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

Abstract

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.

The effect of nozzle geometry over the evaporative spray formation for three different fuels

“…The first important observation that Figure 14 provides is that the spray produced by the cylindrical nozzle k0 spreads immediately after the fuel has exited the orifice, while the spray produced by nozzle k15 starts thin and spreads progressively downstream, as previously seen in non-evaporative isothermal sprays [40,41]. This implies that the nozzle geometry has great effect on what Benajes et al [63] refer to as transitional length, which is the region after the intact liquid core starts to break but before the spray starts its linear evolution. Moreover, fluctuation maps for k0 are more diffuse in the radial direction, which indicates larger fluctuations, which was also seen by Payri et al [40,41] in the non-evaporative isothermal case.…”

“…Lineof-sight fluctuation maps of vapor sprays are presented in Figure 16 for all nozzles and fuels at a particular case of test conditions. Plots in the left column demonstrate that the cylindrical nozzle k0 produces vapor sprays which spread immediately after exiting the orifice, while the conical nozzle produces a thin jet that spreads more progressively downstream, which again suggests that the nozzle geometry is affecting the transitional length [63]. Note that this result is in agreement with the findings for the liquid phase presented here, and those found for non-evaporative isothermal sprays analyzed previously by the authors, for the same nozzles and fuels [41].…”

Investigation of Spray Angle Measurement Techniques

“…The trapezium method is an adapted version of the triangle method, where instead of calculating the angle from the projected triangle, a trapezium area projection is used [38]. Another method that can be found in literature is based on obtaining the spray angle as a sum of left and right half angles from the spray's middle axis [36], [58]. The angle is measured between a line tangent to one of the spray edges and a line running through the centroid's axis [36].…”

Analysis on the effects of turbulent inflow conditions on spray primary atomization in the near-field by direct numerical simulation

“…Very few experimental works are available on near field visualization [37,38,39,40]; furthermore to the best of the authors knowledge, none at low speed (corresponding to low injection pressures), which is mandatory for DNS simulations. For this reason, the liquid/gas parameters, as well as the geometrical parameters were chosen according to a Spray A usual configuration [41], where a low speed Dodecane jet is injected in a pressurized nitrogen vessel.…”