Urea Selective Catalytic Reduction (urea SCR) system is widely used for diesel engine to reduce the emission of NO x by NH 3 which is provided by a hydrolysis of urea water. Concentration distribution of NH 3 in an exhaust pipe is an important factor for improvement of the SCR efficiency and prevention of NH 3 slip and urea deposit. Therefore, it is necessary to measure two-dimensional (2D) concentration of NH 3 in detail. The purpose of this study is to develop the real-time two cross-sectional measurements technology of NH 3 concentration using the computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS). Theoretical NH 3 concentration distribution which was reconstructed by CT agreed to CFD results and quadruple pipe's results showed good resolution by 14th order reconstruction. Therefore, this method has enough resolution and accuracy for measuring the concentration distribution of NH 3. And this method was employed in a bent pipe model demonstrated a urea SCR system. The experimental results of two cross-sectional 2D concentration of NH 3 show differences of the concentration distribution of NH 3 each cross-section and flow pattern like swirl flow. It was found that CT-TDLAS was an effective method to measure concentration distribution of NH 3 and observe characteristics of flow. In addition, observing flow pattern enable to validate CFD results, and it helps to improve efficiency of after treatment system.

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