Quantitative OH-PLIF Technology And Kinetics Study In Mixture Gas Combustion

With the continuous economic development,energy crisis and environmental problems have become increasingly serious.Biomass syngas and natural gas have become more and more widely used as sustainable green clean energy in industrial applications.Due to the diversity of gas components and the complex combustion mechanism,this paper develops The PLIF optical diagnostic method quantitatively measures the concentration of OH groups in the combustion,and then quantitatively analyzes the combustion kinetics of CH₄ and H₂ premixed combustion.This article first deduces the PLIF fluorescence signal formula from detailed theories and finds that its main influencing factors are: the laser aspect,the energy level of the excited medium,the collection system,and the mole fraction of the excited medium.By ensuring that the parameters of the entire PLIF experimental system are unchanged,a laser with an excitation wavelength of 283.55 nm is selected to achieve a proportional relationship between the PLIF fluorescence signal and the molar fraction of OH groups.The selected H₂/Air combustion chemical reaction mechanism includes 13 components and 19 elementary reaction equations.The numerical calculation is compared with the experiment,and the flame structure characteristics and distribution trends of the two are analyzed,and the entire numerical calculation result is obtained.The OH molar concentration distribution of the flame,combined with the fluorescence intensity distribution of the PLIF experiment,calculated a proportional factor of 160,000.Then the same experimental system settings were used to study the CH₄/Air and CH₄/H₂/Air laminar premixed combustion.At the same time,the effect of N₂ dilution on the combustion was also studied.The experimental results were quantitatively analyzed by combining the resulting scale factors.The following conclusions:?1?When the equivalence ratio is kept at a constant value,with the increase of Reynolds number,the flame propagation rate does not change,the OH concentration on the axis gradually decreases,and the OH concentration distribution in the overall flame gradually distributes to the two wings as the Reynolds number increases.?2?When the equivalence ratio is greater than 1,the flame propagation rate decreases and the OH group concentration decreases as the equivalence ratio increases.From the CH₄/Air laminar premixed combustion experiment,it was found that as the equivalence ratio gradually increased from 1 to 1.6,the OH group molar fraction gradually decreased,and the maximum and minimum values were 0.01075 and 0.00146,respectively.?3?From the CH₄/H₂/Air laminar premixed combustion experiments,it is found that the flame propagation rate first increases and then decreases when the equivalence ratio is 0.8 to 1.2.The maximum equivalence ratio is 1 and the flame propagation rate is 0.5598.m/s.When ??1,there are two peaks of the OH group molar concentration on the axis,but there is only one peak when ?<1,and this phenomenon does not occur in the CH₄/Air laminar premixed combustion.?4?In the N₂ dilution experiment,select working condition H7??=1.2,Re=500?.As the dilution ratio increases,the internal flame height increases,the OH group mole fraction on the axis decreases,and the flame propagation rate decreases.?5?The study of the flame propagation rate about laminar premixed combustion shows that the results obtained by obtaining the actual flame front are significantly smaller than the results of traditional calculation methods.This is due to the fact that the actual flame front is presented.Irregularity,the traditional methods of calculation are used approximate fitting,ignoring the local irregularities,resulting in the flame front area is small,the resulting flame propagation rate is large.