Investigation About Quantitative Measurement Of Flame Surface Density Of Premixed Turbulent Flame Based On Orthogonal PLIF And OH/CH₂O-PLIF

By analyzing planar laser induced fluorescence?PLIF?images,the key parameters such as flame surface density???,flame brush thickness and turbulent combustion velocity in turbulent flame can be obtained,and the three-dimensional?3D?flame structure can be reconstructed based on two-dimensional?2D?PLIF images and the key parameters.It is not clear,however,whether the 2D PLIF images can accurately reflect the 3D flame structure,and a lot of work were done to compare the?based on the measurement of single component,which lacked evidence.This article has carried on the related experimental research to these two questions.First,the 2D OH distribution of methane/air turbulent premixed flames was measured using orthogonal PLIF in both horizontal plane?perpendicular to the flame propagation direction?and vertical plane?parallel to the flame propagation direction?,and the?was calculated by analyzing the OH-PLIF images.The?in the two planes was obtained under various conditions,i.e.,different exit velocities,different locations,and different equivalence ratios.The results showed that the?in the vertical plane was smaller than that in the horizontal plane under almost all the conditions,and this indicates that the wrinkled degree of the vertical plane of the flame is less than that of horizontal plane of the flame.In addition,the difference in?between the two planes is decided by the burner exit velocity,the location,and the equivalence ratio,namely the difference in?between the two planes of the flame increases gradually with the increase of the turbulence intensity?Re increasing?,and when the equivalent ratio is close to 1,the difference in?between the two planes of the flame is small,and the difference in?between the two planes of the flame is small at downstream position of the flame.Therefore,the most commonly used two-dimensional PLIF technique for measuring the vertical plane of a tapered flame has some limitations at accurately reflecting the 3D flame structure.Next,in this paper,a method of measuring?by using formaldehyde?CH₂O?is proposed and compared with the method of measuring?by using OH.The OH and CH₂O distribution of methane/air turbulent premixed flames were simultaneously measured using PLIF,and the?was calculated by analyzing the OH-PLIF images and CH₂O-PLIF images,respectively.The?based on the measurement of two components was obtained under various conditions,i.e.,different exit velocities,and different equivalence ratios.The results showed that the?based on the measurement of OH and CH₂O are almost the same when y/d?y is the flame height,d is the outlet diameter of the burner?is smaller?namely upstream of the flame?.While the?based on the measurement of CH₂O is relatively smaller when y/d is large?namely downstream of the flame?.With the exit velocity increase?namely increase turbulence intensity?or the equivalence ratio is close to 1,the?based on the measurement of OH and CH₂O are almost the same at smaller y/d.Therefore,it is feasible to measure the?of the premixed turbulent flame with CH₂O-PLIF quantitatively.Namely,it is can get a more accurate?value using CH₂O-PLIF in the low turbulence or lean burn conditions at the upper part of the flame measurement.