Development and implementation of optical diagnostics for spray characterizations

Research in the field of engine technology has been motivated by the desire to meet increasingly stringent exhaust emissions while consistently improving the performance and efficiency. An important way to achieve this goal is to enhance the performance of the fuel injection system. A better and detailed understanding of spray evolution and atomization is therefore both fundamentally and practically essential. The following work describes the development and implementation of a series of optical spray diagnostic techniques for a spray characteristics investigation for Wankel engine application. The work focused on visually accessing the spray evolution and atomization process and analyzing the spray characteristics on both macroscopic (100 mm×100 mm) and microscopic scales (2mm×2mm). This work presents an experimental investigation into the spray characteristics of aviation fuel (Jet-A) from a customized single-hole injector using Direct photography with the laser sheet illumination technique. The spray imaging system developed visualizes the spray development process with respect to the time elapsed. The spray characteristics such as spray penetration, spray angle and projected area at various conditions are quantitatively measured and analyzed using the image analysis program developed using the Matlab image processing interface in order to obtain a better understanding of the effect on aviation fuel of using specifically designed fuel injector. An image analysis sizing method has been successfully developed. It based on quantitatively analyzing the degree of image focus on the intensity gradient and image contrast value across a droplet shadow image. A specialised optical diagnostics system has been designed specifically for measuring droplet size under investigation ranging from 4 μm to 100 μm. This method has been assessed by performing a series of preliminary experiments and comparing the results obtained at the various testing conditions. A specialised droplet sizing and analysis software which makes use of the Matlab language has been developed and proved to be an effective and affordable droplet sizing tool to explore the spray microscopic characteristics. Furthermore, this study conducts a successful application of a combination of Droplet image analysis sizing method and Direct photography with laser sheet illumination technique for a two-hole nozzle with a pre-heating module. It is applied to acquire both spray macroscopic characteristics and also the droplet images in the microscopic region (2 mm by 2 mm) of interest. Further analyses are implemented to measure the droplet size and then explore the effect of ambient conditions on droplet size, volume and ellipticity distribution using aviation fuel