| Pulse Detonation Engine(PDE)is a novel engine based on detonation,which has a wide prospect of application.The theoretical and experimental researches on PDE have already made great progress,but there are still many problems and challenges to fulfil its engineering application.Real-time parameters variations of flow field parameters such as temperature,velocity,concentration of gas,etc.can provide a direct description of PDE working process.Therefore,the research on the diagnosis of detonation flow can help to improve the performance of PDE,and it has important engineering application value.As a non-contract measuring methods,laser absorption spectroscopy is well suitable for detonation flow diagnosis,since it can provide fast response,nonintrusive,sensitive solution for situ measurements of multiple flow-field parameters,compared with traditional sampling-based sensing method.In this thesis,based on laser absorption spectroscopy,diagnoses of the insides,outlet and external flow field of the detonation tube in the valveless gas-liquid continuous pulse detonation engine are carried out.PDE working process,impulse characteristics and the distribution of gas temperature and H2O concentration are analyzed.The reconstruction algorithm of non-uniform flow field is studied by simulation.The main contents are as follows:(1)CO absorption spectrum of 4388.77cm-1 is chosen to research the absorption spectrum characteristics at negative pressures.The spectral line parameters,such as linestrength,linewidth and self-broadening coefficient,are recalibrated,which provide more accurate line parameters for the diagnosis of CO concentration inside the detonation tube.CO2 absorption spectrum in near-infrared band of 6330?6337cm-1 is chosen to study the characteristics of absorption spectrum at high pressures by simulation and experiment.Considering the absorption spectrum characteristics at high pressures,a new method to obtain spectrum absorption by fitting the whole transmitted signal with absorption parameters is proposed.The research provides the basis of laser absorption spectroscopy applied to the diagnosis of high pressure exhaust injection stage of PDE.(2)Diagnosis of flow field inside the detonation tube is accomplished based on absorption spectroscopy in a gas-liquid valveless pulse detonation engine by wavelength division multiplexing technology,and the working process of PDE is researched.Based on the principle of double spectral line direct absorption spectroscopy technology,a fiber-distributed laser absorption system is establised to realize the remote control of PDE flow field diagnosis.H2O absorption line pairs of 7158.6/7444.35cm-1 are chosen to accomplish the diagnosis of temperature and H2O concentration during single working cycle of PDE.Two new methods of inferring the duration of filling process with the variation of absorption peak and transmitted laser signal intensity are proposed.The detonation performance of PDE under different filling ratio is studied experimentally,and the condition of the filling ratio to support the stable detonation is analyzed.Under experimental conditions,there exists stable detonation inside the tube with a filling rate of no lower than 84%,while the combustion mode is deflagration when the filling rate is equal to,or lower than 76%?The temperature and H2O concentration of flow field inside the PDE are calculated,and are analyzed combining the different stages of the engine.CO absorption line of 4338.77cm-1 is chosen to accomplish the diagnosis of CO concentration during single working cycle of the PDE under different working conditions,and the effects of fuel equivalence ratio on PDE working process are studied.Under experimental conditions,the effect of fuel equivalence ratio on the early stage of PDE working cycle,including the detonation propagation and the period of high-temperature and high-speed gas emission,is lower than that on the slow burning stage.(3)PDE impulse characteristics are researched based on laser absorption spectrum Doppler velocity measurement.H2O line pairs of 7158.6cm-1/7444.35cm-1 are chosen to realize the temperature diagnosis at the outlet of the PDE,and H2O line of 7158.6cm-1 is chosen to realize the diagnosis of flow field velocity.PDE impulse is calculated based on momentum principle,thus the impulse is measured indirectly.Exhaust emission parameters in single working cycle of PDE,such as gas density,impulse and exhaust gas quality,are obtained.Under experimental conditions,the PDE impulse is 1.87 N·s,and the gas momentum contributes 69.7%of the total impulse.The impulse produced by the momentum of detonation exhaust during the expansion stage attached to detonation,gas "choked"expansion stage,weaken expansion stage and slow burning stage are 53.0%?27.8%?6.7%and 12.5%,and the corresponding total mass of gas emission is 17%?29.6%?16%and 37.4%.(4)Considering the situation that the boundary of external flow field of PDE is unknown and changes all the time during the detonation engine works,flow field reconstruction test technology with single optical path is introduced.According to the simulation results of space-time conservation element(CE/SE),the external flow field distribution reconstructed models,including rectangular distribution model,trapezoidal distribution model and Gauss distribution model considering temperature boundary,are established.Based on multispectral absorption technology,more information of the non-uniform flow field can be obtained by increasing the number of absorption lines in the test path.A nonlinear equation group consisting of four lines(7170.28cm-1?7170.28cm-1?7185.60 cm-1 and 7444.35cm-1)is established,and the least square method is used to solve the equation group to obtain the unknown parameters.The flow field parameters of CE/SE simulation are reconstructed under the three models,and the trapezoidal distribution model,which is consistent with the simulation of CE/SE,is selected to monitor the external flow field of PDE.Based on direct absorption method combined with time division multiplexing technology,four absorption lines of H2O scan the detonation flow at the same time.The variation of temperature and H2O concentration are monitored at different distances from the nozzle during single working cycle of PDE.A method is proposed to determine the cut-off point of PDE near and far noise field by using the relative magnitude of detonation wave velocity and local velocity of sound,while the local velocity of sound can be obtained by the temperature distribution of PDE external flow field from experiment.(5)Considering the fact that the temperature of the external flow field is in a large range self-adaptive algebraic tomography algorithm(SAATA)is developed based on two-dimensional flow field reconstruction technology with multi optical path.The feasibility of SAATA in two-dimensional reconstruction of PDE flow field is investigated through simulations.SAATA can both perform well at temperature reconstructions in 300-3000K,and can ensure a better temperature sensitivity than two wavelength scheme.The capability of SAATA to capture the flow shape,peak position and amplitude for both flat and sharp temperature distributions is demonstrated with simulation.SAATA algorithm is less sensitive to measurement noise,and has a better stability which ensures a better reconstruction performance at noise levels from 0.1%to 10%in projections.In this thesis,researches of PDE flow field diagnosis are carried out based on laser absorption spectroscopy technology,and the results directly describe the working process of PDE.A non-uniform flow field testing technique based on SAATA in flow field reconstruction is studied by theory and simulation.The research can provide support for expanding the detonation test field with absorption spectroscopy technology,help to promote the detonation mechanism research and enhance the level of detonation engine control technology. |
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