As a major function of smart transportation in smart cities,vehicle model recognition plays an important role in intelligent transportation.Due to the difference among different vehicle models recognition datasets,the...As a major function of smart transportation in smart cities,vehicle model recognition plays an important role in intelligent transportation.Due to the difference among different vehicle models recognition datasets,the accuracy of network model training in one scene will be greatly reduced in another one.However,if you don’t have a lot of vehicle model datasets for the current scene,you cannot properly train a model.To address this problem,we study the problem of cold start of vehicle model recognition under cross-scenario.Under the condition of small amount of datasets,combined with the method of transfer learning,load the DAN(Deep Adaptation Networks)and JAN(Joint Adaptation Networks)domain adaptation modules into the convolutional neural network AlexNet and ResNet,and get four models:AlexNet-JAN,AlexNet-DAN,ResNet-JAN,and ResNet-DAN which can achieve a higher accuracy at the beginning.Through experiments,transfer the vehicle model recognition from the network image dataset(source domain)to the surveillance-nature dataset(target domain),both Top-1 and Top-5 accuracy have been improved by at least 20%.展开更多
Recommender system (RS) has become a very important factor in many eCommerce sites. In our daily life, we rely on the recommendation from other persons either by word of mouth, recommendation letters, movie, item and ...Recommender system (RS) has become a very important factor in many eCommerce sites. In our daily life, we rely on the recommendation from other persons either by word of mouth, recommendation letters, movie, item and book reviews printed in newspapers, etc. The typical Recommender Systems are software tools and techniques that provide support to people by identifying interesting products and services in online store. It also provides a recommendation for certain users who search for the recommendations. The most important open challenge in Collaborative filtering recommender system is the cold start problem. If the adequate or sufficient information is not available for a new item or users, the recommender system runs into the cold start problem. To increase the usefulness of collaborative recommender systems, it could be desirable to eliminate the challenge such as cold start problem. Revealing the community structures is crucial to understand and more important with the increasing popularity of online social networks. The community detection is a key issue in social network analysis in which nodes of the communities are tightly connected each other and loosely connected between other communities. Many algorithms like Givan-Newman algorithm, modularity maximization, leading eigenvector, walk trap, etc., are used to detect the communities in the networks. To test the community division is meaningful we define a quality function called modularity. Modularity is that the links within a community are higher than the expected links in those communities. In this paper, we try to give a solution to the cold-start problem based on community detection algorithm that extracts the community from the social networks and identifies the similar users on that network. Hence, within the proposed work several intrinsic details are taken as a rule of thumb to boost the results higher. Moreover, the simulation experiment was taken to solve the cold start problem.展开更多
In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicle...In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicles(UAVs)has garnered significant attention.The PEMFC,serving as the primary energy supply,markedly extends the UAV’s operational endurance.However,due to payload limitations and spatial constraints in the airframe layout of UAVs,the stack requires customized adaptation.Moreover,the implementation of auxiliary systems to facilitate cold starts of the PEMFC under low-temperature conditions is not feasible.Relying solely on thermal insulation measures also proves inadequate to address the challenges posed by complex low-temperature startup scenarios.To overcomethis,our study leverages the UAV’s lithium battery to heat the cathode inlet airflow,aiding the cathode-open PEMFC cold start process.To validate the feasibility of the proposed air-assisted heating strategy during the conceptual design phase,this study develops a transient,non-isothermal 3Dcathode-open PEMF Cunitmodel incorporating cathode air-assisted heating and gas-ice phase change.The model’s accuracy was verified against experimental cold-start data from a stack composed of identical single cells.This computational framework enables quantitative analysis of temperature fields and ice fraction distributions across domains under varying air-assisted heating powers during cold starts.Building upon this model,the study further investigates the improvement in cold start performance by heating the cathode intake air with varying power levels.The results demonstrate that the fuel cell achieves self-startup at temperatures as low as−13℃ under a constant current density of 100mA/cm^(2) without air-assisted heating.At an ambient temperature of−20℃,a successful start-up can be achieved with a heating power of 0.45 W/cm^(2).The temperature variation overtime during the cold start process can be represented by a sum of two exponential functions.The air-assisted heating scheme proposed in this study has significantly improved the cold start performance of fuel cells in low-temperature environments.Additionally,it provides critical reference data and validation support for component selection and feasibility assessment of hybrid power systems.展开更多
Water transport is of paramount importance to the cold start of proton exchange membrane fuel cells(PEMFCs).Analysis of water transport in cathode catalyst layer(CCL)during cold start reveals the distinct characterist...Water transport is of paramount importance to the cold start of proton exchange membrane fuel cells(PEMFCs).Analysis of water transport in cathode catalyst layer(CCL)during cold start reveals the distinct characteristics from the normal temperature operation.This work studies the effect of CCL mesoscopic pore-morphology on PEMFC cold start.The CCL mesoscale morphology is characterized by two tortuosity factors of the ionomer network and pore structure,respectively.The simulation results demonstrate that the mesoscale morphology of CCL has a significant influence on the performance of PEMFC cold start.It was found that cold-starting of a cell with a CCL of less tortuous mesoscale morphology can succeed,whereas starting up a cell with a CCL of more tortuous mesoscale morphology may fail.The CCL of less tortuous pore structure reduces the water back diffusion resistance from the CCL to proton exchange membrane(PEM),thus enhancing the water storage in PEM,while reducing the tortuosity in ionomer network of CCL is found to enhance the water transport in and the water removal from CCL.For the sake of better cold start performance,novel preparation methods,which can create catalyst layers of larger size primary pores and less tortuous pore structure and ionomer network,are desirable.展开更多
To enhance the fuel economy of a vehicle powered by a gasoline engine under road conditions,an energy flow test of a vehicle was performed experimentally under the New European Driving Cycle of cold start.The energy d...To enhance the fuel economy of a vehicle powered by a gasoline engine under road conditions,an energy flow test of a vehicle was performed experimentally under the New European Driving Cycle of cold start.The energy distributions and related influencing factors were analyzed using the test data.Results show that the effective power and thermal efficiency are mainly affected by the engine load except in the early stage of the New European Driving Cycle.Because of the retarded CA50 and longer CA10-90,the effective thermal efficiency is lower in the early phase of driving conditions.Initially,the heat transfer loss mainly comprises the loss of the heating,ventilation,and air conditioning system.The radiator then plays the major role,with its percentage affected by the engine load and decreasing under the extra-urban driving cycle.The exhaust gas loss is decided by the temperature and flow rate of the exhaust gas,while its percentage is mainly affected by the temperature of the exhaust gas.In the early phase of driving conditions,the retarded spark advance angle leads to a higher temperature of the exhaust gas and a greater exhaust gas loss.The pumping loss and its percentage are mainly determined by the engine speed under the urban driving cycle,and both decrease under the extra-urban driving cycle except at maximum vehicle speed.展开更多
To reduce the fuel consumption of internal combustion engines, more attention has been paid to the tribological performance of the piston ring pack during the cold start and idle operations. In this research, a numeri...To reduce the fuel consumption of internal combustion engines, more attention has been paid to the tribological performance of the piston ring pack during the cold start and idle operations. In this research, a numerical model considering the cylinder liner deformation and the piston ring conformability is developed to predict the blow-by, lubrication, friction and wear of the piston ring pack under different operating conditions. The gas flow rate, inter-ring gas pressures, minimum oil film thickness, frictional force and wear load during cold start are calculated and compared with those during warm idle operating conditions. The results show that cylinder liner deformation and piston ring conformability together obviously affect blow-by and other tribological performance. Meanwhile, it is found that friction loss is larger during cold start than during warm idle operating conditions. However, the wear process is more severe during warm idle operation than during cold start. From this research, the blow-by and tribological performance of the piston ring pack during cold start and warm idle operations are understood more deeply.展开更多
This paper integrated a two-dimensional axisymmetrical transient model applicable to cold-start emission applications. The model can be used to simulate and explain effects of the flow and temperature distribution on ...This paper integrated a two-dimensional axisymmetrical transient model applicable to cold-start emission applications. The model can be used to simulate and explain effects of the flow and temperature distribution on performance of a converter. The evolutions of distribution of the temperature and concentration in the monolith during the cold-start period and the effects of flow distribution in the monolith on the cold-start performance are simulated in terms of the integrated model. The investigation indicates that the axial and radial gradients of temperature of the solid become steeper as the inlet gas temperature ramp increases; this furthermore results in the movement of reaction region in the monolith, and the flow distribution in the monolith affects the radial distribution of temperature of the solid;the radial gradients of temperature of the solid become greater as the flow uniformity index decreases, whereas the light-off time doesn't always increase as the flow uniformity index decreases. The analyses on the distribution of temperature and concentration in the monolith show that the catalytic reaction zone concentrates in central area near the front face. The predicted curves of the velocity distribution have a good agreement with the experimental data.展开更多
In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about th...In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about the partial working processes of the diesel engine, the amount of heat energy, enough to make the fuel self ignite at the end of compression process at different temperatures of coolant and intake air, was calculated. Several HY20 preheating plugs were used to heat up the intake air. Meanwhile, an electronic control system based on 8 bit micro controller unit (MCS 8031) was designed to automatically control the process of heating intake air. According to the various temperatures of coolant and ambient air, one plug or two plugs can automatically be selected to heat intake air. The demo experiment validated that the total system could operate successfully and achieve the scheduled function.展开更多
Gasoline compression ignition (GCI) is one of the most promising combustion concepts to maintain low pollutant emissions and high efficiency. However, low load combustion stability and firing in cold-start operations ...Gasoline compression ignition (GCI) is one of the most promising combustion concepts to maintain low pollutant emissions and high efficiency. However, low load combustion stability and firing in cold-start operations are two major challenges for GCI combustion. Strategies including negative valve overlap (NVO), advanced injection strategies, fuel reforming, and intake preheating have been proposed in order to solve these difficulties;however, the cold start is still an obstacle. The objective of this work is to study effective methods to achieve GCI engine cold start-up. This work combines NVO, in-cylinder fuel reforming, and intake preheating to achieve quick firing under cold-start conditions and the subsequent warmup conditions. The results show that start of injection (SOI) during the intake stroke yields the best fuel economy, and injection during the compression stroke has the potential to extend the low load limit. Furthermore, SOI during the NVO period grants the ability to operate under engine conditions with cold intake air and coolant. With highly reactive products made by in-cylinder fuel reforming and fast heat accumulation in the combustion chamber, the NVO injection strategy is highly appropriate for GCI firing. An additional assisted technical method, such as intake preheating, is required to ignite the first firing cycle for a cold-start process. With the combination of NVO, in-cylinder fuel reforming, and intake preheating, the GCI engine successfully started within five combustion cycles in the experiment. After the firing process, the engine could stably operate without further intake preheating;thus, this method is appropriate for engine cold-start and warm-up.展开更多
【目的】抽水蓄能机组具有灰启动潜力,将其与综合能源系统(integrated energy system,IES)的多能互补优势相结合,可适用于系统在极端事件下恢复运行。为研究灾后IES的恢复机制,提出一种抽水蓄能灰启动下冷热电互补综合能源系统(cold-hea...【目的】抽水蓄能机组具有灰启动潜力,将其与综合能源系统(integrated energy system,IES)的多能互补优势相结合,可适用于系统在极端事件下恢复运行。为研究灾后IES的恢复机制,提出一种抽水蓄能灰启动下冷热电互补综合能源系统(cold-heat-electricity IES,CHEIES)优化调度模型。【方法】首先,通过随机场景优化处理风光冷热功率不确定性问题,采用拉丁超立方抽样生成大量随机风光冷热场景,并使用概率距离快速削减法对场景数量进行削减。然后,针对灰启动下的CHEIES,以抽水蓄能作为灰启动电源为热电联产机组提供启动电源,并以灰启动效益为核心考量因素,综合构建单目标优化调度模型,引入冷热电功率平衡约束,确保IES在各种负荷情况下的稳定运行。最后,对模型进行仿真求解,并分析了各种运行方案下的优化调度策略和经济效益。【结果】配置抽水蓄能灰启动的CHEIES在应对极端自然灾害情境下展现出较高的灵活性和运行效率,与未配置抽水蓄能灰启动的方案相比,系统运行成本降低了12.14%。【结论】所提方法可充分挖掘紧急状态下CHEIES的可靠性、经济性与灵活性,为极端事件灾后IES的快速恢复提供了策略支持。展开更多
The exponential growth of over-the-top(OTT)entertainment has fueled a surge in content consumption across diverse formats,especially in regional Indian languages.With the Indian film industry producing over 1500 films...The exponential growth of over-the-top(OTT)entertainment has fueled a surge in content consumption across diverse formats,especially in regional Indian languages.With the Indian film industry producing over 1500 films annually in more than 20 languages,personalized recommendations are essential to highlight relevant content.To overcome the limitations of traditional recommender systems-such as static latent vectors,poor handling of cold-start scenarios,and the absence of uncertainty modeling-we propose a deep Collaborative Neural Generative Embedding(C-NGE)model.C-NGE dynamically learns user and item representations by integrating rating information and metadata features in a unified neural framework.It uses metadata as sampled noise and applies the reparameterization trick to capture latent patterns better and support predictions for new users or items without retraining.We evaluate CNGE on the Indian Regional Movies(IRM)dataset,along with MovieLens 100 K and 1 M.Results show that our model consistently outperforms several existing methods,and its extensibility allows for incorporating additional signals like user reviews and multimodal data to enhance recommendation quality.展开更多
Proton exchange membrane fuel cells(PEMFCs)have emerged as important zero-emission power sources due to their efficiency and eco-friendly characteristics.A critical feature required for their widespread adoption is th...Proton exchange membrane fuel cells(PEMFCs)have emerged as important zero-emission power sources due to their efficiency and eco-friendly characteristics.A critical feature required for their widespread adoption is the performance of low-temperature cold start.However,at subzero degrees Celsius,the freezing of the produced water can hinder or even lead to failure of the fuel cell start-up process.To successfully achieve a cold start under such conditions,the PEMFC must rapidly and reliably transition from a fully cooled state to a stable operating condition.Various improvements have been focused on the system engineering aspect to address this challenge,yet many of these methods come with their drawbacks.This paper reviews the recent progress of the PEMFC cold start from the perspective of key materials engineering.It provides a detailed summary of how the proton exchange membrane(PEM),catalyst layer,microporous layer(MPL),and gas diffusion layer(GDL)affect the cold-start performance.Further analysis reveals that the fundamental mechanisms of improving coldstart performance can be summarized into three aspects:increasing the ratio of water bound in the ionomer,hindering the transformation process from supercooled water to ice,improving the removal of supercooled water,or ensuring it is transported to the outside of the membrane electrode assembly(MEA)before it gets frozen.By precisely regulating these key components,it is possible to develop a simple and energy-efi cient solution for improving the cold start performance of the PEMFC.展开更多
基金This work was supported by CETC Joint Research Program under Grant 6141B08020101,6141B08080101National Key R&D Program of China under Grant 2018ZX09201014the National Natural Science Foundation of China under Grant 61002011.
文摘As a major function of smart transportation in smart cities,vehicle model recognition plays an important role in intelligent transportation.Due to the difference among different vehicle models recognition datasets,the accuracy of network model training in one scene will be greatly reduced in another one.However,if you don’t have a lot of vehicle model datasets for the current scene,you cannot properly train a model.To address this problem,we study the problem of cold start of vehicle model recognition under cross-scenario.Under the condition of small amount of datasets,combined with the method of transfer learning,load the DAN(Deep Adaptation Networks)and JAN(Joint Adaptation Networks)domain adaptation modules into the convolutional neural network AlexNet and ResNet,and get four models:AlexNet-JAN,AlexNet-DAN,ResNet-JAN,and ResNet-DAN which can achieve a higher accuracy at the beginning.Through experiments,transfer the vehicle model recognition from the network image dataset(source domain)to the surveillance-nature dataset(target domain),both Top-1 and Top-5 accuracy have been improved by at least 20%.
文摘Recommender system (RS) has become a very important factor in many eCommerce sites. In our daily life, we rely on the recommendation from other persons either by word of mouth, recommendation letters, movie, item and book reviews printed in newspapers, etc. The typical Recommender Systems are software tools and techniques that provide support to people by identifying interesting products and services in online store. It also provides a recommendation for certain users who search for the recommendations. The most important open challenge in Collaborative filtering recommender system is the cold start problem. If the adequate or sufficient information is not available for a new item or users, the recommender system runs into the cold start problem. To increase the usefulness of collaborative recommender systems, it could be desirable to eliminate the challenge such as cold start problem. Revealing the community structures is crucial to understand and more important with the increasing popularity of online social networks. The community detection is a key issue in social network analysis in which nodes of the communities are tightly connected each other and loosely connected between other communities. Many algorithms like Givan-Newman algorithm, modularity maximization, leading eigenvector, walk trap, etc., are used to detect the communities in the networks. To test the community division is meaningful we define a quality function called modularity. Modularity is that the links within a community are higher than the expected links in those communities. In this paper, we try to give a solution to the cold-start problem based on community detection algorithm that extracts the community from the social networks and identifies the similar users on that network. Hence, within the proposed work several intrinsic details are taken as a rule of thumb to boost the results higher. Moreover, the simulation experiment was taken to solve the cold start problem.
基金funded by Zhejiang Province Spearhead and Leading Goose Research and Development Key Program,grant number 2023C01239.
文摘In the realm of all-electric aircraft research,the integration of cathode-open proton exchange membrane fuel cells(PEMFC)with lithiumbatteries as a hybrid power source for small to medium-sized unmanned aerial vehicles(UAVs)has garnered significant attention.The PEMFC,serving as the primary energy supply,markedly extends the UAV’s operational endurance.However,due to payload limitations and spatial constraints in the airframe layout of UAVs,the stack requires customized adaptation.Moreover,the implementation of auxiliary systems to facilitate cold starts of the PEMFC under low-temperature conditions is not feasible.Relying solely on thermal insulation measures also proves inadequate to address the challenges posed by complex low-temperature startup scenarios.To overcomethis,our study leverages the UAV’s lithium battery to heat the cathode inlet airflow,aiding the cathode-open PEMFC cold start process.To validate the feasibility of the proposed air-assisted heating strategy during the conceptual design phase,this study develops a transient,non-isothermal 3Dcathode-open PEMF Cunitmodel incorporating cathode air-assisted heating and gas-ice phase change.The model’s accuracy was verified against experimental cold-start data from a stack composed of identical single cells.This computational framework enables quantitative analysis of temperature fields and ice fraction distributions across domains under varying air-assisted heating powers during cold starts.Building upon this model,the study further investigates the improvement in cold start performance by heating the cathode intake air with varying power levels.The results demonstrate that the fuel cell achieves self-startup at temperatures as low as−13℃ under a constant current density of 100mA/cm^(2) without air-assisted heating.At an ambient temperature of−20℃,a successful start-up can be achieved with a heating power of 0.45 W/cm^(2).The temperature variation overtime during the cold start process can be represented by a sum of two exponential functions.The air-assisted heating scheme proposed in this study has significantly improved the cold start performance of fuel cells in low-temperature environments.Additionally,it provides critical reference data and validation support for component selection and feasibility assessment of hybrid power systems.
文摘Water transport is of paramount importance to the cold start of proton exchange membrane fuel cells(PEMFCs).Analysis of water transport in cathode catalyst layer(CCL)during cold start reveals the distinct characteristics from the normal temperature operation.This work studies the effect of CCL mesoscopic pore-morphology on PEMFC cold start.The CCL mesoscale morphology is characterized by two tortuosity factors of the ionomer network and pore structure,respectively.The simulation results demonstrate that the mesoscale morphology of CCL has a significant influence on the performance of PEMFC cold start.It was found that cold-starting of a cell with a CCL of less tortuous mesoscale morphology can succeed,whereas starting up a cell with a CCL of more tortuous mesoscale morphology may fail.The CCL of less tortuous pore structure reduces the water back diffusion resistance from the CCL to proton exchange membrane(PEM),thus enhancing the water storage in PEM,while reducing the tortuosity in ionomer network of CCL is found to enhance the water transport in and the water removal from CCL.For the sake of better cold start performance,novel preparation methods,which can create catalyst layers of larger size primary pores and less tortuous pore structure and ionomer network,are desirable.
基金This research work is jointly sponsored by the National Natural Science Foundation of China(No.51776061)Young Elite Scientists Sponsorship Program of the China Association for Science and Technology(No.2017QNRC001)Fundamental Research Funds for the Central Universities.
文摘To enhance the fuel economy of a vehicle powered by a gasoline engine under road conditions,an energy flow test of a vehicle was performed experimentally under the New European Driving Cycle of cold start.The energy distributions and related influencing factors were analyzed using the test data.Results show that the effective power and thermal efficiency are mainly affected by the engine load except in the early stage of the New European Driving Cycle.Because of the retarded CA50 and longer CA10-90,the effective thermal efficiency is lower in the early phase of driving conditions.Initially,the heat transfer loss mainly comprises the loss of the heating,ventilation,and air conditioning system.The radiator then plays the major role,with its percentage affected by the engine load and decreasing under the extra-urban driving cycle.The exhaust gas loss is decided by the temperature and flow rate of the exhaust gas,while its percentage is mainly affected by the temperature of the exhaust gas.In the early phase of driving conditions,the retarded spark advance angle leads to a higher temperature of the exhaust gas and a greater exhaust gas loss.The pumping loss and its percentage are mainly determined by the engine speed under the urban driving cycle,and both decrease under the extra-urban driving cycle except at maximum vehicle speed.
基金supported by the National Natural Science Foundation of China(Grant No.51375300)the Research Project of State Key Laboratory of Mechanical System and Vibration(Grant No.MSVZD201401)
文摘To reduce the fuel consumption of internal combustion engines, more attention has been paid to the tribological performance of the piston ring pack during the cold start and idle operations. In this research, a numerical model considering the cylinder liner deformation and the piston ring conformability is developed to predict the blow-by, lubrication, friction and wear of the piston ring pack under different operating conditions. The gas flow rate, inter-ring gas pressures, minimum oil film thickness, frictional force and wear load during cold start are calculated and compared with those during warm idle operating conditions. The results show that cylinder liner deformation and piston ring conformability together obviously affect blow-by and other tribological performance. Meanwhile, it is found that friction loss is larger during cold start than during warm idle operating conditions. However, the wear process is more severe during warm idle operation than during cold start. From this research, the blow-by and tribological performance of the piston ring pack during cold start and warm idle operations are understood more deeply.
基金PhD Discipline Foundation of Educational Department of China (No. 20010248003).
文摘This paper integrated a two-dimensional axisymmetrical transient model applicable to cold-start emission applications. The model can be used to simulate and explain effects of the flow and temperature distribution on performance of a converter. The evolutions of distribution of the temperature and concentration in the monolith during the cold-start period and the effects of flow distribution in the monolith on the cold-start performance are simulated in terms of the integrated model. The investigation indicates that the axial and radial gradients of temperature of the solid become steeper as the inlet gas temperature ramp increases; this furthermore results in the movement of reaction region in the monolith, and the flow distribution in the monolith affects the radial distribution of temperature of the solid;the radial gradients of temperature of the solid become greater as the flow uniformity index decreases, whereas the light-off time doesn't always increase as the flow uniformity index decreases. The analyses on the distribution of temperature and concentration in the monolith show that the catalytic reaction zone concentrates in central area near the front face. The predicted curves of the velocity distribution have a good agreement with the experimental data.
文摘In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about the partial working processes of the diesel engine, the amount of heat energy, enough to make the fuel self ignite at the end of compression process at different temperatures of coolant and intake air, was calculated. Several HY20 preheating plugs were used to heat up the intake air. Meanwhile, an electronic control system based on 8 bit micro controller unit (MCS 8031) was designed to automatically control the process of heating intake air. According to the various temperatures of coolant and ambient air, one plug or two plugs can automatically be selected to heat intake air. The demo experiment validated that the total system could operate successfully and achieve the scheduled function.
基金the National Natural Science Foundation of China (91641203, 51476114, and 91741119)he National Key Research and Development Program of China (2017YFB0103400).
文摘Gasoline compression ignition (GCI) is one of the most promising combustion concepts to maintain low pollutant emissions and high efficiency. However, low load combustion stability and firing in cold-start operations are two major challenges for GCI combustion. Strategies including negative valve overlap (NVO), advanced injection strategies, fuel reforming, and intake preheating have been proposed in order to solve these difficulties;however, the cold start is still an obstacle. The objective of this work is to study effective methods to achieve GCI engine cold start-up. This work combines NVO, in-cylinder fuel reforming, and intake preheating to achieve quick firing under cold-start conditions and the subsequent warmup conditions. The results show that start of injection (SOI) during the intake stroke yields the best fuel economy, and injection during the compression stroke has the potential to extend the low load limit. Furthermore, SOI during the NVO period grants the ability to operate under engine conditions with cold intake air and coolant. With highly reactive products made by in-cylinder fuel reforming and fast heat accumulation in the combustion chamber, the NVO injection strategy is highly appropriate for GCI firing. An additional assisted technical method, such as intake preheating, is required to ignite the first firing cycle for a cold-start process. With the combination of NVO, in-cylinder fuel reforming, and intake preheating, the GCI engine successfully started within five combustion cycles in the experiment. After the firing process, the engine could stably operate without further intake preheating;thus, this method is appropriate for engine cold-start and warm-up.
文摘【目的】抽水蓄能机组具有灰启动潜力,将其与综合能源系统(integrated energy system,IES)的多能互补优势相结合,可适用于系统在极端事件下恢复运行。为研究灾后IES的恢复机制,提出一种抽水蓄能灰启动下冷热电互补综合能源系统(cold-heat-electricity IES,CHEIES)优化调度模型。【方法】首先,通过随机场景优化处理风光冷热功率不确定性问题,采用拉丁超立方抽样生成大量随机风光冷热场景,并使用概率距离快速削减法对场景数量进行削减。然后,针对灰启动下的CHEIES,以抽水蓄能作为灰启动电源为热电联产机组提供启动电源,并以灰启动效益为核心考量因素,综合构建单目标优化调度模型,引入冷热电功率平衡约束,确保IES在各种负荷情况下的稳定运行。最后,对模型进行仿真求解,并分析了各种运行方案下的优化调度策略和经济效益。【结果】配置抽水蓄能灰启动的CHEIES在应对极端自然灾害情境下展现出较高的灵活性和运行效率,与未配置抽水蓄能灰启动的方案相比,系统运行成本降低了12.14%。【结论】所提方法可充分挖掘紧急状态下CHEIES的可靠性、经济性与灵活性,为极端事件灾后IES的快速恢复提供了策略支持。
文摘The exponential growth of over-the-top(OTT)entertainment has fueled a surge in content consumption across diverse formats,especially in regional Indian languages.With the Indian film industry producing over 1500 films annually in more than 20 languages,personalized recommendations are essential to highlight relevant content.To overcome the limitations of traditional recommender systems-such as static latent vectors,poor handling of cold-start scenarios,and the absence of uncertainty modeling-we propose a deep Collaborative Neural Generative Embedding(C-NGE)model.C-NGE dynamically learns user and item representations by integrating rating information and metadata features in a unified neural framework.It uses metadata as sampled noise and applies the reparameterization trick to capture latent patterns better and support predictions for new users or items without retraining.We evaluate CNGE on the Indian Regional Movies(IRM)dataset,along with MovieLens 100 K and 1 M.Results show that our model consistently outperforms several existing methods,and its extensibility allows for incorporating additional signals like user reviews and multimodal data to enhance recommendation quality.
基金the National Key R&D Program of China(2024YFA1509500)the National Natural Science Foundation of China(Grant No.22479010)+2 种基金the China National Petroleum Corporation(CNPC)Innovation Fund(2024DQ02-0212)the Fundamental Research Funds for the Central Universities,Peking University(Grant No.7100604768)the support of the Experimental Center of Advanced Materials at the Beijing Institute of Technology.
文摘Proton exchange membrane fuel cells(PEMFCs)have emerged as important zero-emission power sources due to their efficiency and eco-friendly characteristics.A critical feature required for their widespread adoption is the performance of low-temperature cold start.However,at subzero degrees Celsius,the freezing of the produced water can hinder or even lead to failure of the fuel cell start-up process.To successfully achieve a cold start under such conditions,the PEMFC must rapidly and reliably transition from a fully cooled state to a stable operating condition.Various improvements have been focused on the system engineering aspect to address this challenge,yet many of these methods come with their drawbacks.This paper reviews the recent progress of the PEMFC cold start from the perspective of key materials engineering.It provides a detailed summary of how the proton exchange membrane(PEM),catalyst layer,microporous layer(MPL),and gas diffusion layer(GDL)affect the cold-start performance.Further analysis reveals that the fundamental mechanisms of improving coldstart performance can be summarized into three aspects:increasing the ratio of water bound in the ionomer,hindering the transformation process from supercooled water to ice,improving the removal of supercooled water,or ensuring it is transported to the outside of the membrane electrode assembly(MEA)before it gets frozen.By precisely regulating these key components,it is possible to develop a simple and energy-efi cient solution for improving the cold start performance of the PEMFC.
