The wettability of the solid surface is often characterized by the contact angle of the liquid on the solid surface. However, it has long been found that the contact angle of liquid on a solid surface can take a range...The wettability of the solid surface is often characterized by the contact angle of the liquid on the solid surface. However, it has long been found that the contact angle of liquid on a solid surface can take a range of values between two extremes： the advancing and the receding contact angles. The difference between the advancing and the receding contact angles is conventionally called contact angle hysteresis. Knowledge of contact angle hysteresis is essential to understand surface wettability and control surface wetting behavior. The wettability can be affected, for example, by the roughness of the solid surface. In our work, textile is used as macroscopic roughness surfaces, and smooth plate surface is used as well to determine contact angle hysteresis. The advancing and receding contact angles are measured on polyamide materials.展开更多
Serious commutation lag occurs when a Brushless DC Motor(BLDCM) operates at high speeds,and this leads to torque decline with ripple.In this paper,an advanced conduction control scheme is proposed which can accelerate...Serious commutation lag occurs when a Brushless DC Motor(BLDCM) operates at high speeds,and this leads to torque decline with ripple.In this paper,an advanced conduction control scheme is proposed which can accelerate the commutation and enhance the torque production remarkably.Besides,an on line adjusting algorithm based on the Golden Section Method is adopted to search the optimal advanced conduction angle.Simulation and experimental results verify the feasibility and effectivity of the scheme proposed.展开更多
To study the economic advantages of hydrogen internal combustion engine, an experimen- tal study was carried out using a 2.0 L port fuel-injected （PFI） hydrogen internal combustion engine. Influences of fuel-air equ...To study the economic advantages of hydrogen internal combustion engine, an experimen- tal study was carried out using a 2.0 L port fuel-injected （PFI） hydrogen internal combustion engine. Influences of fuel-air equivalence ratio φ, speed, and ignition advance angle on heat efficiency were determined. Test results showed that indicated thermal efficiency （ ITE ） firstly increased with fuel- air equivalence ratio, achieved the maximum value of 40. 4% （ φ = 0.3 ）, and then decreased when was more than 0. 3. ITE increased as speed rises. Mechanical efficiency increased as fuel-air equiva- lence ratio increased, whereas mechanical efficiency decreased as speed increased, with maximum mechanical efficiency reaching 90%. Brake thermal efficiency （BTE） was influenced by ITE and me- chanical efficiency, at the maximum value of 35% （φ =0.5, 2 000 r/min）. The optimal ignition ad- vance angle of each condition resulting in the maximum BTE was also studied. With increasing fuel- air equivalence ratio, the optimal ignition angle became closer to the top dead center （ TDC ）. The test results and the conclusions exhibited a guiding role on hydrogen internal combustion engine opti- mization.展开更多
In this paper,the operation characteristics of a microscale internal combustion swing engine(MICSE)were investigated experimentally and numerically.The energy flow path of MICSE was comprehensively analyzed based on t...In this paper,the operation characteristics of a microscale internal combustion swing engine(MICSE)were investigated experimentally and numerically.The energy flow path of MICSE was comprehensively analyzed based on the first law of thermodynamics.The accuracy of zero-dimensional model was verified by experiments.The indicative thermal efficiency of the engine increases first and then decreases with the increase of equivalent ratio or ignition advance angle.The results show that there exists an optimum equivalent ratio and ignition advance angle during operation.The maximum efficiency of the engine reaches 12.5%when the equivalent ratio and ignition advance angle are 0.8 and−0.553,respectively.MICSE can operate normally when the equivalent ratio is greater than 0.6.The peak value of net heat release rate lags behind that of pressure change,which is different from the conventional crank engine.Experimental and simulation results show that the leakage of MICSE is serious,and it is the main loss of MICSE.The order of energy terms is as follows:leakage loss>exhaust loss>heat loss>indicative work.展开更多
Quantitative correlation between the critical impact velocity of droplet and geometry of superhydrophobic surfaces with microstructures is systematically studied.Experimental data shows that the critical impact veloci...Quantitative correlation between the critical impact velocity of droplet and geometry of superhydrophobic surfaces with microstructures is systematically studied.Experimental data shows that the critical impact velocity induced wetting transition of droplet on the superhydrophobic surfaces is strongly determined by the perimeter of single micropillar,the space between the repeat pillars and the advancing contact angle of the sidewall of the micropillars.The proposed model agrees well with the experimental results,and clarifies that the underlying mechanism which is responsible for the superhydrophobic surface with hierarchical roughness could sustain a higher liquid pressure than the surfaces with microstructures.展开更多
文摘The wettability of the solid surface is often characterized by the contact angle of the liquid on the solid surface. However, it has long been found that the contact angle of liquid on a solid surface can take a range of values between two extremes： the advancing and the receding contact angles. The difference between the advancing and the receding contact angles is conventionally called contact angle hysteresis. Knowledge of contact angle hysteresis is essential to understand surface wettability and control surface wetting behavior. The wettability can be affected, for example, by the roughness of the solid surface. In our work, textile is used as macroscopic roughness surfaces, and smooth plate surface is used as well to determine contact angle hysteresis. The advancing and receding contact angles are measured on polyamide materials.
基金Supported by College Doctoral- Program Special ResearchFund of the Ministry of Education (No.970 0 562 1 )
文摘Serious commutation lag occurs when a Brushless DC Motor(BLDCM) operates at high speeds,and this leads to torque decline with ripple.In this paper,an advanced conduction control scheme is proposed which can accelerate the commutation and enhance the torque production remarkably.Besides,an on line adjusting algorithm based on the Golden Section Method is adopted to search the optimal advanced conduction angle.Simulation and experimental results verify the feasibility and effectivity of the scheme proposed.
基金Supported by the National Natural Science Foundation of China(51276019)
文摘To study the economic advantages of hydrogen internal combustion engine, an experimen- tal study was carried out using a 2.0 L port fuel-injected （PFI） hydrogen internal combustion engine. Influences of fuel-air equivalence ratio φ, speed, and ignition advance angle on heat efficiency were determined. Test results showed that indicated thermal efficiency （ ITE ） firstly increased with fuel- air equivalence ratio, achieved the maximum value of 40. 4% （ φ = 0.3 ）, and then decreased when was more than 0. 3. ITE increased as speed rises. Mechanical efficiency increased as fuel-air equiva- lence ratio increased, whereas mechanical efficiency decreased as speed increased, with maximum mechanical efficiency reaching 90%. Brake thermal efficiency （BTE） was influenced by ITE and me- chanical efficiency, at the maximum value of 35% （φ =0.5, 2 000 r/min）. The optimal ignition ad- vance angle of each condition resulting in the maximum BTE was also studied. With increasing fuel- air equivalence ratio, the optimal ignition angle became closer to the top dead center （ TDC ）. The test results and the conclusions exhibited a guiding role on hydrogen internal combustion engine opti- mization.
基金This project is funded by the National Natural Science Foundation of China(No.52076007)the National Key Basic Research Program of China(No.2014CB239603).
文摘In this paper,the operation characteristics of a microscale internal combustion swing engine(MICSE)were investigated experimentally and numerically.The energy flow path of MICSE was comprehensively analyzed based on the first law of thermodynamics.The accuracy of zero-dimensional model was verified by experiments.The indicative thermal efficiency of the engine increases first and then decreases with the increase of equivalent ratio or ignition advance angle.The results show that there exists an optimum equivalent ratio and ignition advance angle during operation.The maximum efficiency of the engine reaches 12.5%when the equivalent ratio and ignition advance angle are 0.8 and−0.553,respectively.MICSE can operate normally when the equivalent ratio is greater than 0.6.The peak value of net heat release rate lags behind that of pressure change,which is different from the conventional crank engine.Experimental and simulation results show that the leakage of MICSE is serious,and it is the main loss of MICSE.The order of energy terms is as follows:leakage loss>exhaust loss>heat loss>indicative work.
基金supported by the National Natural Science Foundation of China(Grant Nos.11072126,91326108 and 51206042)
文摘Quantitative correlation between the critical impact velocity of droplet and geometry of superhydrophobic surfaces with microstructures is systematically studied.Experimental data shows that the critical impact velocity induced wetting transition of droplet on the superhydrophobic surfaces is strongly determined by the perimeter of single micropillar,the space between the repeat pillars and the advancing contact angle of the sidewall of the micropillars.The proposed model agrees well with the experimental results,and clarifies that the underlying mechanism which is responsible for the superhydrophobic surface with hierarchical roughness could sustain a higher liquid pressure than the surfaces with microstructures.
