Study And Design Of SCR Control System For Marine Diesel Engine

The NO_x emission of Marine diesel engine and the related health hazards problems to the environment have become a serious global problem.With the stringent IMO Tier III emission regulations being implemented,NO_x emission control technologies are becoming hot research areas.Selective catalytic reduction(SCR)systems utilizing urea as a reducing agent are one of the most promising means of meeting the new stringent diesel emissions standards.When compared to other reduction methods,SCR gets special attention for its advantages such as substantial NO_x reduction and wider operational temperature range,in the context of energy saving and emission reduction.In our research,an marine SCR control system is verified by the experiment and the results accord with the anticipative control aim.Based on the marine SCR system research of predecessors,we studies the SCR control system principle and how to calculate urea solution theoretical injection quantities,and the research result shows that the closed loop control strategy have good control effect through GT-power coupled with the Simulink simulation research.Based on the Scheme design of SCR control system and requirement analysis,Siemens PLC is chosen as a hardware control platform,and the related key signals of circuit design such as NO_x concentration,speed and blowing control are completed.With the hardware platform,we develop the software under the guide of modular design thought.Combining the features of marine SCR system we design the operation control logic and urea injection strategy.We analysis the design methods of NO_x concentration signal processing,speed signal processing,soot blowing control,and develop the SCR monitoring control surface.Finally we carry out the SCR control system for functional testing,including control system communication function between urea supply control system and the SCR control system and blowing control system function.The results show that SCR system has normal function and can be applied to practical system.Through SCR experiment we conducted the effect of control strategies for NO_x conversion efficiency and ammonia leakage.The results showe that NO_x conversion efficiency of open loop strategy reach to 83.8%,and closed loop efficiency of 85%.It is found that NO_x conversion efficiency of closed loop control strategy has good stability under transient operating conditions from the analysis of comparative result.So it will be better than the open loop control strategy.