Schlieren optical visualization technique system is the unique technique due to the ability in producing a neutral image easily-interpretable image of refractive-index-gradient areas. The Schlieren system provides a method for viewing the flow through the transparent media and the most using this technique is to photograph the flow. This paper presents the review of the application of the Schlieren optical visualization system external and internal combustion engine in order to observe the fuel-air mixing and flame development during the burning process. The basic technique of Schlieren system, especially for Z-type and two mirror Schlieren system provide a powerful and clearly image to visualize the changes of the density in a transparent medium. This method can capture spray evaporation, spray interference and mixture formation clearly with real images. Analysis of optical image visualization observations reveals that the mixture formation of fuel and air exhibits the influence of the ignition and flame development. Thus, the observation of systematic control of the creation of a mixture of experimental apparatus allows us to achieve significant progress in the combustion process and will present the information to understanding the basic terms of reduced fuel consumption and exhaust emissions. IntroductionThe first Schlieren system was invented by Robert Hook in the 17th century and Schlieren technique developed in the 19th century by Toepler [1]. The Schlieren technique is an optical technique that detects density gradients occurring in a fluid flow in its simplest from light a slit is collimated by a lens and focused onto a knife-edge by a second lens, the flow pattern is placed between these two lenses and the diffraction pattern that results on a screen or photographic film placed behind the knife-edge is observed. The schlieren technique is often used to investigate heat and mass transfer process in gases and liquid [1][2][3]. Referable to the three dimensionality of the investigated processes, it's virtually inconceivable to get quantitative result about the density gradient from the schlieren image [1,2].The primary reasons why Schlieren technique difficult to produce quantitative results because when the geometry is known or simple like sphere, cylinder or other it is possible to calculate the density gradient. Thither are many types of Schlieren technique, setup, but all the setup are based using the same principle [3][4][5][6].
The Schlieren technique remains to be one of the most powerful technique to visualize the flow and it is relatively easy to implement, high and variable sensitivity, low cost and its used conventional of light. This technique allows us to see the invisible of the optical inhomogeneities in transparent media like air, water and glass that otherwise cause only ghostly distortions of our normal vision. This research investigates the mixture formation and flame development of biodiesel fuel using the Schlieren optical visualization principle. This method can capture spray evaporation, spray interference, mixture formation and flame pattern clearly with real images. During the experiment, the camera lens was used with telephoto lenses (Nikon 70-300mm f/4-5.6G) in order to capture a large amount of light especially the low flame intensity during the initial flame development. The flame development was captured with color images from a color digital video camera. This method can capture the flow of fluids of varying density, such as spray evaporation, spray interference and mixture formation clearly with real images. The result shows that the mechanism of fuel-air mixing and a better comprehension of combustible mixture that can give valuable information to improve and optimize the combustion process. IntroductionThe Schlieren photography technique is a visualization that used to capture the flow. The Schlieren technique remains to be one of the most powerful technique to visualize the flow and it is relatively easy to implement, high and variable sensitivity, low cost and its used conventional of light. Schlieren imaging system has been used since early 1800's to visualize fluxions optical density [1][2]. Schlieren optical visualization technique system [1] is the unique technique because it produce a neutral image easily-interpretable image of refractive-index-gradient fields [3]. The Schlieren technique remains to be one of the most powerful technique to visualize the flow and it is relatively easy to implement, high and variable sensitivity, low cost and its used conventional of light. Schlieren technique also based on the light reflection and in this technique the light reflect by using concave mirror. It is more sensitive than its companion the shadowgraph, and better suited to the qualitative visualization than its cousin the interferometer [1][2][3]. The Schlieren optical system delivers the ability to view the phase of the object that cannot be seen normally by a human eye [4]. Most of the Schlieren technique is utilizing the toopler technique as the benchmark for the most Schlieren systems.However, the traditional instrument of Schlieren have a limitation in the field of view by the cost for the lagers diameter of Schlieren mirror also got the high quality optics. The method of slain
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