Vapor phase penetration measurements with both single and double-pass Schlieren for the same injection event

Abstract

Schlieren imaging has been adopted as a standard optical technique for the analysis of diesel sprays under enginelike conditions. A single-pass Schlieren arrangement is typically used for the study of single-orifice nozzles, asvessels 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 arrangementis employed. As a consequence, the light beams pass through the test section twice, increasing the optical sensitivityof 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 carriedout with a three hole nozzle with a nominal orifice diameter of 90 μm, named Spray B from the Engine CombustionNetwork, using commercially available diesel fuel and in non-reactive conditions. The impact of different injectionpressures and chamber densities on the spray captured by each setup was assessed. On the results, vapor phasepenetration followed the expected trend found in the literature, as it increases with increasing injection pressure anddecreasing chamber density. Comparing the optical setups, vapor phase penetration obtained with the double-passarrangement was marginally higher. The deviation was observed throughout all tested conditions. Although thediscrepancy was approximately constant for different injection pressures and chamber temperature, it increasedwith increasing density. These results highlight the importance of a proper understanding regarding the limitationsof optical diagnostics, in particular for results used in calibration of computational models.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4884