In order to study the effects of variable nozzle turbocharger(VNT)

exhaust gas recirculation(EGR) and atmospheric pressure on the performance and emissions of a vehicle diesel engine

a relevant test was conducted by using an atmospheric pressure simulation device. Based on response surface methodology

the influence of the interaction effect of VNT nozzle opening

EGR valve opening and atmospheric pressure on the engine performance and emissions was studied and analyzed. The results show that with the decrease of atmospheric pressure and the increase of EGR valve opening

the engine output power declines and the fuel economy deteriorates. When VNT is combined with EGR and the EGR valve is closed or has a small opening

the torque increases and the brake specific fuel consumption decreases gradually at peak torque condition as the VNT nozzle opening decreases; while the torque comes down and BSFC goes up at the same condition with the decrease of VNT nozzle opening when the EGR valve has a large opening or full opening. However

no matter what the EGR opening may be at the rated power condition

the torque increases and BSFC declines as the VNT opening decreases. As the atmospheric pressure goes up

the brake specific nitrogen oxides(NOx) emissions increase and smoke decreases. When VNT is combined with EGR

the power

brake specific NOx emissions and smoke demonstrate different trends at different operation conditions. In order to obtain a good overall engine performance

it is necessary to match VNT nozzle opening with EGR valve opening properly according to different operation conditions.