Abstract
The development of quantitatively robust spray measurements is important for advancing model development and fundamental understanding. However, the physical interpretation of both experimental measurements and model predictions needs to be carefully considered when making comparisons between them. One such example occurs in the measurement of liquid-phase of sprays injected under an evaporating environment. Various experimental techniques are applied to quantify the maximum liquid penetration, but the selection of the measurement technique and the details of the experimental arrangement may significantly influence the results. Moreover, the liquid length measured through one experimental setup may not be consistent with the definition used in a model, making a comparison between the two indirect. Hence, there is still a need to assess the physical meaning of experimentally measured liquid lengths in order to provide a direct relationship with model-based predictions. The aim of this work is to experimentally study the liquid penetration and steady liquid length in diesel sprays by applying diffused back-illumination imaging. Compared to Mie scattering, diffused back-illumination offers advantages because a reference image without the injected spray provides an intensity reference that can be used to calculate light extinction; thus leading to a better standardization of the measurement among researchers. Recent standards developed for gasoline sprays along with a suggestion made by the Engine Combustion Network call for diffused back-illumination imaging to evaluate liquid length. An analysis of the results provided by this technique has been carried out to evaluate the potential to measure liquid length of evaporating diesel sprays injected in a high-pressure, high-temperature optical vessel. The results of this study showed that the diffused back-illumination provides measurements of the liquid penetration that are fairly consistent with Mie scattering experiments in capturing the trends. On the other hand, the experiments showed that the effects of beam-steering limited the technical capabilities to extract quantitative measurements of the liquid length under diesel engine conditions and that a methodology must be implemented to satisfactory measure the liquid-phase of the sprays.
