Research On Accurate Urea Injection Control Of SCR System In A Diesel Engine

Diesel engine is widely used in people's production and life for its good power and economy performance.But the high NO_X emission of diesel engine also brings serious environmental pollution.With the increasingly stringent emissions regulation,new technological routes must be adopted that combine in-cylinder purification and aftertreatment technologies.SCR technology has good fuel economy,good NOx purification effect,and little change in engine structure,which has become the main technology for reducing NOx emissions in China.In recent years,China has made great progress in SCR technology,but there is still a gap compared with foreign countries.SCR closed-loop system can achieve higher NO_X conversion rate,but as a key component of SCR closed-loop system,NO_X sensor has not been deeply studied in China.Therefore,the research on SCR system control software and NO_X sensor controller has theoretical significance and practical value.Based on the analysis of current SCR technology and control requirements of SCR system at home and abroad,the SCR system control software was designed for air-assisted SCR system,and the DCU and control software of the closed-loop SCR system were studied.In terms of application layer software,according to the SCR system control strategy,the SCR application layer software was designed,which mainly included the system state switching module that controls the working state of the SCR system,and the information acquisition module used for acquiring signals of engine ECU signal and each sensor signal.The urea amount calculation module was also included,which was used to determine the injection amount of urea.The task execution module that drives the various components of the SCR system was designed.According to the working principle of NOx sensor,the temperature control module was designed.The PID heating control strategy was adopted,and the temperature of the NOx sensor was controlled at 800°C.The signal processing module was used to collect and process the current and voltage signals of various parts of the NOx sensor ceramic chip,and to control the entire working process of the NOx sensor.For the requirements of SCR system and NOx sensor,underlying driver toolkit was developed and target system was configured.The file was compiled which guided the procedure of automatic code generation.After the application layer software was built,the automatic code was generated directly and the process of system software development was simplified.The SCR system control software was tested separately for each bottom module and the system state switching module was also tested,and the simulation test bench was built to verify the function of the software as a whole.Test results showed that each underlying module can realize its basic functions,and the system state switching module can accurately switch the system state.The overall software in the simulation bench test can accurately control the system working process.A preliminary calibration test are performed on the NOx sensor by importing the generated code into the NOx sensor controller hardware.Test results showed that the measured current had a good linear relationship with the NOx concentration.The controller can realize the NO_X sensor to accurately measure the nitrogen and oxygen concentration.