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Aerosol Shock Tube |
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This diagram shows the entire aerosol shock tube consisting of a driver section and a driven section separated by a thin diaphragm. The sections are 3.5 and 9.6 m in length, respectively, giving between 1-4 ms of test time, depending on the temperature and pressure conditions. There is a vacuum port located in the driven section to evacuate the tube and to help suck the aerosol into the tube from the endwall. There are also many pressure transducers that are used to measure the shock speed. Then at the far end of the driven section is the test section where the laser diagnostics are located. |
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The images above show schematically the three steps in the operation of the aerosol shock tube. The first step is to fill the shock tube with a nebulizer-generated aerosol of the test gas mixture. The second step is to heat and compress the aerosol mixture behind the incident shock which evaporates the fuel fully. The third step is to heat and compress the test gas mixture to the final conditions behind the reflected shock. |
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| The aerosol shock tube uses an ultrasonic nebulizer to create the aerosol. Pictured above to the left is a close-up of a nebulizer. The gold disc is a piezoelectric transducer, which will expand and contract when an oscillating current is applied. The resultant vibration is strong enough to form micron sized droplets at the liquid surface. The picture above on the right shows the nebulizer creating a water aerosol in a cylindrical, glass container. |
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| The images above show a more detailed cross section of the aerosol shock tube. A liquid fuel aerosol is created using an ultrasonic nebulizer. The aerosol created has a lognormal size distribution with a count median diameter (CMD) of 2.8 µm. A dry bath gas is flowed over the surface of the liquid and serves to carry the aerosol into the shock tube through poppet valves in the endwall and down the shock tube. Once a uniform spatial distribution is obtained, all valves are closed and the shock tube diaphragm is broken. |
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The test section connects to an existing circular-section driven section of the shock tube using a round-to-square transition section to satisfy the optical access requirements of these experiments. |
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Fog produced by ultrasonic nebulizers is introduced to the shock tube through a specially-designed endwall that incorporates four poppet valves. |
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By controlling the carrier-gas flowrate and tube pressure, the tube is filled with a spatially-uniform cloud of droplets. When outfitted with large windows, the test section has excellent optical access. |
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This shows the pneumatic cylinder that actuates the poppet valves. The fog is produced by the nebulizer which is located below the 90-degree elbow. |
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Dave's eye view of the facility. Lasers are pitched through the shock tube test section toward detectors located in the foreground. |
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The shock tube valves, pumps, and data acquisition is controlled through a programmable touch-screen panel. |