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The aim of this work was to develop a new method for studies of diesel spray behavior based on the shadowgraph technique using high speed photography. This novel technique is based on the construction of two types of images; one averaged and one PPI (Presence Probability Image) spray image. Each average image is a result of averaging the images from a series of test replicates. On the other hand, the PPI images are constructed from addition of the binarized images from the same replicate tests. In these binarized images, a certain gray scale value is defined as the limit for the presence of liquid fuel spray, i.e. areas in the image represented by gray scale values below this threshold is defining the liquid fuel core of the spray. Using these images one track the regions where liquid fuel is most probably present in the spray. A comparison is then performed of these two approaches, using averaged images and PPI images.

The diesel combustion process involves complex physical and chemical processes. Given this complexity it is not surprising that a wide range of fuel effects on emissions are reported in the literature. In the European Auto/Oil study the EPEFE programme showed that interactions between fuel and engine hardware could partially explain the observed emissions effects. Variations in fuel physical properties can lead to variations in injection timing, fuel delivery, exhaust gas recirculation (EGR) and other parameters. To understand fuel effects on emissions it is clear that we need to separate these different mechanisms. In this programme a modem, electronically controlled, direct-injection (DI) passenger car engine has been studied using a sophisticated test bed system which makes it possible to monitor and control all key engine variables. Seven fuels were tested, including four varying in density and poly-aromatics content taken from the EPEFE programme.