Currently the extruded effect,roughness to the lubricant shear thinning,temperature changes and other factors or some combination of a single factor mainly considered in the lubrication study of piston ring-cylinder.I...Currently the extruded effect,roughness to the lubricant shear thinning,temperature changes and other factors or some combination of a single factor mainly considered in the lubrication study of piston ring-cylinder.In the study of the energy equation,the oil viscosity-temperature properties,adsorption layer characteristics are usually not considered.So the theoretical research is different from the actual situation of engineering.The lubrication of piston ring-cylinder liner system in internal combustion(IC) engines is studied here based on the theory of thermal flow.An unsteady and compressible hydrodynamic lubrication model with an equivalent viscosity based on shear and extruded flow factor is derived by employing the viscosity-temperature relationship,meanwhile,characteristics such as lubricating oil’s density varying with pressure and temperature,thickness of adsorbent layer and oil film’s geometry are also considered in this model.While setting up the energy equation,the effect of lubricating oil’s volume expansion and viscous dissipation on temperature,the heat conduction along oil film’s thickness direction are considered.Finite difference equation is formed by using a first-order difference scheme in time scale and second-order difference scheme in space scale.A common diesel engine is introduced as an instance to predict the distribution of the minimum oil film thickness in the piston ring-cylinder liner system.The results of simulation calculation show that the minimum oil film thickness will decrease especially around the top dead center when the oil’s volume expansion,viscous dissipation and heat conduction are considered,which implies that:it is essential to take the thermal flow idea into account during investigating piston ring-cylinder liner system’s lubrication.A more complete piston ring-cylinder liner lubrication theory was established according to thermal fluids from the perspective of research.It is more helpful to guide the practical application of engineering to improve the accuracy of forecasting the minimum film thickness.On the other hand,distribution of the minimum oil film thickness shows a nonlinear property if the thickness of piston rings and cylinder liner adsorbent layer are involved in the analysis.It may be feasible to increase the minimum oil film thickness by varying surface roughness and material properties of piston rings and cylinder liner.展开更多
A set of compressed natural gas (CNG) multi-point direct injection system of spark-ignited engines and the corresponding measurement and data acquisition systems were developed in this paper. Based on different inject...A set of compressed natural gas (CNG) multi-point direct injection system of spark-ignited engines and the corresponding measurement and data acquisition systems were developed in this paper. Based on different injection modes, the mixture formation and combustion of CNG low-pressure direct injection (LPDI) engines were studied under varying factors such as air/ fuel ratio, injection timing. Meanwhile, three-dimensional simulations were adopted to explain the mixture formation mechanisms of CNG low-pressure compound direct injection (LPCDI) mode. On the basis of test results and simulation of the mixture homogeneous degree, the conception of injection window was proposed, and the LPCDI mode was proved to be more beneficial to the mixture concentration stratification formation in cylinder under lean-burning conditions, which resulted in effective combustion and stability.展开更多
The flame structure of gasoline engine is complicated and has the characteristic of fractal geometry. A fractal combustion model was used to simulate the engine working cycle. Based on this model, the fractal dimensio...The flame structure of gasoline engine is complicated and has the characteristic of fractal geometry. A fractal combustion model was used to simulate the engine working cycle. Based on this model, the fractal dimension and laminar flame surface area of turbulent premixed flames were studied under different working conditions. The experimental system mainly includes an optical engine and a set of photography equipment used to shoot the images of turbulent flame of spark-ignition engine. The difference box-counting method was used to process 2D combustion images. In contrast to the experimental results, the computational results show that the fractal combustion model is an effective method of simulating the engine combustion process. The study provides a better understanding for flame structure and its propagation.展开更多
Numerous vibration-based techniques are rarely used in diesel engines fault diagnosis in a direct way, due to the surface vibration signals of diesel engines with the complex non-stationary and nonlinear time-varying ...Numerous vibration-based techniques are rarely used in diesel engines fault diagnosis in a direct way, due to the surface vibration signals of diesel engines with the complex non-stationary and nonlinear time-varying fea- tures. To investigate the fault diagnosis of diesel engines, fractal correlation dimension, wavelet energy and entropy as features reflecting the diesel engine fault fractal and energy characteristics are extracted from the decomposed signals through analyzing vibration acceleration signals derived from the cylinder head in seven different states of valve train. An intelligent fault detector FastICA-SVM is applied for diesel engine fault diagnosis and classification. The results demonstrate that FastlCA-SVM achieves higher classification accuracy and makes better general- ization performance in small samples recognition. Besides, the fractal correlation dimension and wavelet energy and entropy as the special features of diesel engine vibration signal are considered as input vectors of classifier FastlCA- SVM and could produce the excellent classification results. The proposed methodology improves the accuracy of fea- ture extraction and the fault diagnosis of diesel engines.展开更多
Many simple nonlinear main journal bearing models have been studied theoretically, but the connection to existing engineering system has not been equally investigated. The consideration of the characteristics of engin...Many simple nonlinear main journal bearing models have been studied theoretically, but the connection to existing engineering system has not been equally investigated. The consideration of the characteristics of engine main journal bearings may provide a prediction of the bearing load and lubrication. Due to the strong non-linear features in bearing lubrication procedure, it is difficult to predict those characteristics. A non-linear dynamic model is described for analyzing the characteristics of engine main journal bearings. Components such as crankshaft, main journals and con rods are found by applying the finite element method. Non-linear spring/dampers are introduced to imitate the constraint and supporting functions provided by the main bearing and oil film. The engine gas pressure is imposed as excitation on the model via the engine piston, con rod, etc. The bearing reaction force is calculated over one engine cycle, and meanwhile, the oil film thickness and pressure distribution are obtained based on Reynolds differential equation. It can be found that the maximum bearing reaction force always occurs when the maximum cylinder pressure arises in the cylinder adjacent to that bearing. The simulated minimum oil film thickness, which is 3 μm, demonstrates the reliability of the main journal bearings. This non-linear dynamic analysis may save computing efforts of engine main bearing design and also is of good precision and close connection to actual engine main journal bearing conditions.展开更多
This paper reports results of the authors’ studies on the virtual design method used in the development of low noise intake system of I.C. engine. The resulting high pass-by noise at level above the legislative targe...This paper reports results of the authors’ studies on the virtual design method used in the development of low noise intake system of I.C. engine. The resulting high pass-by noise at level above the legislative target at full throttle when engine speed was around 5200 r/min necessitated a BEM-aided redesign task, following the typical process of design and development of an intake system. During the initial design, based on the acoustic theory and the requirements (1. The air flux of the redesigned should equal to or exceed the value of the original flux; 2. The filtering area must not be degraded), and considering the constraint of space in the engine compartment, total volume and rough internal dimensions were determined. During the detailed design, the exact internal dimensions of the air cleaner were determined, and an effective method was applied to improve the acoustic performance at low frequency. The predicted sound power of the intake system indicated that the objective of reducing the overall engine noise by minimizing intake system noise was achieved.展开更多
Experimental study on homogeneous charge compression ignition （HCCI） combustion process was carried out on a single-cylinder direct injection diesel engine fueled with dimethyl ether（DME）. The influence of inert g...Experimental study on homogeneous charge compression ignition （HCCI） combustion process was carried out on a single-cylinder direct injection diesel engine fueled with dimethyl ether（DME）. The influence of inert gas CO2 on the ignition and combustion process was investigated. The research results indicate that because of the high cetane number of DME, the stable HCCI operating range is quite narrow while the engine has a high compression ratio. The HCCI operating range can be largely extended when the inert gas is inducted into the charging air. HCCI combustion of DME presents remarkable characteristic of two-stage combustion process. As the concentration of inert gas increases, the ignition timing of the first combustion stage delays, the peak heat release rate decreases, and the combustion duration extends. Inducting inert gas into charging air cannot make the combustion and heat release of DME occur at a perfect crank angle position. Therefore,to obtain HCCI operation for the fuel with high cetane number,other methods such as reducing engine compression ratio should be adopted. Emission results show that under HCCI operation, a nearly zero NOx emission can be obtained with no smoke emissions. But the HC and CO emissions are high, and both rise with the increase of the concentration of inert gases.展开更多
Dependent on automatically generated unstructured grids, a comprehensive computational fluid dynamics(CFD)numerical simulation is performed to analyze the influence of nozzle geometry on the internal flow characterist...Dependent on automatically generated unstructured grids, a comprehensive computational fluid dynamics(CFD)numerical simulation is performed to analyze the influence of nozzle geometry on the internal flow characteristics of a multi-hole diesel injector with the multi-phase flow model based on Eulerian multi-fluid method.The diesel components in nozzle are considered as two continuous phases, diesel liquid and diesel vapor respectively.Considering that both of them are fully coupled and interpenetrated, sepa...展开更多
Using carbon tetrachloride （CCl4） as extraction agent, the activated sludge from Tianjin Jizhuangzi Sewage Treatment Plant as inoculum, the test study on biodegradability of lubricants was carried out. The test flas...Using carbon tetrachloride （CCl4） as extraction agent, the activated sludge from Tianjin Jizhuangzi Sewage Treatment Plant as inoculum, the test study on biodegradability of lubricants was carried out. The test flasks containing the mineral medium, the test oil and the inoculum were placed in incubation together with flasks containing poisoned blanks for periods of 0 and 21 days, respectively. Flasks containing the reference materials in place of the test oil were run in parallel. At the end of the incubation period, the contents of the flasks were subjected to sonic vibration, and were acidified and extracted by using CCI4. The extracts were then analysed by infra-red （IR） spectrometer to measure the maximum absorption of the C-H stretch of CH2-CH3 band at wavelength of 2 930 cm^-1. The absorption values were used to calculate the residual oil contents of the poisoned and test flasks. Consequently the biodegradability of the test oil was calculated. The test results indicate that the differences in the biodegradability of test materials in different tests are within 5.5%, and consistent with the data described in Coordinating European Council （CEC） L-33- A-93. The biodegradability of lubricants can be evaluated by this method effectively.展开更多
Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrati...Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrations is designed. The actuator employs electro-hydraulic system and can provide a high and circumferential load. To initialize new research, the characteristics of various kinds of active actuators to control rotor shaft vibration are briefly introduced. The purpose of this paper is to introduce the preliminary results via presenting the structure, functions and operating principles, in particular, the working process of the electro-hydraulic system of the new actuator which includes a set of high speed electromagnetic valves and a series of sloping cone-shaped openings, and presenting the transmission relationships among the control parameters from control signals into the valves to active load onto shaft. The course of the work is dynamic, and a series of spatial forces and moments are put on the shaft to get an external resultant force to reduce excitations that induce vibration of shafts. By checking states of vibration, the actuator can control the impulse width and the interval of injection time for applying different control force to a vibration shaft in two circumference directions through the regulating action of a set of combination directional control valves. The results from simulating analysis and experiment show evidence of that this design can satisfy the case of active process of decreasing of flexural and torsional vibrations.展开更多
The definition of J-integral of interfacial crack was introduced. The three-point bending tests were can＇ied out to obtain the critical loading values when the interfacial crack initiation occurred between coatings a...The definition of J-integral of interfacial crack was introduced. The three-point bending tests were can＇ied out to obtain the critical loading values when the interfacial crack initiation occurred between coatings and substrates. The finite element analysis （FEA） was adopted to analyze the stress distribution in the specimens and compute the J-integral of the interracial crack between LX88A coating and Chinese Q345 steel. The results showed that the average value of critical J-integral is 0.70 N/m, which can be taken as the fracture parameter to evaluate the interracial fracture behavior for the three-point bending specimens of LX88A coating/Q345 steel system.展开更多
This paper developed 3D product models of motorcycle and engine by UGNX as well as virtual prototyping by ADAMS program with road roughness generated by MATLAB. Under the straight-line running condition, the dynamic r...This paper developed 3D product models of motorcycle and engine by UGNX as well as virtual prototyping by ADAMS program with road roughness generated by MATLAB. Under the straight-line running condition, the dynamic responses of motorcycle multibody system to both road and engine excitations were compared with those to only road excitation in terms of vertical acceleration response, amplitude frequency response and power spectral density. The comparisons of simulation data showed that the response due to flat road excitation was around 20 Hz, while that to the combined excitations was in a wide frequency band, of which the major components focused on 10 Hz, 15 Hz, 35 Hz ,70 Hz, 100 Hz and even higher frequencies, reflecting the characteristics of engine excitation based on its unbalanced inertia force and torque. It is concluded that the high fidelity virtual prototyping can simulate the dynamics of motorcycle product well in investigating the vibration and ride comfort performance.展开更多
WMTC,which means a worldwide motorcycle testing cycle,is now regarded as the most possible choice for the global motorcycle emission testing cycle,but whether or not it can be used in China is still unknown.In this st...WMTC,which means a worldwide motorcycle testing cycle,is now regarded as the most possible choice for the global motorcycle emission testing cycle,but whether or not it can be used in China is still unknown.In this study,a large number of data on the speed-time trace of motorcycles were sampled from various kinds of roads in 5 cities in China.Based on a series of criterion numbers defined,the driving character of motorcycles in the real-road conditions of China was obtained.With the aid of a specially designed program,an emission testing cycle that can indicate the driving characteristics of motorcycle in the real-road conditions was synthesized,and the exhaust emission tests of 20 motorcycles under the synchronized cycle and WMTC were carried out based on a CVS system and a motorcycle chassis dynamometer.The results show that although there do exist differences in some criterion numbers between the real-road condition and WMTC,such as proportion of idling mode,mean speed,mean running speed and the average acceleration and deceleration rates,the driving behaviors are similar.The results of exhaust emission tests indicate that the emission values of motorcycles under the synchronized cycle and WMTC have a relatively strong correlation.This means that WMTC can be introduced as a standard motorcycle emission test regulation into China.展开更多
Degradation prediction of proton exchange membrane fuel cell(PEMFC)stack is of great significance for improving the rest useful life.In this study,a PEMFC system including a stack of 300 cells and subsystems has been ...Degradation prediction of proton exchange membrane fuel cell(PEMFC)stack is of great significance for improving the rest useful life.In this study,a PEMFC system including a stack of 300 cells and subsystems has been tested under semi-steady operations for about 931 h.Then,two different models are respectively established based on semi-empirical method and data-driven method to investigate the degradation of stack performance.It is found that the root mean square error(RMSE)of the semi-empirical model in predicting the stack voltage is around 1.0 V,while the predicted voltage has no local dynamic characteristics,which can only reflect the overall degradation trend of stack performance.The RMSE of short-term voltage degradation predicted by the DDM can be less than 1.0 V,and the predicted voltage has accurate local variation characteristics.However,for the long-term prediction,the error will accumulate with the iterations and the deviation of the predicted voltage begins to fluctuate gradually,and the RMSE for the long-term predictions can increase to 1.63 V.Based on the above characteristics of the two models,a hybrid prediction model is further developed.The prediction results of the semi-empirical model are used to modify the input of the data-driven model,which can effectively improve the oscillation of prediction results of the data-driven model during the long-term degradation.It is found that the hybrid model has good error distribution(RSEM=0.8144 V,R2=0.8258)and local performance dynamic characteristics which can be used to predict the process of long-term stack performance degradation.展开更多
Based on the linear instability analysis, the study on the relationship between breakup modes and gas-liquid interfaces of a viscous annular liquid jet moving in two swirling gas streams has been car- ried out. From t...Based on the linear instability analysis, the study on the relationship between breakup modes and gas-liquid interfaces of a viscous annular liquid jet moving in two swirling gas streams has been car- ried out. From the numerical results of the dispersion equation, the relevancy of the breakup mode between an annular liquid jet and two liquid jets of limiting cases, namely the cylindrical liquid jet and hollow gas jet, as well as the effects of injecting factors on the instability of an annular liquid jet, is studied in detail. Considering the effects of inner and outer interface radii on the instability of the jet, it is proved that the para-sinuous mode mainly relates to the inner interface, whereas the para-varicose mode mainly relates to the outer interface. The results also indicate that all the forces produced by liquid jet have similar impacts on either the instability of para-sinuous mode or para-varicose mode due to the fact that they can affect both inner and outer gas-liquid interfaces. On the other hand, all the forces exerting only on the inner interface have more powerful effects on the instability of para-sinuous mode, and all the forces exerting only on the outer interface have more powerful effects on the insta- bility of para-varicose mode. That is to say, the effects of forces are weakened greatly when penetrating the liquid jet.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50975192)
文摘Currently the extruded effect,roughness to the lubricant shear thinning,temperature changes and other factors or some combination of a single factor mainly considered in the lubrication study of piston ring-cylinder.In the study of the energy equation,the oil viscosity-temperature properties,adsorption layer characteristics are usually not considered.So the theoretical research is different from the actual situation of engineering.The lubrication of piston ring-cylinder liner system in internal combustion(IC) engines is studied here based on the theory of thermal flow.An unsteady and compressible hydrodynamic lubrication model with an equivalent viscosity based on shear and extruded flow factor is derived by employing the viscosity-temperature relationship,meanwhile,characteristics such as lubricating oil’s density varying with pressure and temperature,thickness of adsorbent layer and oil film’s geometry are also considered in this model.While setting up the energy equation,the effect of lubricating oil’s volume expansion and viscous dissipation on temperature,the heat conduction along oil film’s thickness direction are considered.Finite difference equation is formed by using a first-order difference scheme in time scale and second-order difference scheme in space scale.A common diesel engine is introduced as an instance to predict the distribution of the minimum oil film thickness in the piston ring-cylinder liner system.The results of simulation calculation show that the minimum oil film thickness will decrease especially around the top dead center when the oil’s volume expansion,viscous dissipation and heat conduction are considered,which implies that:it is essential to take the thermal flow idea into account during investigating piston ring-cylinder liner system’s lubrication.A more complete piston ring-cylinder liner lubrication theory was established according to thermal fluids from the perspective of research.It is more helpful to guide the practical application of engineering to improve the accuracy of forecasting the minimum film thickness.On the other hand,distribution of the minimum oil film thickness shows a nonlinear property if the thickness of piston rings and cylinder liner adsorbent layer are involved in the analysis.It may be feasible to increase the minimum oil film thickness by varying surface roughness and material properties of piston rings and cylinder liner.
基金Supported by National High Technology Research and Development Program ("863" Program) of China (No.2008AA11A114)
文摘A set of compressed natural gas (CNG) multi-point direct injection system of spark-ignited engines and the corresponding measurement and data acquisition systems were developed in this paper. Based on different injection modes, the mixture formation and combustion of CNG low-pressure direct injection (LPDI) engines were studied under varying factors such as air/ fuel ratio, injection timing. Meanwhile, three-dimensional simulations were adopted to explain the mixture formation mechanisms of CNG low-pressure compound direct injection (LPCDI) mode. On the basis of test results and simulation of the mixture homogeneous degree, the conception of injection window was proposed, and the LPCDI mode was proved to be more beneficial to the mixture concentration stratification formation in cylinder under lean-burning conditions, which resulted in effective combustion and stability.
基金Supported by National Natural Science Foundation of China (No. 50876072) Tianjin Municipal Science and Technology Commission (No. 07JCYBJC03900 )
文摘The flame structure of gasoline engine is complicated and has the characteristic of fractal geometry. A fractal combustion model was used to simulate the engine working cycle. Based on this model, the fractal dimension and laminar flame surface area of turbulent premixed flames were studied under different working conditions. The experimental system mainly includes an optical engine and a set of photography equipment used to shoot the images of turbulent flame of spark-ignition engine. The difference box-counting method was used to process 2D combustion images. In contrast to the experimental results, the computational results show that the fractal combustion model is an effective method of simulating the engine combustion process. The study provides a better understanding for flame structure and its propagation.
基金Supported by National Science and Technology Support Program of China(Grant No.2015BAF07B04)
文摘Numerous vibration-based techniques are rarely used in diesel engines fault diagnosis in a direct way, due to the surface vibration signals of diesel engines with the complex non-stationary and nonlinear time-varying fea- tures. To investigate the fault diagnosis of diesel engines, fractal correlation dimension, wavelet energy and entropy as features reflecting the diesel engine fault fractal and energy characteristics are extracted from the decomposed signals through analyzing vibration acceleration signals derived from the cylinder head in seven different states of valve train. An intelligent fault detector FastICA-SVM is applied for diesel engine fault diagnosis and classification. The results demonstrate that FastlCA-SVM achieves higher classification accuracy and makes better general- ization performance in small samples recognition. Besides, the fractal correlation dimension and wavelet energy and entropy as the special features of diesel engine vibration signal are considered as input vectors of classifier FastlCA- SVM and could produce the excellent classification results. The proposed methodology improves the accuracy of fea- ture extraction and the fault diagnosis of diesel engines.
基金supported by National Natural Science Foundation of China (Grant No. 60879002)National Hi-tech Research and Development Program of China (863 Program, Grant No. 2006AA110112)
文摘Many simple nonlinear main journal bearing models have been studied theoretically, but the connection to existing engineering system has not been equally investigated. The consideration of the characteristics of engine main journal bearings may provide a prediction of the bearing load and lubrication. Due to the strong non-linear features in bearing lubrication procedure, it is difficult to predict those characteristics. A non-linear dynamic model is described for analyzing the characteristics of engine main journal bearings. Components such as crankshaft, main journals and con rods are found by applying the finite element method. Non-linear spring/dampers are introduced to imitate the constraint and supporting functions provided by the main bearing and oil film. The engine gas pressure is imposed as excitation on the model via the engine piston, con rod, etc. The bearing reaction force is calculated over one engine cycle, and meanwhile, the oil film thickness and pressure distribution are obtained based on Reynolds differential equation. It can be found that the maximum bearing reaction force always occurs when the maximum cylinder pressure arises in the cylinder adjacent to that bearing. The simulated minimum oil film thickness, which is 3 μm, demonstrates the reliability of the main journal bearings. This non-linear dynamic analysis may save computing efforts of engine main bearing design and also is of good precision and close connection to actual engine main journal bearing conditions.
文摘This paper reports results of the authors’ studies on the virtual design method used in the development of low noise intake system of I.C. engine. The resulting high pass-by noise at level above the legislative target at full throttle when engine speed was around 5200 r/min necessitated a BEM-aided redesign task, following the typical process of design and development of an intake system. During the initial design, based on the acoustic theory and the requirements (1. The air flux of the redesigned should equal to or exceed the value of the original flux; 2. The filtering area must not be degraded), and considering the constraint of space in the engine compartment, total volume and rough internal dimensions were determined. During the detailed design, the exact internal dimensions of the air cleaner were determined, and an effective method was applied to improve the acoustic performance at low frequency. The predicted sound power of the intake system indicated that the objective of reducing the overall engine noise by minimizing intake system noise was achieved.
文摘Experimental study on homogeneous charge compression ignition （HCCI） combustion process was carried out on a single-cylinder direct injection diesel engine fueled with dimethyl ether（DME）. The influence of inert gas CO2 on the ignition and combustion process was investigated. The research results indicate that because of the high cetane number of DME, the stable HCCI operating range is quite narrow while the engine has a high compression ratio. The HCCI operating range can be largely extended when the inert gas is inducted into the charging air. HCCI combustion of DME presents remarkable characteristic of two-stage combustion process. As the concentration of inert gas increases, the ignition timing of the first combustion stage delays, the peak heat release rate decreases, and the combustion duration extends. Inducting inert gas into charging air cannot make the combustion and heat release of DME occur at a perfect crank angle position. Therefore,to obtain HCCI operation for the fuel with high cetane number,other methods such as reducing engine compression ratio should be adopted. Emission results show that under HCCI operation, a nearly zero NOx emission can be obtained with no smoke emissions. But the HC and CO emissions are high, and both rise with the increase of the concentration of inert gases.
基金Supported by National Natural Science Foundation of China (No. 50876072)Tianjin Municipal Science and Technology Commission (No. 07JCYBJC03900 )
文摘Dependent on automatically generated unstructured grids, a comprehensive computational fluid dynamics(CFD)numerical simulation is performed to analyze the influence of nozzle geometry on the internal flow characteristics of a multi-hole diesel injector with the multi-phase flow model based on Eulerian multi-fluid method.The diesel components in nozzle are considered as two continuous phases, diesel liquid and diesel vapor respectively.Considering that both of them are fully coupled and interpenetrated, sepa...
基金China Petroleum & Chemical Corporation (No. 104141)
文摘Using carbon tetrachloride （CCl4） as extraction agent, the activated sludge from Tianjin Jizhuangzi Sewage Treatment Plant as inoculum, the test study on biodegradability of lubricants was carried out. The test flasks containing the mineral medium, the test oil and the inoculum were placed in incubation together with flasks containing poisoned blanks for periods of 0 and 21 days, respectively. Flasks containing the reference materials in place of the test oil were run in parallel. At the end of the incubation period, the contents of the flasks were subjected to sonic vibration, and were acidified and extracted by using CCI4. The extracts were then analysed by infra-red （IR） spectrometer to measure the maximum absorption of the C-H stretch of CH2-CH3 band at wavelength of 2 930 cm^-1. The absorption values were used to calculate the residual oil contents of the poisoned and test flasks. Consequently the biodegradability of the test oil was calculated. The test results indicate that the differences in the biodegradability of test materials in different tests are within 5.5%, and consistent with the data described in Coordinating European Council （CEC） L-33- A-93. The biodegradability of lubricants can be evaluated by this method effectively.
基金supported by National Natural Science Foundation of China (No.50475112)National Hi-Tech Research and Development Program of China (863 Program,No.2006AA110112).
文摘Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrations is designed. The actuator employs electro-hydraulic system and can provide a high and circumferential load. To initialize new research, the characteristics of various kinds of active actuators to control rotor shaft vibration are briefly introduced. The purpose of this paper is to introduce the preliminary results via presenting the structure, functions and operating principles, in particular, the working process of the electro-hydraulic system of the new actuator which includes a set of high speed electromagnetic valves and a series of sloping cone-shaped openings, and presenting the transmission relationships among the control parameters from control signals into the valves to active load onto shaft. The course of the work is dynamic, and a series of spatial forces and moments are put on the shaft to get an external resultant force to reduce excitations that induce vibration of shafts. By checking states of vibration, the actuator can control the impulse width and the interval of injection time for applying different control force to a vibration shaft in two circumference directions through the regulating action of a set of combination directional control valves. The results from simulating analysis and experiment show evidence of that this design can satisfy the case of active process of decreasing of flexural and torsional vibrations.
基金Supported by Tianjin Natural Science Foundation (No.08JCYBJC09100)New Teacher Research Fund for the Doctoral Program of Higher Education of China (No.20070056096) and New Century Outstanding Talented Person Plan of China.
文摘The definition of J-integral of interfacial crack was introduced. The three-point bending tests were can＇ied out to obtain the critical loading values when the interfacial crack initiation occurred between coatings and substrates. The finite element analysis （FEA） was adopted to analyze the stress distribution in the specimens and compute the J-integral of the interracial crack between LX88A coating and Chinese Q345 steel. The results showed that the average value of critical J-integral is 0.70 N/m, which can be taken as the fracture parameter to evaluate the interracial fracture behavior for the three-point bending specimens of LX88A coating/Q345 steel system.
基金Supported by National Natural Science Foundation of China (No. 51176138)
文摘This paper developed 3D product models of motorcycle and engine by UGNX as well as virtual prototyping by ADAMS program with road roughness generated by MATLAB. Under the straight-line running condition, the dynamic responses of motorcycle multibody system to both road and engine excitations were compared with those to only road excitation in terms of vertical acceleration response, amplitude frequency response and power spectral density. The comparisons of simulation data showed that the response due to flat road excitation was around 20 Hz, while that to the combined excitations was in a wide frequency band, of which the major components focused on 10 Hz, 15 Hz, 35 Hz ,70 Hz, 100 Hz and even higher frequencies, reflecting the characteristics of engine excitation based on its unbalanced inertia force and torque. It is concluded that the high fidelity virtual prototyping can simulate the dynamics of motorcycle product well in investigating the vibration and ride comfort performance.
基金Supported by Tianjin Municipal Science and Technology Commission(No.05YFJMJC11100and No.07JCYBJC03900)Ministry of Education of China(No.20020056046).
文摘WMTC,which means a worldwide motorcycle testing cycle,is now regarded as the most possible choice for the global motorcycle emission testing cycle,but whether or not it can be used in China is still unknown.In this study,a large number of data on the speed-time trace of motorcycles were sampled from various kinds of roads in 5 cities in China.Based on a series of criterion numbers defined,the driving character of motorcycles in the real-road conditions of China was obtained.With the aid of a specially designed program,an emission testing cycle that can indicate the driving characteristics of motorcycle in the real-road conditions was synthesized,and the exhaust emission tests of 20 motorcycles under the synchronized cycle and WMTC were carried out based on a CVS system and a motorcycle chassis dynamometer.The results show that although there do exist differences in some criterion numbers between the real-road condition and WMTC,such as proportion of idling mode,mean speed,mean running speed and the average acceleration and deceleration rates,the driving behaviors are similar.The results of exhaust emission tests indicate that the emission values of motorcycles under the synchronized cycle and WMTC have a relatively strong correlation.This means that WMTC can be introduced as a standard motorcycle emission test regulation into China.
基金supported by the National Key Research and Development Program of China(Grant No.SQ2021YFE011145)the Science and Technology Development Program of Jilin Province(Grant No.20200501010GX).
文摘Degradation prediction of proton exchange membrane fuel cell(PEMFC)stack is of great significance for improving the rest useful life.In this study,a PEMFC system including a stack of 300 cells and subsystems has been tested under semi-steady operations for about 931 h.Then,two different models are respectively established based on semi-empirical method and data-driven method to investigate the degradation of stack performance.It is found that the root mean square error(RMSE)of the semi-empirical model in predicting the stack voltage is around 1.0 V,while the predicted voltage has no local dynamic characteristics,which can only reflect the overall degradation trend of stack performance.The RMSE of short-term voltage degradation predicted by the DDM can be less than 1.0 V,and the predicted voltage has accurate local variation characteristics.However,for the long-term prediction,the error will accumulate with the iterations and the deviation of the predicted voltage begins to fluctuate gradually,and the RMSE for the long-term predictions can increase to 1.63 V.Based on the above characteristics of the two models,a hybrid prediction model is further developed.The prediction results of the semi-empirical model are used to modify the input of the data-driven model,which can effectively improve the oscillation of prediction results of the data-driven model during the long-term degradation.It is found that the hybrid model has good error distribution(RSEM=0.8144 V,R2=0.8258)and local performance dynamic characteristics which can be used to predict the process of long-term stack performance degradation.
基金the Natural Science Foundation of Tianjin (Grant Nos. 05YFJMJC11100 and 07JCYBJC03900)
文摘Based on the linear instability analysis, the study on the relationship between breakup modes and gas-liquid interfaces of a viscous annular liquid jet moving in two swirling gas streams has been car- ried out. From the numerical results of the dispersion equation, the relevancy of the breakup mode between an annular liquid jet and two liquid jets of limiting cases, namely the cylindrical liquid jet and hollow gas jet, as well as the effects of injecting factors on the instability of an annular liquid jet, is studied in detail. Considering the effects of inner and outer interface radii on the instability of the jet, it is proved that the para-sinuous mode mainly relates to the inner interface, whereas the para-varicose mode mainly relates to the outer interface. The results also indicate that all the forces produced by liquid jet have similar impacts on either the instability of para-sinuous mode or para-varicose mode due to the fact that they can affect both inner and outer gas-liquid interfaces. On the other hand, all the forces exerting only on the inner interface have more powerful effects on the instability of para-sinuous mode, and all the forces exerting only on the outer interface have more powerful effects on the insta- bility of para-varicose mode. That is to say, the effects of forces are weakened greatly when penetrating the liquid jet.
