Effects of operation conditions and suction pipeline parameters on flow characteristics and metering accuracy for selective catalytic reduction air-assisted urea dosing system

Selective catalytic reduction is the main technology to reduce oxides of nitrogen of diesel exhaust. As an important part of the selective catalytic reduction system, the air-assisted urea dosing system regulates the flow rate by adjusting the pump speed, and the flow rate and its metering accuracy directly affect the efficiency of oxides of nitrogen conversion. A mathematical model coupled with the air-assisted urea dosing system and the suction pipeline was built, and the influences of the discharge pressure, pump speed, suction pipeline length, and diameter on the flow characteristics and metering accuracy of the air-assisted urea dosing system were analyzed. The flow rate and metering accuracy of a prototype of the air-assisted urea dosing system were tested under different conditions on a test rig. Results show that the flow stability and metering accuracy of the prototype elevate with increasing the discharge pressure when the prototype has no overfeeding, and it gets down under any discharge pressure when the prototype occurs overfeeding. The flow stability and metering accuracy of the prototype improve with increasing the pump speed, and increase significantly when the suction pipeline length becomes shorter and the diameter gets larger. The metering accuracy of the prototype can achieve to ±2% by optimizing the suction pipeline parameters. The experimental results prove that the proposed mathematical model is effective.