Normal diffusion flame(NDF)of acid gas with a H_(2)S concentration below 50.0%(vol)generally exhibits a low flame temperature in a low-level oxygen enrichment atmosphere under Claus conditions,resulting in flame insta...Normal diffusion flame(NDF)of acid gas with a H_(2)S concentration below 50.0%(vol)generally exhibits a low flame temperature in a low-level oxygen enrichment atmosphere under Claus conditions,resulting in flame instability.This research proposed that inverse diffusion flame(IDF)was applied to acid gas combustion for enhancing flame temperature.IDF of acid gas was compared with fuel gas cocombustion(FGC),split flow of acid gas(SFAG)and high-level oxygen enrichment combustion(OEC).Additionally,the effect of CO_(2)addition on the IDF of H_(2)S was investigated.The results indicated that a stable flame could be observed in the IDF of acid gas,its peak flame temperature was about 801.0 K,which was higher than that in the OEC,FGC and SFAG with a value of about 591.0,684.0 and 734.0 K,respectively.IDF of acid gas was contributed to the formation of sulfur and H_(2),and mainly involved the oxidation zone and the chemical decomposition and oxidation zone in sequence.In the IDF,CO_(2)exhibited a better oxidation performance,and the peak flame temperature was decreased by about 21.0 K with an increase in CO_(2)addition from 50.8%to 59.5%(vol),whereas significantly enhanced the oxidation reaction rate of H_(2)S,and the peak volume fraction of SO_(2)was increased from 5.812%to 7.075%.The application of IDF to acid gas combustion achieved the objective for improving flame temperature in low-level oxygen enrichment atmosphere under Claus conditions,providing a new perspective in the sulfur recovery and hydrogen production from acid gas.展开更多
Biodiesel is a kind of clean and renewable energy. The effect of ethanol addition on the flame characteristics of waste oil biodiesel is studied by using OH-PLIF technique from the perspective of OH radical evolution....Biodiesel is a kind of clean and renewable energy. The effect of ethanol addition on the flame characteristics of waste oil biodiesel is studied by using OH-PLIF technique from the perspective of OH radical evolution. Ethanol addition leads to the appearance of diffusion flame reaction interface ahead of schedule and shortens the diffusion flame height. The experimental results show a linear correlation between the flame height and the fuel flow rate for a given fuel and oxidant. The same conclusion is drawn from the theoretical analysis of the approximate model. In addition. ethanol addition makes the average OH signal intensity of flame at different fuel flow rate tend to be consistent and the fuel flow rate enlarge where the flame field shows the strongest oxidation performance. Average OH signal intensity begins to weaken at larger fuel flow rate, which indicates that fuel flow rate of fuels blended with ethanol can change in larger range and does not significantly affect the uniformity of combustion.展开更多
This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ...This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ） is varied from 3% to 80% and the temperature （Tcof） from 1200 K to 1700 K. The Eddy Dissipation Concept （EDC） model with detailed reaction mechanisms GRI-Mech 3.0 is used for all simulations. To validate the modeling, several JHC flames are predicted under the experimental conditions of Dally et al. [Proc. Combust. Inst., 29 （1）, 1147-1154 （2002）] and the results obtained match well with the measurements. Results demonstrate that, when Yo2 decreased, the diffusion combustion is likely to transform from traditional combustion to MILD （Moderate or Intense Low-oxygen Dilution） combustion mode. When Tcof is higher, the temperature distribution over the whole domain trends to be more uniform. Reducing yo2 or Tcof leads to less production of intermediate species OH and CO. It is worth noting that if Yo2 is high enough （ Yo2 〉80%）, increasing Yo2 does not cause obvious temperature increase.展开更多
Soot,a product of insufficient combustion,is usually in the form of aggregate. The multi-scattering of soot fractal aggregates has been proved to play an important role in studying the soot radiative properties,which ...Soot,a product of insufficient combustion,is usually in the form of aggregate. The multi-scattering of soot fractal aggregates has been proved to play an important role in studying the soot radiative properties,which is rarely considered in predicting the radiative heat transfer in combustion flame. In the present study,based on the weighted sum of gray soot fractal aggregate(WSGSA) model,which is used to predict the temperature field and soot aggregates in turbulent diffusion flame,the flame temperature distribution and soot volume fraction distribution under the conditions of the model without considering radiation,the default radiation model in Fluent software and the WSGSA model are calculated respectively. The results show that the flame temperature will be seriously overestimated without considering radiation and the maximum relative discrepancy of flame centerline temperature is about 64.5%. The accuracy will be improved by the default radiation model in the Fluent software,but the flame temperature is still overestimated and the maximum relative discrepancy of flame centerline temperature is about 42.1%. However,more satisfactory results can be obtained by the WSGSA model,and the maximum relative discrepancy of flame centerline temperature is no more than 15.3%. Similar conclusions can also be obtained in studying the temperature distribution along different flame heights. Moreover,the soot volume fraction can be predicted more accurately with the application of the WSGSA model. Both without considering radiation and using the default radiation model in the Fluent software will result in the underestimating of soot volume fraction. All the results reveal that the WSGSA model can be used to predict the temperature and soot aggregates in the CH/air turbulent diffusion flame.展开更多
A combined computational and experimental investigation to examine temperature and soot volume fraction in coflow ethylene-air diffusion flames was presented.A numerical simulation was conducted by using a relatively ...A combined computational and experimental investigation to examine temperature and soot volume fraction in coflow ethylene-air diffusion flames was presented.A numerical simulation was conducted by using a relatively detailed gas-phase chemistry and complex thermal and transport properties coupled with a semi-empirical two-equation soot model.Thermal radiation was calculated using the discrete ordinates method.An image processing technique and a decoupled reconstruction method were used to simultaneously measure the distributions of temperature and soot volume fraction.The results show that the maximum error for temperature does not exceed 10% between the prediction and the measurement.And the maximum error is 6.9% for soot volume fraction between prediction and measurement.Additional simulations were performed to explore the effects of global equivalence ratio on diffusion flames and the soot formation.The results display that the soot formation increases with decreasing the coflow air velocity.And the soot formation in each case appears in the annular region,where the temperature ranges from about 1 000 K to 2 000 K and the profile becomes taller and wider when the coflow air is decreased.展开更多
The buoyancy effect on micro hydrogen jet flames in still air was numerially studied.The results show that when the jet velocity is relatively large(V≥0.2 m/s),the flame height,width and temperature decrease,whereas ...The buoyancy effect on micro hydrogen jet flames in still air was numerially studied.The results show that when the jet velocity is relatively large(V≥0.2 m/s),the flame height,width and temperature decrease,whereas the peak OH mass fraction increases significantly under normal gravity(g=9.8 m/s^2).For a very low jet velocity(e.g.,V=0.1 m/s),both the peak OH mass fraction and flame temperature under g=9.8 m/s^2 are lower than the counterparts under g=0 m/s^2.Analysis reveals that when V≥0.2 m/s,fuel/air mixing will be promoted and combustion will be intensified due to radial flow caused by the buoyancy effect.However,the flame temperature will be slightly decreased owing to the large amount of entrainment of cold air into the reaction zone.For V=0.1 m/s,since the heat release rate is very low,the entrainment of cold air and fuel leakage from the rim of tube exit lead to a significant drop of flame temperature.Meanwhile,the heat loss rate from fuel to inner tube wall is larger under g=9.8 m/s^2 compared to that under g=0 m/s^2.Therefore,the buoyancy effect is overall negative at very low jet velocities.展开更多
In order to provide guideline for choosing a suitable tube-wall thickness(d)for the micro-jet methane diffusion flame,the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in...In order to provide guideline for choosing a suitable tube-wall thickness(d)for the micro-jet methane diffusion flame,the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in the present work.The results show that the blow-off limit of micro-jet methane diffusion flame firstly increases and then decreases with the increase of tube-wall thickness.Subsequently,the underlying mechanisms responsible for the above non-monotonic blow-off limit are discussed in terms of the flow filed,strain effect and conjugate heat exchange.The analysis indicates that the flow field is insignificant for the non-monotonic blow-off limit.A smaller strain effect can induce the increase of the blow-off limit fromd=0.1 to 0.2 mm,and a worse heat recirculation effect can induce the decrease of the blow-off limit fromd=0.2 to 0.4 mm.The non-monotonic blow-off limit is mainly determined by the heat loss of flame to the tube-wall and the performance of tube-wall on preheating unburned fuel.The smallest heat loss of flame to the tube-wall and the best performance of tube-wall on preheating unburned fuel result in the largest blow-off limit atd=0.2 mm.Therefore,a moderate tube-wall thickness is more suitable to manufacture the micro-jet burner.展开更多
Any biogas produced by the anaerobic fermentation of organic materials has the advantage of being an environmentally friendly biofuel.Nevertheless,the relatively low calorific value of such gases makes their effective...Any biogas produced by the anaerobic fermentation of organic materials has the advantage of being an environmentally friendly biofuel.Nevertheless,the relatively low calorific value of such gases makes their effective utilization in practical applications relatively difficult.The present study considers the addition of hydrogen as a potential solution to mitigate this issue.In particular,the properties of turbulent diffusion jet flames and the related pollutant emissions are investigated numerically for different operating pressures.The related numerical simulations are conducted by solving the RANS equations in the frame of the Reynolds Stress Model in combination with the flamelet approach.Radiation effects are also taken into account and the combustion kinetics are described via the GRI-Mech 3.0 reaction model.The considered hydrogen fuel enrichment spans the range from 0%to 50%in terms of volume.Pressure varies between 1 and 10 atm.The results show that both hydrogen addition and pressure increase lead to an improvement in terms of mixing quality and have a significant effect on flame temperature and height.They also reduce CO_(2)emissions but increase NOx production.Prompt NO is shown to be the predominant NO formation mechanism.展开更多
A turbulent nonpremixed flame of methanol air stabilized on a bluff body is simulated by the conditional moment closure(CMC) model. An elliptic, conservative formulation of the CMC is employed with the turbulent diff...A turbulent nonpremixed flame of methanol air stabilized on a bluff body is simulated by the conditional moment closure(CMC) model. An elliptic, conservative formulation of the CMC is employed with the turbulent diffusion term modeled by the turbulent eddy viscosity. Results of flow, conditional temperature and species concentration profiles with respect to mixture fraction, and unconditional temperature, OH and NO fields are obtained. Reasonable agreement between experiments and predictions to show that the CMC model is capable to predicting the species concentration and temperature in turbulent nonpremixed combustion characterized by a finite reaction rate. Discrepancy on the rich side may partly be due to limitation of the singly conditional moment closure, substitution of the unconditional mean variables for the conditional ones, or lack of adequate chemical kinetics on the rich side of methanol air reaction.展开更多
To study the configuration and conductivity effects on micro-scale methane-air flames by electric field and iron wind,different electric field forces and iron winds are generated by needle,circle and plate electrodes ...To study the configuration and conductivity effects on micro-scale methane-air flames by electric field and iron wind,different electric field forces and iron winds are generated by needle,circle and plate electrodes respectively in different electrodes heights under both AC and DC fields though experiments. Experimental results showed that the flame characteristics are affected by needle electrodes mainly through the action of ion wind,by plate type electrodes mainly through the action of electric field force and by annular electrodes through both the electric field force and ion wind at the same time. Under DC field 's effects of all electrodes types,the flame will consequently go down while the voltage reached to a limit value,and it will breakdown under the strong effect of the ion wind by needle electrodes. The results also showed the influence by different electrodes types to the current characteristics,resistance properties and configuration of themicro-scale flames.展开更多
The operating range of the flow rate or flow velocity for the micro-jet flame is quite wide,which can be used as the heat source.In order to optimize the micro-jet tube combustor in terms of the solid material,the pre...The operating range of the flow rate or flow velocity for the micro-jet flame is quite wide,which can be used as the heat source.In order to optimize the micro-jet tube combustor in terms of the solid material,the present paper numerically investigates the impact of thermal conductivity(λs)on the operating limit of micro-jet flame.Unexpectedly,the non-monotonic blow-off limits with the increase ofλs is found,and the corresponding generation mechanisms are analyzed in terms of the thermal coupling effect,flow field,and strain effect.At first,the lower preheating temperature of the fuel and larger heat loss amount to the environment lead to a larger blow-off limit at a largerλs.After that,the smaller local flow velocity in the vicinity of flame root and smaller strain effect slightly increase the blow-off limit with the continuously increasingλs.Therefore,it is deduced that the applied performance of micro-jet combustor with a smaller thermal conductivity is better in terms of the blow-off limit.展开更多
An experimental study investigated the characteristics of a stretched cylindrical diffusion flame, with a convex curvature with respect to the air stream, in response to periodic air flow velocity oscillation. The fue...An experimental study investigated the characteristics of a stretched cylindrical diffusion flame, with a convex curvature with respect to the air stream, in response to periodic air flow velocity oscillation. The fuel was methane diluted with nitrogen, and the oxidizer air. The oscillation frequency was varied from 5 to 250 Hz. The results are summarized as follows. Though the fluctuation amplitude of the air stream velocity gradient was constant with respect to the frequency, the amplitude of the fuel stream increased. The fluctuation amplitude of the flame radius changed quasi-steadily from 5 to 25 Hz, and decreased with increasing frequency in the frequency range greater than 50 Hz. The flame luminosity did not respond quasi-steadily at 5 Hz, and the oscillation amplitude of flame luminosity was less than that of a steady flame, over the same velocity fluctuation range. The oscillation amplitude of luminosity peaked at 50 Hz, and was greater than that of a steady flame. It is considered that this complex change in flame luminosity with respect to frequency was closely related to the phase difference in the respective time variations in the ratio of flame thickness to radius, the velocity gradients of the air and fuel streams, and the magnitude of these values, with the ratio of flame thickness to radius related to the flame curvature effect, the velocity gradient of the air stream correlated to the flame stretch effect, and the velocity gradient of the fuel stream impacting the fuel transportation.展开更多
Combustion is a chemical phenomenon in which a multitude of elementary chemical reactions take place, resulting in the overall process of fuel oxidation. Natural gas fuel has been explored for a few decades and extrac...Combustion is a chemical phenomenon in which a multitude of elementary chemical reactions take place, resulting in the overall process of fuel oxidation. Natural gas fuel has been explored for a few decades and extracted for a few years in the region of Paraguayan Chaco, near Bolivia border. Currently, natural gas is not very important in Paraguay＇s energy matrix, however it could be in the near future if higher volumes are extracted and transported to the most populated cities, specially to the capital. In order to improve Paraguayan natural gas combustion performance, an understanding of its fundamental properties and the combustion pathways is required. This study presents new data for Paraguayan Chaco natural gas combustion in a laminar counterflow diffusion flame configuration at atmospheric pressure. Visible chemiluminescence of excited radicals CH＊ and C2^＊ is employed experimentally. 1D numerical simulation was carried out using Paraguayan Chaco natural gas chemical composition and a standard kinetic mechanism, to which we added CH＊ and C] reactions. Typical flame structures resulting from simulation are presented and a validation of the model is realized comparing experimental and numerical CH＊ and C~ radicals profiles.展开更多
Oxygen rich combustion is a mean to increase the energy efficiency and to contribute to CO2 capture. Influence of oxygen enriched air on the stability of methane flames from non premixed laminar jets has been investig...Oxygen rich combustion is a mean to increase the energy efficiency and to contribute to CO2 capture. Influence of oxygen enriched air on the stability of methane flames from non premixed laminar jets has been investigated experimentally. The burner consists of two coaxial jets： methane flowing out of the inner, oxidizer from the outer. The flame behavior is studied according to the proportion of oxygen in the oxidizer jet, the oxidizer and the methane jets velocities. The flame is either anchored to the burner, lifted, stationary or not or blown-out. The addition of oxygen produces a decrease of the lift height, a reduction of the length of the reaction zone and an increase in the soot emission. These results have been reported into diagrams of stability where the flame configurations are connected to the competition between the dynamic effect of the injection velocity and the chemical effect of oxygen addition.展开更多
Oxygenated fuels can reduce harmful emissions without affecting engine performance,meeting the big challenge in the transportation industry,which keeps the environment safe and reduces global warming.This study invest...Oxygenated fuels can reduce harmful emissions without affecting engine performance,meeting the big challenge in the transportation industry,which keeps the environment safe and reduces global warming.This study investigates the impact of biodiesel injection strategies and fuel injection pressures(FIP)on diesel engine exhaust emission characteristics.The engine is fuelled with 20%Jatropha biodiesel(JB)and 80%diesel,named JB20D.The ratios of fuel injection pressures started with injecting the fuel(diesel and JB20D)from 200 bar to 500 bar.The experimental outcomes indicate that the engine performance of brake-specific fuel consumption increased by 21.36%from the burning of JB20D compared with diesel,while brake thermal efficiency improved by 6.54%for low and high FIP compared to the diesel.The high fuel injection pressures slightly decrease the nitrogen oxide(NOX)emissions for both diesel and biodiesel.The emissions of NOX decreased from the combustion of JB20D by 18.7%under high fuel injection pressures compared to diesel.The concentration of soot particulate decreased by 20.4%form JB20D combustion than those combusted from diesel fuel.展开更多
The computer simulation of the combustion process in blast furnace(BF) stove has been studied by using the k-ε-g turbulent diffusion flame model.The combustion process in blunt annular ceramic burner was calculated b...The computer simulation of the combustion process in blast furnace(BF) stove has been studied by using the k-ε-g turbulent diffusion flame model.The combustion process in blunt annular ceramic burner was calculated by using the software.The profiles of gas and air velocity,temperature of the combustion products,concentration of the components,and the shape and length of the flame during combustion have been researched.Compared with the original annular ceramic burner,the new design of the blunt one improves the mixing of the gas and the air significantly,and shortened the length of the flame.展开更多
One way for reducing tar is oxidative and thermal cracking by partial combustion of the biomass producer gas in the gas reformer. Cracking and polymerization of the tar occur simultaneously at the proximity of inverse...One way for reducing tar is oxidative and thermal cracking by partial combustion of the biomass producer gas in the gas reformer. Cracking and polymerization of the tar occur simultaneously at the proximity of inverse diffusion flame. Experimental study has been performed to clarify the effect of hydrogen concentration on soot formation and the growth of polycyclic aromatic hydrocarbons. In the present study, hydrogen concentration is controlled by the small amount of hydrogen addition to the oxidizer. The main results are as follows. Soot formation is suppressed by the small amount of hydrogen addition. The suppression of soot formation is caused by higher concentration of hydrogen. Carbon yield increases by hydrogen addition since carbon content in the undetectable components by the integrated gas chromatograph decreases. In addition, the increase in carbon yield is caused mainly by the increase in carbon monoxide stemmed from reforming of high-boiling components.展开更多
The utilization of ammonia as an alternative fuel is of great significance in the carbon neutrality strategy. However, the ammonia flame extinction mechanism induced by growing oscillations with its cramped flammabili...The utilization of ammonia as an alternative fuel is of great significance in the carbon neutrality strategy. However, the ammonia flame extinction mechanism induced by growing oscillations with its cramped flammability range, sluggish propagation speed, and poor stability is still not studied in sufficient details. In this paper, the high-fidelity simulations with efficient continuation computation and detailed models are conducted to investigate the ammonia extinction dynamics as a function of hydrogen blending ratio, and to reveal the governing sub-processes in flame extinction and oscillation development. It is found that the extinction and onset of oscillatory instability in the ammonia/hydrogen spherical diffusion flame (SDF) derive from the interaction of competing chemistry with diffusive leakage losses. Chemical oscillations occurring at the maximum temperature iso-contour are primarily responsible for the near-limit flame oscillations. In the rich-side low-temperature region, although the local heat production is inappreciable, the strong diffusive losses with governing, adverse contributions to the ignition chemistry play a leading role in flame extinction. The reactions dominating the extinction limit are also important for the oscillation frequency;the reactions that help to extend the extinction limit also tend to increase the frequency, and vice versa. The extinction limit and frequency depend mainly on the major reactant diffusivities (including NH_(3), H_(2), and O_(2)) and heat conduction, while the diffusivities of other radicals and products are fairly unimportant. Hydrogen addition could remarkably extend the steady-state and oscillatory extinction limits of ammonia SDFs, and reduce the oscillation frequency since the imaginary eigenvalue is depressed.展开更多
The plenoptic imaging technique provides a promising approach to the non-invasive three-dimensional measurement, especially for the high-temperature combustion diagnosis. We establish a light-field convolution imaging...The plenoptic imaging technique provides a promising approach to the non-invasive three-dimensional measurement, especially for the high-temperature combustion diagnosis. We establish a light-field convolution imaging model for diffusion flame in this work, considering the radiation transfer process inside the diffusion flame and the light transfer process inside the focused plenoptic camera together. The radiation transfer process is described by the radiation transfer equation and solved by the generalized source multi-flux method. Wave optics theory is adopted to describe the light transfer process, combining Fresnel diffraction and the phase conversion of the lens. The flame light-field image is obtained by the light-field convolution imaging model and adopted as the measurement signal to reconstruct three-dimensional temperature field. The inverse problem of temperature reconstruction is solved by the least square QR decomposition method. The simulative temperature reconstruction work is conducted, including the inverse analysis, the uncertainty analysis, and the measurement noise influence. All the results show that the proposed measurement method is available to reconstruct three-dimensional temperature with satisfactory accuracy and acceptable uncertainty. Both symmetric and asymmetric distributed temperature fields are investigated, and the reconstructed results prove the validity and universality of the measurement method.展开更多
Flame structures of a syngas swirl-stabilized diffusion flame in a model combustor were measured using the OH-PLIF method under different fuel and air swirl intensity.The flame operated under atmospheric pressure with...Flame structures of a syngas swirl-stabilized diffusion flame in a model combustor were measured using the OH-PLIF method under different fuel and air swirl intensity.The flame operated under atmospheric pressure with air and a typical low heating-value syngas with a composition of 28.5% CO,22.5% H2 and 49% N2 at a thermal power of 34 kW.Results indicate that increasing the air swirl intensity with the same fuel,swirl intensity flame structures showed little difference except a small reduction of flame length;but also,with the same air swirl intensity,fuel swirl intensity showed great influence on flame shape,length and reaction zone distribution.Therefore,compared with air swirl intensity,fuel swirl intensity appeared a key effect on the flame structure for the model combustor.Instantaneous OH-PLIF images showed that three distinct typical structures with an obvious difference of reaction zone distribution were found at low swirl intensity,while a much compacter flame structure with a single,stable and uniform reaction zone distribution was found at large fuel-air swirl intensity.It means that larger swirl intensity leads to efficient,stable combustion of the syngas diffusion flame.展开更多
基金supported by the National Natural Science Foundation of China(22178114,U23A20131)the social development science and technology tackling project of 2021"Scientific and Innovative Action Plan of Shanghai"(21DZ1209000)。
文摘Normal diffusion flame(NDF)of acid gas with a H_(2)S concentration below 50.0%(vol)generally exhibits a low flame temperature in a low-level oxygen enrichment atmosphere under Claus conditions,resulting in flame instability.This research proposed that inverse diffusion flame(IDF)was applied to acid gas combustion for enhancing flame temperature.IDF of acid gas was compared with fuel gas cocombustion(FGC),split flow of acid gas(SFAG)and high-level oxygen enrichment combustion(OEC).Additionally,the effect of CO_(2)addition on the IDF of H_(2)S was investigated.The results indicated that a stable flame could be observed in the IDF of acid gas,its peak flame temperature was about 801.0 K,which was higher than that in the OEC,FGC and SFAG with a value of about 591.0,684.0 and 734.0 K,respectively.IDF of acid gas was contributed to the formation of sulfur and H_(2),and mainly involved the oxidation zone and the chemical decomposition and oxidation zone in sequence.In the IDF,CO_(2)exhibited a better oxidation performance,and the peak flame temperature was decreased by about 21.0 K with an increase in CO_(2)addition from 50.8%to 59.5%(vol),whereas significantly enhanced the oxidation reaction rate of H_(2)S,and the peak volume fraction of SO_(2)was increased from 5.812%to 7.075%.The application of IDF to acid gas combustion achieved the objective for improving flame temperature in low-level oxygen enrichment atmosphere under Claus conditions,providing a new perspective in the sulfur recovery and hydrogen production from acid gas.
基金Project(51766007)supported by the National Natural Science Foundation of ChinaProject(U1602272)supported by the NSFC-Yunnan Joint Fund Project+1 种基金Project(2015FB128)supported by the Natural Science Fund Project in Yunnan Province,ChinaProject(CNMRCUTS1704)supported by the Research Fund from State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization,China
文摘Biodiesel is a kind of clean and renewable energy. The effect of ethanol addition on the flame characteristics of waste oil biodiesel is studied by using OH-PLIF technique from the perspective of OH radical evolution. Ethanol addition leads to the appearance of diffusion flame reaction interface ahead of schedule and shortens the diffusion flame height. The experimental results show a linear correlation between the flame height and the fuel flow rate for a given fuel and oxidant. The same conclusion is drawn from the theoretical analysis of the approximate model. In addition. ethanol addition makes the average OH signal intensity of flame at different fuel flow rate tend to be consistent and the fuel flow rate enlarge where the flame field shows the strongest oxidation performance. Average OH signal intensity begins to weaken at larger fuel flow rate, which indicates that fuel flow rate of fuels blended with ethanol can change in larger range and does not significantly affect the uniformity of combustion.
基金Supported by the National Natural Science Foundation of China （51276002）, and the Specific Research Fund for the Doctoral Program of Higher Education of China （20110001130014）.
文摘This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ） is varied from 3% to 80% and the temperature （Tcof） from 1200 K to 1700 K. The Eddy Dissipation Concept （EDC） model with detailed reaction mechanisms GRI-Mech 3.0 is used for all simulations. To validate the modeling, several JHC flames are predicted under the experimental conditions of Dally et al. [Proc. Combust. Inst., 29 （1）, 1147-1154 （2002）] and the results obtained match well with the measurements. Results demonstrate that, when Yo2 decreased, the diffusion combustion is likely to transform from traditional combustion to MILD （Moderate or Intense Low-oxygen Dilution） combustion mode. When Tcof is higher, the temperature distribution over the whole domain trends to be more uniform. Reducing yo2 or Tcof leads to less production of intermediate species OH and CO. It is worth noting that if Yo2 is high enough （ Yo2 〉80%）, increasing Yo2 does not cause obvious temperature increase.
基金supported by the National Natural Science Foundation of China (No. 51806103)the Aeronautical Science Foundation of China (No.201928052002)the Fundamental Research Funds for the Central Universities(No.NT2021007)。
文摘Soot,a product of insufficient combustion,is usually in the form of aggregate. The multi-scattering of soot fractal aggregates has been proved to play an important role in studying the soot radiative properties,which is rarely considered in predicting the radiative heat transfer in combustion flame. In the present study,based on the weighted sum of gray soot fractal aggregate(WSGSA) model,which is used to predict the temperature field and soot aggregates in turbulent diffusion flame,the flame temperature distribution and soot volume fraction distribution under the conditions of the model without considering radiation,the default radiation model in Fluent software and the WSGSA model are calculated respectively. The results show that the flame temperature will be seriously overestimated without considering radiation and the maximum relative discrepancy of flame centerline temperature is about 64.5%. The accuracy will be improved by the default radiation model in the Fluent software,but the flame temperature is still overestimated and the maximum relative discrepancy of flame centerline temperature is about 42.1%. However,more satisfactory results can be obtained by the WSGSA model,and the maximum relative discrepancy of flame centerline temperature is no more than 15.3%. Similar conclusions can also be obtained in studying the temperature distribution along different flame heights. Moreover,the soot volume fraction can be predicted more accurately with the application of the WSGSA model. Both without considering radiation and using the default radiation model in the Fluent software will result in the underestimating of soot volume fraction. All the results reveal that the WSGSA model can be used to predict the temperature and soot aggregates in the CH/air turbulent diffusion flame.
基金Projects(50806024,50806023 and 50806026) supported by the National Natural Science Foundation of China
文摘A combined computational and experimental investigation to examine temperature and soot volume fraction in coflow ethylene-air diffusion flames was presented.A numerical simulation was conducted by using a relatively detailed gas-phase chemistry and complex thermal and transport properties coupled with a semi-empirical two-equation soot model.Thermal radiation was calculated using the discrete ordinates method.An image processing technique and a decoupled reconstruction method were used to simultaneously measure the distributions of temperature and soot volume fraction.The results show that the maximum error for temperature does not exceed 10% between the prediction and the measurement.And the maximum error is 6.9% for soot volume fraction between prediction and measurement.Additional simulations were performed to explore the effects of global equivalence ratio on diffusion flames and the soot formation.The results display that the soot formation increases with decreasing the coflow air velocity.And the soot formation in each case appears in the annular region,where the temperature ranges from about 1 000 K to 2 000 K and the profile becomes taller and wider when the coflow air is decreased.
基金Project(51576084)supported by the National Natural Science Foundation of China。
文摘The buoyancy effect on micro hydrogen jet flames in still air was numerially studied.The results show that when the jet velocity is relatively large(V≥0.2 m/s),the flame height,width and temperature decrease,whereas the peak OH mass fraction increases significantly under normal gravity(g=9.8 m/s^2).For a very low jet velocity(e.g.,V=0.1 m/s),both the peak OH mass fraction and flame temperature under g=9.8 m/s^2 are lower than the counterparts under g=0 m/s^2.Analysis reveals that when V≥0.2 m/s,fuel/air mixing will be promoted and combustion will be intensified due to radial flow caused by the buoyancy effect.However,the flame temperature will be slightly decreased owing to the large amount of entrainment of cold air into the reaction zone.For V=0.1 m/s,since the heat release rate is very low,the entrainment of cold air and fuel leakage from the rim of tube exit lead to a significant drop of flame temperature.Meanwhile,the heat loss rate from fuel to inner tube wall is larger under g=9.8 m/s^2 compared to that under g=0 m/s^2.Therefore,the buoyancy effect is overall negative at very low jet velocities.
基金Project(51876074)supported by the National Natural Science Foundation of China。
文摘In order to provide guideline for choosing a suitable tube-wall thickness(d)for the micro-jet methane diffusion flame,the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in the present work.The results show that the blow-off limit of micro-jet methane diffusion flame firstly increases and then decreases with the increase of tube-wall thickness.Subsequently,the underlying mechanisms responsible for the above non-monotonic blow-off limit are discussed in terms of the flow filed,strain effect and conjugate heat exchange.The analysis indicates that the flow field is insignificant for the non-monotonic blow-off limit.A smaller strain effect can induce the increase of the blow-off limit fromd=0.1 to 0.2 mm,and a worse heat recirculation effect can induce the decrease of the blow-off limit fromd=0.2 to 0.4 mm.The non-monotonic blow-off limit is mainly determined by the heat loss of flame to the tube-wall and the performance of tube-wall on preheating unburned fuel.The smallest heat loss of flame to the tube-wall and the best performance of tube-wall on preheating unburned fuel result in the largest blow-off limit atd=0.2 mm.Therefore,a moderate tube-wall thickness is more suitable to manufacture the micro-jet burner.
文摘Any biogas produced by the anaerobic fermentation of organic materials has the advantage of being an environmentally friendly biofuel.Nevertheless,the relatively low calorific value of such gases makes their effective utilization in practical applications relatively difficult.The present study considers the addition of hydrogen as a potential solution to mitigate this issue.In particular,the properties of turbulent diffusion jet flames and the related pollutant emissions are investigated numerically for different operating pressures.The related numerical simulations are conducted by solving the RANS equations in the frame of the Reynolds Stress Model in combination with the flamelet approach.Radiation effects are also taken into account and the combustion kinetics are described via the GRI-Mech 3.0 reaction model.The considered hydrogen fuel enrichment spans the range from 0%to 50%in terms of volume.Pressure varies between 1 and 10 atm.The results show that both hydrogen addition and pressure increase lead to an improvement in terms of mixing quality and have a significant effect on flame temperature and height.They also reduce CO_(2)emissions but increase NOx production.Prompt NO is shown to be the predominant NO formation mechanism.
文摘A turbulent nonpremixed flame of methanol air stabilized on a bluff body is simulated by the conditional moment closure(CMC) model. An elliptic, conservative formulation of the CMC is employed with the turbulent diffusion term modeled by the turbulent eddy viscosity. Results of flow, conditional temperature and species concentration profiles with respect to mixture fraction, and unconditional temperature, OH and NO fields are obtained. Reasonable agreement between experiments and predictions to show that the CMC model is capable to predicting the species concentration and temperature in turbulent nonpremixed combustion characterized by a finite reaction rate. Discrepancy on the rich side may partly be due to limitation of the singly conditional moment closure, substitution of the unconditional mean variables for the conditional ones, or lack of adequate chemical kinetics on the rich side of methanol air reaction.
基金Sponsored by National Natural Science Foundation of China(Grant No.51376021)
文摘To study the configuration and conductivity effects on micro-scale methane-air flames by electric field and iron wind,different electric field forces and iron winds are generated by needle,circle and plate electrodes respectively in different electrodes heights under both AC and DC fields though experiments. Experimental results showed that the flame characteristics are affected by needle electrodes mainly through the action of ion wind,by plate type electrodes mainly through the action of electric field force and by annular electrodes through both the electric field force and ion wind at the same time. Under DC field 's effects of all electrodes types,the flame will consequently go down while the voltage reached to a limit value,and it will breakdown under the strong effect of the ion wind by needle electrodes. The results also showed the influence by different electrodes types to the current characteristics,resistance properties and configuration of themicro-scale flames.
文摘The operating range of the flow rate or flow velocity for the micro-jet flame is quite wide,which can be used as the heat source.In order to optimize the micro-jet tube combustor in terms of the solid material,the present paper numerically investigates the impact of thermal conductivity(λs)on the operating limit of micro-jet flame.Unexpectedly,the non-monotonic blow-off limits with the increase ofλs is found,and the corresponding generation mechanisms are analyzed in terms of the thermal coupling effect,flow field,and strain effect.At first,the lower preheating temperature of the fuel and larger heat loss amount to the environment lead to a larger blow-off limit at a largerλs.After that,the smaller local flow velocity in the vicinity of flame root and smaller strain effect slightly increase the blow-off limit with the continuously increasingλs.Therefore,it is deduced that the applied performance of micro-jet combustor with a smaller thermal conductivity is better in terms of the blow-off limit.
文摘An experimental study investigated the characteristics of a stretched cylindrical diffusion flame, with a convex curvature with respect to the air stream, in response to periodic air flow velocity oscillation. The fuel was methane diluted with nitrogen, and the oxidizer air. The oscillation frequency was varied from 5 to 250 Hz. The results are summarized as follows. Though the fluctuation amplitude of the air stream velocity gradient was constant with respect to the frequency, the amplitude of the fuel stream increased. The fluctuation amplitude of the flame radius changed quasi-steadily from 5 to 25 Hz, and decreased with increasing frequency in the frequency range greater than 50 Hz. The flame luminosity did not respond quasi-steadily at 5 Hz, and the oscillation amplitude of flame luminosity was less than that of a steady flame, over the same velocity fluctuation range. The oscillation amplitude of luminosity peaked at 50 Hz, and was greater than that of a steady flame. It is considered that this complex change in flame luminosity with respect to frequency was closely related to the phase difference in the respective time variations in the ratio of flame thickness to radius, the velocity gradients of the air and fuel streams, and the magnitude of these values, with the ratio of flame thickness to radius related to the flame curvature effect, the velocity gradient of the air stream correlated to the flame stretch effect, and the velocity gradient of the fuel stream impacting the fuel transportation.
文摘Combustion is a chemical phenomenon in which a multitude of elementary chemical reactions take place, resulting in the overall process of fuel oxidation. Natural gas fuel has been explored for a few decades and extracted for a few years in the region of Paraguayan Chaco, near Bolivia border. Currently, natural gas is not very important in Paraguay＇s energy matrix, however it could be in the near future if higher volumes are extracted and transported to the most populated cities, specially to the capital. In order to improve Paraguayan natural gas combustion performance, an understanding of its fundamental properties and the combustion pathways is required. This study presents new data for Paraguayan Chaco natural gas combustion in a laminar counterflow diffusion flame configuration at atmospheric pressure. Visible chemiluminescence of excited radicals CH＊ and C2^＊ is employed experimentally. 1D numerical simulation was carried out using Paraguayan Chaco natural gas chemical composition and a standard kinetic mechanism, to which we added CH＊ and C] reactions. Typical flame structures resulting from simulation are presented and a validation of the model is realized comparing experimental and numerical CH＊ and C~ radicals profiles.
文摘Oxygen rich combustion is a mean to increase the energy efficiency and to contribute to CO2 capture. Influence of oxygen enriched air on the stability of methane flames from non premixed laminar jets has been investigated experimentally. The burner consists of two coaxial jets： methane flowing out of the inner, oxidizer from the outer. The flame behavior is studied according to the proportion of oxygen in the oxidizer jet, the oxidizer and the methane jets velocities. The flame is either anchored to the burner, lifted, stationary or not or blown-out. The addition of oxygen produces a decrease of the lift height, a reduction of the length of the reaction zone and an increase in the soot emission. These results have been reported into diagrams of stability where the flame configurations are connected to the competition between the dynamic effect of the injection velocity and the chemical effect of oxygen addition.
文摘Oxygenated fuels can reduce harmful emissions without affecting engine performance,meeting the big challenge in the transportation industry,which keeps the environment safe and reduces global warming.This study investigates the impact of biodiesel injection strategies and fuel injection pressures(FIP)on diesel engine exhaust emission characteristics.The engine is fuelled with 20%Jatropha biodiesel(JB)and 80%diesel,named JB20D.The ratios of fuel injection pressures started with injecting the fuel(diesel and JB20D)from 200 bar to 500 bar.The experimental outcomes indicate that the engine performance of brake-specific fuel consumption increased by 21.36%from the burning of JB20D compared with diesel,while brake thermal efficiency improved by 6.54%for low and high FIP compared to the diesel.The high fuel injection pressures slightly decrease the nitrogen oxide(NOX)emissions for both diesel and biodiesel.The emissions of NOX decreased from the combustion of JB20D by 18.7%under high fuel injection pressures compared to diesel.The concentration of soot particulate decreased by 20.4%form JB20D combustion than those combusted from diesel fuel.
基金Item Sponsored by National Natural Science Foundation(50104001)Science and Technology Tackle Key Foundation of Inner Mongolia(980307-4)
文摘The computer simulation of the combustion process in blast furnace(BF) stove has been studied by using the k-ε-g turbulent diffusion flame model.The combustion process in blunt annular ceramic burner was calculated by using the software.The profiles of gas and air velocity,temperature of the combustion products,concentration of the components,and the shape and length of the flame during combustion have been researched.Compared with the original annular ceramic burner,the new design of the blunt one improves the mixing of the gas and the air significantly,and shortened the length of the flame.
文摘One way for reducing tar is oxidative and thermal cracking by partial combustion of the biomass producer gas in the gas reformer. Cracking and polymerization of the tar occur simultaneously at the proximity of inverse diffusion flame. Experimental study has been performed to clarify the effect of hydrogen concentration on soot formation and the growth of polycyclic aromatic hydrocarbons. In the present study, hydrogen concentration is controlled by the small amount of hydrogen addition to the oxidizer. The main results are as follows. Soot formation is suppressed by the small amount of hydrogen addition. The suppression of soot formation is caused by higher concentration of hydrogen. Carbon yield increases by hydrogen addition since carbon content in the undetectable components by the integrated gas chromatograph decreases. In addition, the increase in carbon yield is caused mainly by the increase in carbon monoxide stemmed from reforming of high-boiling components.
基金supported by the National Natural Science Foundation of China(Grant No.22178032)the Natural Science Foundation of Chongqing(Grant No.CSTB2023NSCQ-MSX1045)National Key Research and Development Program of China(Grant No.2022YFB4004404).
文摘The utilization of ammonia as an alternative fuel is of great significance in the carbon neutrality strategy. However, the ammonia flame extinction mechanism induced by growing oscillations with its cramped flammability range, sluggish propagation speed, and poor stability is still not studied in sufficient details. In this paper, the high-fidelity simulations with efficient continuation computation and detailed models are conducted to investigate the ammonia extinction dynamics as a function of hydrogen blending ratio, and to reveal the governing sub-processes in flame extinction and oscillation development. It is found that the extinction and onset of oscillatory instability in the ammonia/hydrogen spherical diffusion flame (SDF) derive from the interaction of competing chemistry with diffusive leakage losses. Chemical oscillations occurring at the maximum temperature iso-contour are primarily responsible for the near-limit flame oscillations. In the rich-side low-temperature region, although the local heat production is inappreciable, the strong diffusive losses with governing, adverse contributions to the ignition chemistry play a leading role in flame extinction. The reactions dominating the extinction limit are also important for the oscillation frequency;the reactions that help to extend the extinction limit also tend to increase the frequency, and vice versa. The extinction limit and frequency depend mainly on the major reactant diffusivities (including NH_(3), H_(2), and O_(2)) and heat conduction, while the diffusivities of other radicals and products are fairly unimportant. Hydrogen addition could remarkably extend the steady-state and oscillatory extinction limits of ammonia SDFs, and reduce the oscillation frequency since the imaginary eigenvalue is depressed.
基金supported by the National Natural Science Foundation of China(Grant No.51976044)the National Science and Technology Major Project(Grant No.2017-V-0016-0069)the Foundation for Heilongjiang Touyan Innovation Team Program。
文摘The plenoptic imaging technique provides a promising approach to the non-invasive three-dimensional measurement, especially for the high-temperature combustion diagnosis. We establish a light-field convolution imaging model for diffusion flame in this work, considering the radiation transfer process inside the diffusion flame and the light transfer process inside the focused plenoptic camera together. The radiation transfer process is described by the radiation transfer equation and solved by the generalized source multi-flux method. Wave optics theory is adopted to describe the light transfer process, combining Fresnel diffraction and the phase conversion of the lens. The flame light-field image is obtained by the light-field convolution imaging model and adopted as the measurement signal to reconstruct three-dimensional temperature field. The inverse problem of temperature reconstruction is solved by the least square QR decomposition method. The simulative temperature reconstruction work is conducted, including the inverse analysis, the uncertainty analysis, and the measurement noise influence. All the results show that the proposed measurement method is available to reconstruct three-dimensional temperature with satisfactory accuracy and acceptable uncertainty. Both symmetric and asymmetric distributed temperature fields are investigated, and the reconstructed results prove the validity and universality of the measurement method.
基金support by the National High Technology R&D Project of China (No. 2006AA05A104)National Natural Science Foundation of China (No. 50806076,50876110)to the research work
文摘Flame structures of a syngas swirl-stabilized diffusion flame in a model combustor were measured using the OH-PLIF method under different fuel and air swirl intensity.The flame operated under atmospheric pressure with air and a typical low heating-value syngas with a composition of 28.5% CO,22.5% H2 and 49% N2 at a thermal power of 34 kW.Results indicate that increasing the air swirl intensity with the same fuel,swirl intensity flame structures showed little difference except a small reduction of flame length;but also,with the same air swirl intensity,fuel swirl intensity showed great influence on flame shape,length and reaction zone distribution.Therefore,compared with air swirl intensity,fuel swirl intensity appeared a key effect on the flame structure for the model combustor.Instantaneous OH-PLIF images showed that three distinct typical structures with an obvious difference of reaction zone distribution were found at low swirl intensity,while a much compacter flame structure with a single,stable and uniform reaction zone distribution was found at large fuel-air swirl intensity.It means that larger swirl intensity leads to efficient,stable combustion of the syngas diffusion flame.
