Based on a high-pressure common rail heavy-duty diesel engine

a one-dimensional thermodynamic simulation model was built. Firstly

the effects of single-stage turbocharger(1TC) and two-stage turbocharger(2TC) on the operational characteristics of diesel engine under variable altitudes were compared. Afterward

the high-pressure stage of 2TC was replaced with a variable geometry turbocharger to investigate the effects of the blade opening on the performance of the diesel engine at an altitude of 4km. The results show that compared with 1TC

2TC can further improve the adaptability of diesel engine to altitude changes

especially in low speed conditions. In low speed conditions

the regulated two stage turbocharger system diesel engine has a maximum torque

highest effective thermal efficiency and lowest break specific fuel consumption(BSFC) when the blade opening were between 40% and 70%. As the speed increases

enlarging the blade opening can reduce the exhaust back pressure and residual exhaust gas in the cylinders

increase the efficiency of the turbocharger

and decrease NOx emissions and BSFC. At low speed conditions

the heat transfer loss rate decreases firstly and then increases with the increase of the blade opening. At medium and high speed conditions

the heat transfer loss rate decreases with the increase of the blade opening.