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The effects of reduced fuel injection pressure on the cold start performance of a GDI engine have been studied in a single-cylinder, optically-accessible research engine. Two Delphi Automotive Systems DI-G injectors, with included spray cone angles of 60° and 80° respectively, were studied. Both injectors are designed to operate at a nominal fuel line pressure of 10 MPa. For the study they were operated at several fuel feed pressures between 10 MPa and 2 MPa. Two start of injection timings (50° and 100° ATDC) were examined. Cold start performance was characterized by measurements of the GIMEP, COV of GIMEP, and total engine out UHCs. Simultaneous Planar Laser Induced Fluorescence (PLIF) and Mie Scattering images of the fuel spray were used to observe spray penetration, mixing, and in-cylinder fuel distribution throughout the intake and compression strokes. Ultimately these images were used to explain observed performance differences.

A Laser Induced Fluorescence (LIF) based technique has been employed to examine the transient fuel film behavior on an intake valve during cold start of a PFI engine. Fluorescence from a tracer in the fuel was collected through a Borescope and imaged onto a CCD camera, providing a 2-D image of the fuel film on the valve. The average intensity of the fluorescence, over a Region of Interest (ROI), was taken to be proportional to the total amount of fuel present in the film. Images were collected (at a fixed crank angle) on every second engine cycle, resolving changes in the fuel film during the cold start transient. Changes in the fuel film were resolved within a cycle by collecting images at varying crank angles during successive experiments. Results from four fuel mixtures are reported. Two simulated “single component fuels” one with a higher volatility (HV) and one with a lower volatility (LV), were examined.