Particulate Emission from Gasoline Direct Injection Engine

Abstract

Gasoline direct injection (GDI) engines can reach considerably higher efficiencies than the port fuel-injected engine (PFI) due to the stratified charge technology. The higher volumetric efficiency as well as better charge cooling helps to increase the compression ratios of these engines, hence, increasing the overall brake efficiency. One of the drawbacks of this engine type, however, is the short premixing time prior to ignition. In particular, for these kinds of engines, the fuel is generally injected when the intake valve is open, or later, in order to increase airflow and volumetric efficiency as well as to reach a specific stratification level. Since the droplet does not have adequate time for complete evaporation at the time of ignition, a significantly larger portion of the charge burns in diffusion combustion, which increases the soot formation. Even during operation utilizing early injection, there is an occurrence of small fuel films on the combustion chamber walls, which are diffusively combusted during the cycle. GDI engines are generally considered an important source of both nucleation and accumulation mode particulate matter, consisting both of carbonaceous and metal oxide particles. To counteract this issue, both particle number (PN), as well as Particulate Matter (PM), are now regulated according to EU 6 standards. In this chapter, a general overview of soot formation in GDI engines is given. In particular, they will explain the general process of soot formation in engines, the main physical parameters that affect its formation and those that affect the particulate emissions in GDI engines, considering also the effect of the use of biofuels.