The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine ...The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry（PIV）system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.展开更多
This paper studies the flame dynamics near lean blowout(LBO)conditions in a stratified swirl burner.The novel BASIS burner is used and fueled with premixed methane/air mixture at atmospheric conditions.In the experime...This paper studies the flame dynamics near lean blowout(LBO)conditions in a stratified swirl burner.The novel BASIS burner is used and fueled with premixed methane/air mixture at atmospheric conditions.In the experiments,only the pilot flame works with four different equivalent ratios.It is found that as the flame changes from stable combustion to near LBO,the flame macrostructure changes from V-shape to M-shape.Meanwhile,a characteristic frequency of 405 Hz is found in the spectrum of heat release signal.The closer to LBO,the higher amplitude is found at the frequency peak.Post-processing of flame images illustrates that the 405 Hz comes from the circumferential movement of the flame.Large-eddy simulations(LESs)via OpenFOAM reproduce the flame dynamics near LBO,which agrees with the experimental results.LESs provide more insights into the flow fields,showing that the characteristic frequency of 405 Hz comes from the flame-vortex interaction.This study reveals the mechanism of flame and vortex interactions in a stratified swirl burner near LBO.The heat release signal is also found can be used as a candidate precursor for LBO.展开更多
Characteristics of a premixed, swirl methane/air diffusion flame at atmospheric pressure are measured by filtered Rayleigh scattering(FRS). Three operating conditions are investigated with the equivalence ratios of th...Characteristics of a premixed, swirl methane/air diffusion flame at atmospheric pressure are measured by filtered Rayleigh scattering(FRS). Three operating conditions are investigated with the equivalence ratios of the methane/air flame covering a range of 0.67–0.83. Under each condition, single-shot and averaged FRS images over a region measured 39.3×65.6 mm^(2) at seven cross sections of the flame are collected to demonstrate the flame behavior. A gradient calculation algorithm is applied to identify reaction zone locations and structures in the instantaneous FRS measurements.Statistical analysis for the mean FRS measurements is performed by means of joint probability density functions. The experimental results indicate that thermochemical state of the swirl flame is strongly influenced by equivalence ratio, leading to varieties of flame structures and temperature distributions. The gradient of the instantaneous FRS images clearly illustrates the characteristics of the reaction zone. The results also demonstrate that FRS can provide detailed insights into the behavior of turbulent flames.展开更多
The coupling of swirl flame with discrete plasma or particle phases offers promising opportunities in combustion control and nanomaterial synthesis.Over recent years,studies on the dynamics and stabilization of swirl ...The coupling of swirl flame with discrete plasma or particle phases offers promising opportunities in combustion control and nanomaterial synthesis.Over recent years,studies on the dynamics and stabilization of swirl flames have produced significant progress.Starting from swirl-stabilized combustion,we focus mainly on two recent trends in reviewing these new concepts in the field of combustion related to electrically/plasma-assisted dynamics control and flame aerosol synthesis of nanomaterials.We organize the material by four themes:(a)unsteady combustion dynamics and control methods;(b)electrically-and plasma-assisted combustion dynamics control;(c)swirl-flame-based synthesis of nanocomposites;and(d)in situ diagnostic methods for the complex combustion above.展开更多
The study of flame development characteristics is crucial in the study of flame propagation, extinction, and for the investigation of combustion cyclic variability in SI engine. The aim of this study is to investigate...The study of flame development characteristics is crucial in the study of flame propagation, extinction, and for the investigation of combustion cyclic variability in SI engine. The aim of this study is to investigate the characteristics of flame development in a lean-stratified combustion of Natural Gas Engine （CNG） in a single cylinder direct injection （DI） engine at a specific motor speed, and fixed injection timing and air-fuel ratio by varying only the swirl level at the intake. The engine was set to run at 1800 rpm with half-load throttled. The ignition advance was set at 21.5 BTDC, and to create an overall lean and stratified mixture, injection timing was set at 61 BTDC with an air-fuel-ratio of 40.5 （λ=2.35）. Variable turbulent flow conditions near spark-plug were created by positioning the swirl control valves （SCV） at the intake port just before the two intake valves. This was done by setting one of the valves at full open position and the other one at 0% closed, 50% closed and 100% closed positions in order to achieve medium tumble （no swirl）, medium swirl and high swirl flows in the cylinder, respectively. An endoscope and CCD camera assembly was utilized to capture the flame images from the tumble plane at the intake side of the engine ever）, 2 CA degrees after ignition timing （AIT） for 40 CAs. It was observed that flame growth rate and flame convection velocity are increasing with increasing the swirl level. The total combustion duration is, thus, shorter in swirl induced combustion than without. However, COV in IMEP is greater in swirl induced flow cases than the medium tumble.展开更多
基金Supported by the Ministry of Higher Education Malaysia and Universiti Teknologi Malaysia(Research University Grant Tier-1,Grant No.06H29)Ministry of Science,Technology and Innovation(MOSTI)Malaysia(Grant No.03-01-06-KHAS01)
文摘The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry（PIV）system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.
基金This work was financially supported by the National Science and Technology Major Project(2017-III-0004-0028)National Natural Science Foundation of China(91641109).
文摘This paper studies the flame dynamics near lean blowout(LBO)conditions in a stratified swirl burner.The novel BASIS burner is used and fueled with premixed methane/air mixture at atmospheric conditions.In the experiments,only the pilot flame works with four different equivalent ratios.It is found that as the flame changes from stable combustion to near LBO,the flame macrostructure changes from V-shape to M-shape.Meanwhile,a characteristic frequency of 405 Hz is found in the spectrum of heat release signal.The closer to LBO,the higher amplitude is found at the frequency peak.Post-processing of flame images illustrates that the 405 Hz comes from the circumferential movement of the flame.Large-eddy simulations(LESs)via OpenFOAM reproduce the flame dynamics near LBO,which agrees with the experimental results.LESs provide more insights into the flow fields,showing that the characteristic frequency of 405 Hz comes from the flame-vortex interaction.This study reveals the mechanism of flame and vortex interactions in a stratified swirl burner near LBO.The heat release signal is also found can be used as a candidate precursor for LBO.
基金Project supported by National Science and Technology Major Projects of China (Grant No. J2019-V-005-0096)。
文摘Characteristics of a premixed, swirl methane/air diffusion flame at atmospheric pressure are measured by filtered Rayleigh scattering(FRS). Three operating conditions are investigated with the equivalence ratios of the methane/air flame covering a range of 0.67–0.83. Under each condition, single-shot and averaged FRS images over a region measured 39.3×65.6 mm^(2) at seven cross sections of the flame are collected to demonstrate the flame behavior. A gradient calculation algorithm is applied to identify reaction zone locations and structures in the instantaneous FRS measurements.Statistical analysis for the mean FRS measurements is performed by means of joint probability density functions. The experimental results indicate that thermochemical state of the swirl flame is strongly influenced by equivalence ratio, leading to varieties of flame structures and temperature distributions. The gradient of the instantaneous FRS images clearly illustrates the characteristics of the reaction zone. The results also demonstrate that FRS can provide detailed insights into the behavior of turbulent flames.
基金funded mainly by the National Natural Science Foundation of China(Grant Nos.91641204 and 51676109)
文摘The coupling of swirl flame with discrete plasma or particle phases offers promising opportunities in combustion control and nanomaterial synthesis.Over recent years,studies on the dynamics and stabilization of swirl flames have produced significant progress.Starting from swirl-stabilized combustion,we focus mainly on two recent trends in reviewing these new concepts in the field of combustion related to electrically/plasma-assisted dynamics control and flame aerosol synthesis of nanomaterials.We organize the material by four themes:(a)unsteady combustion dynamics and control methods;(b)electrically-and plasma-assisted combustion dynamics control;(c)swirl-flame-based synthesis of nanocomposites;and(d)in situ diagnostic methods for the complex combustion above.
文摘The study of flame development characteristics is crucial in the study of flame propagation, extinction, and for the investigation of combustion cyclic variability in SI engine. The aim of this study is to investigate the characteristics of flame development in a lean-stratified combustion of Natural Gas Engine （CNG） in a single cylinder direct injection （DI） engine at a specific motor speed, and fixed injection timing and air-fuel ratio by varying only the swirl level at the intake. The engine was set to run at 1800 rpm with half-load throttled. The ignition advance was set at 21.5 BTDC, and to create an overall lean and stratified mixture, injection timing was set at 61 BTDC with an air-fuel-ratio of 40.5 （λ=2.35）. Variable turbulent flow conditions near spark-plug were created by positioning the swirl control valves （SCV） at the intake port just before the two intake valves. This was done by setting one of the valves at full open position and the other one at 0% closed, 50% closed and 100% closed positions in order to achieve medium tumble （no swirl）, medium swirl and high swirl flows in the cylinder, respectively. An endoscope and CCD camera assembly was utilized to capture the flame images from the tumble plane at the intake side of the engine ever）, 2 CA degrees after ignition timing （AIT） for 40 CAs. It was observed that flame growth rate and flame convection velocity are increasing with increasing the swirl level. The total combustion duration is, thus, shorter in swirl induced combustion than without. However, COV in IMEP is greater in swirl induced flow cases than the medium tumble.
基金This work was supported by the National Natural Science Foundation of China(No.52206222,No.22227901)State Key Laboratory of Laser Interaction with Matter Foundation(SKLLIM2009).
