Design And Matching Of Regulated Two-stage Turbocharging System For V6 Diesel Engine

Compared to single-stage turbocharger,the two-stage turbocharging system has higher boost pressure and wide flow range,which means that the diesel engine has better performance,i.e.high power ratio,low fuel consumption and low emission.In recent years,two-stage turbocharging system is becoming more and more widely used.This thesis presents the design process of a two-stage turbocharging system for a V6 diesel engine.The main contents of this thesis are design and matching of a regulated two-stage turbocharging system,the performance simulation of diesel engine at plain and plateau,the matching strategy for enhancing diesel engine performance at low speed range at high altitude.The regulated two-stage turbocharging system is made up of two turbochargers in a sequential way.There is a regulated valve between high-pressure turbine and low-pressure turbine,which is used to avoid overboost.After the design parameters of the turbocharging system were determined,JP76 N and J91 compressor was selected as high-pressure and lowpressure compressor respectively.Two turbine flow characteristic curves were constructed based on the design parameters.Based on the simulation model of the single-cylinder engine,the model of V6 diesel engine matched with the regulated two-stage turbocharging system was set up.Firstly the engine performance simulation at plain was carried out to determine the optimal fuel supply parameters and the regulated valve opening.The simulation results show that the engine performance can meet the design requirements and the designed two-stage turbocharging system has a high overall efficiency and a good match with the engine.The engine performance simulation results at 4500 meter altitude show that when the regulated valve is close and the fuel injection parameters are adjusted,the engine can have a good power recovery.The power can reach 98% at maximum torque point compared that at plain and 86.3% at rated point.But since the overall pressure ratio and mass flow rate decrease significantly at low-speed range,the engine will face the problem of start and acceleration due to the low torque.In orde to improve the engine power output at low speed range at high altitude,changing high-pressure turbine to variable geometry turbine which can increase the boost pressure,is present in this thesis.The simulation results show that through this method the engine power output can be increased to reach 91.3% and 72.5% respectively under 1300r/min and 1100r/min at 4500 meter altitude.