@inproceedings{,
    author = {Son, Min; Zigan, Lars; Pfitzner, Michael; Sander, Tobias},
    title = {Integrated Optical Diagnostics of Cyclopentane Sprays to Characterize Transcritical Phase Transitions},
    editor = {},
    booktitle = {Proceedings of the 21st International Symposium on Application of Laser and Imaging Techniques to Fluid Mechanics 2024},
    series = {},
    journal = {},
    address = {},
    publisher = {},
    edition = {},
    year = {2024},
    isbn = {978-989-53637-1-1},
    volume = {},
    number =  {},
    pages = {},
    url = {https://www.lisbonsymposia.org/proceedings},
    doi = {},
    keywords = {injection ; transcritical ; spray ; shadowgraphy ; infrared radiation},
    abstract = {This research investigates spray phase transitions under subcritical and transcritical conditions relevant to highpressure
combustion systems. Using advanced optical diagnostic techniques, including shadowgraphy (SH), Mie scattering
(MS), and infrared radiation (IR) measurements, the study focuses on cyclopentane sprays in a high-pressure,
high-temperature chamber filled with gaseous nitrogen. Three cases are studied to understand spray behavior under
varying injection conditions. SH and MS analyzes reveal significant differences across the cases. As the chamber
temperature increases, the liquid core length shortens, indicating enhanced vaporization. This is particularly evident
in the MS images, where step-like transitions in the axial distribution highlight abrupt phase changes from liquid to
gas in subcritical conditions. Such transitions are absent under supercritical conditions, suggesting a smoother phase
transition process. IR measurements provide additional insights into the spray dynamics, especially under transcritical
conditions. The IR images display complex downstream (at x/D > 125) signal patterns with bimodal distributions.
The application of inverse Abel deconvolution highlights negative intensities near the spray axis downstream, indicative
of regions near the pseudo-critical temperature. This phenomenon, characterized by blocked background
radiation due to critical opalescence, offers indirect evidence of the pseudo-critical temperature and the associated
phase transition dynamics. Dynamic Mode Decomposition (DMD) analysis identifies dominant frequencies around
4.5 kHz, corresponding to injection pressure fluctuations. This correlation suggests that injection pressure variations
significantly influence spray fluctuations. Differences in mode shapes among the cases are also observed; lateral fluctuations
near the injector nozzle exit are present in Cases 1 and 2 but not in Case 3. The axial fluctuations beyond a
certain length are consistent in all cases. The lateral fluctuations are related to the chamber pressure and the potential
large-scale vortex formation or cavitation in the nozzle. The combined use of SH, MS, and IR methodologies provides
a comprehensive understanding of transcritical spray dynamics, emphasizing the effectiveness of combining multiple
optical diagnostic techniques. These findings will improve numerical simulations and contribute to the development
of more efficient high-pressure combustion systems. The research underscores the complexity of phase transitions in
sprays and the critical role of precise diagnostics in the advancement of combustion technology.},
    note = {},
    institution = {Universität der Bundeswehr München, Fakultät für Luft- und Raumfahrttechnik, LRT 10 - Institut für Thermodynamik, Professur: Zigan, Lars},
    
    
}