetric counterflow burner usedfor speciation studies of Oxyfuel combustion. As LHAT reconstructs spectrally resolved localabsorption coefficient spectra, the physical plausibility of these reconstructed spectra degradeswith an over-regularization of the tomographic problem. As presented in this work, this behaviorcan be employed in a novel regularization parameter choice method based on the residuals of localspectroscopic fits to the reconstructed spectra. After determining the regularization parameter,the reconstructions of the temperature and water mole fraction profiles of different flames arecompared to numerical simulations, showing a good agreement.

In this work, wavelengths were determined for the robust and simultaneous measurement of film thickness, urea concentration and fluid temperature. Film parameters such as film thickness, film temperature and the composition of the film are typically dynamically and interdependently changing. To gain knowledge of these quantities, a measurement method is required that offers a high temporal resolution while being non-intrusive so as to not disturb the film as well as the process conditions. We propose the extension of the FMLAS method, which was previously validated for the film thickness measurement of thin liquid films, to determine temperatures and concentrations using an adapted evaluation approach.