Study On The CH₄/O₂/N₂Flame Temperature And OH Radical Concentration By Ultra-violet Absorption Spectroscopy

Higher requirements are put forward to study the combustion process and increasethe combustion efficiency because of the more prominent environment pollution and therapid development of aerospace propulsion technology. The essence of the combustiondiagnosis is to collect all kinds of information which can reflect combustion condition,including temperature, concentration of substances, flow field, and so on. The researchof temperature and reactant concentration information in the process of combustionreaction is two important aspects in the study of the combustion process. Absorptionspectrum technology has many advantages, such as high measuring accuracy, shortresponse, simple system, and strong anti-jamming capacity. These advantages make itmaybe become a kind of important means of diagnosis. At the same time, it is a kind ofstandardization method for the planar laser induced fluorescence (PLIF) technique.Based on tunable ultraviolet pulse laser absorption spectrum technology, the paperselects the absorption lines of P1(2)(308.639nm) and Q1(8)(309.240nm) which arethe OH (A-X) transition spectrum, makes use of the wavelength scanning technology,adopts flat flame burner experimental platform, and study the temperature and OHconcentration in the CH4/O2/N2premixed flame.Firstly, theoretically deduces theory formula and determines the measurementmethod of the flame temperature and the concentration of OH according to the LambertBeer-absorption law and calculate some theoretical parameters, such as the linesintensity, the ratio of the integral absorption rate, temperature sensitivity, linear function,and so on, combining the OH base ground spectral analysis and the data which comefrom the LIFBASE.Secondly, designs the ultraviolet absorption spectroscopy experiment plan, sets upthe experimental platform, and uses the PLIF technique to measure the fluorescence ofOH in the flat flame burner. The result shows that OH distribution is uniform and stable.So the flame is a suitable object to the quantitative research of the combustiondiagnosis.Finally, conducts the ultraviolet absorption spectroscopy experiment to measure theabsorption spectrums at different positions under the equivalent ratio of CH4/O2/N2mixed flame is0.8, and fit with the theoretical calculation to determine the two-dimensional distribution of the flame temperature and flame OH concentration, theexperiment finally get the temperature is2000K and the concentration is26000ppmnear the face of the burner and the result is consistent with the university of Cambridgeand Stanford University. Then, we obtain the temperature and OH concentration ofdifferent equivalent ratios under different rates of flow using the same method.