Experimental Investigation of Mixer Plate Temperature and Wall Impingement Regimes in Selective Catalytic Reduction Systems

Selective Catalytic Reduction (SCR) is a technique based on urea-water solution (uws) to reduce nitrogen oxides (NOx) emitted from diesel engines. In this work, experimental investigation on injection of water and uws spray interaction with a hot mixer plate in exhaust gas test bench is presented. The work was performed with a commercial six-hole pressure-driven injector dosing into a flow channel emulating typical diesel exhaust flow conditions. Kinetic properties of the droplets were studied using Phase Doppler Anemometry (PDA) measuring the droplet sizes and velocities prior to the wall impingement. Based on these, characterization of the influence of gas velocity, fluid flow rate and change of spray fluid from water to uws was deduced. A decrease in the spray cooling effect was observed when the gas velocity was increased due to increased interaction of the droplets with the gas flow before impingement. An increase in the gas velocity results in higher wall temperatures and a higher spray mass flow shifts the spray/wall interaction regime towards deposition for smaller droplets. The breakup regimes are seen to shift from rebound and thermal breakup to deposition and splash on reaching a steady state wall temperature.