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Low cost shadowgraph technique for flammable vapor visualization

The vapors of many fuels are extremely hazardous if they are present at concentrations within the flammability limits. Unfortunately, these hazardous fuel vapors are invisible under normal conditions. Flammable vapors have been visualized using schlieren systems; however, the expense of schlieren systems and the limited size of the test section that could be observed severely limits its applicability. This paper reports on a very low cost technique that was developed to visualize these flammable vapors in a large test section. Using solar illumination to drive a simple shadowgraph installation, the density variations were dramatically seen in a test section of several feet as opposed to several inches. The concentration levels of the flammable vapors in the test section were estimated by direct measurement and ignition tests.