Pulse Detonation Engine Characterization and Control Using Tunable Diode-Laser Sensors
Mattison, Daniel W.
Brophy, Christopher M.
Sanders, Scott T.
Hinckley, Kevin M.
Jeffries, Jay B.
Hanson, Ronald K.
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One of the phenomena limiting the performance of pulse detonation engines (PDEs) is detonation failure due to pulse-to-pulse interference. To better understand and control such interferences, two novel laser diagnostic techniques, based on absorption spectroscopy, have been developed and then used to demonstrate effective realtime control. The rst technique utilizes a tunable diode-laser (TDL) sensor to measure H2O temperature and concentration in the tube tail end at the Naval Postgraduate School’s (NPS) PDE facility and in the tube head end at Stanford University’s (SU) PDE facility. This sensor, capable of measuring temperatures from 300 to 1300 K at 3.33 kHz, reveals the temporal history of temperature for multipulse engines. In its application to the NPS facility, the sensor shows a distinct change in temperature pro le when the engine pulse rate is changed from 5 Hz, where successful detonations are achieved, to 7 Hz, where interference produces undesirable ame holding and subsequent de agrations on some pulses.We observed that the geometry evaluated possessed excess recirculation at the higher pulse rates resulting in ame holding at or near the point of injection. In its application to the SU PDE, this sensor reveals a temperature pro le characteristic of detonation failure that could be used in future control schemes. The second diagnostic technique developed is used to monitor fuel and is employed in an active, real-time control scheme. For this sensor, we monitor the C2H4 (ethylene) concentration at the tail end of the NPS PDE initiator tube, which is operating at 20 Hz. When fuel is detected at the tail end, the sensor sends a signal to re the ignitor. Compared to xed-timing ignitor actuation, this control promotes more consistent detonation initiation and reduces mis re events. These two new laser diagnostic techniques provide useful tools for studying pulse-to-pulse interference and lay the groundwork for future,more advanced TDL-based PDE control strategies.
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