Research On True Temperature Measurement Technique Of Solid Propellant Rocket Engine Flame

The plume of a solid fuel rocket motor is a kind of special flame,which presents the dynamic characteristics of high temperature,high speed and gas-solid two-phase flow.The plume temperature is an important parameter to study the propellant combustion process of the rocket engine and to evaluate the engine performance in order to optimize the engine characteristics.It is very difficult to measure the plume temperature for the complicated plume flow field and the harsh measurement environment.With the development of energy,national defense and aerospace industry,the plume temperature measurement of a solid propellant rocket engine has attracted increasing attention.It is of great significance for the scientific research and practice to research on the true temperature measurement technology of the plume.Multi-wavelength pyrometry is a non-contact method.The principle is to measure the brightness temperatures of the target at multiple wavelengths at a given moment,and then to obtain the true temperature of the target.The method has no special requirement for the target,and is especially suitable for the true temperature measurement of high temperature and very high temperature targets.In this thesis,the true temperature of a solid rocket motor plume is measured by multi-wavelength pyrometry.The aims of the thesis are threefold: first to explore the theoretical basis of emissivity sample choice to research on a new method of true temperature construction;second to develop a wide-range fiber-optic multi-wavelength pyrometer for true temperature measurement of the solid rocket motor plume to solve the problem that existing multi-wavelength pyrometers cannot obtain the plume true temperature when the temperature is lower than 1173K;third to research on a new method of effective wavelength calibration to solve the problem that traditional calibration method of the effective wavelength is invalid in the calibration of a fiber-optic multi-wavelength pyrometer because the signal is too weak.For these purposes,a series of jobs for true temperature measurement technique of a solid propellant rocket engine flame have been done.The main research contents are as follows:(1)In order to solve the problem of the lack of theoretical basis of emissivity sample selection in traditional multi-wavelength true temperature construction method,a new method based on model constraints is proposed to solve the true temperature.The traditional multi-wavelength true temperature construction method is summarized,and the main problems are analyzed.On the basis of the brightness temperature model,the relationship between the variation of brightness temperature and emissivity is found by theoretical deduction.Universal constraint conditions of emissivity model are proposed and based on the conditions,a multi-model true temperature construction method with constraints is established.The simulation results show that compared with the second measurement method,the calculation speed of this method can be improved by 81.3%;the emissivity model constraints can be used to effectively select emissivity samples,which provide a theoretical basis for emissivity sample choice.(2)It is difficult to measure the true temperature of the plume due to the difficulty of wide-range calibrating with a single blackbody radiation source.In order to solve the problem,a wide-range fiber-optic multi-wavelength pyrometer for the true temperature measurement of a solid rocket plume is developed.Radiation characteristics of a solid rocket plume are analyzed.Each system of the pyrometer is designed according to the actual demand.The optical system adopts optical fiber transmission technique to improve pyrometer reliability;and optics are separated from prisms to accurately locate targets.Based on preamplifier circuits,parallelly adjacent pixels of the photodiode detectors,and a proposed calibration method for 900K~1173K temperature zone on the basis of the logarithmic function,the measurement lower limit can reach 900 K and the measurement range of pyrometer can be widened to 900K~2700K.(3)To solve the traditional effective wavelength calibration problem of the fiber-optic multi-wavelength pyrometer,an effective wavelength calibration method is put forward based on the temperature calibration.Traditional wavelength calibration method of the pyrometer is analyzed.The inherent law of pyrometer temperature calibration data is studied according to the actual calibration data.Based on Planck's law,the relation model between the temperature calibration data and the effective wavelength is established,and the method to determine the effective wavelength from the temperature calibration data is proposed.This method not only provides a new way to get the effective wavelength fast,but also avoids the complexity of the wavelength calibration process.Simulations and experiments are used to verify the method.The simulation results show that after after random errors of ±1% are added to the temperature calibration data,the relative error between the wavelength result of the new method and the theoretical value is less than 4.7%,then the maximum absolute value of the relative error between the true temperature result and the theoretical value is 0.7%.The experimental results show that compared with the traditional calibration method,the maximum absolute value of the relative error of the wavelength from the new method is 1.9%,then the maximum value of the absolute error of the true temperature is 2.4K.So the method is feasible.(4)The experimental results and the uncertainty analysis of the pyrometer are presented.The proposed pyrometer is used for temperature measurement experiments of a tungsten halogen lamp filament and a blackbody furnace in the laboratory.The results show the validity and rationality of the pyrometer.The whole process of the plume true temperature of a solid rocket motor was measured in ground test and the experimental results were analyzed.The validity of the multi-wavelength true temperature construction method with model constraints is further verified based on the experimental data.The measurement uncertainty of the pyrometer is analyzed and its combined uncertainty is 2.07%.