To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations,an experimental study has been conducted,taking account of the number of obstacles,obstacle di...To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations,an experimental study has been conducted,taking account of the number of obstacles,obstacle distance from ignition source,and stream-wise and cross-wise obstacle positions.The results show that the flame speed and peak overpressure increase with the increasing number of obstacles,while the time to reach the peak is not fully determined by it.And the configuration having the farthest obstacle produces a higher overpressure and takes a longer time to reach the peak,but a slower flame propagation speed is obtained.Similar explosion characteristics are also observed in the configurations with two obstacles fixed at different stream-wise positions.Furthermore,the experimental results demonstrate that the peak overpressures and flame speeds in configurations with central or staggered obstacles are relatively higher,which should to be avoided in practical processes to minimize the risk associated with methane–air explosion.展开更多
To research the characteristics of vented explosion of methane-air mixture in the pipeline,coal mine tunnel or other closed space,the experiments and numerical simulations were carried out.In this work,explosion chara...To research the characteristics of vented explosion of methane-air mixture in the pipeline,coal mine tunnel or other closed space,the experiments and numerical simulations were carried out.In this work,explosion characteristics and flame propagation characteristics of methane in pipeline and coal mine tunnel are studied by using an explosion test system,combined with FLACS software,under different vented conditions.The numerical simulation results of methane explosion are basically consistent with the physical experiment results,which indicates that the numerical simulation for methane explosion is reliable to be applied to the practice.The results show that explosion parameters(pressure,temperature and product concentration)of methane at five volume fractions have the same change trend.Nevertheless,the explosion intension of 10.0%methane is the largest and that of 9.5%methane is relatively weak,followed by 11.0%methane,8.0%methane and 7.0%methane respectively.Under different vented conditions,the pressure and temperature of methane explosion are the highest in the pipeline without a vent,followed by the pipeline where ignition or vent position is in each end,and those are the lowest in the pipeline with ignition and vent at the same end.There is no significant effect on final product concentration of methane explosion under three vented conditions.For coal mine tunnel,it is indicated that the maximum explosion pressure at the airproof wall in return airway with the branch roadway at 50 m from goaf is significantly decreased while that in intake airway does not change overwhelmingly.In addition,when the branch roadway is longer or its section is larger,the peak pressure of airproof wall reduces slightly.展开更多
The performance of microwave-assisted spark ignition(MAI)under exhaust gas recirculation conditions was explored with CO_(2)-diluted CH-air premixed spherical flames in a constant volume combustion chamber.The flame k...The performance of microwave-assisted spark ignition(MAI)under exhaust gas recirculation conditions was explored with CO_(2)-diluted CH-air premixed spherical flames in a constant volume combustion chamber.The flame kernel radius at 5 ms after spark started was selected to evaluate the property of MAI for CO_(2)dilution ratio of 0-20%and equivalence ratio of 0.6-1.4 with 1 kHz microwave pulse repetition frequency under 0.2 MPa ambient pressure.The results showed that the addition of microwave induced some wrinkles on the flame surface and strongly deformed the flame.MAI expanded the limit of CO_(2)dilution ratio to 16%with an equivalence ratio of 0.75,in which case the spark only(SI)failed to ignite the mixture.With the CO_(2)dilution ratio increasing,the wrinkles induced by microwave pulses decreased apparently,and the enhancement value of MAI peaked at 4%CO_(2)dilution ratio.The effect of microwave was considered in two aspects,namely,reaction kinetics and thermal effect,which shows a“trade-off”as CO_(2)dilution ratio rose.With 8%volume of CO_(2)added,the flammable interval(equivalence ratio 0.6-1.2)of mixture in SI mode shrunk,and MAI can maintain a flammable interval consistency with the case that no CO_(2)was added.展开更多
The flame structure of gasoline engine is complicated and has the characteristic of fractal geometry. A fractal combustion model was used to simulate the engine working cycle. Based on this model, the fractal dimensio...The flame structure of gasoline engine is complicated and has the characteristic of fractal geometry. A fractal combustion model was used to simulate the engine working cycle. Based on this model, the fractal dimension and laminar flame surface area of turbulent premixed flames were studied under different working conditions. The experimental system mainly includes an optical engine and a set of photography equipment used to shoot the images of turbulent flame of spark-ignition engine. The difference box-counting method was used to process 2D combustion images. In contrast to the experimental results, the computational results show that the fractal combustion model is an effective method of simulating the engine combustion process. The study provides a better understanding for flame structure and its propagation.展开更多
The supersonic mixing layer flow,consisting of a relatively cold,slow diluted hydrogen stream and a hot,faster air stream,is numerically simulated with detailed transport properties and chemical reaction mechanisms.Th...The supersonic mixing layer flow,consisting of a relatively cold,slow diluted hydrogen stream and a hot,faster air stream,is numerically simulated with detailed transport properties and chemical reaction mechanisms.The evolution of the combustion process in the supersonic reacting mixing layer is observed and unsteady phenomena of ignition,flame propagation and extinction are successfully captured.The ignition usually takes place at the air stream side of braid regions between two vortexes due to much higher temperature of premixed gases.After ignition,the flame propagates towards two vortexes respectively located on the upstream and downstream of the ignition position.The apparent flame speed is 1569.97 m/s,which is much higher than the laminar flame speed,resulting from the effects of expansion,turbulence,vortex stretching and consecutive ignition.After the flame arrives at the former vortex,the flame propagates along the outer region of the vortex in two branches.Then the upper flame branch close to fuel streamside distinguishes gradually due to too fuel-riched premixed mixtures in the front of the flame and the strong cooling effect of the adjacent cool fuel flow,while the lower flame branch continues to propagate in the vortex.展开更多
The leaks of pressurized hydrogen can be ignited if an ignition source is within a certain distance from the source of the leaks, and jet ftres or explosions may take place. In this paper, a high speed camera was used...The leaks of pressurized hydrogen can be ignited if an ignition source is within a certain distance from the source of the leaks, and jet ftres or explosions may take place. In this paper, a high speed camera was used to investigate the ignition kernel development, ignition probability and flame propagation along the axis of hydrogen jets, which leaked from a 3-ram-internal-diameter nozzle and were ignited by an electric spark. Experimental results indicate that for successful ignition events, the ignition delay time increases with an increase of the distance between the nozzle and the electrode. Ignitable zone of the hydrogen jets is underestimated if using the predicted hydrogen concentration along the jets centerline. The average rate of downstream flame decreases but that of the upstream flame increases with the electrode going far from the nozzle.展开更多
基金supported by the National Natural Science Foundation of China (Nos.51106044 and 51176021)the Research Foundation of Education Bureau of Henan Province of China (No.14A410007)
文摘To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations,an experimental study has been conducted,taking account of the number of obstacles,obstacle distance from ignition source,and stream-wise and cross-wise obstacle positions.The results show that the flame speed and peak overpressure increase with the increasing number of obstacles,while the time to reach the peak is not fully determined by it.And the configuration having the farthest obstacle produces a higher overpressure and takes a longer time to reach the peak,but a slower flame propagation speed is obtained.Similar explosion characteristics are also observed in the configurations with two obstacles fixed at different stream-wise positions.Furthermore,the experimental results demonstrate that the peak overpressures and flame speeds in configurations with central or staggered obstacles are relatively higher,which should to be avoided in practical processes to minimize the risk associated with methane–air explosion.
基金Project(51674193)supported by the National Natural Science Foundation of ChinaProject(2019-JLM-9)supported by the Natural Science Foundation of Shaanxi Province,ChinaProject(2019-M-663780)supported by the Postdoctoral Science Foundation,China。
文摘To research the characteristics of vented explosion of methane-air mixture in the pipeline,coal mine tunnel or other closed space,the experiments and numerical simulations were carried out.In this work,explosion characteristics and flame propagation characteristics of methane in pipeline and coal mine tunnel are studied by using an explosion test system,combined with FLACS software,under different vented conditions.The numerical simulation results of methane explosion are basically consistent with the physical experiment results,which indicates that the numerical simulation for methane explosion is reliable to be applied to the practice.The results show that explosion parameters(pressure,temperature and product concentration)of methane at five volume fractions have the same change trend.Nevertheless,the explosion intension of 10.0%methane is the largest and that of 9.5%methane is relatively weak,followed by 11.0%methane,8.0%methane and 7.0%methane respectively.Under different vented conditions,the pressure and temperature of methane explosion are the highest in the pipeline without a vent,followed by the pipeline where ignition or vent position is in each end,and those are the lowest in the pipeline with ignition and vent at the same end.There is no significant effect on final product concentration of methane explosion under three vented conditions.For coal mine tunnel,it is indicated that the maximum explosion pressure at the airproof wall in return airway with the branch roadway at 50 m from goaf is significantly decreased while that in intake airway does not change overwhelmingly.In addition,when the branch roadway is longer or its section is larger,the peak pressure of airproof wall reduces slightly.
基金Project(KF2028)supported by the State key Laboratory of Automotive Safety and Energy,ChinaProject(KF2028)supported by the State Key Laboratory of Automotive Safety and Energy,China。
文摘The performance of microwave-assisted spark ignition(MAI)under exhaust gas recirculation conditions was explored with CO_(2)-diluted CH-air premixed spherical flames in a constant volume combustion chamber.The flame kernel radius at 5 ms after spark started was selected to evaluate the property of MAI for CO_(2)dilution ratio of 0-20%and equivalence ratio of 0.6-1.4 with 1 kHz microwave pulse repetition frequency under 0.2 MPa ambient pressure.The results showed that the addition of microwave induced some wrinkles on the flame surface and strongly deformed the flame.MAI expanded the limit of CO_(2)dilution ratio to 16%with an equivalence ratio of 0.75,in which case the spark only(SI)failed to ignite the mixture.With the CO_(2)dilution ratio increasing,the wrinkles induced by microwave pulses decreased apparently,and the enhancement value of MAI peaked at 4%CO_(2)dilution ratio.The effect of microwave was considered in two aspects,namely,reaction kinetics and thermal effect,which shows a“trade-off”as CO_(2)dilution ratio rose.With 8%volume of CO_(2)added,the flammable interval(equivalence ratio 0.6-1.2)of mixture in SI mode shrunk,and MAI can maintain a flammable interval consistency with the case that no CO_(2)was added.
基金Supported by National Natural Science Foundation of China (No. 50876072) Tianjin Municipal Science and Technology Commission (No. 07JCYBJC03900 )
文摘The flame structure of gasoline engine is complicated and has the characteristic of fractal geometry. A fractal combustion model was used to simulate the engine working cycle. Based on this model, the fractal dimension and laminar flame surface area of turbulent premixed flames were studied under different working conditions. The experimental system mainly includes an optical engine and a set of photography equipment used to shoot the images of turbulent flame of spark-ignition engine. The difference box-counting method was used to process 2D combustion images. In contrast to the experimental results, the computational results show that the fractal combustion model is an effective method of simulating the engine combustion process. The study provides a better understanding for flame structure and its propagation.
文摘The supersonic mixing layer flow,consisting of a relatively cold,slow diluted hydrogen stream and a hot,faster air stream,is numerically simulated with detailed transport properties and chemical reaction mechanisms.The evolution of the combustion process in the supersonic reacting mixing layer is observed and unsteady phenomena of ignition,flame propagation and extinction are successfully captured.The ignition usually takes place at the air stream side of braid regions between two vortexes due to much higher temperature of premixed gases.After ignition,the flame propagates towards two vortexes respectively located on the upstream and downstream of the ignition position.The apparent flame speed is 1569.97 m/s,which is much higher than the laminar flame speed,resulting from the effects of expansion,turbulence,vortex stretching and consecutive ignition.After the flame arrives at the former vortex,the flame propagates along the outer region of the vortex in two branches.Then the upper flame branch close to fuel streamside distinguishes gradually due to too fuel-riched premixed mixtures in the front of the flame and the strong cooling effect of the adjacent cool fuel flow,while the lower flame branch continues to propagate in the vortex.
基金Supported by the Fundamental Research Funds for the Central UniversitiesNational Natural Science Foundation of China(No.50806071)and(No.51276177)
文摘The leaks of pressurized hydrogen can be ignited if an ignition source is within a certain distance from the source of the leaks, and jet ftres or explosions may take place. In this paper, a high speed camera was used to investigate the ignition kernel development, ignition probability and flame propagation along the axis of hydrogen jets, which leaked from a 3-ram-internal-diameter nozzle and were ignited by an electric spark. Experimental results indicate that for successful ignition events, the ignition delay time increases with an increase of the distance between the nozzle and the electrode. Ignitable zone of the hydrogen jets is underestimated if using the predicted hydrogen concentration along the jets centerline. The average rate of downstream flame decreases but that of the upstream flame increases with the electrode going far from the nozzle.
