Measurement and Evaluation of Near-field Spray Kinematics For Nozzles with Asymmetrical Inlet Geometries

Doctoral thesis, 2025

This study digs into the complex dynamics and morphology of fuel sprays in diesel engines, with a special emphasis on the primary break-up phase. The main objective is to improve the basic knowledge of diesel fuel sprays by providing critical insights into their near-field behavior and velocity profiles. Furthermore, this study serves an additional purpose in providing statistical data required for validating computational spray models, which improves the accuracy of mixing and combustion simulation.

The core of this thesis is the investigation of near-field sprays, generated by nozzles with particular geometries at a range of injection pressures. The nozzles studied in this work include single-hole configurations with on-axis and off-axis orifices. In addition, a two-hole nozzle with angled orifices served as another case study. The study is based on optical measurements using time-gated ballistic imaging. This method provides clarity in identifying the liquid/gas interface and enables precise tracking of spray structures. This yields the temporal displacement of the spray interface between successive photos allowing the measurement of spray kinematics in two dimensions.

The findings highlight the major impact of asymmetrical inlet geometries on near-field spray profiles, introducing significant asymmetry in the distribution of velocity magnitude on either side of the spray. In addition, the investigation delves into the steady-state morphology of sprays for off-axis and two-hole nozzles. In the case of the off-axis nozzle, the spray deviates to the side with a sharper inlet edge, even at low injection pressures. The results show that this deviation is intensified with injection pressure. Furthermore, at higher pressures, the radial velocity component increases noticeably along the side with sharper orifice edges, resulting in a deviation of the spray axis.

The research also reveals details about velocity magnitude changes along the spray axis. The amplitude and frequency of these oscillations are significantly changed as injection pressure increases. Higher injection pressures cause greater amplitude in fluctuations, while the number of local peaks alongside the spray axis is decreased.

Finally, a comparison was made between simulated spray dynamics and the experimental data acquired throughout the project. The results of this comparative study show a notable agreement between the simulation model and the experimental data, particularly in cases with the empty sac as the initial condition (with 5% liquid fuel present in the sac before the start of injection). Here, the alignment in axial velocities shines out, while
small discrepancies in radial velocities are noted. This detailed comparison indicates the overall performance of the model, highlighting the strengths and limitations of the simulation model in capturing the complexities of spray behavior.