Influences of a variable nozzle turbocharger on the combustion and emissions of a light-duty diesel engine at different altitudes

Abstract

With social and economic developments, more light-duty vehicles are operating at high altitudes, but the reduced intake air flow in plateau areas, leads to poorer engine combustion and greater emissions. An effective means of improving plateau adaptability are light-duty diesel engines employing variable nozzle turbochargers (VNTs), but the research to date on how VNTs influence the combustion and emissions of diesel engines at high altitudes has lacked both depth and a systematic approach. Therefore, in the present research, experiments were conducted to investigate the influences of a VNT on the combustion and emissions of a light-duty diesel engine at different altitudes (0 m, 1000 m, and 2000 m) by using a plateau-environment simulation device. Also, the influences of altitude and VNT nozzle opening on the in-cylinder working process and pollutant generation were studied by means of three-dimensional numerical simulations. The results show that the VNT had almost the same ability to enhance the intake air flow at different altitudes within the same range of VNT nozzle opening, and the effect of increasing altitude on diesel engine performance was similar to that of increasing VNT nozzle opening. With increasing altitude or VNT nozzle opening, the spray penetration length increased, the in-cylinder equivalence-ratio distribution became less even, the start of combustion was delayed slightly, the combustion duration was extended, and the in-cylinder mean temperature increased. With increasing altitude or VNT nozzle opening, the emission of NOx decreased gradually, while those of CO, HC, and soot increased. Compared with the case at sea level, the influence of VNT nozzle opening on CO, HC, and soot emissions was more significant in plateau areas.