Design And Study Of The SCR Embedded Control System For High-power Low Speed Diesel Engine

With the high-speed development of maritime transportation,the problem of marine diesel engine exhaust emission pollution is becoming more and more serious and Tier III standard will be enforced since 2016,which is intended to reduce the pollution.So the selective catalytic reduction technology as the most economic and efficient exhaust after-treatment technology has become a hot study topic among the national research institutions and the marine diesel engine manufacturers.According to the characteristics of the marine diesel engine SCR system,this paper adopts the idea of module design for the high power diesel engine in the design of the embedded control system of SCR.The main points of the study are as follows:Firstly,based on the law of conservation of catalysts,the SCR catalytic converter internal chemical reaction is analyzed and the process of the SCR system with the differential equation of dynamic response is built.Furthermore,promote a simplified mathematical model of the SCR system.Secondly,after extensive investigation and study in relevant design data home and abroad,put forward the general principle of design of the embedded control system of marine diesel engine SCR system.And by taking SCR system of low-speed marine diesel engine as the control object,carry on the design of hardware and software for the system.Moreover accomplish the hardware system of embedded control system of SCR.Thirdly,with the comprehensive analysis of the control strategy for SCR system both at home and abroad,an open loop feedforward control and closed loop model predictive control strategy are developed for the amount of reducing agent spraying in marine diesel engine..A reductant amount feedforward controller is developed which utilizes the upstream NOx emission of the catalyst to calibrate the downstream ammonia concentration and calculate the amount of needed reduction.A closed loop model predictive controller is developed to improve control accuracy and robustness performance of the system.Through real-time monitoring parameters of the engine and on-line optimization,the controller contributes to less NH₃ slip.Finally,simulation results show that the average NOx conversion efficiency of the two controllers is about 80%,but compared with feedforward control,the average and the peak of ammonia slip of the adaptive control can decrease 25ppm and 40ppm respectively.Apparently,the closed-loop model predictive control can effectively reduce the ammonia slip without affecting the NOx conversion efficiency.