Application of Schlieren Optical Visualization System in External Combustion and Internal Combustion Engine: A Review

Abstract

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].