Research On Control Strategy Of Two-stage Sequential Supercharging System Of Marine Diesel Engine

Exhaust gas turbocharging technology is the most common measure to improve the performance of diesel engines.After turbocharging technology is used,the intake pressure can be greatly increased,the excess air coefficient in the cylinder,and the economy and emissions can be improved.However,due to the different working methods,the diesel engine and the supercharging system cannot be matched efficiently and stably under all working conditions,and the successive supercharging technology can solve this problem well.Based on a certain type of marine diesel engine,this paper combines two-stage supercharging technology while adopting sequential supercharging technology to further increase the intake pressure.Through simulation research,the control strategy of steady-state process and transient process is determined.The details are as follows:(1)GT-power is used to establish a one-dimensional simulation model of the original engine(single-stage successively supercharged diesel engine),and through simulation calculations under different working conditions,the calculated values are compared with the experimental values to complete the calibration of the model.And based on the original engine simulation model,a one-dimensional simulation model of a two-stage successive supercharged diesel engine was further established.(2)Through the calculation of load characteristics,the operating area of 1TC and 2TC modes,the universal characteristic curve of effective fuel consumption rate and the economic switching boundary line are determined,and the optimal switching point speed on the propulsion characteristic curve is determined.For the problems of low air-fuel ratio and high exhaust temperature before the vortex under certain working conditions,the intake and exhaust bypass system is used to solve the problem.The optimal diameter of the intake and exhaust bypass pipe is determined through simulation calculation,and the comparison is analyzed.The changes of the operating area before and after the bypass are analyzed,and the control strategy of the intake and exhaust bypass valve is determined through calculation.For the problem of excessive exhaust back pressure and excessive pumping loss in 1TC mode,a high-pressure turbine bypass valve is used to solve the problem.Through simulation calculation,the adjustment characteristics of the butterfly valve are discussed,the variation law of diesel engine parameters with the opening of the bypass valve is analyzed,and the control strategy of the high-pressure turbine bypass valve is determined.(3)A coupled simulation platform was established using MATLAB/Simulink software,and the optimal switching delay time of the air valve during the upward switching process and the optimal switching point speed of the downward switching process were determined through the coupled simulation calculation.A fuel injection timing variation algorithm is designed to optimize the switching process and determine the best gain value for the switching process.For the rapid acceleration process,the optimal switching point speed is determined,and by comparing with the original engine,the optimization effect of the two-stage sequential supercharging system on the diesel engine’s rapid acceleration performance is analyzed.⑷Analyzed the influence of the environmental temperature change on the performance of the two-stage successive diesel engine,calculated and determined the fitting curve of the switching point speed with the environmental temperature change.In order to solve the problem that the maximum burst pressure easily exceeds the limit value when the ambient temperature is low,a bleed valve is introduced for the booster system,the appropriate diameter of the bleed valve is determined through simulation calculation,and the bleed valve at different ambient temperatures is finally determined Control strategy.