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Owing to the small size of engines and high injection pressures, it is difficult to avoid the fuel spray impingement on the combustion cylinder wall and piston head in Direct Injection Spark Ignition (DISI) engine, which is a possible source of hydrocarbons and soot emission. As a result, the droplets size and distribution are significantly important to evaluate the atomization and predict the impingement behaviors, such as stick, spread or splash. However, the microscopic behaviors of droplets are seldom reported due to the high density of small droplets, especially under high pressure conditions. In order to solve this problem, a “spray slicer” was designed to cut the spray before impingement as a sheet one to observe the droplets clearly. The experiment was performed in a constant volume chamber under non-evaporation condition, and a mini-sac injector with single hole was used.

Spray characteristics under very small injection amount injected by the hole-type nozzle for a D.I. Diesel engine were investigated using the spray test rig consisting a high-pressure and high-temperature constant volume vessel with optical accesses and a common rail injection system. The Laser Absorption Scattering (LAS) technique was used to visualize the liquid and vapor phase distributions in the evaporating spray. In the very small injection amount condition of the evaporating and free (no wall impingement) spray, the both spray tip penetration and spray angle are larger than those of the non-evaporating free spray. This tendency contradicts the previous observation of the diesel spray with large injection amount and the quasi steady state momentum theory. In the case of the spray impinging on a 2-dimensional piston cavity wall, the spray tip penetration of the evaporating spray is larger than that of the non-evaporating spray.