| The rapid development of the vehicle industry has brought a great deal of convenience for people’s life. However, the environment pollution resulted from the vehicle emissions is becoming an increasingly serious problem. Lowering the particle emissions and achieving the high pressure ratio have become indispensable methods to improve diesel engine’s performance. The two-stage turbocharging technology, with the advantages of high pressure ratio, flexible adjustments and the wide application conditions, has been gradually focused. After matching the two-stage turbocharger, its air input will get significantly increased, and the fuel consumption and the particle emissions will be reduced significantly. For the two-stage turbocharging, EGR can suppress NOx generations. Through control between EGR and the injection strategies, the diesel engine can achieve the goal of low fuel consumption and emissions.This paper was based on a vehicle heavy-duty diesel engine. The two-stage turbocharging test bench and simulation model were built in paper. Firstly, the opening strategies of by-pass were established under different conditions. Results turned out that the by-pass valve need not to open in low speed. But it should open linear with load increase under high speed. Then the effect of inter-cooler was studied, results turned out that reducing inter-stage temperature can increase intake air. The fuel consumption and NOx emission decreased corresponding. Then the cooling temperature was optimized under different conditions. The research of EGR and injection strategies was based on above. The results turned out that pilot injection can improve the trade-off relation between NOx and soot. To ensure the fuel consumption, the quantity of pilot injection was controlled within 10%. The time of main injection mainly influenced engine’s performance, so it should be reasonably controlled to ensure CA50 in a proper range. EGR coupled with proper injection strategies can decrease engine’s fuel consumption and NOx emissions, and the range of low fuel consumption and emissions can be broadened.To study the effect of combustion system parameters on two-stage turbocharging engine, three-dimensional simulation software AVL-Fire was used in paper. The in-cylinder flow field was studied after building different combustion chamber. The results turned out that decreasing compression ratio can reduce the max firing pressure and temperature, NO emissions decrease while soot emissions increase. When EGR was introduced in, the trade-off relation between NOx and soot can be improved when the reentrant combustion chamber was used. At last, the post injection strategies were studied. The results turned out that post injection can reduce NO and soot emissions at the same time. So the 20% post injection and 4—8°CA interval were the final optimized results.Finally, experiments were conducted to verify the simulation results. The results showed that the lift of high pressure stage turbine by-pass valve influenced the distribution of pressure ratio. There exits best pressure ratio distribution coefficient that improves engine’s performance in different conditions. Reducing inter-stage intake air temperature can further increase intake air and fuel consumption and NOx emission decrease. Little pilot injection coupled with main-injection timing delayed can reduce original engine emissions. Catalytic DPF can reduce the NOx、CO、HC and smoke emission. The particle emissions are mainly nuclear particles. With the increase of EGR ratio, accumulated particles gradually increased in the proportion of exhaust particles. All modes particles decreased significantly when particles trapped by DPF. DPF fractional efficiency on number of nuclear particles remains high level at different EGR rates. |
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