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The atomization process of fuel spray injection in internal combustion engines affects the spray mixture formation process, the combustion characteristics, and the formation of toxic substances. Therefore, several optical measurement procedures have been developed and applied to capture spray features, including imaging methods and laser diagnostics. It has been concluded that the spatial resolution of fine spray droplets detection in imaging with silver halide film is much better than with a CCD imaging device. Therefore, the authors previously developed a novel imaging technique called Super High Spatial Resolution Photography (SHSRP), which allows for whole spray imaging while maintaining the spatial resolution of tiny droplets. This is a wide-field, high-resolution imaging method that can measure the entire spray area at the droplet scale. However, the image analysis method analyzes the intensity gradient of the outer edge of the droplet, and the accuracy of droplet analysis deteriorates as the droplet diameter is small. In this study, a new image analysis method with wide-field and high-resolution images acquired by SHSRP was developed to improve the analysis accuracy of spray droplets. The analysis method of depth of object field, which depends on droplet size, was changed from one-dimensional analysis of the intensity gradient of the outer edge of the droplet to two-dimensional analysis using the intensity deviation of the entire droplet area. For the developed analysis method, analysis of error based on scattering theory was conducted and the droplet capture ratio in diesel spray was analyzed to verify the accuracy. As a result, it was found that the particle size distribution obtained has no peaks due to noise effects, and that the presented analysis method is accurate enough to characterize the particle size distribution of diesel spray.

Direct fuel injection spray is used to improve thermal efficiency and environmental performance in SI engines. A mixture is formed through momentum exchange between fuel droplets and ambient gas, along with mixing accompanied by droplets evaporation and diffusion. Both the droplets development derived from the liquid fuel atomization and the entrainment ambient air predominate the mixture formation process. The purpose of this study is to elucidate the momentum exchange characteristics of the spray formed by a single-hole injector for direct injection gasoline engines. To clarify the momentum exchange characteristics of spray droplets, the spray was visualized by optical experiments and the spray development process was analyzed. The parameters are injection pressure and ambient density. A comparison of experimental results and a model analysis of a single droplet movement was conducted, and different of deceleration characteristics were evaluated. In the case of the fuel spray, the induced ambient air by the spray tip droplets decreases the relative velocity between the spray droplets and the spray internal flow. A model for predicting the temporal variation of the spray tip penetration from the different of momentum exchange characteristics between the spray and the droplet was proposed.