On the relation between the external structure and the internal characteristics in the near-nozzle field of diesel sprays

In this paper, a high-resolution visualization technique was used in combination with an extensively validated zero-dimensional model in order to relate the external structure of a diesel spray to the internal properties in the vicinity of the nozzle. For this purpose, three single-hole convergent nozzles with different diameters were tested for several pressure conditions. The analysis of the obtained images shows that the spray width significantly changes along the first few millimetres of the spray. From the high-resolution images obtained, two parameters were evaluated. The first is the external non-perturbed length, where droplet detachment was not observed. The second is a transitional length, which is defined as the axial position where the spray width increases linearly after transient behaviour, making it possible to establish a spray cone angle definition. Furthermore, the internal liquid core length was estimated for these nozzles using an extensively validated zero-dimensional model. The liquid core length proved to be correlated with both the transitional length and the non-perturbed length with a very high degree of reliability. In the case of the transitional length, a quadratic correlation was observed, whereas a linear relationship was confirmed between the liquid core length and the non-perturbed length. The results presented here may help to shed light on better understanding of such a complex process as atomization.