Performance Analysis And Optimization Study Based On VGT Technology For Passenger Car Diesel Engine

As fossil fuel conservation and emission reduction becomes increasinglyprominent, diesel engine has gradually become one of the main choices of thepassenger car powertrain. As the key technologies of contemporary passenger cardiesel engine, Variable geometry turbocharger (VGT) and Exhaust gas recirculation(EGR) have been drawn more and more attentions from major auto OEMs andresearch institutions. Being one of the most important tools of engine performancecycle simulation, GT-Power plays an important role in the field of design parameteroptimization and engine performance development.Therefore, based on the National High Technology Research and DevelopmentProgram [2008AA11A116], GT-Power is utilized to match and optimize VGT andEGR to the diesel engine in this study, aimed to provide optimized maps to easeengine bench calibration tests, as well as to provide guidelines for engine EMScontrol strategy development.The main research work and innovations are expressedas follows:1) Working process of a diesel is described using mathematical equations, thesimulation kernel is discussed in theory. On this basis, the GT-Power simulationmodel is built and calibrated against experimental data. This lays the foundation andassures the validity for the subsequent simulation.Then, the theory and evaluationsystem of diesel and turbocharger matching is analyzed, guiding the selection andmatching of the turbocharger. Comparing the matching results of differentturbochargers, a more suitable turbcharger is chosen for subsequent detailedcalculations.2) The superiorities of a VGT turb over a conventional waste-gated turbochargeris analysed in theory. The changes of performance caused by VGT are simulated andanalysed under different operating conditions without EGR. Choosing the boostpressure as the response and the VGT rack position as the actuator, a PID controlmodel aiming the full load power target is set up. Based on this model, the best VGTrack positions are found in different speed operating conditions.3) Fixing the VGT rack position, the simulation of different EGR rate at differentloads of2500r/min is taken.The changes of intake conditions and diesel engineperformance associated with the introduction of high-pressure EGR are analysed. And the requirement to the VGT rack position is also proposed. Then, a DOE simulationscheme with the two parameters of VGT rack positions and EGR rates varying thesame time is built at the selected conditions, in order to research the inter-effect onengine performance by the two. Using DOE post-processing tools, selecting theappropriate optimization strategy, the best VGT Rack and EGR rate are found at theselected condition. Using this method, the optimization is extended to the entire dieselengine operating range to get the MAPs of them.