船舶柴油机SCR系统尿素喷射控制仿真

Simulation of Urea Injection Control for SCR System of Marine Diesel Engine

选择性催化还原技术是一种柴油机尾气排放后处理技术。针对船舶柴油机SCR系统非线性、难以建模与控制的特点,分析系统内部的化学反应,根据能量和质量守恒确定各状态量满足的微分方程,建立SCR系统数学模型,并验证其特性。为了实现SCR系统的控制目标,即在保证NH3逃逸量不超过限定值的前提下,尽可能提高NOX转化率,以NH3逃逸量为约束输出,NOX出口浓度为控制输出,氨喷射量为控制变量,设计了非线性模型预测控制器,实时计算系统所需尿素喷射量。试验仿真表明了非线性模型预测控制器的有效性,稳态工况和瞬态工况下NOX转化率分别达到了93.803%和91.760%,NH3逃逸量均低于10 ppm,满足TierⅢ标准对船舶柴油机尾气氮氧化物排放的限制。

Selective catalytic reduction is a kind of diesel engine exhaust after-treatment technology.In view of that characteristic of the vessel diesel SCR system nonlinear,which is difficult to model and control,the chemical reaction inside the system is analyzed.According to the conservation of energy and mass,the differential equation of each state quantity is determined,the mathematical model of SCR system is established,and its characteristics are verified.In order to achieve the control objective of the SCR system,on the premise of ensuring that the amount of NH3 escaping does not exceed the limit value,the NOX conversion rate should be increased as much as possible.The NH3 escape amount is taken as the constrained output,the NOX outlet concentration as the control output,and the ammonia injection amount as the control variable,a nonlinear model prediction controller is designed to calculate the amount of urea injection required by the system in real time.Experimental simulation shows the effectiveness of the nonlinear model predictive controller for SCR system.Under the steady-state condition and transient condition,the NOX conversion rate reaches 93.803%and 91.760%respectively,and the NH3 escape amount is lower than 10 ppm,which meets the TierⅢstandard’s limit on nitrogen oxide emissions from marine diesel exhaust.