Schulz, F., Schmidt, J., Kufferath, A., and Samenfink, W., "Gasoline Wall Films and Spray/Wall Interaction Analyzed by Infrared Thermography," SAE Int. J. Engines 7(3):1165-1177, 2014, doi:10.4271/2014-01-1446.
Due to the principle of direct injection, which is applied in modern homogeneously operated gasoline engines, there are various operation points with significant particulate emissions. The spray droplets contact the piston surface during the warm-up and early injections, in particular. The fuel wall films and the resulting delayed evaporation of the liquid fuel is one of the main sources of soot particles. It is therefore necessary to carry out investigations into the formation of wall film. The influence of the spray impact angle is of special interest, as this is a major difference between engines with side-mounted injectors and centrally positioned injectors.This paper describes an infrared thermography-based method, which we used to carry out a systematic study of fuel deposits on the walls of the combustion chamber. The boundary conditions of the test section were close to those of real GDI engines operated with homogeneous charge. We took the measurements under normal ambient conditions, substituting the piston by a heated plate and positioning an infrared camera underneath it. The single component fuel, n-heptane, was injected using a high-pressure multihole injector. The influence of four test parameters was examined - the wall temperature, the injection pressure, the distance between nozzle and wall and the spray impact angle.The results we obtained include the heat flux at the spray impingement zone, the wall film area and the wall film mass. The heat flux at the spray impingement zone leads to a considerable decrease in the temperature of the wall surface and is influenced by all test parameters. The effect of the test parameter on the wall film area is not identical to that of the wall film mass. For this reason, the amount of fuel deposits is not proportional to the area of the wall film. High injection pressures and impact angle adjustment, in particular, can help to reduce the wall film mass.