柴油机SCR系统气液两相流准一维数值模拟

Quasi One-Dimensional Numerical Simulation of Gas-Liquid Two Phase Flow in SCR System of Diesel Engine

对柴油机选择性催化还原(SCR)系统气液两相流进行了准一维建模,并开发了模拟计算程序.用欧拉方法求解气相流动,其中压力速度耦合问题采用Simple算法求解.用拉格朗日方法求解液滴的蒸发、热解、运动和碰壁等过程,气液两相耦合通过在气相方程中附加源项的方式实现.模拟计算结果表明:随着排气平均温度的升高和排气流量的降低,尿素分解效率都会逐渐升高;尿素水溶液喷射速率对尿素分解效率影响不大;总体上液滴初始直径的减小能够促进尿素的分解,在不产生壁膜的前提下,合理组织尿素水溶液喷雾碰壁,可以促进大直径喷雾(50,μm以上)的尿素分解;增大排气管直径能够显著提高尿素分解效率,降低压力损失,是优化SCR系统性能的有效方法.

A quasi one-dimensional model of gas-liquid two phase flow of SCR system was proposed. Gas phase flow was solved by the Euler method in which pressure-velocity coupling used the Simple algorithm. Evaporation, thermal decomposition, motion and wall interaction of droplets were solved by the Lagrange method. The interaction between two phases was considered by adding the source terms in gas phase equation. Simulation results show that higher exhaust temperature and lower exhaust mass flow result in higher urea decomposition efficiency. Meanwhile, ureawater-solution injection rate has little effect on urea decomposition efficiency. In general, the decrease of droplet initial diameter promotes the urea decomposition, and appropriate spray wall interaction is helpful to large droplet decomposition if no wall film formation appears. In addition, the increase of pipe diameter is an effective approach for improving the performance of SCR system since it not only enhances the urea decomposition efficiency significantly, but also reduces the pressure loss. © 2015, Chinese Society for Internal Combustion Engines. All right reserved.