Determination of the Characteristics of Diesel Spray by the Bidirectional Light Scattering Image Processing Method

Abstract

To clearly understand the phenomena of combustion in Diesel engines the spatial and temporal distributions of droplet size and volume density in the spray have to be determined accurately. The fuel used in a non-hypothetical situation is sprayed into the engine cylinder which is less than 100 mm long. In that case, the spray is not greatly diffused. Therefore the spray has high volume density. For that reason, the size and volume density in such high density spray cannot be measured by a particle counting method [1] or a holographic technique [2]. These are suitable for measurement of low concentration sprays having number densities below 103 (particles/cm3). Also, the Fraunhofer diffraction method [3] cannot be used for such high concentration sprays. The macroscopic movement of high concentration spray such as spread and penetration of spray can be measured with high-speed photographic movies using forward light attenuation. But the size and density of the spray cannot be measured quantitatively [4]. Therefore, the development of an effective measuring method was needed to simultaneously and quantitatively determine the spatial distributions of droplet sizes and densities in Diesel spray changing every moment. To meet such a need, a new measuring method has been developed by Shimizu [5–7]. This is done by using equipment which can continuously determine the macroscopic spread and movement of spray and can microscopically and quantitatively determine the distributions of droplet sizes and volume densities in the Diesel spray using light scattering and image processing method. The present work can quantitatively determine the time history of the spatial distributions of the droplet size and volume density along the entire passage of jet spray which could not be measured by other methods because of high concentration. The main paper on this measuring method was published five years ago [5]. Much work has been accomplished by investigating the experimental results obtained during these five years. This paper is a comprehensive survey of the past studies on this subject. Here, the same experimental conditions have been used consistently, although the latest data which was obtained by the corrections of measuring theory and improvements of measuring equipment has been included. In this paper the results of the study of this measuring method and experimental results of Diesel sprays obtained by this optical method are described.