Development On Urea Dosing Electric Control System Of SCR For Marine Diesel Engine

With the implementation of the IMO Tier III emission control standard in Annex VI of the MARPOL Convention,the internal purification technology of marine diesel engine has difficulty in meeting the needs of Tier III regulations about NO_x emissions.Selective Catalytic Reduction(SCR)technology is one of most effective measures to control NO_x emission from marine diesel engines.At the moment,the key technology of SCR system for marine diesel engine is in the hands of foreign companies,it is indispensable to develop high performance electrical control system of SCR with independent intellectual property rights.Therefore,the urea dosing electrical control system of SCR for marine diesel engine was developed in this dissertation,the primary research contents are presented as follows:Firstly,design objective was proposed based on the IMO Tier III emission control standard and the Guidelines for Approval and Survey of SCR Systems,the general scheme of SCR electric control system was presented and the components were selected.Secondly,according to the hardware functional requirements of SCR system,the electrical control unit of SCR system was integrated with PLC of S20M0T and HMI of HD102TC.The design of the power supply network,Modbus communication network and CAN communication network realised components connection to each other,which constituted a complete hardware system.Thirdly,the software architecture was designed based on the goal of electrical control system for SCR.With the Communication Setup Tool of Configuration Software,the underlying driver software which enable the communication of the hardware resources was designed.The upper application software was also designed using modularized design methods.These modularizations were used for fault diagnosis,look-up table mapping,calibration and so on.Fourthly,the open loop control strategy,closed-loop control strategy,feedforward correction model and transient correction model were established.The distribution of NO_x conversion rate was established based on the weighted NO_x rate emission.The logical control program of multiple control strategies unified control was designed,realized the package of upper application software,which constituted a complete software system.Finally,the performance test of SCR electrical control system was carried out in the diesel engine test bench.The results of error test for urea dosing pump indicated that the error of dosing pump increased with dosing volume,the designed program of error compensation improved the accuracy of dosing significantly.The urea dosing electrical control system of SCR was studied in the test bench,the results show that the SCR system applied the open-loop control strategy based on feedforward correcation,the weighted specific emissions of NOx in E3 and D2 test cycle are1.77 g/kWh and 1.73 g/kWh,respectively,the maximal specific emissions of NOx at every engine mode are 2.69 g/kWh and 2.73 g/kWh,the mean concentration of maximal ammonia slip are 0.9ppm and 1.5 ppm.The SCR system applied the closed-loop control strategy based on feedforward correcation,the weighted specific emissions of NOx in E3 and D2 test cycle are 1.91 g/kWh and2.00 g/kWh,respectively,the maximal specific emissions of NOx at every engine mode are 2.61g/kWh and 2.94 g/kWh,the mean concentration of maximal ammonia slip are 10 ppm and 6.0ppm.Therefore,the SCR system applied the open loop and closed loop respectively,the marine diesel engine equipped with the developed urea dosing electrical control system of SCR could satisfy the weighted specific emissions and specific emissions of Tier III for NOx emission regulation,and ammonia slip meet the regulation limit(10 ppm)requirements.Compared with the open-loop control strategy,the closed-loop control strategy could reduce the urea comsuption,in E3 and D2 test cycle the comsuption of urea decreased by 3.99%and 1.28%respectively,closed-loop control has a better economics.