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The occurrence of flash boiling in the fuel spray of a Port Fuel Injected (PFI) spark ignition engine has been observed and photographed during normal automotive vehicle operating conditions. The flash boiling of the PFI spray has a dramatic affect on the fuel spray characteristics such as droplet size and spray cone angle which can affect engine transient response, intake valve temperature and possibly hydrocarbon emissions. A new method of correlating the spray behavior using the equilibrium vapor/liquid (V/L) volume ratio of the fuel at the measured fuel temperature and manifold pressure is introduced.

The effects of injector targeting and fuel volatility on transient fuel dynamics were studied with a comprehensive quasi-dimensional model and compared with experimental results from Part I of this report (1). The model includes the transient, convective vaporization of four multi-component fuel films coupled with a transient thermal warm-up model for realistic valve, port and cylinder temperatures (2, 3). Two injector targetings were analyzed, first with the fuel impacting the intake valve and in addition, the fuel impacting the port floor directly in front of the intake valve. The model demonstrates the importance of both component temperature and fuel impaction area on fuel vaporization, transient air fuel ratio (AFR) response and the amount of liquid fuel entering the cylinder. Generally, a smaller injector footprint area will lead to more liquid fuel entering the cylinder even if the spray is targeted at the back of the intake valve.

In modeling of engine fuel-air mixing, it is desired to be able to predict fuel spray atomization under different injection and ambient conditions. In this work, a previously developed sheet atomization model was studied for this purpose. For sprays from a pressure-swirl injector, it is assumed in the model that the fuel flows out the injector forming a conical liquid film (sheet), and the sprays are formed due to the disintegration of the sheet. Modified formulations are proposed to estimate sheet parameters including sheet thickness and velocity at the nozzle exit. It was found that the fuel flow rate of a swirl injector satisfied the correlation well. Computations of correlation well. Computations of the sprays injected in an engine with a side-mounted injector were performed for conditions that duplicated a set of experiments performed in an optical engine. The computed results were compared with the spray images obtained from the optical engine using elastic (Mie) scattering.