Abstract
Tomographic measurements of ammonia concentration in diesel engine exhaust dosed with diesel exhaust fluid are demonstrated through spatial scanning of a 10.4 mu m quantum cascade laser beam. Optical access through the exhaust pipe was facilitated by a polyimide film. The laser beam was translated in 0.5 cm increments and rotated in 6 degree angular increments, resulting in 2130 unique laser beam positions per experiment. The data was then used to reconstruct ammonia concentration images through an inverse Radon transform. The laser was driven by a current ramp at 200 Hz and phase-locked with the doser. Data were collected for a duration of 500 ms at each laser beam position. Each laser current ramp was used to create one image, resulting in a total of 100 images per experiment. The images were compiled into a 500 ms-duration video showing the evolution of the phase-averaged ammonia concentration field, assuming a repeatable periodic concentration field with respect to each doser pulse. The experiments were performed for the exhaust temperature range of 453-574 K, nominal pipe diameters of 28 cm and 33 cm, and for different mixers to observe the ammonia concentration distribution upstream of an SCR catalyst. The spatially averaged ammonia concentration was within 10% of average values simultaneously obtained from an FTIR system.