Research On Online Gas Temperature Measurement In Underwater Detonation Process Based On Laser Absorption Spectroscopy Technology

The detonation-powered new type of underwater propulsion mode has the outstanding advantages of high theoretical thermal cycle efficiency,high specific impulse,and structural simplicity.Limited by the harsh environment such as strong vibration,high temperature and high pressure when the detonation engine is working,traditional contact test methods are difficult to obtain the transient change characteristics of the gas in the detonation tube during the underwater detonation process,and there are very few relevant studies at present.Tunable semiconductor laser absorption spectroscopy technology is an effective method to achieve non-contact combustion diagnosis in the detonation process,and has achieved fruitful results in combustion flow field diagnosis in the fields of aero engines and large combustion power generation devices.In this thesis,a study on the online testing of gas in the tube during underwater detonation process based on laser absorption spectroscopy was conducted,followed by an analysis of the characteristic parameters such as high-temperature gas temperature platform and exhaust duration,and an in-depth study on the evolution of the flow field at the exit of the tube during underwater explosion was conducted by combining the bubble pulsation images obtained by high-speed camera.The main contents of this study are as follows.（1）In view of the high temperature and high pressure environment in the tube during the underwater detonation process,a simulation study of laser absorption spectroscopy measurement was carried out.A physical model of underwater detonation was established,in which time-space conservation element and solution element algorithm were used to simulate the detonation development process in the tube,so as to establish a model to verify the feasibility of the laser absorption spectroscopy method to measure the characteristic changes of detonation gas in the tube.Meanwhile,a gas absorption spectrum wavelength modulation signal processing method based on frequency division multiplexing technology was proposed.The spectral characteristics of wavelength modulation absorption spectrum signals were analyzed,and the selection principle of modulation frequency in the application of frequency division multiplexing technology is given.The measurement accuracy of the absorption spectrum signal under noise interference conditions is analyzed.（2）In order to meet the demand of gas testing in the tube during underwater detonation,a laser absorption spectroscopy test device applicable to combustion chamber environment of strong vibration and high temperature and high pressure was designed and developed,and a distributed fiber optic based underwater detonation experimental test system was built in the laboratory,including a detailed description of each component of the test system.The wavelength scanning characteristics of tunable semiconductor lasers in the 7185.6 cm^-1 and7444.35 cm^-1 bands were tested and analyzed using etalon,and the accuracy of the laser absorption spectrum temperature measurement was verified using a three-zone tube furnace.（3）The temperature variation of the detonation gas in the tube during the underwater detonation under typical operating conditions is tested and studied.Combined with the bubble pulsation characteristics of the underwater detonation gas captured by high-speed cameras,the influence of the equivalent ratio,water depth,filling pressure and other factors on the temperature change of gas inside the tube in the underwater blast environment is in depth analyzed.Compared with that in air environment,the duration of the high temperature gas in the detonation tube in the underwater environment is proved to be significantly prolonged.Under conditions of the presence of negative pressure inside the detonation tube and the detonation gas bubble escaping from the tube exit,the water medium will enter into the tube,resulting in the loss of laser measured signal,and this is verified by detonation experiments in transparent tube.The thesis combines numerical simulation and experimental study to develop an online test method for detonation gas in the tube for underwater detonation environment,and achieves accurate measurement of the gas temperature and duration of the underwater detonation process.The study results can provide theoretical and data support for the development of diagnosis technology for underwater detonation propulsion.