The interaction mechanism of internally-staged-swirling stratified flame is complex,and the pilot flame has a manifest influence on flame stability.To study this,a series of experimental investigations for the pilot f...The interaction mechanism of internally-staged-swirling stratified flame is complex,and the pilot flame has a manifest influence on flame stability.To study this,a series of experimental investigations for the pilot flame has been carried out in a model swirl combustor by only supplying the pilot fuel.The CH*chemiluminescence images of the pilot flame are acquired by a high-speed camera with a CH*bandpass filter,whose dynamic characteristics are identified by image statistical analysis and proper orthogonal decomposition(POD)analysis.And the fast algorithm based on matrix theory proposed in this paper increases the operation efficiency and operability of POD.With the pilot equivalence ratioΦincrease,the pilot flame gradually shows an unstable state,whose POD energy distribution is significantly different.In the unstable state,the flame dynamics include three modes—spiral motion mode,flame shedding mode,and axial oscillation mode,whose formation reasons have also been further analyzed in combination with the experimental characteristics.And the fast Fourier transform(FFT)analysis of the time coefficients for the first four POD modes indicates all the dominant frequency is 280 Hz,which means the model combustor is in resonance.In addition,a sensitivity analysis based on the different image resolutions further reveals the robustness of the POD method and its optimization direction.These results emphasize the important influence of the pilot fuel flow rate on the stability of the pilot flame.展开更多
Facile strategy enabling the fabrication of carbon dots(CDs)with favorable performance useful for various applications is highly desirable.Here,we report the fabrication of highly fluorescent carbon dots(CDs)towards s...Facile strategy enabling the fabrication of carbon dots(CDs)with favorable performance useful for various applications is highly desirable.Here,we report the fabrication of highly fluorescent carbon dots(CDs)towards sensitive metal ion detection,brightly fluorescent printing pattern,as well as green flame retardants for synthetic polymeric materials.CDs are synthesized by solvothermal treatment of polypropylene carbonate(PPC)with ethylenediamine,and the quantum yield of CDs could increase from 30%to 86%by further adding trace of citric acid.The abundant functional groups on the surface of CDs allow CDs well incorporated into polymers to form CD-loaded polystyrene(PS)microspheres,which are employed to construct fluorescent supraballs via triphase microfluidic technique and used as“inks”for uniform fluorescent patterns.Interestingly,the resultant CDs show good flame retardancy for highly flammable polymeric foams and fibers.The CDs surpass previously reported flame-retardant additives,to show excellent combustion resistance that the addition of 20 wt%CDs causes 75%decrease in the peak of heat release rate(P-HRR)for polyurethane(PU)foams.Significantly,a molecular dynamics simulation process for PU/CDs combustion is constructed.This work may spur the preparation and application of highperformance carbon-based nanomaterials.展开更多
Since serious fire occurred frequently in recent years, fire safety of high-rise building has attracted extensive attention. A National Basic Research Program （973 program） of China has been set up by Ministry of Sc...Since serious fire occurred frequently in recent years, fire safety of high-rise building has attracted extensive attention. A National Basic Research Program （973 program） of China has been set up by Ministry of Science and Technology （MOST） of China in 2012 to meet the research requirements of fire safety in high-rise buildings. This paper reviews the current state of art of research on fire dynamics of high-rise buildings, including the up-to-date progress of this project. The following three subjects on fire dynamics of high-rise buildings are addressed in this review： the ejected flame and fire plume behavior over facade out of the compartment window, the flame spread behavior over facade thermal insulation materiMs, and the buoyancy-driven smoke transportation characteristics along long vertical channels in high-rise buildings. Prospective future works are discussed and summarized.展开更多
Lean Blow Out(LBO)poses a significant safety hazard when occurring in aero-engines.Understanding the lower stability limits of gas turbine combustors and the characteristics of spray flame close to LBO are imperative ...Lean Blow Out(LBO)poses a significant safety hazard when occurring in aero-engines.Understanding the lower stability limits of gas turbine combustors and the characteristics of spray flame close to LBO are imperative for safe operation.The objective of this work is to evaluate the effects of fuel decreasing rates and pressure drops of the injector on LBO performances in a multiswirl staged combustor equipped with an airblast injector.A set of hardware and control system was developed to realize a user-defined fuel supply law.High-speed imaging was applied to record complete LBO processes under the conditions of linear fuel reduction and stable airflow.Partical Image Velocimetry(PIV)and Planar Mie(PMie)scattering were used to acquire the flow fields and spray fields under non-reacting conditions.Experimental results have shown that LBO limits extend to leaner conditions as the pressure drop of the injector increases.With an increase of the fuel decreasing rate,the exhaust temperature before flame extinction increases,and the LBO Fuel-to-Air-Ratio(FAR)decreases.The time evolution of the integral CH*intensity conforms to a linear function during the LBO process.Proper Orthogonal Decomposition(POD)was used to analyze the dynamic characteristics of lean-burn flames.Under different fuel decreasing rates and pressure drops of the injector,flames close to LBO present similar modal spatial distributions,alternately appearing axial,radial,high-order axial,and high-order radial oscillations.展开更多
Today,with nonstop improvement in computational power,Large-Eddy Simulation(LES) is a high demanding research tool for predicting engineering flows.Such flows on high pressure condition like diesel engines is extensiv...Today,with nonstop improvement in computational power,Large-Eddy Simulation(LES) is a high demanding research tool for predicting engineering flows.Such flows on high pressure condition like diesel engines is extensively employed in ground and marine transportation,oblige the designer to control and predict toxic pollutants,while maintaining or improving their high thermal efficiency.This becomes one of the main challenging issues in decades.In the present work,numerical investigation of diffusion flame dynamics is performed in the near-field of high-Reynolds jet flow on high pressure condition encountered in diesel engine applications.This work discusses the implementation of Partially Stirred Reactor(PaSR) combustion model by the approaches of large eddy simulation(LES).The simulation results show that LES,in comparison with Reynolds-Averaged Navier-Stokes(RANS) simulation predicts and captures transient phenomena very well.These phenomena such as unsteadiness and curvature are inherent in the near-field of high Reynolds diffusion flame.The outcomes of this research are compared and validated by other researchers' results.Detailed comparisons of the statistics show good agreement with the corresponding experiments.展开更多
基金Youth Program of National Natural Science Foundation of China(Grant No.51806219)National Science and Technology Major Project(2017-V-0010)。
文摘The interaction mechanism of internally-staged-swirling stratified flame is complex,and the pilot flame has a manifest influence on flame stability.To study this,a series of experimental investigations for the pilot flame has been carried out in a model swirl combustor by only supplying the pilot fuel.The CH*chemiluminescence images of the pilot flame are acquired by a high-speed camera with a CH*bandpass filter,whose dynamic characteristics are identified by image statistical analysis and proper orthogonal decomposition(POD)analysis.And the fast algorithm based on matrix theory proposed in this paper increases the operation efficiency and operability of POD.With the pilot equivalence ratioΦincrease,the pilot flame gradually shows an unstable state,whose POD energy distribution is significantly different.In the unstable state,the flame dynamics include three modes—spiral motion mode,flame shedding mode,and axial oscillation mode,whose formation reasons have also been further analyzed in combination with the experimental characteristics.And the fast Fourier transform(FFT)analysis of the time coefficients for the first four POD modes indicates all the dominant frequency is 280 Hz,which means the model combustor is in resonance.In addition,a sensitivity analysis based on the different image resolutions further reveals the robustness of the POD method and its optimization direction.These results emphasize the important influence of the pilot fuel flow rate on the stability of the pilot flame.
基金supported by National Key Research and Development Program of China(2016YFB0401700,2018YFC1602800)National Natural Science Foundation of China(21736006)+1 种基金Fund of State Key Laboratory of Materials-Oriented Chemical Engineering(ZK201704,ZK201716)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)。
文摘Facile strategy enabling the fabrication of carbon dots(CDs)with favorable performance useful for various applications is highly desirable.Here,we report the fabrication of highly fluorescent carbon dots(CDs)towards sensitive metal ion detection,brightly fluorescent printing pattern,as well as green flame retardants for synthetic polymeric materials.CDs are synthesized by solvothermal treatment of polypropylene carbonate(PPC)with ethylenediamine,and the quantum yield of CDs could increase from 30%to 86%by further adding trace of citric acid.The abundant functional groups on the surface of CDs allow CDs well incorporated into polymers to form CD-loaded polystyrene(PS)microspheres,which are employed to construct fluorescent supraballs via triphase microfluidic technique and used as“inks”for uniform fluorescent patterns.Interestingly,the resultant CDs show good flame retardancy for highly flammable polymeric foams and fibers.The CDs surpass previously reported flame-retardant additives,to show excellent combustion resistance that the addition of 20 wt%CDs causes 75%decrease in the peak of heat release rate(P-HRR)for polyurethane(PU)foams.Significantly,a molecular dynamics simulation process for PU/CDs combustion is constructed.This work may spur the preparation and application of highperformance carbon-based nanomaterials.
基金supported by National Basic Research Program of China (2012CB719702)
文摘Since serious fire occurred frequently in recent years, fire safety of high-rise building has attracted extensive attention. A National Basic Research Program （973 program） of China has been set up by Ministry of Science and Technology （MOST） of China in 2012 to meet the research requirements of fire safety in high-rise buildings. This paper reviews the current state of art of research on fire dynamics of high-rise buildings, including the up-to-date progress of this project. The following three subjects on fire dynamics of high-rise buildings are addressed in this review： the ejected flame and fire plume behavior over facade out of the compartment window, the flame spread behavior over facade thermal insulation materiMs, and the buoyancy-driven smoke transportation characteristics along long vertical channels in high-rise buildings. Prospective future works are discussed and summarized.
基金supported by National Science and Technology Major Project (Nos. 2017-Ⅲ-0007-0032 and J2019-Ⅲ-00020045)
文摘Lean Blow Out(LBO)poses a significant safety hazard when occurring in aero-engines.Understanding the lower stability limits of gas turbine combustors and the characteristics of spray flame close to LBO are imperative for safe operation.The objective of this work is to evaluate the effects of fuel decreasing rates and pressure drops of the injector on LBO performances in a multiswirl staged combustor equipped with an airblast injector.A set of hardware and control system was developed to realize a user-defined fuel supply law.High-speed imaging was applied to record complete LBO processes under the conditions of linear fuel reduction and stable airflow.Partical Image Velocimetry(PIV)and Planar Mie(PMie)scattering were used to acquire the flow fields and spray fields under non-reacting conditions.Experimental results have shown that LBO limits extend to leaner conditions as the pressure drop of the injector increases.With an increase of the fuel decreasing rate,the exhaust temperature before flame extinction increases,and the LBO Fuel-to-Air-Ratio(FAR)decreases.The time evolution of the integral CH*intensity conforms to a linear function during the LBO process.Proper Orthogonal Decomposition(POD)was used to analyze the dynamic characteristics of lean-burn flames.Under different fuel decreasing rates and pressure drops of the injector,flames close to LBO present similar modal spatial distributions,alternately appearing axial,radial,high-order axial,and high-order radial oscillations.
文摘Today,with nonstop improvement in computational power,Large-Eddy Simulation(LES) is a high demanding research tool for predicting engineering flows.Such flows on high pressure condition like diesel engines is extensively employed in ground and marine transportation,oblige the designer to control and predict toxic pollutants,while maintaining or improving their high thermal efficiency.This becomes one of the main challenging issues in decades.In the present work,numerical investigation of diffusion flame dynamics is performed in the near-field of high-Reynolds jet flow on high pressure condition encountered in diesel engine applications.This work discusses the implementation of Partially Stirred Reactor(PaSR) combustion model by the approaches of large eddy simulation(LES).The simulation results show that LES,in comparison with Reynolds-Averaged Navier-Stokes(RANS) simulation predicts and captures transient phenomena very well.These phenomena such as unsteadiness and curvature are inherent in the near-field of high Reynolds diffusion flame.The outcomes of this research are compared and validated by other researchers' results.Detailed comparisons of the statistics show good agreement with the corresponding experiments.
