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In gasoline direct injection engines it is important to optimize fuel spray characteristics, which strongly affect stratified combustion process. Spray simulation is anticipated as a tool for optimizing nozzle design, but conventional simulation, which is based on experimental data and/or empirical laws regarding spray boundary condition at the nozzle exit, cannot predict the effect of various nozzle geometries on spray characteristics. In Japan, a fan spray injected from a slit type nozzle has recently been adopted for gasoline direct injection engines. This paper proposes a computational model for the fan spray. The structure of two-phase flow inside the nozzle is numerically analyzed using the volume of fluid (VOF) method in a three-dimensional CFD code based on the nozzle geometry. The results of these analyses are applied to classical linear instability theory to calculate fuel droplet mean diameter after primary breakup.

To develop injection nozzles and to improve the numerical simulation technology of fuel spray, a measuring technology to analyze the process of disintegration into droplets accurately is required. Performances required by a spray droplets measuring device are: “ability to measure in the combustion condition inside the engine cylinder”, “ability to measure the diameter of spray droplets in high-density fields”, “ability to measure the structure of spray droplets in 3D”, and an improved measuring accuracy of non-spherical droplets. These elements are required in order to analyze the spray droplets structure of gasoline direct injection engines. As a promising method to satisfy these requirements, the laser holography method has been already suggested. However, it has some drawbacks, such as a difficulty in measuring spray droplets in high-density fields and over a long analysis period.