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28 November 2019, Volume 53 Issue 11 Previous Issue    Next Issue

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The Effects of Operating Conditions and Direct Injection Timing on the Particulates Emissions in a Dual-Injection Gasoline Engine CHEN Wenhao, XIA Chun, MAO Kerang, TAO Jie, FANG Junhua, HUANG Zhen 2019, 53 (11):  1269-1275.  doi: 10.16183/j.cnki.jsjtu.2019.11.001 Abstract ( 1069 )   PDF (1758KB) ( 466 )   Save A DMS500 fast particulate spectrometer was employed to explore the particle emissions characteristics of a dual-injection gasoline engine. The main goal is to investigate the effects of operating conditions (speed and load ) and direct injection timings on the particle size distributions and particulate emissions in steady state conditions. The experimental results indicate that the combustion characteristics of dual-injection are similar to that of the direct-injection mode at low loads. While at middle and high loads, the peak of in-cylinder pressure curve of dual-injection is a little higher than that of the direct-injection mode. Dual-injection yields great particulate emissions reduction. As the speed and load rise, the particulate emissions of dual-injection gradually increase. At middle and high loads, the particulate emission improvement of dual-injection with 50% fuel directly injected declines significantly. Compared to the direct-injection mode, the particle size distributions of dual-injection tend to shift towards the smaller size region. There exists the best injection timing for the direct-injection mode to yield the lowest particulate emissions. For the dual-injection mode, the best direct injection timing is much closer to the exhaust top dead center than that of the direct-injection mode. References | Related Articles | Metrics

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Effects of Main Carbon Chain Length on Soot Formation and Evolution in Laminar Diffusion Flames of Fatty Acid Methyl Esters ZOU Xinyao,GAO Zhan,HUANG Zhen,ZHU Lei 2019, 53 (11):  1276-1284.  doi: 10.16183/j.cnki.jsjtu.2019.11.002 Abstract ( 1076 )   PDF (19606KB) ( 266 )   Save The effect of main carbon chain length on soot formation and evolution of fatty acid methyl esters (FAMEs) diffusion flames were studied in this work. Laminar coflow diffusion flames of methyl butyrate, methyl octanoate and methyl decanoate were selected as target flames. Laser induced incandescence (LII) and thermophoretic sampling particles diagnostics (TSPD) were adopted as experimental methods to analyze the soot volume fraction and soot particle morphology evolution in tested flames. Transmission electron microscopy (TEM) analysis was applied to obtain morphology information of soot particles sampled by TSPD. The results show that as the length of main carbon chain in FAMEs increases, soot volume fraction along the centreline of laminar diffusion flames increases too. Soot formation is also enhanced with earlier soot inception process and faster surface growth and aggregation. Chemical kinetic simulations of FAMEs decomposition and oxidation are employed to verify and illustrate the experimental results. It can be observed that FAMEs with longer main carbon chain are decomposed at lower temperature and intermediate species such as C2H2 and C2H4 are produced more in the decomposition and oxidation process, which enhances the formation of polycyclic aromatic hydrocarbon. Sensitivity analysis of benzene production suggests that the first aromatic ring in methyl butyrate decomposition mainly forms in C4+C2 pathway. While in methyl octanoate and methyl decanoate decomposition, benzene is produced in both C4+C2 and C3+C3 pathway and C3+C3 pathway takes the lead. References | Related Articles | Metrics

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Experimental Study on the Effect of Lubricating Oil Parameters on Constituent and Characteristics of Diesel Engine Particle Emission GAO Shen,XU Changmao,ZHAO Lei,LEI Ling,TIAN Qiang,ZHANG Wugao 2019, 53 (11):  1285-1293.  doi: 10.16183/j.cnki.jsjtu.2019.11.003 Abstract ( 1111 )   PDF (2008KB) ( 354 )   Save The effect of lubricating oil parameters on the constituent of particle emitted from diesel engine was investigated on a turbo charged diesel engine with four kinds of specially formulated lubricating oils. The effect of base oil type and quantity of ash content on the oxidation activity, metallic element and paraffin of particle emitted was studied. This study focuses on the original particle emission of diesel engine, and has reference value of the regeneration of diesel particle filter. The results show that base oil has little impact on oxidation activity of particle at low engine load when oxidation is more active. And high engine load leads to lower oxidation activity of particle. The emitted particle has a higher oxidation activity when poly alpha olefin (PAO) lubricants as well as lubricants of lower ash content are used. A smaller quantity of metallic elements is found in emitted particle when tested lubricants has the similar base oil but lower ash content. Compared with ordinary mineral oil, ordinary PAO shows more metallic element emission in particle, but the difference is not as obvious when PAO and mineral oil of low ash content is used. It can be concluded that high load of engine leads to more paraffin emission in particle, and when PAO lubricants are used, less paraffin is emitted. Low ash content leads to less paraffin emission. References | Related Articles | Metrics

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Capillary Performance of Superhydrophilic Copper Foams with Volatile Working Fluid JIANG Yuting，ZHANG Peng，LÜ Fengyong 2019, 53 (11):  1294-1301.  doi: 10.16183/j.cnki.jsjtu.2019.11.004 Abstract ( 1036 )   PDF (4073KB) ( 355 )   Save In order to study the capillary properties of superhydrophilic copper foam and the effect of evaporation of volatile working fluid on capillary performance parameters, the experiments on the capillary rise of superhydrophilic copper foam were carried out with water and ethanol as working fluids. The capillary performance parameters corresponding to different working fluids were obtained by using different theoretical models. The capillary performance parameters of different working fluids in the same sample were analyzed and compared. The results show that the evaporation of ethanol has a great influence on the capillary rise process. Based on the results, a method for accurately obtaining capillary performance parameters is proposed for volatile working fluids，and the capillary properties of superhydrophilic copper foam are systematically analyzed. References | Related Articles | Metrics

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Baffles Optimization of a Flat Plat Solar Air Collector with Double Channels ZHANG Dong，ZHANG Jianjun，ZHANG Yuezhi，LI Jinping，WANG Linjun 2019, 53 (11):  1302-1307.  doi: 10.16183/j.cnki.jsjtu.2019.11.005 Abstract ( 948 )   PDF (2995KB) ( 391 )   Save A flat plate solar air collector with double channels is established. The optimization schemes with perforated baffles are proposed. The thermal performance of optimized collector is anlyzed and compared with the commom plane baffle and non-baffle types. The results show that flow dead zones in back of baffles appear generally. The solar air collector with perforated baffles has a higher collector efficiency and thermal perfromance because of the forceful destabilization of flow dead zone. Compared with the model without baffles, the collecor efficiency increases from 53.4% to 67.9%. References | Related Articles | Metrics

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Surface Properties of Neural Electrodes Based on Oriented Electrodeposition YU Qian,ZHANG Wenguang,YIN Xuele 2019, 53 (11):  1308-1315.  doi: 10.16183/j.cnki.jsjtu.2019.11.006 Abstract ( 954 )   PDF (5575KB) ( 350 )   Save A new oriented electrodeposition method was used to obtain regular microstructure on platinum electrode surface. The treatment effects of electrodeposition with different experimental conditions were evaluated by electrochemical performance tests. Mechanical and electrochemical stability of electrodeposited electrode were respectively verified by ultrasonic treatment and electric pulse stimulation. The results showed that the microstructure obtained on electrode surface could increase the area for charge absorption. Addition of crystal modifier NH4Cl resulted in more regular microstructure on electrode surface. Compared with the irregular electrodeposition, double-layer capacitance and cathodic charge storage capacity of neural electrode were improved respectively by 26.8%, 85.7%. When the concentration of crystal modifier was 4 mol/L, the electrolyte temperature was 50 ℃, the best optimization effect could be achieved. References | Related Articles | Metrics

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Degradation Modeling of Capacitors Based on Time Series Analysis ZHANG Tian,PAN Ershun 2019, 53 (11):  1316-1325.  doi: 10.16183/j.cnki.jsjtu.2019.11.007 Abstract ( 1177 )   PDF (1336KB) ( 495 )   Save For the problem of predicting the capacity degradation of capacitors at elevated temperatures, based on the auto-regressive integrated moving average (ARIMA) model and the auto-regressive fractionally integrated moving average (ARFIMA) model, time series analysis methods are introduced to predict the degradation path of capacity. For the ARIMA model, when the degradation process of the capacitors obeys Wiener distribution, the over-differential prediction method (OPM) can be used to predict the difference order of the original time series that cause over-difference. According to the calculation results from unit root test, auto-correlation function and partial auto-correlation function, it will be verified that whether the time series can become stationary through the first order difference. For the ARFIMA model, the re-scaled range analysis is used to determine whether the degradation data has long-term memory. The orders and related parametric estimated values are obtained by using minimum information criterion and maximum likelihood estimation. Finally, the residual test is used to verify the ability of the OPM-ARIMA model and the ARFIMA model for extracting valuable information and accurate prediction. Furthermore, the feasibility and effectiveness of two models are also analyzed. References | Related Articles | Metrics

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Time-Domain Nonlinear Damage Detection Based on GARCH Effect and Improved Penalty Index GUO Huiyong，HUANG Qi 2019, 53 (11):  1326-1334.  doi: 10.16183/j.cnki.jsjtu.2019.99.003 Abstract ( 905 )   PDF (3821KB) ( 318 )   Save In service period, some structures may exist damages like cracks, and the opening and closing of cracks make the damage display a time-domain nonlinear characteristic. In addition，time-domain model methods mainly provide the characteristic change of degree of freedom of adjacent nodes caused by stiffness damage, but it is difficult to directly show the inter-storey stiffness information. To solve these problems, a damage detection method based on GARCH model and improved penalty index was presented. Firstly, basic theory of GARCH model was described, and the order estimation and the parameter estimation of GARCH model were proposed. Then, the bilinear stiffness characteristic of time-domain nonlinearity was analyzed, and the nonlinear damage identification principle and basic GARCH index of stiffness identification were presented. Finally, an improved GARCH penalty index method was established to enhance the identification reliability for the inter-storey stiffness damage. Simulation and experiment results indicate that the improved GARCH penalty index can well identify the structural nonlinear damage, and the identification effect of the proposed index is obviously better than those of the basic GARCH index and those combined with autoregressive model and the cepstral metric index. References | Related Articles | Metrics

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Fabrication and Mechanical Properties of Biodegradable Jute/Polylactic Acid Composites DU Siqi，WANG Jichong，PENG Xiongqi，GU Hailin 2019, 53 (11):  1335-1341.  doi: 10.16183/j.cnki.jsjtu.2019.11.009 Abstract ( 1169 )   PDF (9930KB) ( 335 )   Save Completely biodegradable jute fiber reinforced polylactic acid (PLA) composites were fabricated by compression molding in one step. Alkali treatment was conducted to improve material performance. The surface morphology of jute fabrics was observed by scanning electron microscope. The 0°/90° uni-axial tensile test and ±45° bias-tensile test were conducted for jute woven fabrics. The 0°/90° uni-axial tensile test was also performed for jute/PLA biocomposites. The surface morphology of jute fabrics demonstrated that alkali treatment leads to the removal of surface impurities of fabrics, the refinement of fiber structures and the emergence of rougher fiber surface. The results of the tensile tests showed that the strengths of jute fabrics and jute/PLA composites decline after alkali treatment while the moduli increase. And the experimental results also indicated that compared with woven jute fabrics, the mechanical properties of composites were greatly improved via adding PLA. Meanwhile, compared to jute fiber reinforced polypropylene composites, jute/PLA composites are completely degradable, non-toxic and harmless, and they have greater strength and modulus. References | Related Articles | Metrics

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Numerical Simulation of Temperature Rise Distribution of Particle Reinforced Composites Under Thermal Loads YANG Wanyou,WANG Jiaxu,HUANG Yanyan,ZHOU Qinghua,YANG Yong 2019, 53 (11):  1342-1351.  doi: 10.16183/j.cnki.jsjtu.2019.11.010 Abstract ( 883 )   PDF (4611KB) ( 427 )   Save Alternation between high and low temperatures is one of the key factors that severely affect the performance of the particle reinforced composites applied on the spacecrafts serving in rigorous space environment. Thermal loads result in surface and subsurface temperature rise changes of the materials, further lead to the surface thermal deformation and the interior thermal stress, and severely influence the mechanical performance of the materials. In the particle reinforced composites, the reinforcement has the heat conduction properties which are inconsistant with the base material, and whose distribution is irregular. Thus, steady state heat conduction in composites and its temperature rise distribution become quite complicated. Based on the equivalent inclusion method, a numerical analysis method for solving the temperature rise distribution of the composites under thermal loads was proposed, and its efficiency was promoted by appling a conjugate gradient method (CGM) and fast Fourier transform (FFT) method. The results demonstrate that the shape, the size, the location and the heat conduction property of the particle reinforcements have a significant influence on the temperature rise distribution inside of the particle reinforced composites. References | Related Articles | Metrics

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Thermal Characteristics of Reciprocating Friction of Rubber O-Ring Against Stainless Steel Surface KONG Yabin，SHEN Mingxue，ZHANG Zhinan，MENG Xiangkai，PENG Xudong 2019, 53 (11):  1352-1358.  doi: 10.16183/j.cnki.jsjtu.2019.11.011 Abstract ( 1099 )   PDF (2341KB) ( 288 )   Save The thermal characteristics of reciprocating friction of the nitrile rubber O-ring against stainless steel surface were successfully simulated by FEA (finite element analysis) and varified by experiments base on the Mooney-Rivlin model with high-order terms. The effects of reciprocating frequency, friction coefficient, contact pressure and ambient temperature on the temperature field of counterpart were investigated by using variable parameter method. Results showed that the FEA model could accurately analyze the characteristics of frictional heat generation at the rubber/metal friction interface. The temperature of the friction interface during the steady phase increased with increase of reciprocating frequency, friction coefficient and contact pressure. The temperature rise rate of the friction interface was independent of the initial ambient temperature. The stable value of the friction interface temperature had a linear relationship with the reciprocating frequency and had a positive parabolic relationship with the friction coefficient and the contact pressure. Zones close to the friction heat source had dense isotherms and great temperature gradient. References | Related Articles | Metrics

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Static Sealing Performance of Glyd-Ring Seal with Two Precompression Models CAI Zhiyuan,WANG Bingqing,PENG Xudong,GUO Shengrong,MENG Xiangkai 2019, 53 (11):  1359-1366.  doi: 10.16183/j.cnki.jsjtu.2019.11.012 Abstract ( 957 )   PDF (4393KB) ( 355 )   Save The two-dimensional axisymmetric geometry model of hydraulic Glyd-ring seal was established by applying the ANSYS software, which was used to analyze the effects of two precompression finite element models, the axial push and the radial compression, that were used to simulate the sealing ring installation process, and the related simulation results were compared and studied. Firstly, the stress distribution differences of two FEA models were given. Secondly, the influences of compression rate and sealed pressure on the static sealing performance with the two FEA models were compared and analyzed. The results indicate that the effect law on the static sealing performance of the two FEA models is basically the same, and the stress distribution is basically similar, but there is a deviation in the prediction of the stress concentration parts of the seal ring, which shows that the stress concentration of the radial compression model is closer to the air side. In addition, the simulation results of the axial push precompression FEA model reveal that the chamfer of polytetrafluoroethylene ring near the oil side is easier to meet with wear, which is in consistency with engineering practice. References | Related Articles | Metrics

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Hot-Gas Bypass Defrosting Method and Analysis of Defrosting Time for Transcritical CO2 Heat Pump WANG Yikai，YE Zuliang，PAN Zudong，ZHAO Jianfeng，HU Bin，CAO Feng 2019, 53 (11):  1367-1374.  doi: 10.16183/j.cnki.jsjtu.2019.11.013 Abstract ( 1362 )   PDF (1208KB) ( 507 )   Save When the air-source heat pump system is operated under low temperature conditions, there exists some problems such as frost formation on the evaporator and deterioration of system heating performance. Considering the limitations of traditional defrosting methods applied in the transcritical CO2 heat pump system, the hot-gas bypass defrosting method was experimentally investigated. The platform of air-source transcritical CO2 heat pump system was designed and a copper bypass tube with an outer diameter of 12.7mm was used as the expansion device. The platform was tested under various conditions to analyze the dynamic parameters during defrosting process and the effect of ambient temperature on the defrosting time. Meanwhile, the defrosting process at different times was depicted in the pressure-enthalpy diagram. The experimental results show that the hot-gas bypass defrosting process is relatively stable, and the parameters of each measuring point change relatively gently. According to the experimental data, it can be found that the hot-gas bypass defrosting method can significantly increase the evaporator inlet temperature to about 30℃, effectively shortening the defrosting time. The defrosting time was greatly affected by the defrosting stability period. The decrease of environmental temperature or the increase of environmental humidity would extend the defrosting time of the system. The change trend of defrosting energy consumption ratio is basically consistent with the defrosting time ratio. The defrosting efficiency is calculated to be 46.5% and 33.62% higher than that of other defrosting methods and the defrosting time is shortened by 100s, which indicates that the hot-gas bypass defrosting method is more suitable for the air-source transcritical CO2 heat pump. References | Related Articles | Metrics

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Study on Flange Wrinkling Prediction in Preforming Stage During Multi-Pass Conventional Spinning LI Xuelong,YU Zhongqi,ZHAO Yixi,EVSYUKOV S A 2019, 53 (11):  1375-1380.  doi: 10.16183/j.cnki.jsjtu.2019.11.014 Abstract ( 931 )   PDF (4043KB) ( 365 )   Save The multi-pass conventional spinning includes the shaping stage and preforming stage. This paper focuses on the flange wrinkling prediction in the preforming stage. According to the deformation characteristics in the preforming stage, the assumptions that the inner side of the instability region at the flange is a simple support condition and the outside is a free boundary condition are proposed, and the deflection surface equation for describing the wrinkling wave shape that meets the boundary conditions is established. The prediction model of the flange wrinkling is developed based on the energy method. Combining the geometries and the stress fields in the conventional spinning numerical simulation, the flange wrinkling prediction in the preforming stage is realized. Compared with the spinning experiment in an aluminum alloy hemispherical component, the developed model can accurately predict the flange wrinkling in the preforming stage. References | Related Articles | Metrics

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Microstructure and Mechanical Properties of 7A60 Aluminum Alloy by Friction Stir Processing LI Ping,ZHANG Kai,WANG Boxiaotian,XUE Kemin 2019, 53 (11):  1381-1388.  doi: 10.16183/j.cnki.jsjtu.2019.11.015 Abstract ( 1062 )   PDF (15025KB) ( 310 )   Save Friction stir processing (FSP) were carried out to modify the mechanical properties of 7A60 aluminum alloy. The effect of friction stir processing parameters on the microstructure and mechanical properties of 7A60 aluminum alloy were investigated. The results showed that the uniform and fine equiaxed grains were formed due to dynamic recrystallization and the second phases were refined by severe plastic deformation with homogeneous distribution in the Al matrix. Meanwhile the content of η (MgZn2) phase decreased under the action of FSP heat, indicating the occurrence of the dissolution of η(MgZn2) phase into the Al matrix. Velocity ratio factor (ω/v) was a decisive impact factor of the mechanical performance of the nugget zone. With the increase of ω/v, the microhardness of the FSP-processed sample firstly increased and then decreased. The highest Vickers hardness was 120, which was 37.5% higher than the base metal, was obtained when ω/v reached 5, and the tensile strength increased to 449.9MPa. With the increase of ω/v, more heat produced by the stirring head led to significant grain coarsening and the dimples of the tensile specimens fractography become shallow, which in turn severely affected the tensile strength and plasticity of the material. References | Related Articles | Metrics

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Blank Optimization for Sheet Metal Forming Using Inverse Finite Element Method and Mesh Mapping ZHANG Xiangkui,WANG Yang,WANG Changsheng,HU Ping 2019, 53 (11):  1389-1394.  doi: 10.16183/j.cnki.jsjtu.2019.11.016 Abstract ( 959 )   PDF (3520KB) ( 408 )   Save The transformation of the sheet into products without failure and excess of material in a sheet metal forming operation means that the blanks should be correctly designed. Due to the earing or non-uniform flange in sheet metal forming, caused by non-uniform material flow and planar anisotropy in the sheet, shape differences exist between the forming parts and target parts. In order to obtain a reasonable blank, the node mesh mapping method is proposed. Combining with the inverse finite element analysis and incremental analysis, the blank shape is optimized according to the mapping relationship and the flow tendency of material points. To test the proposed method, blank shape optimizations in the forming processes of a square box part and an electric car B-pillar are presented respectively. The results show that for more complex industrial parts, the method proposed in this paper can obtain a reasonable blank shape after a finite optimization, and the required shape of the target part is consistent with the shape after forming with a reasonable blank. References | Related Articles | Metrics