| Planar Laser-Induced Flourescence of H2-O2 Combustion |
| Faculty: Frank K. Lu, Ph.D. |
| Student: Takashi Yokomae |
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The question of how detonations are initiated remains an intriguing one that is extremely pertinent in the development of pulse detonation engines. The consensus is that direct initiation is not practical and a certain deflagration-to-detonation transition length is required. This distance should be made as short as possible for a practical engine. It is believed that a detonation is initiated at “hot spots” where heat and pressure are sufficient to trigger a rapid chemical reaction. In an oxyhydrogen system, these sites of chemical activity are expected to be richly populated with hydroxyl. We are conducting experiments to study the formation of hydroxyl to support the development of pulse detonation engines. |
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The study of hydroxyl formation makes use of planar laser induced fluorescence. Initial experiments are being performed in an atmospheric oxyhydrogen flame using a flat burner. Diagnostics are an excimer laser and an intensified camera. The figure below to the left shows the test rig. Oxygen and hydrogen are supplied from bottles to the left. The laser is seen on the right and in the foreground is the camera. The UV optics and the flat flame burner are also visible on the test cart. |
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A schematic of the experimental setup is shown above to the right. The lens system (1) is used to shape the laser beam into a sheet that shines through the flame from a flat burner (2). The image system (3) collects the fluorescence into the ICCD camera. The incident laser beam is stopped by the beam stop (4). Regulators with flowmeters (5) are used to control the flow of oxygen (6), hydrogen (7) and nitrogen (to stabilize the flame). The test rig is mounted on a cart (8). Tubing for cooling water and gases are indicated in (9). |
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| The next phase of the project is to study OH formation in detonations. For this purpose, a special shock-induced detonation tube is being developed. It is shown schematically below. This shock tube is specifically designed to study deflagration-to-detonation transition. A driver tube is charged to high pressure with air or helium while the driven tube is filled with a combustible mixture. When the double diaphragms are ruptured, the driver gas initiates a flame in the driven tube. Based on previous experience, such a flame will rapidly transition into a detonation wave. The driven tube is designed to withstand detonation pressures. It has a 1.5 in. square section and is 42 in. long. The tube is equipped with observation ports for PLIF and schlieren. Nine high-frequency pressure transducers are also mounted along its length to monitor the wave evolution. The tube is designed to allow the wave to be observed along its entire length. A photograph of the driver tube and of the partially assembled detonation tube are shown below. |
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