The interaction of multiple fires may lead to a higher flame height and more intense radiation flux than a single fire,which increases the possibility of flame spread and risks to the surroundings.Experiments were con...The interaction of multiple fires may lead to a higher flame height and more intense radiation flux than a single fire,which increases the possibility of flame spread and risks to the surroundings.Experiments were conducted using three burners with identical heat release rates(HRRs)and propane as the fuel at various spacings.The results show that flames change from non-merging to merging as the spacing decreases,which result in a complex evolution of flame height and merging point height.To facilitate the analysis,a novel merging criterion based on the dimensionless spacing S/z_(c) was proposed.For non-merging flames(S/z_(c)>0.368),the flame height is almost identical to a single fire;for merging flames(S/z_(c)≤0.368),based on the relationship between thermal buoyancy B and thrust P(the pressure difference between the inside and outside of the flame),a quantitative analysis of the flame height,merging point height,and air entrainment was formed,and the calculated merging flame heights show a good agreement with the measured experimental values.Moreover,the multi-point source model was further improved,and radiation fraction of propane was calculated.The data obtained in this study would play an important role in calculating the external radiation of propane fire.展开更多
Hystereses and catastrophes were experimentally investigated in a cavity-based scramjet combustor.The inflow Mach number was 3.0.Fuel Equivalence Ratio(ER)was continuously regulated with multi-steps to explore influen...Hystereses and catastrophes were experimentally investigated in a cavity-based scramjet combustor.The inflow Mach number was 3.0.Fuel Equivalence Ratio(ER)was continuously regulated with multi-steps to explore influences of historical regulation directions on combustion states.Two divided hysteresis loops with catastrophes were observed.By 1-D flow estimations,the first loop occurred with shock-free/separated scramjet mode transitions,while the second kept in the separated scramjet mode.This breaks through the traditional knowledge that hysteresis and catastrophe were certainly related to ramjet/scramjet mode transitions.The first hysteresis and catastrophes were attributed to flame stabilization mode transitions between the cavity shearlayer stabilized and the jet-wake stabilized,with flow separation establishment/vanishment upstream the cavities.The obvious variations of flame and shock/separation structures meant large wall-pressure changes in the expansive duct,and generated obvious thrust catastrophes.Besides,transition ER and catastrophe were larger in historical ER-increasing path because combustion efficiency became obviously larger as flow separation established.Difference of critical transition ERs meant the first hysteresis.The second hysteresis and catastrophes in the jet-wake stabilized mode were attributed to flame/shock interaction mode transitions between the flame/shock weak interaction mode and intensive interaction mode.Each transition caused slightly stronger/weaker flame interacting with slightly larger/smaller flow separation,which meant small wall-pressure changes in the expansive duct,and thus thrust catastrophe was unobvious.Hysteresis occurred as the critical transition ER was slightly higher in historical ER-increasing path because of slightly lower combustion efficiency under slightly smaller separation.展开更多
In order to develop a burner with uniform temperature field,the combustion characteristics and thermal performance of partially premixed methane/air jet flames were experimentally studied by using micro jet array burn...In order to develop a burner with uniform temperature field,the combustion characteristics and thermal performance of partially premixed methane/air jet flames were experimentally studied by using micro jet array burners.The circular tubes of 1.0-mm inner diameter and 1.5-mm outer diameter were used as nozzles.The effects of nozzle spacing and equivalence ratio on flame phenomenology,temperature distribution and pollutant emissions were respectively investigated by camera photography,thermocouple measurement and sampling analysis.Results show that there are two clean flame patterns:clean merged-flame and clean non-merging flames.The flame patterns depend on the strength of flame interaction,the equivalence ratio of the mixture and the quantity of air entrainment through the gap between nozzles.The burners with small nozzle spacing such as 2 mm and 2.5 mm tend to produce fully merged flame with low equivalence ratio limit and the corresponding temperature fields are very uniform with fluctuations less than 0.3%,but a small increase in equivalence ratio will lead to rapid deterioration of combustion property.The burner with a medium spacing of 3 mm can produce partially merged flame in a wide equivalence ratio range with low emissions,and the temperature fluctuation can be less than 0.5%(<7 K)in the optimal region.The burner with a large spacing of 4 mm will basically form independent array flames with the largest temperature fluctuation over 1%,while it can achieve clean combustion under high equivalence ratio due to large air entrainment.Comprehensive analysis shows that the micro jet array burner with medium nozzle spacing of 3 mm has the best combustion characteristics and thermal performance.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52036009 and 51722605).
文摘The interaction of multiple fires may lead to a higher flame height and more intense radiation flux than a single fire,which increases the possibility of flame spread and risks to the surroundings.Experiments were conducted using three burners with identical heat release rates(HRRs)and propane as the fuel at various spacings.The results show that flames change from non-merging to merging as the spacing decreases,which result in a complex evolution of flame height and merging point height.To facilitate the analysis,a novel merging criterion based on the dimensionless spacing S/z_(c) was proposed.For non-merging flames(S/z_(c)>0.368),the flame height is almost identical to a single fire;for merging flames(S/z_(c)≤0.368),based on the relationship between thermal buoyancy B and thrust P(the pressure difference between the inside and outside of the flame),a quantitative analysis of the flame height,merging point height,and air entrainment was formed,and the calculated merging flame heights show a good agreement with the measured experimental values.Moreover,the multi-point source model was further improved,and radiation fraction of propane was calculated.The data obtained in this study would play an important role in calculating the external radiation of propane fire.
基金National Natural Science Foundation of China(Nos.11902325 and 11672309)。
文摘Hystereses and catastrophes were experimentally investigated in a cavity-based scramjet combustor.The inflow Mach number was 3.0.Fuel Equivalence Ratio(ER)was continuously regulated with multi-steps to explore influences of historical regulation directions on combustion states.Two divided hysteresis loops with catastrophes were observed.By 1-D flow estimations,the first loop occurred with shock-free/separated scramjet mode transitions,while the second kept in the separated scramjet mode.This breaks through the traditional knowledge that hysteresis and catastrophe were certainly related to ramjet/scramjet mode transitions.The first hysteresis and catastrophes were attributed to flame stabilization mode transitions between the cavity shearlayer stabilized and the jet-wake stabilized,with flow separation establishment/vanishment upstream the cavities.The obvious variations of flame and shock/separation structures meant large wall-pressure changes in the expansive duct,and generated obvious thrust catastrophes.Besides,transition ER and catastrophe were larger in historical ER-increasing path because combustion efficiency became obviously larger as flow separation established.Difference of critical transition ERs meant the first hysteresis.The second hysteresis and catastrophes in the jet-wake stabilized mode were attributed to flame/shock interaction mode transitions between the flame/shock weak interaction mode and intensive interaction mode.Each transition caused slightly stronger/weaker flame interacting with slightly larger/smaller flow separation,which meant small wall-pressure changes in the expansive duct,and thus thrust catastrophe was unobvious.Hysteresis occurred as the critical transition ER was slightly higher in historical ER-increasing path because of slightly lower combustion efficiency under slightly smaller separation.
基金This work was supported by the National Natural Science Foundation of China(NO.51176193)Key R&D Projects of Guangdong Province(NO.2020B1111360004)Self-financing Science and Technology Projects in Foshan(NO.2020001004571).
文摘In order to develop a burner with uniform temperature field,the combustion characteristics and thermal performance of partially premixed methane/air jet flames were experimentally studied by using micro jet array burners.The circular tubes of 1.0-mm inner diameter and 1.5-mm outer diameter were used as nozzles.The effects of nozzle spacing and equivalence ratio on flame phenomenology,temperature distribution and pollutant emissions were respectively investigated by camera photography,thermocouple measurement and sampling analysis.Results show that there are two clean flame patterns:clean merged-flame and clean non-merging flames.The flame patterns depend on the strength of flame interaction,the equivalence ratio of the mixture and the quantity of air entrainment through the gap between nozzles.The burners with small nozzle spacing such as 2 mm and 2.5 mm tend to produce fully merged flame with low equivalence ratio limit and the corresponding temperature fields are very uniform with fluctuations less than 0.3%,but a small increase in equivalence ratio will lead to rapid deterioration of combustion property.The burner with a medium spacing of 3 mm can produce partially merged flame in a wide equivalence ratio range with low emissions,and the temperature fluctuation can be less than 0.5%(<7 K)in the optimal region.The burner with a large spacing of 4 mm will basically form independent array flames with the largest temperature fluctuation over 1%,while it can achieve clean combustion under high equivalence ratio due to large air entrainment.Comprehensive analysis shows that the micro jet array burner with medium nozzle spacing of 3 mm has the best combustion characteristics and thermal performance.
