Micron-sized silicon anodes offer significant industrial advantages over nanoscale counterparts due to their cost-effectiveness and scalability.However,their practical applications are significantly hindered by severe...Micron-sized silicon anodes offer significant industrial advantages over nanoscale counterparts due to their cost-effectiveness and scalability.However,their practical applications are significantly hindered by severe stress-induced fragmentation,leading to rapid capacity decay.Addressing this challenge,we introduce a novel dual-conformal encapsulated micron-sized porous Si(μm-pSi)anode by utilizingμm-Si recycled from the photovoltaic industry as the Si precursor.This encapsulation design of the internal conformal SiO_(x)/C layer and external Ti_(3)C_(2)Tx MXene layer forms intergranular and intragranular protective skins onμm-pSi,ensuring simultaneous mechanical and electrochemical stability for efficient Li+storage.As a result,the fabricated WpSi@SiO_(x)/C@MXene anode demonstrates an exceptional cycling performance,delivering 535.1 mA h g^(−1)after 1500 cycles at 5 A g^(−1)with a minimal capacity decay of 0.003%per cycle.Chemo-mechanical modeling and SEI analysis reveal that the dual-conformal coating achieves exceptional mechanical and electrochemical stability through robust mechanical confinement and ultra-fast Li+diffusion kinetics during lithiation,coupled with a Li_(2)CO_(3)/LiF-rich hybrid SEI that facilitates Li+transport,collectively enabling rate-insensitive stress evolution,long-term structural durability,and stable cycling under high-rate conditions.This work provides a compelling design strategy for leveraging sustainableμm-Si to achieve high-rate and long-life lithium-ion batteries.展开更多
Engine tests are both costly and time consuming in developing a new internal combustion engine.Therefore,it is of great importance to predict engine characteristics with high accuracy using artificial intelligence.Thu...Engine tests are both costly and time consuming in developing a new internal combustion engine.Therefore,it is of great importance to predict engine characteristics with high accuracy using artificial intelligence.Thus,it is possible to reduce engine testing costs and speed up the engine development process.Deep Learning is an effective artificial intelligence method that shows high performance in many research areas through its ability to learn high-level hidden features in data samples.The present paper describes a method to predict the cylinder pressure of a Homogeneous Charge Compression Ignition(HCCI)engine for various excess air coefficients by using Deep Neural Network,which is one of the Deep Learning methods and is based on the Artificial Neural Network(ANN).The Deep Learning results were compared with the ANN and experimental results.The results show that the difference between experimental and the Deep Neural Network(DNN)results were less than 1%.The best results were obtained by Deep Learning method.The cylinder pressure was predicted with a maximum accuracy of 97.83%of the experimental value by using ANN.On the other hand,the accuracy value was increased up to 99.84%using DNN.These results show that the DNN method can be used effectively to predict cylinder pressures of internal combustion engines.展开更多
A reduced chemical kinetic model （44 species and 72 reactions） for the homogeneous charge compression ignition （HCCI） combustion of n-heptane was optimized to improve its autoignition predictions under different e...A reduced chemical kinetic model （44 species and 72 reactions） for the homogeneous charge compression ignition （HCCI） combustion of n-heptane was optimized to improve its autoignition predictions under different engine operating conditions. The seven kinetic parameters of the optimized model were determined by using the combination of a micro-genetic algorithm optimization methodology and the SENKIN program of CHEMKIN chemical kinetics software package. The optimization was performed within the range of equivalence ratios 0.2-1.2, initial temperature 310- 375 K and initial pressure 0, 1-0.3 MPa, The engine simulations show that the optimized model agrees better with the detailed chemical kinetic model （544 species and 2 446 reactions） than the original model does.展开更多
Replacing the conventional carbonate electrolyte by solid-state electrolyte (SSE) will offer improved safety for lithium-ion batteries.To further improve the energy density,Silicon (Si) is attractive for next generati...Replacing the conventional carbonate electrolyte by solid-state electrolyte (SSE) will offer improved safety for lithium-ion batteries.To further improve the energy density,Silicon (Si) is attractive for next generation solid-state battery (SSB) because of its high specific capacity and low cost.High energy density and safe Si-based SSB,however,is plagued by large volume change that leads to poor mechanical stability and slow lithium ions transportation at the multiple interfaces between Si and SSE.Herein,we designed a self-integrated and monolithic Si/two dimensional layered T_(3)C_(2)T_(x)(MXene,T_(x) stands for terminal functional groups) electrode architecture with interfacial nitrogen engineering.During a heat treatment process,the polyacrylonitrile not only converts into amorphous carbon (a-C) that shells Si but also forms robust interfacial nitrogen chemical bonds that anchors Si and MXene.During repeated lithiation and delithiation processes,the robust interfacial engineered Si/MXene configuration enhances the mechanical adhesion between Si and MXene that improves the structure stability but also contributes to form stable solid-electrolyte interphase (SEI).In addition,the N-MXene provides fast lithium ions transportation pathways.Consequently,the Si/MXene with interfacial nitrogen engineering (denoted as Si-N-MXene) deliveres high-rate performance with a specific capacity of 1498 m Ah g^(-1) at a high current of 6.4 A g^(-1).A Si-N-MXene/NMC full cell exhibited a capacity retention of 80.5%after 200 cycles.The Si-N-MXene electrode is also applied to SSB and shows a relative stable cycling over 100 cycles,demonstrating the versatility of this concept.展开更多
A numerical model is presented to investigate the performance of homogeneous charge compression ignition(HCCI) engines fueled with ethanol. Two approaches are studied. On one hand, two-step reaction mechanisms with Ar...A numerical model is presented to investigate the performance of homogeneous charge compression ignition(HCCI) engines fueled with ethanol. Two approaches are studied. On one hand, two-step reaction mechanisms with Arrhenius reaction rates are implemented in combustion chemistry modeling. On the other hand, a reduced mechanism containing important reactions of ethanol involving heat release rate and reaction rates compatible with experimental data is employed. Since controls of combustion phenomenon and ignition timing are the main issues of these engines, the effects of inlet temperature and equivalence ratio as the controlling factors on the operating parameters such as ignition timing, burn duration, in-cylinder temperature and pressure of HCCI engines are explored. The results show that the maximum predicted pressures for thermodynamic model are about 71.3×10~5 Pa and 79.79×10~5 Pa, and for chemical kinetic model, they are about 71.48×10~5 Pa and 78.123×10~5 Pa, fairly comparable with corresponding experimental values of 72×10~5 Pa and 78.7×10~5 Pa. It is observed that increasing the initial temperature advances the ignition timing, decreases the burn duration and increases the peak temperature and pressure. Moreover, the maximum temperature and pressure are associated with richer mixtures.展开更多
For homogeneous charge compression ignition （HCCI） combustion, the auto-ignition process is very sensitive to in-cylinder conditions, including in-cylinder temperature, in-cylinder components and concentrations. The...For homogeneous charge compression ignition （HCCI） combustion, the auto-ignition process is very sensitive to in-cylinder conditions, including in-cylinder temperature, in-cylinder components and concentrations. Therefore, accurate control is required for reliable and efficient HCCI combustion. This paper outlines a simplified gasoline-fueled HCCI engine model implemented in Simulink environment. The model is able to run in real-time and with fixed simulation steps with the aim of cycle-to-cycle control and hardware- in-the-loop simulation. With the aim of controlling the desired amount of the trapped exhaust gas recirculation （EGR） from the previous cycle, the phase of the intake and exhaust valves and the respective profiles are designed to vary in this model. The model is able to anticipate the auto-ignition timing and the in-cylinder pressure and temperature. The validation has been conducted using a comparison of the experimental results on Ricardo Hydro engine published in a research by Tianjin University and a JAGUAR V6 HCCI test engine at the University of Birmingham. The comparison shows the typical HCCI combustion and a fair agreement between the simulation and experimental results.展开更多
Homogeneous charge compression ignition(HCCI) mode of combustion is popularly known for achieving simultaneous reduction of NOx as well as soot emissions as it combines the compression ignition(CI) and spark ignition(...Homogeneous charge compression ignition(HCCI) mode of combustion is popularly known for achieving simultaneous reduction of NOx as well as soot emissions as it combines the compression ignition(CI) and spark ignition(SI) engine features. In this work, a CI engine was simulated to work in HCCI mode and was analyzed to study the effect of induction induced swirl under varying speeds using three-zone extended coherent flame combustion model(ECFM-3Z, compression ignition) of STAR-CD. The analysis was done considering speed ranging from 800 to 1600 r/min and swirl ratios from 1 to 4. The present study reveals that ECFM-3Z model has well predicted the performance and emissions of CI engine in HCCI mode. The simulation predicts reduced in-cylinder pressures, temperatures, wall heat transfer losses, and piston work with increase in swirl ratio irrespective of engine speed. Also, simultaneous reduction in CO2 and NOx emissions is realized with higher engine speeds and swirl ratios. Low speeds and swirl ratios are favorable for low CO2 emissions. It is observed that increase in engine speed causes a marginal reduction in in-cylinder pressures and temperatures. Also, higher turbulent energy and velocity magnitude levels are obtained with increase in swirl ratio, indicating efficient combustion necessitating no modifications in combustion chamber design. The investigations reveal a total decrease of 38.68% in CO2 emissions and 12.93% in NOx emissions when the engine speed increases from 800 to 1600 r/min at swirl ratio of 4. Also an increase of 14.16% in net work done is obtained with engine speed increasing from 800 to 1600 r/min at swirl ratio of 1. The simulation indicates that there is a tradeoff observed between the emissions and piston work. It is finally concluded that the HCCI combustion can be regarded as low temperature combustion as there is significant decrease in in-cylinder temperatures and pressures at higher speeds and higher swirl ratios.展开更多
A three dimensional model which considers the effects of turbulence and detailed chemi cal kinetics is built to simulate the combustion process of engine fueled by compressed nature gas （CNG）. The model is accompli...A three dimensional model which considers the effects of turbulence and detailed chemi cal kinetics is built to simulate the combustion process of engine fueled by compressed nature gas （CNG）. The model is accomplished by integrating CFD software KIVA3V and chemical kinetic soft- ware CHEMKINII. Meanwhile, a turbulence combustion model which is suitable for describing the reaction rate under the coupled simulation is developed to balance the effects of turbulence and de tailed chemical kinetics. To reduce the computation time, subsequent development of the simulation code is realized, which enables the simulation code to have the function of parallel computing and run on parallel computing facility based on message passing interface （MPI）. The coupled software is used to simulate the combustion process of spark ignition CNG engine. The results show that sim ulation data have a good consistency with experimental results and parallel computing has good effi ciency and accelerate ratio.展开更多
Fast depletion of fossil fuels with its resources already passed its mid depletion region and the pollution levels already reached unsafe levels which make it utmost necessity to search for alternative fuels to meet s...Fast depletion of fossil fuels with its resources already passed its mid depletion region and the pollution levels already reached unsafe levels which make it utmost necessity to search for alternative fuels to meet sustainable energy demand with minimum environmental impact. Among alternative fuels, hydrogen is considered as the near future, long term renewable, sustainable and non-polluting fuel. In the present paper, hydrogen fueled internal combustion engine fundamentals highlighted and presented relating to hydrogen combustion properties. A Mat lab programmed hydrogen temperature-entropy-energy chart is developed and presented for fresh charge and products of combustion at different excess air factors per mole combustion gases. The chart, then, used to represent a SI hydrogen-fueled fuel/air cycle analysis, which proved to be valuable design tool for engine sizing and for prediction of engine performance. Predictions carried out using the hydrogen F/A cycle analysis at different λ show low brake specific fuel consumption and low volume specific power compared with conventional SI engine.展开更多
As the practicability of a hydrogen-fueled economy emerges, intermediate technologies would be necessary for the transition between hydrocarbon fueled internal combustion engines and hydrogen powered fuel cells. In th...As the practicability of a hydrogen-fueled economy emerges, intermediate technologies would be necessary for the transition between hydrocarbon fueled internal combustion engines and hydrogen powered fuel cells. In the present study, the hydrogen engine efficiency and the load control are the two main parameters that will be improved by using the combined operation of in-cylinder direct fuel injection (DI) and port fuel injection (PFI) strategies to obtain maximum engine power outputs with acceptable efficiency equivalent to gasoline engines. Wide open throttle (WOT) operation has been used to take advantage of the associated increase in engine efficiency, in which the loads have been regulated with mixture richness (qualitative control) instead of volumetric efficiency (quantitative control). The capabilities of a 3D-CFD code have been developed and employed to simulate the whole engine physicochemical process which includes the hydrogen injection through the intake manifold (PFI) and/or the hydrogen DI in the engine compression stroke. Conditions with simulated PFI, PFI + DI and DI have been analyzed to study the effects of mixture preparation behaviors on the hydrogen ignition and its flame propagation inside the engine combustion chamber. Numerically, the CFD code has been intensively validated against experimental engine data which provided remarkable agreement in terms of in-cylinder pressure history evaluation.展开更多
The intake air control system of a gasoline engine is a typical nonlinear system, and included among the adverse fac-tors that always induce poor idle-speed control stability are dead time and disturbances in the inta...The intake air control system of a gasoline engine is a typical nonlinear system, and included among the adverse fac-tors that always induce poor idle-speed control stability are dead time and disturbances in the intake air control process. In this paper, to improve the responsiveness when idling with regard to disturbances, a mean-value engine model (MVEM) with dead time was constructed as the control object, and the two servo structures of sliding mode control (SMC) were studied for better idle control performance, especially in transient process of speed change. The simulation results confirmed that under the constraint condition of control input, the robustness of idle speed control that is being subjected to torque disturbances and noise disturbances can be greatly improved by use of the servo structure II.展开更多
NOx and soot emissions from diesel engines can be greatly reduced by pressure wave supercharging(PWS).The diesel engine matched with PWS needs redesigning its exhaust pipes.Except for meeting the installation requirem...NOx and soot emissions from diesel engines can be greatly reduced by pressure wave supercharging(PWS).The diesel engine matched with PWS needs redesigning its exhaust pipes.Except for meeting the installation requirements,the exhaust gas must be stable in pressure before rushing into PWS.In this paper the lateral and center ported divergent exhaust pipes are designed,modeled geometrically and analyzed structurally based on a 3-D design software-CATIA to determine the structure of two exhaust pipes having the required inner volume.Then flow analysis for two exhaust pipes is done using a flow analysis software-ANASYS.Moreover,the optimal exhaust pipes are determined comprehensively and cast for engine test.Engine test results show that PWS is superior to turbocharging at low engine speeds and inferior to turbocharging in power and emissions at medium-to-high engine speeds.The performance of PWS engine under high speed operating conditions can be improved by contriving larger surge volume intake and exhaust pipes.展开更多
The fuel dynamic transfer process,including fuel injection,fuel film deposition and evaporation in the intake port,was analyzed for spark ignition(SI) engines with port fuel injection(PFI).The influence of wall-wettin...The fuel dynamic transfer process,including fuel injection,fuel film deposition and evaporation in the intake port,was analyzed for spark ignition(SI) engines with port fuel injection(PFI).The influence of wall-wetting fuel film,especially its evaporation rate,upon the air-fuel ratio of in-cylinder mixtures was also discussed.According to the similarity principle,Fick's law,the ideal gas equation and the Gilliland correlation,an evaporate prediction model of wall-wetting fuel film was set up and an evaporate prediction based dynamic fuel film compensator was designed.Through engine cold start tests,the wall-wetting temperature,which is the key input of the fuel film evaporate prediction model,was also modeled and predicted.Combined with the experimental data of the evaporation characteristics of ethanol-gasoline blends and engine calibration tests,all the parameters of the wall-wetting fuel film evaporate prediction model used in the fuel film compensator were identified.Square-wave disturbance tests of fuel injection showed that with the help of the fuel film compensator the response of the in-cylinder air-fuel ratio was significantly improved and the real air-fuel ratio always closely matched the expected ratio.The fuel film compensator was then integrated into the final air-fuel ratio controller,and the engine tests showed that the air-fuel ratio control error was less than 2% in steady-state conditions,and less than 4% in transient conditions.The fuel film compensator also showed good adaptability to different ethanol-gasoline blends.展开更多
Design for life-time performance and proper maintenance measures are usually needed to prolong the mean-time-between-failures of complex equipments such as internal combustion engines.To reach this,it is important to ...Design for life-time performance and proper maintenance measures are usually needed to prolong the mean-time-between-failures of complex equipments such as internal combustion engines.To reach this,it is important to obtain the information of time-varying system performance in design stage and to identify the structural change at each moment.So a multidisciplinary model based method is studied in this paper to unify the time-varying performance(TVP) prediction and system identification(SI) of equipments.The related multidisciplinary model in this paper should be not only precise to give simulation results but also sensitive to the variation of system parameters.So the varying history of system performance along with the structural change can be obtained from the model.Then the value of system parameters can be identified by seeking roots with given detected responding data and relationship between system responding data and system parameters.A case study on a low power gasoline engine shows that the method presented in this paper can provide useful information for the development and maintenance of complex equipments.展开更多
基金the financial support from the Natural Science Foundation of Shanghai(23ZR1423800)Open Research Fund of Shanghai Key Laboratory of Green Chemistry and Chemical Processes(East China Normal University,202503)+1 种基金State Key Laboratory of Advanced Fiber Materials(Donghua University,KF2406)Key Laboratory of Advanced Energy Materials Chemistry(Ministry of Education),Nankai University。
文摘Micron-sized silicon anodes offer significant industrial advantages over nanoscale counterparts due to their cost-effectiveness and scalability.However,their practical applications are significantly hindered by severe stress-induced fragmentation,leading to rapid capacity decay.Addressing this challenge,we introduce a novel dual-conformal encapsulated micron-sized porous Si(μm-pSi)anode by utilizingμm-Si recycled from the photovoltaic industry as the Si precursor.This encapsulation design of the internal conformal SiO_(x)/C layer and external Ti_(3)C_(2)Tx MXene layer forms intergranular and intragranular protective skins onμm-pSi,ensuring simultaneous mechanical and electrochemical stability for efficient Li+storage.As a result,the fabricated WpSi@SiO_(x)/C@MXene anode demonstrates an exceptional cycling performance,delivering 535.1 mA h g^(−1)after 1500 cycles at 5 A g^(−1)with a minimal capacity decay of 0.003%per cycle.Chemo-mechanical modeling and SEI analysis reveal that the dual-conformal coating achieves exceptional mechanical and electrochemical stability through robust mechanical confinement and ultra-fast Li+diffusion kinetics during lithiation,coupled with a Li_(2)CO_(3)/LiF-rich hybrid SEI that facilitates Li+transport,collectively enabling rate-insensitive stress evolution,long-term structural durability,and stable cycling under high-rate conditions.This work provides a compelling design strategy for leveraging sustainableμm-Si to achieve high-rate and long-life lithium-ion batteries.
文摘Engine tests are both costly and time consuming in developing a new internal combustion engine.Therefore,it is of great importance to predict engine characteristics with high accuracy using artificial intelligence.Thus,it is possible to reduce engine testing costs and speed up the engine development process.Deep Learning is an effective artificial intelligence method that shows high performance in many research areas through its ability to learn high-level hidden features in data samples.The present paper describes a method to predict the cylinder pressure of a Homogeneous Charge Compression Ignition(HCCI)engine for various excess air coefficients by using Deep Neural Network,which is one of the Deep Learning methods and is based on the Artificial Neural Network(ANN).The Deep Learning results were compared with the ANN and experimental results.The results show that the difference between experimental and the Deep Neural Network(DNN)results were less than 1%.The best results were obtained by Deep Learning method.The cylinder pressure was predicted with a maximum accuracy of 97.83%of the experimental value by using ANN.On the other hand,the accuracy value was increased up to 99.84%using DNN.These results show that the DNN method can be used effectively to predict cylinder pressures of internal combustion engines.
基金SUPPORTED BY NATIONAL KEY BASIC RESEARCH PLAN ("973" PLAN, NO. 2001CB209202).
文摘A reduced chemical kinetic model （44 species and 72 reactions） for the homogeneous charge compression ignition （HCCI） combustion of n-heptane was optimized to improve its autoignition predictions under different engine operating conditions. The seven kinetic parameters of the optimized model were determined by using the combination of a micro-genetic algorithm optimization methodology and the SENKIN program of CHEMKIN chemical kinetics software package. The optimization was performed within the range of equivalence ratios 0.2-1.2, initial temperature 310- 375 K and initial pressure 0, 1-0.3 MPa, The engine simulations show that the optimized model agrees better with the detailed chemical kinetic model （544 species and 2 446 reactions） than the original model does.
基金supported by the National Natural Science Foundation of China(51902165,12004145,52072323)the Natural Science Foundation of Jiangsu Province(BK20200800)+2 种基金the Natural Science Foundation of Jiangxi Province(20192ACBL20048)the Jiangxi Provincial Natural Science Foundation(20212BAB214032)the Nanjing Science&Technology Innovation Project for Personnel Studying Abroad。
文摘Replacing the conventional carbonate electrolyte by solid-state electrolyte (SSE) will offer improved safety for lithium-ion batteries.To further improve the energy density,Silicon (Si) is attractive for next generation solid-state battery (SSB) because of its high specific capacity and low cost.High energy density and safe Si-based SSB,however,is plagued by large volume change that leads to poor mechanical stability and slow lithium ions transportation at the multiple interfaces between Si and SSE.Herein,we designed a self-integrated and monolithic Si/two dimensional layered T_(3)C_(2)T_(x)(MXene,T_(x) stands for terminal functional groups) electrode architecture with interfacial nitrogen engineering.During a heat treatment process,the polyacrylonitrile not only converts into amorphous carbon (a-C) that shells Si but also forms robust interfacial nitrogen chemical bonds that anchors Si and MXene.During repeated lithiation and delithiation processes,the robust interfacial engineered Si/MXene configuration enhances the mechanical adhesion between Si and MXene that improves the structure stability but also contributes to form stable solid-electrolyte interphase (SEI).In addition,the N-MXene provides fast lithium ions transportation pathways.Consequently,the Si/MXene with interfacial nitrogen engineering (denoted as Si-N-MXene) deliveres high-rate performance with a specific capacity of 1498 m Ah g^(-1) at a high current of 6.4 A g^(-1).A Si-N-MXene/NMC full cell exhibited a capacity retention of 80.5%after 200 cycles.The Si-N-MXene electrode is also applied to SSB and shows a relative stable cycling over 100 cycles,demonstrating the versatility of this concept.
文摘A numerical model is presented to investigate the performance of homogeneous charge compression ignition(HCCI) engines fueled with ethanol. Two approaches are studied. On one hand, two-step reaction mechanisms with Arrhenius reaction rates are implemented in combustion chemistry modeling. On the other hand, a reduced mechanism containing important reactions of ethanol involving heat release rate and reaction rates compatible with experimental data is employed. Since controls of combustion phenomenon and ignition timing are the main issues of these engines, the effects of inlet temperature and equivalence ratio as the controlling factors on the operating parameters such as ignition timing, burn duration, in-cylinder temperature and pressure of HCCI engines are explored. The results show that the maximum predicted pressures for thermodynamic model are about 71.3×10~5 Pa and 79.79×10~5 Pa, and for chemical kinetic model, they are about 71.48×10~5 Pa and 78.123×10~5 Pa, fairly comparable with corresponding experimental values of 72×10~5 Pa and 78.7×10~5 Pa. It is observed that increasing the initial temperature advances the ignition timing, decreases the burn duration and increases the peak temperature and pressure. Moreover, the maximum temperature and pressure are associated with richer mixtures.
文摘For homogeneous charge compression ignition （HCCI） combustion, the auto-ignition process is very sensitive to in-cylinder conditions, including in-cylinder temperature, in-cylinder components and concentrations. Therefore, accurate control is required for reliable and efficient HCCI combustion. This paper outlines a simplified gasoline-fueled HCCI engine model implemented in Simulink environment. The model is able to run in real-time and with fixed simulation steps with the aim of cycle-to-cycle control and hardware- in-the-loop simulation. With the aim of controlling the desired amount of the trapped exhaust gas recirculation （EGR） from the previous cycle, the phase of the intake and exhaust valves and the respective profiles are designed to vary in this model. The model is able to anticipate the auto-ignition timing and the in-cylinder pressure and temperature. The validation has been conducted using a comparison of the experimental results on Ricardo Hydro engine published in a research by Tianjin University and a JAGUAR V6 HCCI test engine at the University of Birmingham. The comparison shows the typical HCCI combustion and a fair agreement between the simulation and experimental results.
文摘Homogeneous charge compression ignition(HCCI) mode of combustion is popularly known for achieving simultaneous reduction of NOx as well as soot emissions as it combines the compression ignition(CI) and spark ignition(SI) engine features. In this work, a CI engine was simulated to work in HCCI mode and was analyzed to study the effect of induction induced swirl under varying speeds using three-zone extended coherent flame combustion model(ECFM-3Z, compression ignition) of STAR-CD. The analysis was done considering speed ranging from 800 to 1600 r/min and swirl ratios from 1 to 4. The present study reveals that ECFM-3Z model has well predicted the performance and emissions of CI engine in HCCI mode. The simulation predicts reduced in-cylinder pressures, temperatures, wall heat transfer losses, and piston work with increase in swirl ratio irrespective of engine speed. Also, simultaneous reduction in CO2 and NOx emissions is realized with higher engine speeds and swirl ratios. Low speeds and swirl ratios are favorable for low CO2 emissions. It is observed that increase in engine speed causes a marginal reduction in in-cylinder pressures and temperatures. Also, higher turbulent energy and velocity magnitude levels are obtained with increase in swirl ratio, indicating efficient combustion necessitating no modifications in combustion chamber design. The investigations reveal a total decrease of 38.68% in CO2 emissions and 12.93% in NOx emissions when the engine speed increases from 800 to 1600 r/min at swirl ratio of 4. Also an increase of 14.16% in net work done is obtained with engine speed increasing from 800 to 1600 r/min at swirl ratio of 1. The simulation indicates that there is a tradeoff observed between the emissions and piston work. It is finally concluded that the HCCI combustion can be regarded as low temperature combustion as there is significant decrease in in-cylinder temperatures and pressures at higher speeds and higher swirl ratios.
基金Supported by the National Natural Science Foundation of China(50976012)
文摘A three dimensional model which considers the effects of turbulence and detailed chemi cal kinetics is built to simulate the combustion process of engine fueled by compressed nature gas （CNG）. The model is accomplished by integrating CFD software KIVA3V and chemical kinetic soft- ware CHEMKINII. Meanwhile, a turbulence combustion model which is suitable for describing the reaction rate under the coupled simulation is developed to balance the effects of turbulence and de tailed chemical kinetics. To reduce the computation time, subsequent development of the simulation code is realized, which enables the simulation code to have the function of parallel computing and run on parallel computing facility based on message passing interface （MPI）. The coupled software is used to simulate the combustion process of spark ignition CNG engine. The results show that sim ulation data have a good consistency with experimental results and parallel computing has good effi ciency and accelerate ratio.
文摘Fast depletion of fossil fuels with its resources already passed its mid depletion region and the pollution levels already reached unsafe levels which make it utmost necessity to search for alternative fuels to meet sustainable energy demand with minimum environmental impact. Among alternative fuels, hydrogen is considered as the near future, long term renewable, sustainable and non-polluting fuel. In the present paper, hydrogen fueled internal combustion engine fundamentals highlighted and presented relating to hydrogen combustion properties. A Mat lab programmed hydrogen temperature-entropy-energy chart is developed and presented for fresh charge and products of combustion at different excess air factors per mole combustion gases. The chart, then, used to represent a SI hydrogen-fueled fuel/air cycle analysis, which proved to be valuable design tool for engine sizing and for prediction of engine performance. Predictions carried out using the hydrogen F/A cycle analysis at different λ show low brake specific fuel consumption and low volume specific power compared with conventional SI engine.
文摘As the practicability of a hydrogen-fueled economy emerges, intermediate technologies would be necessary for the transition between hydrocarbon fueled internal combustion engines and hydrogen powered fuel cells. In the present study, the hydrogen engine efficiency and the load control are the two main parameters that will be improved by using the combined operation of in-cylinder direct fuel injection (DI) and port fuel injection (PFI) strategies to obtain maximum engine power outputs with acceptable efficiency equivalent to gasoline engines. Wide open throttle (WOT) operation has been used to take advantage of the associated increase in engine efficiency, in which the loads have been regulated with mixture richness (qualitative control) instead of volumetric efficiency (quantitative control). The capabilities of a 3D-CFD code have been developed and employed to simulate the whole engine physicochemical process which includes the hydrogen injection through the intake manifold (PFI) and/or the hydrogen DI in the engine compression stroke. Conditions with simulated PFI, PFI + DI and DI have been analyzed to study the effects of mixture preparation behaviors on the hydrogen ignition and its flame propagation inside the engine combustion chamber. Numerically, the CFD code has been intensively validated against experimental engine data which provided remarkable agreement in terms of in-cylinder pressure history evaluation.
文摘The intake air control system of a gasoline engine is a typical nonlinear system, and included among the adverse fac-tors that always induce poor idle-speed control stability are dead time and disturbances in the intake air control process. In this paper, to improve the responsiveness when idling with regard to disturbances, a mean-value engine model (MVEM) with dead time was constructed as the control object, and the two servo structures of sliding mode control (SMC) were studied for better idle control performance, especially in transient process of speed change. The simulation results confirmed that under the constraint condition of control input, the robustness of idle speed control that is being subjected to torque disturbances and noise disturbances can be greatly improved by use of the servo structure II.
文摘NOx and soot emissions from diesel engines can be greatly reduced by pressure wave supercharging(PWS).The diesel engine matched with PWS needs redesigning its exhaust pipes.Except for meeting the installation requirements,the exhaust gas must be stable in pressure before rushing into PWS.In this paper the lateral and center ported divergent exhaust pipes are designed,modeled geometrically and analyzed structurally based on a 3-D design software-CATIA to determine the structure of two exhaust pipes having the required inner volume.Then flow analysis for two exhaust pipes is done using a flow analysis software-ANASYS.Moreover,the optimal exhaust pipes are determined comprehensively and cast for engine test.Engine test results show that PWS is superior to turbocharging at low engine speeds and inferior to turbocharging in power and emissions at medium-to-high engine speeds.The performance of PWS engine under high speed operating conditions can be improved by contriving larger surge volume intake and exhaust pipes.
基金Project (Nos. 51106136 and 50776078) supported by the National Natural Science Foundation of China
文摘The fuel dynamic transfer process,including fuel injection,fuel film deposition and evaporation in the intake port,was analyzed for spark ignition(SI) engines with port fuel injection(PFI).The influence of wall-wetting fuel film,especially its evaporation rate,upon the air-fuel ratio of in-cylinder mixtures was also discussed.According to the similarity principle,Fick's law,the ideal gas equation and the Gilliland correlation,an evaporate prediction model of wall-wetting fuel film was set up and an evaporate prediction based dynamic fuel film compensator was designed.Through engine cold start tests,the wall-wetting temperature,which is the key input of the fuel film evaporate prediction model,was also modeled and predicted.Combined with the experimental data of the evaporation characteristics of ethanol-gasoline blends and engine calibration tests,all the parameters of the wall-wetting fuel film evaporate prediction model used in the fuel film compensator were identified.Square-wave disturbance tests of fuel injection showed that with the help of the fuel film compensator the response of the in-cylinder air-fuel ratio was significantly improved and the real air-fuel ratio always closely matched the expected ratio.The fuel film compensator was then integrated into the final air-fuel ratio controller,and the engine tests showed that the air-fuel ratio control error was less than 2% in steady-state conditions,and less than 4% in transient conditions.The fuel film compensator also showed good adaptability to different ethanol-gasoline blends.
基金the National Natural Science Foundation of China (Nos. 50805091 and 50705055)the National Basic Research Program (973) of China(No. 2006CB705402)the Basic Research Programs of Science and Technology Commission of Shanghai City(No. 07JC14027)
文摘Design for life-time performance and proper maintenance measures are usually needed to prolong the mean-time-between-failures of complex equipments such as internal combustion engines.To reach this,it is important to obtain the information of time-varying system performance in design stage and to identify the structural change at each moment.So a multidisciplinary model based method is studied in this paper to unify the time-varying performance(TVP) prediction and system identification(SI) of equipments.The related multidisciplinary model in this paper should be not only precise to give simulation results but also sensitive to the variation of system parameters.So the varying history of system performance along with the structural change can be obtained from the model.Then the value of system parameters can be identified by seeking roots with given detected responding data and relationship between system responding data and system parameters.A case study on a low power gasoline engine shows that the method presented in this paper can provide useful information for the development and maintenance of complex equipments.
