The hot extrusion die is a key tool for determining the surface quality and dimensional accuracy of extruded products.Because its service process is subject to high temperature,high pressure,and wear,it must be resist...The hot extrusion die is a key tool for determining the surface quality and dimensional accuracy of extruded products.Because its service process is subject to high temperature,high pressure,and wear,it must be resistant to these conditions.In this paper,the high-temperature friction and wear properties of a cobalt(Co)-based alloy were investigated and compared with those of a titanium carbide(TiC)cemented material.The results show that the high-temperature wear performance of the Co-based alloy is better than that of the TiC cemented material,and that Co-based materials have the potential for replacing TiC cemented materials as hot-extrusion-die materials.Due to the high density and good combination of the matrix and carbide,the carbides do not easily peel off from the matrix during the wear process.Due to the higher impact toughness of the Co-based alloys,microcracks that can cause worn-surface peeling are not easily generated.As a result,the high-temperature wear performance of Co-based alloys is found to be better than that of TiC cemented materials.展开更多
In this study,the multi-objective intelligent optimization of the crevice structure in a rapid compression machine(RCM)is carried out based on the RCM simulation model modified with the KIVA-3V program.A multi-objecti...In this study,the multi-objective intelligent optimization of the crevice structure in a rapid compression machine(RCM)is carried out based on the RCM simulation model modified with the KIVA-3V program.A multi-objective optimization simulation model of the crevice structure based on the large eddy simulation model coupled with the genetic algorithm NSGA-Ⅲis established.Six optimization parameters and seven optimization objectives are selected in the optimization process.The results show that the genetic algorithm can quickly find the values of the optimized parameters.The crevice volume ratio shows a trade-off relationship with the dimensionless temperature ratio T_(max)/T_(aver)and the tumble ratio.A larger crevice volume can reduce the flow of boundary layer cryogenic gas into the combustion chamber,thus improving the temperature uniformity.In addition,the crevice entrance width and the connecting channel length should be smaller,while the volume of the crevice main chamber should be larger,so as to sufficiently introduce the low-temperature gas of the boundary layer into the crevice and reduce their influence on the temperature field of the combustion chamber.When the crevice volume accounts for10%of the total volume,the temperature uniformity of the combustor is significantly enhanced,and when the crevice volume accounts for 30.4%,there is almost no low-temperature vortex in the combustion chamber.展开更多
The effect of nitrogen dilution on the premixed combustion characteristics and flame structure of laminar premixed methanol-air-nitrogen mixtures are analyzed numerically based on an extended methanol oxidation mechan...The effect of nitrogen dilution on the premixed combustion characteristics and flame structure of laminar premixed methanol-air-nitrogen mixtures are analyzed numerically based on an extended methanol oxidation mechanism. The laminar burning velocities, the mass burning fluxes, the adiabatic flame temperature, the global activation temperature, the Zeldovich number, the effective Lewis number and the laminar flame structure of the methanol-air-nitrogen mixtures are obtained under different nitrogen dilution ratios. Comparison between experiments and numerical simulations show that the extended methanol oxidation mechanism can well reproduce the laminar burning velocities for lean and near stoichiometric methanol-air-nitrogen mixtures. The laminar burning velocities and the mass burning fluxes decrease with the increase of nitrogen dilution ratio and the effect is more obvious for the lean mixture. The effective Lewis number of the mixture increases with the increase of nitrogen dilution ratio, and the diffusive-thermal instability of the flame front is decreased by the nitrogen addition. Nitrogen addition can suppress the hydrodynamic instability of methanol-air-nitrogen flames. The decrease of the mole fraction of OH and H is mainly responsible for the suppressed effect of nitrogen diluent on the chemical reaction in the methanol-air-nitrogen laminar premixed flames, and the NOx and formaldehyde emissions are decreased by the nitrogen addition.展开更多
文摘The hot extrusion die is a key tool for determining the surface quality and dimensional accuracy of extruded products.Because its service process is subject to high temperature,high pressure,and wear,it must be resistant to these conditions.In this paper,the high-temperature friction and wear properties of a cobalt(Co)-based alloy were investigated and compared with those of a titanium carbide(TiC)cemented material.The results show that the high-temperature wear performance of the Co-based alloy is better than that of the TiC cemented material,and that Co-based materials have the potential for replacing TiC cemented materials as hot-extrusion-die materials.Due to the high density and good combination of the matrix and carbide,the carbides do not easily peel off from the matrix during the wear process.Due to the higher impact toughness of the Co-based alloys,microcracks that can cause worn-surface peeling are not easily generated.As a result,the high-temperature wear performance of Co-based alloys is found to be better than that of TiC cemented materials.
基金supported by the National Natural Science Foundation of China(No.52076011)the Fundamental Research Funds for the Central Universities(No.2021JBM020)。
文摘In this study,the multi-objective intelligent optimization of the crevice structure in a rapid compression machine(RCM)is carried out based on the RCM simulation model modified with the KIVA-3V program.A multi-objective optimization simulation model of the crevice structure based on the large eddy simulation model coupled with the genetic algorithm NSGA-Ⅲis established.Six optimization parameters and seven optimization objectives are selected in the optimization process.The results show that the genetic algorithm can quickly find the values of the optimized parameters.The crevice volume ratio shows a trade-off relationship with the dimensionless temperature ratio T_(max)/T_(aver)and the tumble ratio.A larger crevice volume can reduce the flow of boundary layer cryogenic gas into the combustion chamber,thus improving the temperature uniformity.In addition,the crevice entrance width and the connecting channel length should be smaller,while the volume of the crevice main chamber should be larger,so as to sufficiently introduce the low-temperature gas of the boundary layer into the crevice and reduce their influence on the temperature field of the combustion chamber.When the crevice volume accounts for10%of the total volume,the temperature uniformity of the combustor is significantly enhanced,and when the crevice volume accounts for 30.4%,there is almost no low-temperature vortex in the combustion chamber.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50521604 and 50876086)
文摘The effect of nitrogen dilution on the premixed combustion characteristics and flame structure of laminar premixed methanol-air-nitrogen mixtures are analyzed numerically based on an extended methanol oxidation mechanism. The laminar burning velocities, the mass burning fluxes, the adiabatic flame temperature, the global activation temperature, the Zeldovich number, the effective Lewis number and the laminar flame structure of the methanol-air-nitrogen mixtures are obtained under different nitrogen dilution ratios. Comparison between experiments and numerical simulations show that the extended methanol oxidation mechanism can well reproduce the laminar burning velocities for lean and near stoichiometric methanol-air-nitrogen mixtures. The laminar burning velocities and the mass burning fluxes decrease with the increase of nitrogen dilution ratio and the effect is more obvious for the lean mixture. The effective Lewis number of the mixture increases with the increase of nitrogen dilution ratio, and the diffusive-thermal instability of the flame front is decreased by the nitrogen addition. Nitrogen addition can suppress the hydrodynamic instability of methanol-air-nitrogen flames. The decrease of the mole fraction of OH and H is mainly responsible for the suppressed effect of nitrogen diluent on the chemical reaction in the methanol-air-nitrogen laminar premixed flames, and the NOx and formaldehyde emissions are decreased by the nitrogen addition.
