Performance Simulation Research On Switching Process Of Sequential Turbocharging System Of Diesel Engine

Sequential turbocharging technology can improve the matching problem between diesel engine and turbocharger,improve the fuel economy at low working conditions,and expand the efficient operation range of diesel engine.However,in the switching process of sequential turbocharging system,there will be speed fluctuation,compressor surge,and in-cylinder combustion deterioration.With the continuous improvement of the emission standard of diesel engine,the emission problem in the switching process of sequential turbocharging has attracted attention.In this paper,a certain type of sequential turbocharging system of diesel engine is taken as the research object,and the switching process of sequential turbocharging is studied to obtain a better control strategy.Through three-dimensional simulation,the combustion emission law in the switching process of sequential turbocharging is obtained.Details are as follows :Firstly,the sequential turbocharging model of diesel engine is established,and the accuracy of the sequential turbocharging system model is verified by comparing with the experimental data.Based on the principle of optimal fuel consumption rate,the cut-in working point of the controlled turbocharger is determined to be 1429 r/min.In order to prevent repeated switching,the cut-out working point of the controlled turbocharger is determined to be 1385 r/min.A transient switching simulation platform for sequential pressurization is established to study the influence of the delay time of the air valve,the response process of the air valve and the gas valve,and the response time on the cut-in and cut-out process of sequential pressurization.Combined with the parameters such as speed fluctuation,fuel consumption and surge margin,the control strategy of the air valve and the gas valve of the controlled turbocharger is finally determined.Secondly,in the process of sequential turbocharging switching,the classical PID is usually used to adjust the relationship between speed and fuel injection.Due to the limitations of the classical PID,a double-layer fuzzy adaptive PID is proposed in this paper.The fuzzy PID control module is established to study the influence on the sequential turbocharging switching process.The results show that the double-layer fuzzy PID has small overshoot and fast response time,which makes the sequential turbocharging switching process more stable.Finally,a three-dimensional combustion chamber model was established for model verification,and the combustion characteristics of the sequential pressurization cut-in process were analyzed.The results show that in the process of sequential pressurization,compared with the post-switching(2TC),the velocity field before switching(1TC)has obvious velocity vortex,which is more conducive to fuel atomization and sufficient combustion.The combustion characteristics at the speed trough and the peak were analyzed for different switching delays.Combined with soot emissions and NOx emissions,it was concluded that 0.8 s switching delay was better.The combustion emission analysis of the switching process between the classical PID and the double-layer fuzzy PID shows that at the peak of the rotational speed,the double-layer fuzzy adaptive PID reduces the emissions of soot and NOx in the switching process of sequential pressurization by adjusting the control parameters.