| As supplement Ⅵ MARPOL convention in Tier Ⅲ emission control standards,the implementation of the international maritime bureau,forcibly launched Tier Ⅲemissions standards,since 2016 for implementation.Compared with Tier Ⅱ emissions standards,Tier Ⅲ emission regulations in NOx emissions reduce by 75%.Now today only internal purification technology has been unable to meet the Tier Ⅲ limit of NOx emission regulations.Currently in-use non-electronic marine diesel engines for reaching Tier Ⅲ standards,which are still running,must add additional closed purification technology to meet the requirements of the law.At present,among the various off-machine purification technology solutions,selective catalytic reduction(SCR)technology is the most suitable for the transformation of ship after-treatment technology,which can effectively reduce the NOx emission by 80%to 98%.This paper studies the SCR control system of Marine diesel engine,and develops a set of intelligent ship SCR system,whose control strategies mainly include the state control strategy and the urea injection control strategy.The key to ship SCR system control is the urea injection control strategy.Taking the diesel engine of Yueguang Ship 801 as an example,Establish control system in Matlab/Simulink software,design a set of urea injection system,and its rationality are verified through the simulation test,and Finally passed the test of the actual vessel emissions verification to the Tier Ⅲstandards..The main content of research are as follows:Firstly,the working principle of SCR system is described.SCR is a selective catalytic reduction reaction,which uses ammonia gas(NH3)to reduce nitrogen oxides(NOx).Under the action of SCR catalyst,NOx in diesel engine exhaust can be reduced to nitrogen(N2)and water(H2O)without pollution to the atmosphere.Secondly,according to the Tier Ⅲ emission control standards and The Selective Catalytic Reduction(SCR)System of Approval And Inspection Guide determine the SCR electric control system design objectives,overall design for electric control system and component selection.Thirdly,according to the exhaust volume of the main engine of the Marine diesel engine emission reduction system,it is divided into several waste gas after-treatment branches.each waste gas after-treatment branch is equipped with a set of urea injection control unit.According to the overall modular design scheme of the emission reduction system,the emission reduction control system designs independent urea injection control unit with a single waste gas after-treatment branch,and the whole ship is configured with a master controller,forming a topology structure.Then,the control strategy of SCR system is designed,which mainly includes state control strategy and urea injection control strategy.The urea injection control strategy is mainly to calculate the amount of urea that should be injected into the exhaust pipe under different diesel engine conditions.It mainly includes two sub-modules,which are basic urea demand calculation module and feed-forward correction module.Then the simulation test was carried out on Simulink,and the results showed that the simulated NOx conversion efficiency was basically the same as the target conversion efficiency,and the simulated NOx conversion efficiency was higher than 90%under the four loads of 25%,50%,75%and 100%,indicating that the system design could achieve the goal.Finally,the emission tests of left and right diesel engines of Yueguang Ship 801 were carried out under four stable load conditions of 25%,50%,75%and 100%respectively.During the experiment,the system can run normally and continuously,Port and starboard host comprehensive NOx conversion rate were higher than IMO Tier Ⅲ standards required by 85%,shows that the design of the system of SCR system can satisfy the emissions of two hosts IMO Tier Ⅲ standards. |
