The volume of fluid(VOF) formulation is applied to model the combustion process of a single droplet in a hightemperature convective air free stream environment.The calculations solve the flow field for both phases,and...The volume of fluid(VOF) formulation is applied to model the combustion process of a single droplet in a hightemperature convective air free stream environment.The calculations solve the flow field for both phases,and consider the droplet deformation based on an axisymmetrical model.The chemical reaction is modeled with one-step finite-rate mechanism and the thermo-physical properties for the gas mixture are species and temperature dependence.A mass transfer model applicable to the VOF calculations due to vaporization of the liquid phases is developed in consideration with the fluctuation of the liquid surface.The model is validated by examining the burning rate constants at different convective air temperatures,which accord well with experimental data of previous studies.Other phenomena from the simulations,such as the transient history of droplet deformation and flame structure,are also qualitatively accordant with the descriptions of other numerical results.However,a different droplet deformation mechanism for the low Reynolds number is explained compared with that for the high Reynolds number.The calculations verified the feasibility of the VOF computational fluid dynamics(CFD) formulation as well as the mass transfer model due to vaporization.展开更多
The study of flame development characteristics is crucial in the study of flame propagation, extinction, and for the investigation of combustion cyclic variability in SI engine. The aim of this study is to investigate...The study of flame development characteristics is crucial in the study of flame propagation, extinction, and for the investigation of combustion cyclic variability in SI engine. The aim of this study is to investigate the characteristics of flame development in a lean-stratified combustion of Natural Gas Engine （CNG） in a single cylinder direct injection （DI） engine at a specific motor speed, and fixed injection timing and air-fuel ratio by varying only the swirl level at the intake. The engine was set to run at 1800 rpm with half-load throttled. The ignition advance was set at 21.5 BTDC, and to create an overall lean and stratified mixture, injection timing was set at 61 BTDC with an air-fuel-ratio of 40.5 （λ=2.35）. Variable turbulent flow conditions near spark-plug were created by positioning the swirl control valves （SCV） at the intake port just before the two intake valves. This was done by setting one of the valves at full open position and the other one at 0% closed, 50% closed and 100% closed positions in order to achieve medium tumble （no swirl）, medium swirl and high swirl flows in the cylinder, respectively. An endoscope and CCD camera assembly was utilized to capture the flame images from the tumble plane at the intake side of the engine ever）, 2 CA degrees after ignition timing （AIT） for 40 CAs. It was observed that flame growth rate and flame convection velocity are increasing with increasing the swirl level. The total combustion duration is, thus, shorter in swirl induced combustion than without. However, COV in IMEP is greater in swirl induced flow cases than the medium tumble.展开更多
In order to burn a hydrocarbon fuel efficiently using conventional cycles,very high temperatures are required.Chemical looping combustion（CLC）offers an alternative cycle for large scale power production.In CLC a car...In order to burn a hydrocarbon fuel efficiently using conventional cycles,very high temperatures are required.Chemical looping combustion（CLC）offers an alternative cycle for large scale power production.In CLC a carrier molecule is used to transport oxygen between two redox reactions,one where the carrier is oxidised and another where it is reduced by reaction with a fuel.Separation of the oxygen carrier from fuel ash can be aided by means of phase difference and this is a key advantage of fluid phase CLC where the carrier medium proposed is sodium,potassium or zinc.The principle exploited in fluid phase CLC is the recirculation of both energy and entropy.High thermal efficiencies,circa 75% at 35 bar are theoretically achievable taking into account component efficiencies,with separation of nitrogen and carbon dioxide,in combination with the water shift gas reaction,as an inherent part of the cycle if air is used as the oxygen source.展开更多
实验对比了以甘氨酸和CH6N4O作为燃烧反应的还原剂,与硝酸氧锆配制成氧化-还原性水溶液,在微波炉内加热升温,经历一个约2 m in的快速燃烧后,得到二氧化锆产物。结果表明,用CH6N4O能得到纯度高、粒度分布窄、细小的二氧化锆。通过X衍射...实验对比了以甘氨酸和CH6N4O作为燃烧反应的还原剂,与硝酸氧锆配制成氧化-还原性水溶液,在微波炉内加热升温,经历一个约2 m in的快速燃烧后,得到二氧化锆产物。结果表明,用CH6N4O能得到纯度高、粒度分布窄、细小的二氧化锆。通过X衍射法测定,平均粒径为53 nm。展开更多
基金supported by the National Basic Research Program (973) of China (No. 2011CB706501)the Fundamental Research Funds for the Central Universities (No. 1A4000172210101[67]),China
文摘The volume of fluid(VOF) formulation is applied to model the combustion process of a single droplet in a hightemperature convective air free stream environment.The calculations solve the flow field for both phases,and consider the droplet deformation based on an axisymmetrical model.The chemical reaction is modeled with one-step finite-rate mechanism and the thermo-physical properties for the gas mixture are species and temperature dependence.A mass transfer model applicable to the VOF calculations due to vaporization of the liquid phases is developed in consideration with the fluctuation of the liquid surface.The model is validated by examining the burning rate constants at different convective air temperatures,which accord well with experimental data of previous studies.Other phenomena from the simulations,such as the transient history of droplet deformation and flame structure,are also qualitatively accordant with the descriptions of other numerical results.However,a different droplet deformation mechanism for the low Reynolds number is explained compared with that for the high Reynolds number.The calculations verified the feasibility of the VOF computational fluid dynamics(CFD) formulation as well as the mass transfer model due to vaporization.
文摘The study of flame development characteristics is crucial in the study of flame propagation, extinction, and for the investigation of combustion cyclic variability in SI engine. The aim of this study is to investigate the characteristics of flame development in a lean-stratified combustion of Natural Gas Engine （CNG） in a single cylinder direct injection （DI） engine at a specific motor speed, and fixed injection timing and air-fuel ratio by varying only the swirl level at the intake. The engine was set to run at 1800 rpm with half-load throttled. The ignition advance was set at 21.5 BTDC, and to create an overall lean and stratified mixture, injection timing was set at 61 BTDC with an air-fuel-ratio of 40.5 （λ=2.35）. Variable turbulent flow conditions near spark-plug were created by positioning the swirl control valves （SCV） at the intake port just before the two intake valves. This was done by setting one of the valves at full open position and the other one at 0% closed, 50% closed and 100% closed positions in order to achieve medium tumble （no swirl）, medium swirl and high swirl flows in the cylinder, respectively. An endoscope and CCD camera assembly was utilized to capture the flame images from the tumble plane at the intake side of the engine ever）, 2 CA degrees after ignition timing （AIT） for 40 CAs. It was observed that flame growth rate and flame convection velocity are increasing with increasing the swirl level. The total combustion duration is, thus, shorter in swirl induced combustion than without. However, COV in IMEP is greater in swirl induced flow cases than the medium tumble.
文摘In order to burn a hydrocarbon fuel efficiently using conventional cycles,very high temperatures are required.Chemical looping combustion（CLC）offers an alternative cycle for large scale power production.In CLC a carrier molecule is used to transport oxygen between two redox reactions,one where the carrier is oxidised and another where it is reduced by reaction with a fuel.Separation of the oxygen carrier from fuel ash can be aided by means of phase difference and this is a key advantage of fluid phase CLC where the carrier medium proposed is sodium,potassium or zinc.The principle exploited in fluid phase CLC is the recirculation of both energy and entropy.High thermal efficiencies,circa 75% at 35 bar are theoretically achievable taking into account component efficiencies,with separation of nitrogen and carbon dioxide,in combination with the water shift gas reaction,as an inherent part of the cycle if air is used as the oxygen source.
