H2O absorption tomography in a diesel aftertreatment system using a polymer film for optical access

Film-optical-access H 2 O absorption tomography is, for the first time, applied to a practical diesel aftertreatment system. A single rotation stage and a single translation stage are used to move a single laser beam to obtain each of the 3480 line-of-sight measurements used in the tomographic reconstruction. It takes 1 h to acquire one image in a 60-view-angle measurement. H 2 O images are acquired in a 292.4-mm-diameter selective catalytic reduction (SCR) can with a 5-mm spatial resolution at temperatures in the 158–185 °C range. When no liquid H 2 O is injected into the gas, the L1 norm-based uniformity index is 0.994, and the average mole fraction error is − 6% based on a separate FTIR measurement. When liquid water is injected through the reductant dosing system designed to inject diesel exhaust fluid, nonuniformity is observed, as evidenced by measured uniformity indices for H 2 O in the 0.977–0.986 range. A mixing plate installed into the system is able to improve the uniformity of the H 2 O mole fraction.