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 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.

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“…Figure 11 shows the results of spray angle evolvements when applying injection strategy under the same injection pressure, and density of the fuel conditions had shown with only different cylinder combustion chamber geometry. The reason for the large spray angle in the initial injection phase because that the fuel was injected into a relatively stationary air environment and the air at the nozzle outlet was squeezed and pushed into the radial direction however, the spray angle remains nearly stable during the later injection stage ( Taşkiran and Ergeneman, 2011 ; Payri et al., 2017 ; Wu et al., 2019 ). This can be attributed to the increased momentum exchange at higher surrounding gas densities as the fuel droplets are more closely surrounded by environmental gases.…”