Experimental Research On The Fuel Consumption In GDI Engine Matching With VVT And Turbocharger

In order to meet the increasing requirements on emissions resulted fromthe new stringent emission regulations and the need to improve power andfuel economy, the technology of gasoline direct injection (GDI) is becomingmore and more important.Matching with the variable valve timing (VVT) and turbocharger, not only abetter fuel consumption can be got while the same the power will not be worse, butalso the the cost of aftertreatment can be reduced using the conventional three-waycatalyst in the GDI engine utilizing homogeneous stoichiometric operations. Owingto these advantages, the homogeneous stoichiometric GDI engine is becoming amainstream technology.The potential of fuel consumption improvement achieved by VVT is studiedunder the part load, and it is also tested utilizing the scavenging strategy to reducethe knocking tendency carried on a GDI engine in this paper. The results ofexperiment show that both the positive and negative valve overlap cann help torealize the internal exhaust gas recirculation (EGR) and reduce the pumping losseffectively with the help of the VVT under part load, so the fuel economy can beimproved. At pme=0.2MPa/2000(r/min), the GDI engine reaches a remarkablebe ofonly375g/kW·h using the valve overlap strategy, and the fuel economy is improvedmore than9%.Equiped with turbochargers rationally in GDI engines, the strategy ofscavenging can be realized utilizing the advantage that the intake pressure can behigher than the exhaust pressure during the gas exchange process under heavy load.With optimizing the positive valve overlap, the scavenging can reduce the mass ofresidual gas and lower the cylinder temperature, which helps to reduce the knockingtendency in GDI engines.With the load of the engine increasing, the duration of scavenging is longer andthe pressure of scavenging is higher. The ignition timing will not retard, but fluctuate in a certain interval. Utilizing lean burn strategy, the effects of scavenging can bebetter, and the ignition timing of engine can be earlier compared to homogeneousstoichiometric operations. At200N·m/1800(r/min) with air-fuel ratio of18.5，theignition timing is8oCA before the top dead center(BTDC), which is4oCA earlierthan the stoichiometric operation. At the same time using the VVT can also improvethe charge efficiency to better the power performance under heavy load. The torquecan be increased more than50N·m at1800r/min.