Simultaneous two cross-sectional measurements of NH3 concentration in bend pipe flow using CT-tunable diode laser absorption spectroscopy

Urea Selective Catalytic Reduction (urea SCR) system is widely used for diesel engine to reduce the emission of NO_x by NH₃ which is provided by a hydrolysis of urea water. Concentration distribution of NH₃ in an exhaust pipe is an important factor for improvement of the SCR efficiency and prevention of NH₃ slip and urea deposit. Therefore it is necessary to measure two-dimensional (2D) concentration of NH₃ in detail. The purpose of this study is to develop the real-time two cross-sectional measurements technology of NH₃ concentration using the computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS). This method was employed in a bend pipe model demonstrated a urea SCR system. The experimental results of two cross-sectional 2D concentration of NH₃ show differences of the concentration distribution of NH₃ each cross-section and flow pattern like swirl flow. These results were compared to calculated results using computational fluid dynamics (CFD) and the experimental results of NH₃ flow characteristics are agree very well with the calculated results. It was found that CT-TDLAS was an effective method to measure concentration distribution of NH₃ and observe characteristics of flow.