Quantifying liquid boundary and vapor distributions in a fuel spray by rainbow schlieren deflectometry

Abstract

The rainbow schlieren deflectometry (RSD) technique is used to determine the liquid boundary and the fuel volume fraction distributions in the vapor region of a high-pressure fuel spray. Experiments were conducted in a constant pressure flow vessel, whereby a customized single-hole common-rail diesel injector is used to introduce n-heptane fuel into a coflow of low-speed ambient air at two different test conditions. Only the quasi-steady period of the fuel spray is considered, and multiple injections are performed to acquire statistically significant data at an image acquisition rate of 20 kHz. An algorithm to identify the liquid boundary using intensity recorded by the RSD images is presented. The results are compared against measurements obtained by the Mie scattering technique. Results demonstrate that the RSD can be a powerful optical diagnostics technique to simultaneously quantify both the vapor and liquid regions in the high-pressure fuel sprays.

Visualização de Escoamentos pelos Métodos Ópticos Shadowgraph e Schlieren

“…Como mencionado anteriormente, existem variações dos métodos shadowgraph e schlieren. Por exemplo, a técnica Schlieren Colorido (Rainbow Schlieren) permite a determinação dos campos bidimensionais de densidade e de temperatura de escoamentos [6,7], enquanto a técnica de Velocimetria por Imagem Schlieren (Schlieren Image Velocimetry -SIV) possibilita medir o campo bidimensional de velocidade de escoamentos [8,9]. Em comum às técnicas SIV e Schlieren Colorido está a possibilidade de se adotar um arranjo óptico do tipo Toepler para aquisição das imagens que tem como principais vantagens a sensibilidade, a facilidade de alinhamento, baixo custo dos seus componentes ópticos e possibilidade de imageamento de escoamentos de diferentes tamanhos [10].…”

Characterization of the liquid phase of vaporizing GDI sprays from Schlieren imaging

“…The procedure worked well in all investigated experimental conditions, always providing a reliable threshold value that takes into account nothing more than spray areas. In our previous document [23], the iterative thresholding was guided to some extent by a stopping criterion selected based on experimental conditions. This inevitably introduced a certain degree of discretion in the procedure.…”

“…They carried out a thorough invest igation of beamsteering due to the refractive index gradients and its effects on measuring the liquid length, which would make schlieren imaging unsuitable for liquid quantification. The above assertions, on the other hand, have been ques tioned by a recent study [23], in which the authors applied the schlieren rainbow deflectometry (RSD) technique to detect both vapour and liquid zones in a diesel spray. They stressed, however, that the method suffers the drawbacks and the need for a very wide temporal average, thus losing the details of the process to a certain extent and limiting the field of applica tion.…”

High-Speed Schlieren Imaging of Vapor Formation in Electrospray Plume

“…This key manipulation increases the sensitivity to refractive index gradient, and distinguishes the schlieren method from direct shadowgraph method. ,, One of the research areasusually utilizing schlieren shadowgraphy to obtain information, is visualization of the combustion process in a diesel engine. To investigate the combustion efficiency of the engine, a chamber with high temperature and pressure is usually utilized to simulate the engine conditions. − Schlieren imaging has also been adopted in the field of analytical chemistry research to visualize processes in the ionization techniques such as desorption electrospray ionization, direct analysis in real time, flowing atmospheric pressure afterglow, , and inductively coupled plasma . In these applications, schlieren imaging served as a powerful tool to identify potential variables, evaluate mass transport efficiency, obtain a temperature profile, calculate air flow density, and verify the character of flow (turbulent vs. laminar).…”

“…In some cases, images obtained by schlieren photography were used to characterize flow changes during the change of experimental parameters. ,,− If similar information can be obtained for the ESI source using schlieren imaging, it may bring further insight into the ionization mechanism. Overall, given that there is much literature about visualization of evaporation in the engineering fields ,,,− and several applications in ion source studies in the analytical chemistry field, ,− we envisaged that it would be feasible to use schlieren photography for visualizing the evaporation process in electrospray. Therefore, we developed a schlieren imaging system for observation of the vapors emanating from desolvating electrospray droplets.…”