Gasoline direct injection engine injector tip drying

In gasoline direct injection (GDI) engines, carbonaceous deposits are formed on surfaces wetted with gasoline. Of particular concern is the formation of carbonaceous deposits on the injector tip as they lead to injector plugging and particulate emissions from these engines. The drying of the injector tip is an essential parameter in the build-up of deposits. This paper reports the effect of parameters such as system pressure, injector tip temperature and air flow on the drying rate of an isooctane thin film on an injector tip. Depending on the injector tip superheat, the fuel film drying out process can be dominated by either evaporation or boiling. At injector tip superheat up to 10 C, evaporation at the contact line is the dominating mechanism. The drying rate is this regime increases with injector tip temperature and air velocity. Above this temperature, bubbles or funnel-shaped structures were formed in the film. The drying rate due to boiling depends on the system pressure and temperature but shows little dependence on the air velocity. The drying rate increases with the reduction in system pressure. In the Leidenfrost state, the fuel bounces-off the injector tip and this temperature decreases with system pressure.