Stable combustion in an afterburner can help increase the thrust of the engine in a short time,thereby improving the maneuverability of a fighter.To improve the ignition performance of an afterburner,a twin-duct ignit...Stable combustion in an afterburner can help increase the thrust of the engine in a short time,thereby improving the maneuverability of a fighter.To improve the ignition performance of an afterburner,a twin-duct ignition platform was designed to study the performance of a gliding arc plasma igniter in close-to-real afterburner conditions.The research was carried out by a combination of experiments and simulations.The working environment of the igniter was explored through a numerical simulation.The results showed that the airflow ejected from the radiating holes formed a swirling sheath,which increased the anti-interference ability of the airflow jet.The influence of the pressure difference between the inlet and outlet of the igniter(Δp),the flow rate outside the igniter outlet(W_(2)),and the installation angle(α)on the singlecycle discharge energy(E)as well as the maximum arc length(L)were studied through experiments.Three stages were identified:the airflow breakdown stage,the arc evolution stage,and the arc fracture stage.E and L increased by 107.3%and 366.2%,respectively,withΔp increasing from 10 to 70 Torr.The relationship between L andΔp obtained by data fitting is L=3-2.47/(1+(Δp/25)^(4)).The relationship of L at differentαis L_(α=0°)>(L_(α=45°)and L_(α=135°))>L_(α=180°)>L_(α=90°).E and L decrease by 18.2%and 37.3%,respectively,whenΔp=45 Torr and W_(2) is increased from 0 to 250 l min^(-1).展开更多
Geopolymers are inorganic aluminosilicate materials,which have been a great research interest as a material for sustainable development.However,they possess relatively low toughness properties similar to brittle solid...Geopolymers are inorganic aluminosilicate materials,which have been a great research interest as a material for sustainable development.However,they possess relatively low toughness properties similar to brittle solids.The limitation may be altered by fiber reinforcement to improve their strength and toughness.This research describes the synthesis of bamboo shaving(BS)reinforced geopolymer composites and the characterization of their mechanical properties.The effect of BS content(0–2 wt.%)on the physical and mechanical properties and microstructure of metakaolin based geopolymer paste were investigated.The workability,setting time,bulk density,apparent porosity,thermal conductivity,compressive strength,flexural strength,scanning electron microscopy(SEM),and X-ray diffraction(XRD)of geopolymer paste were determined.The results showed that the workability,setting time,density,and thermal conductivity decreased with the increasing of BS content.The BS content was proportional to the apparent porosity and a good linear relation was found between apparent porosity and BS content.The highest mechanical properties were achieved at an optimum BS content of 1.0 wt.%.The results of microstructural analysis revealed that BS act as inforcing phase in matrix,reducing cracks and making a dense geopolymer,which leads to favorable adhesion of the composites and produces a geopolymer composite with better mechanical properties than that of pure geopolymer.However,when the BS content exceeded 1.0 wt.%,interfacial bonding between BS and geopolymer matrix became less.XRD analysis showed that BS has little effect on the mineral composition of metakaolin-based geopolymer and no new phase is formed.展开更多
Catalysts play a critical role in improving the hydrogen storage kinetics in Mg/MgH2 system.Exploring highly efficient catalysts and catalyst design principles are hot topics but challenging.The catalytic activity of ...Catalysts play a critical role in improving the hydrogen storage kinetics in Mg/MgH2 system.Exploring highly efficient catalysts and catalyst design principles are hot topics but challenging.The catalytic activity of metallic elements on dehydrogenation kinetics generally follows a sequence of Ti>Nb>Ni>V>Co>Mo.Herein,we report a highly efficient alloy catalyst composed of low-active elements of Mo and Ni(i.e.MoNi alloy)for MgH2 particles.MoNi alloy nanoparticles show excellent catalytic effect,even outperforming most advanced Ti-based catalysts.The synergy between Mo and Ni elements can promote the break of Mg-H bonds and the dissociation of hydrogen molecules,thus significantly improves the kinetics of Mg/MgH2 system.The MoNi-catalyzed Mg/MgH2 system can absorb and release 6.7 wt.%hydrogen within 60 s and 10 min at 300℃,respectively,and exhibits excellent cycling stability and low-temperature hydrogen storage performance.This study provides a strategy for designing efficient catalysts for hydrogen storage materials using the synergy of metal elements.展开更多
At room temperature,crystalline Mg-based alloys,including Mg2 Ni,MgNi,REMg12 and La2 Mg17,have been proved with weak electrochemical hydrogen storage performances.For improving their electrochemical property,the Mg is...At room temperature,crystalline Mg-based alloys,including Mg2 Ni,MgNi,REMg12 and La2 Mg17,have been proved with weak electrochemical hydrogen storage performances.For improving their electrochemical property,the Mg is partially substituted by Ce in Mg-Ni-based alloys and the surface modification treatment is performed by mechanical coating Ni.Mechanical milling is utilized to synthesize the amorphous and nanocrystalline Mg1-xCexNi0.9Al0.1(x=0,0.02,0.04,0.06,0.08)+50 wt%Ni hydrogen storage alloys.The effects made by Ce substitution and mechanical milling on the electrochemical hydrogen storage property and structure have been analyzed.It shows that the as-milled alloys electrochemically absorb and desorb hydrogen well at room temperature.The as-milled alloys,without any activation,can reach their maximal discharge capacities during first cycling.The maximal value of the 30-h-milled alloy depending on Ce content is 578.4 mAh/g,while that of the x=0.08 alloy always grows when prolonging milling duration.The maximal discharge capacity augments from337.4 to 521.2 mAh/g when milling duration grows from 5 to 30 h.The cycle stability grows with increasing Ce content and milling duration.Concretely,the S100 value augments from 55 to 82%for the alloy milled for 30 h with Ce content rising from 0 to 0.08 and from 66 to 82%when milling the x=0.08 alloy mechanically from 5 to 30 h.The alloys’electrochemical dynamics parameters were measured as well which have maximum values depending on Ce content and keep growing up with milling duration extending.展开更多
基金supported by National Science and Technology Major Project (No. 2017-Ⅲ-0007-0033)
文摘Stable combustion in an afterburner can help increase the thrust of the engine in a short time,thereby improving the maneuverability of a fighter.To improve the ignition performance of an afterburner,a twin-duct ignition platform was designed to study the performance of a gliding arc plasma igniter in close-to-real afterburner conditions.The research was carried out by a combination of experiments and simulations.The working environment of the igniter was explored through a numerical simulation.The results showed that the airflow ejected from the radiating holes formed a swirling sheath,which increased the anti-interference ability of the airflow jet.The influence of the pressure difference between the inlet and outlet of the igniter(Δp),the flow rate outside the igniter outlet(W_(2)),and the installation angle(α)on the singlecycle discharge energy(E)as well as the maximum arc length(L)were studied through experiments.Three stages were identified:the airflow breakdown stage,the arc evolution stage,and the arc fracture stage.E and L increased by 107.3%and 366.2%,respectively,withΔp increasing from 10 to 70 Torr.The relationship between L andΔp obtained by data fitting is L=3-2.47/(1+(Δp/25)^(4)).The relationship of L at differentαis L_(α=0°)>(L_(α=45°)and L_(α=135°))>L_(α=180°)>L_(α=90°).E and L decrease by 18.2%and 37.3%,respectively,whenΔp=45 Torr and W_(2) is increased from 0 to 250 l min^(-1).
基金the Excellent Youth Foundation of Education Department of Hunan Province,China(20B612)Changsha Natural Science Foundation of China(kq2014158).
文摘Geopolymers are inorganic aluminosilicate materials,which have been a great research interest as a material for sustainable development.However,they possess relatively low toughness properties similar to brittle solids.The limitation may be altered by fiber reinforcement to improve their strength and toughness.This research describes the synthesis of bamboo shaving(BS)reinforced geopolymer composites and the characterization of their mechanical properties.The effect of BS content(0–2 wt.%)on the physical and mechanical properties and microstructure of metakaolin based geopolymer paste were investigated.The workability,setting time,bulk density,apparent porosity,thermal conductivity,compressive strength,flexural strength,scanning electron microscopy(SEM),and X-ray diffraction(XRD)of geopolymer paste were determined.The results showed that the workability,setting time,density,and thermal conductivity decreased with the increasing of BS content.The BS content was proportional to the apparent porosity and a good linear relation was found between apparent porosity and BS content.The highest mechanical properties were achieved at an optimum BS content of 1.0 wt.%.The results of microstructural analysis revealed that BS act as inforcing phase in matrix,reducing cracks and making a dense geopolymer,which leads to favorable adhesion of the composites and produces a geopolymer composite with better mechanical properties than that of pure geopolymer.However,when the BS content exceeded 1.0 wt.%,interfacial bonding between BS and geopolymer matrix became less.XRD analysis showed that BS has little effect on the mineral composition of metakaolin-based geopolymer and no new phase is formed.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51971008,U1832138,51731002 and 51920105001)Beijing Municipal Natural Science Foundation(No.2172031)Fundamental Research Funds for the Central Universities.
文摘Catalysts play a critical role in improving the hydrogen storage kinetics in Mg/MgH2 system.Exploring highly efficient catalysts and catalyst design principles are hot topics but challenging.The catalytic activity of metallic elements on dehydrogenation kinetics generally follows a sequence of Ti>Nb>Ni>V>Co>Mo.Herein,we report a highly efficient alloy catalyst composed of low-active elements of Mo and Ni(i.e.MoNi alloy)for MgH2 particles.MoNi alloy nanoparticles show excellent catalytic effect,even outperforming most advanced Ti-based catalysts.The synergy between Mo and Ni elements can promote the break of Mg-H bonds and the dissociation of hydrogen molecules,thus significantly improves the kinetics of Mg/MgH2 system.The MoNi-catalyzed Mg/MgH2 system can absorb and release 6.7 wt.%hydrogen within 60 s and 10 min at 300℃,respectively,and exhibits excellent cycling stability and low-temperature hydrogen storage performance.This study provides a strategy for designing efficient catalysts for hydrogen storage materials using the synergy of metal elements.
基金financially supported by the National Natural Science Foundations of China(Nos.51761032 and 51871125)
文摘At room temperature,crystalline Mg-based alloys,including Mg2 Ni,MgNi,REMg12 and La2 Mg17,have been proved with weak electrochemical hydrogen storage performances.For improving their electrochemical property,the Mg is partially substituted by Ce in Mg-Ni-based alloys and the surface modification treatment is performed by mechanical coating Ni.Mechanical milling is utilized to synthesize the amorphous and nanocrystalline Mg1-xCexNi0.9Al0.1(x=0,0.02,0.04,0.06,0.08)+50 wt%Ni hydrogen storage alloys.The effects made by Ce substitution and mechanical milling on the electrochemical hydrogen storage property and structure have been analyzed.It shows that the as-milled alloys electrochemically absorb and desorb hydrogen well at room temperature.The as-milled alloys,without any activation,can reach their maximal discharge capacities during first cycling.The maximal value of the 30-h-milled alloy depending on Ce content is 578.4 mAh/g,while that of the x=0.08 alloy always grows when prolonging milling duration.The maximal discharge capacity augments from337.4 to 521.2 mAh/g when milling duration grows from 5 to 30 h.The cycle stability grows with increasing Ce content and milling duration.Concretely,the S100 value augments from 55 to 82%for the alloy milled for 30 h with Ce content rising from 0 to 0.08 and from 66 to 82%when milling the x=0.08 alloy mechanically from 5 to 30 h.The alloys’electrochemical dynamics parameters were measured as well which have maximum values depending on Ce content and keep growing up with milling duration extending.
