An Analysis of Diesel Spray Characteristics with Small Injection Amount under Similarity Law Condition

In this paper, the Diesel spray characteristics were studied by HS video camera and the Laser Absorbing Scattering (LAS) technique means of the combustion deterioration problem caused by the engine downsizing based on the geometrical similarity was investigated. In the experiments, three Diesel injectors with the hole diameters of 0.07mm, 0.101mm and 0.133mm were used. The injection pressures of the injectors with three different diameters were 45MPa, 93MPa and 160MPa, respectively. The Diffused Background Illumination (DBI) method was employed for the nonevaporating spray experiment to obtain spray tip penetration and spray angle at room temperature. The LAS technique was employed for the evaporating spray experiment to obtain the equivalence ratio distributions, evaporation rate, and vapor phase tip penetration. Moreover, the Wakuri Momentum Theory was applied to analyze the data obtained by both the non-evaporating and the evaporating spray experiments. The non-evaporating results show that the spray tip penetrations scaled by the similarity law matched well from the injectors of different hole diameters. However, the scaled spray angle of the injector with smaller hole diameter is smaller than that of the injector with larger hole diameter. Furthermore, the spray of the smaller hole diameter injector seems to have smaller mean equivalence ratio than that of the larger hole diameter injector. The scaled vapor phase penetration of the injector with medium hole diameter is larger than that of other injectors. The fuel spray from the injector with smaller hole diameter has slower evaporation rate.