Study On Combustion Characteristics Of 2-acetylfuran Spherical Premixed Flame Based On Schlieren Imaging Measurement Technology

Furan derivatives such as 2-acetyl furan（AF）have been regarded as a promising fossil fuel substitute or fossil fuel additive because of their excellent physical and chemical properties.However,although the research on furan derivatives has made some progress in recent years,the basic combustion characteristics of most furan derivatives still need to be studied.Therefore,this work studied the basic combustion characteristics of AF,including laminar burning velocity（LBV）and flame instability,and compared the combustion characteristics of 2-ethyl furan（EF）and 2-methyl furan（MF）.Firstly,a high-speed schlieren imaging system for spherical expansion flame was built.Based on this system,the flame morphology images of AF under the conditions of initial temperature of 433-493 K,initial pressure of 1-3 bar,and equivalence ratio of0.8-1.4 were taken in this study.On this basis,the LBV of AF under these conditions was measured using the constant pressure method（CPM）.According to the LBV data of AF under different working conditions,the initial temperature,initial pressure,and equivalence ratio can affect its LBV.Meanwhile,the relationship between the stretch rate and flame radius of AF spherical flame has been also obtained.It is found that the initial pressure can have a remarkable impact on the stretching rate of AF flame:under the same flame radius,the higher the initial pressure is,the smaller the flame stretch rate is.Secondly,considering the flame cellular morphology is complex and the unstable characteristics are difficult to quantify,this work quantitatively analyzed the cellular unstable characteristics of flame using image processing technology and a three-dimensional reconstruction algorithm,to quantitatively show the cellular development of AF flame.In addition,combined with the linear instability theory,this study made an in-depth study and analysis of AF instability both experimentally and theoretically.The linear stability analysis showed that the intrinsic instability of AF flame is affected by the initial pressure and equivalence ratio,which is consistent with the experimental results.At the same time,the theoretical results also showed that the stabilization effect caused by the thermal diffusion effect(effective Lewis number Le_eff>1 in this study) weakened with the increase of initial pressure or equivalence ratio,resulting in the decrease of critical flame radius.Thirdly,the local cellular region of AF spherical flame was experimentally and theoretically analyzed to investigate the effect of initial crack on cellular structure.The results showed that the spontaneous formation of hydrodynamic small cells is the main stage of AF flame cellularization,which is stronger than crack bifurcation.In addition,although the linear stability theory overestimates the minimum wavelength of the flame,there is a consistent trend between the theoretical and experimental results,and the experimental average cell wave number is within the unstable region predicted by the theory.Last but not least,the combustion characteristics of AF,EF,and MF were compared.Under the same initial conditions,EF has higher flame LBV than MF and AF.In terms of instability propensity,MF becomes unstable earlier than EF and AF,and MF flame has a faster cell proliferation rate before reaching the cut-off of hydrodynamic saturation.In contrast,AF is more prone to instability.When the initial pressure is less than 3 bar and the flame radius is less than 45 mm,AF will not be cellular.