Study On Detection Technology Of Combustion Products CO With Frequency Modulation Spectroscopy

Carbon monoxide(CO)is not only the final product of hydrocarbons that are not fully combusted but also an intermediate product in the full combustion of hydrocarbons,which plays an important role in diagnosing combustion reaction pathways and processes.Observing the state of carbon monoxide in the combustion reaction helps to the understanding of the chemical mechanism of the elementary element and the microscopic mechanism of the combustion reaction and the further control of the combustion process so as to improve the combustion efficiency.Therefore,there is an urgent need for a more comprehensive observation of the chemical reaction parameters of carbon monoxide during combustion to control the combustion process precisely.The main work of this paper includes:Firstly,frequency modulation spectroscopy(FMS)experimental system was built by a laser direct-injection current.The laser was subjected to high-frequency modulation(in the order of GHz)by means of direct-injection current.The FMS was built for the first time in the research group,which realized the functions such as visualization and automatic acquisition.Through Allan analysis,the minimum detection absorbance of the absorption term of the FMS system was 2.15E-5,and the minimum detection absorbance of the dispersion term was 2.24E-5.The synthetic uncertainty of the absorption term and the dispersion term was measured,which was 8.29E-4 and 1.08E-3,respectively.Secondly,an improved method of FMS was proposed to solve the influence of light intensity fluctuation and phase random on FMS signal.A method of correcting the light intensity fluctuation through the direct current component in the detected signal was put forward.This paper made a theoretical analysis and experimental verification on this method,which proved that it can reduce the error by 16.8%.Based on the lineshape of FMS,the quantitative relationship between the extremal frequency of demodulated signal and the modulation frequency and linewidth was derived.And the signal was successfully modulated by this quantitative relationship.Thirdly: an experimental study on the online detection of combustion products CO was carried out.The direct absorption spectroscopy and FMS signals in the combustion reaction were measured to obtain the CO concentration and temperature.The difference of FMS signals in CO standard gas and CO in flame was compared.The CO absorption lines in the infrared band of the ethylene flame and the ethanol flame were detected to plot the temperature distribution of the flame and the CO concentration distribution.In this paper,the improved FMS technique was proposed to reduce the error caused by the fluctuation of light intensity and eliminate the demodulation phase uncertainty caused by phase randomization.Through the research on FMS technology and CO concentration and temperature measurement in flame,the new combustion diagnosis technology is explored to provide measurement technology support for the development of new combustion technology.