Studies On Temperature Measurements And Soot Properties In Methane/Oxygen Premixed Flames

Soot is one of the main solid pollutants exhausted from incomplete combustion of hydrocarbon fuels.It has negative impacts on combustion equipments,environmental air and people's health,while it also has positive effects during the industrial production due to its special optical and structural properties.For the aim of better controlling the production of soot and taking advantage of its positive side,making an intensive study of its physical and chemical mechanisms of soot formation is the major task for all researchers.Hence,this dissertation chose two main diagnostics techniques-TPD and TSPD methods and focused on temperature and soot volume fraction in laminar methane/oxygen premixed flames under different working conditions and spatial positions.Also,TEM images of soot particles were achieved and analyzed quantificationally.The major research work and results of this dissertation are listed as follows:(1)Combustion system was built based on one MeKenna Flat Flame Burner,with flexible controlling of working conditions and the height of flame;TPD system was built in order to temperature data acquisition.Subsequent codes were programmed for temperature data calibration and soot volume fraction calculation;TSPD system was built with the function of sampling soot particles at target position.(2)According to the temperature histories,flame could be divided into two parts-soot containing part and non-soot containing part.TPD method could be available during the soot containing positions mostly,while temperature data could be available during all positions.During the TPD experiments,one new stage appeared after three classical stages and was named “Steady-Diameter Stage”.(3)Soot volume fraction calculated from TPD method matched well with results from LE method during the soot containing areas(HAB>7mm)except nascent-soot containing area(HAB=3?7mm),as errors increase with the appearance of “Steady-Diameter Stage”.C/O ratio and the outlet velocity are two main reasons controlling the appearance of it,and C/O ratio has the major impact during the nascent-soot containing area.(4)Analysis from TSPD shows,inside the beginning part of the flame,soot's surfacegrowth reaction is more active than its oxidation reaction,the size of primary particles increases from 20nm(HAB=10mm)to 29nm(HAB=25mm).With the process of combustion,surface-growth reaction still has the initiative,while its growth rate descreases from 28.83% to 5.65%,until the size of primary particle reaches the peak value,?30nm.(5)Analysis from the calculation of aggregate fractal dimension results shows,with the process of fuel combustion,aggregate fractal dimension descreases from 1.62 to 1.39,which means the size of soot aggregations increases and the structure becomes loose,but more ordered inside primary particles according to the TEM images.