Schlieren visualization of a GDI spray impacting on a heated wall: Non-vaporizing and vaporizing evolutions

The DI (Direct Injection) in SI (Spark Ignition) engines is rapidly developing and seems very attractive offering the possibility of multi-mode operation, homogeneous and stratified charge, with valuable benefits respect to conventional PFI (Port Fuel Injection). One of the major drawbacks of the GDI-fueled engine is the impingement of liquid fuel on the combustion chamber walls that generally produces an increasing of HC emissions and detrimental effects on the combustion process, like soot formation in the wall guided engines due to the diffusive combustion of fuel film deposits on the piston head. This paper investigates the structure of gasoline spray-wall interaction generated by a single-hole injector for GDI engines in an optically-accessible quiescent vessel. The axially-disposed hole diameter is 0.200 mm with a L/d ratio of 1.0 while the injection pressure and the wall temperature varied in the range of 10.0e20.0 MPa and ambient to 300 C, respectively. Injection duration of 1.0 ms was investigated and the nozzle tip-wall distance was 22.5 mm. Optical investigations were carried out at atmospheric backpressure by an in-line schlieren optical setup using a LED source while the cycle-resolved images of the evolving impact were captured by a CMos high-speed camera with a time resolution of 80 ms and a window size of 640 464 pixels. The opticgeometrical setup realized a spatial resolution of 0.039 mm/pixel. The images were treated by a digital processing software for background subtraction and both liquid and vapor contour extractions. The spatial and temporal evolution of the liquid and vapor phases as a function of the wall temperature is described for the different operative conditions