| Under the background of that two-stage turbo system can be used to improve the plateau adaptability of turbocharging diesel engine, carried out the researches of matching, regulated method at steady-state condition and control strategy at transient loading condition for twostage turbo system of diesel working at different altitude.The simulation model of the regulated two-stage turbocharging diesel engine at different altitudes(0m and 4.5km) were set up, based on calibrated original diesel engine model. A regulated two-stage turbocharging system was matched for a 6V diesel engine for the purposes of improving its performance at plateau,as well as solving the problems of turbo surge, overspeed and overheat of exhaust when diesel engine running at high altitude(4.5km).The maximal torque and rate power at 4.5km are improved by 20% and 17.7% compared to the value of original, recovered to 98.7% and 93.5% of plain level, respectively. And the BSFC at above two conditions are decreased by 3% and 4% respectively.The influence rule of bypass flow rate of high-pressure stage turbine on performance parameters of diesel and turbo system at different altitudes(0m and 4.5km) were investigated. And the influence mechanism of bypass flow rate of high-pressure stage turbine on fuel economy was carried out, IMEPg and PMEP are key factors which seriously affect the BSFC when adjust the bypass flow rate of high-pressure stage turbine. Meanwhile, the influence rule of altitude on IMEPg and PMEP was illuminated, which could be used to explain the influence mechanism of altitude on BSFC of diesel engine. The economic regulated law and reliability regulated law of the turbo system at different altitudes(0m and 4.5km) were obtained through the optimization of bypass flow rate. The range of economic regulated law were wider than reliability regulated law, and it could observably reduce the BSFC within its regulated area compared with reliability regulated law. At 4.5km, the range of economic regulated law is narrower than it at 0m. In addition, at medium and high load, the BSFC is higher than it at 0m; however, at low load, the BSFC is lower than it at 0m.The control strategies of turbo system and fuel supply system at transient loading conditions at different altitude are investigated. The strategy that delaying the closing of compressor bypass valve has been used to avoid the phenomenon that the fluctuations of torque and inlet pressure in the transient loading conditions. closed-loop control has been applied to turbo bypass valve, with which the response time of torque is shortened by 1s at 0m1900r/min,and 1.4s at 4.5km1900r/min compared to open-loop control. The impact low of injection delay on response time of torque has been studied. Obtained the injection delay angle of design conditions through calibration. With 10°CA injection delay at 4.5km1000r/min, the response time of torque could be shortened by 2.4s. Finally, established the transient control model, and coupling it with engine performance simulation model. Compared the transient response characters of two-stage turbo diesel at different altitude, and the influence law of speed and altitude on response time of key parameters has been investigated. |
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