Título: Vapor phase penetration measurements with both single and double-pass Schlieren for the same injection event
Autor: Payri, Raul; Salvador Rubio, Francisco Javier; Bracho León, Gabriela Cristina; Viera Sotillo, Alberto Antonio
Resumen: [EN] Schlieren imaging has been adopted as a standard optical technique for the analysis of diesel sprays under engine
like conditions. A single-pass Schlieren arrangement is typically used for the study of single-orifice nozzles, as
vessels with multiple optical accesses regularly allow line of sight visualization. Contrarily, for multi-spray nozzles,
measurements are commonly performed through a single optical access, in which case a double-pass arrangement
is employed. As a consequence, the light beams pass through the test section twice, increasing the optical sensitivity
of the Schlieren setup. However, the impact this has on the macroscopic spray characteristics is still unclear.
The scope of this study is to analyze the differences in vapor phase penetration for the same injection event,
through high-speed imaging, for both single and double-pass Schlieren configurations. Experiments were carried
out with a three hole nozzle with a nominal orifice diameter of 90 µm, named Spray B from the Engine Combustion
Network, using commercially available diesel fuel and in non-reactive conditions. The impact of different injection
pressures and chamber densities on the spray captured by each setup was assessed. On the results, vapor phase
penetration followed the expected trend found in the literature, as it increases with increasing injection pressure and
decreasing chamber density. Comparing the optical setups, vapor phase penetration obtained with the double-pass
arrangement was marginally higher. The deviation was observed throughout all tested conditions. Although the
discrepancy was approximately constant for different injection pressures and chamber temperature, it increased
with increasing density. These results highlight the importance of a proper understanding regarding the limitations
of optical diagnostics, in particular for results used in calibration of computational models.
