The ignition and combustion of aluminum particles are crucial to achieve optimal energy release in propulsion and power systems within a limited residence time.This study seeks to develop theoretical ignition and comb...The ignition and combustion of aluminum particles are crucial to achieve optimal energy release in propulsion and power systems within a limited residence time.This study seeks to develop theoretical ignition and combustion models for aluminum particles ranging from 10 nm to 1000μm under wide pressure ranges of normal to beyond 10 MPa.Firstly,a parametric analysis illustrates that the convective heat transfer and heterogeneous surface reaction are strongly influenced by pressure,which directly affects the ignition process.Accordingly,the ignition delay time can be correlated with pressure through the p^(b)relationship,with b increasing from-1 to-0.1 as the system transitions from the free molecular regime to the continuum regime.Then,the circuit comparison analysis method was used to interpret an empirical formula capable of predicting the ignition delay time of aluminum particles over a wide range of pressures in N_(2),O_(2),H_(2)O,and CO_(2)atmospheres.Secondly,an analysis of experimental data indicates that the exponents of pressure dependence in the combustion time of large micron-sized particles and nanoparticles are-0.15 and-0.65,respectively.Further,the dominant combustion mechanism of multiscale aluminum particles was quantitatively demonstrated through the Damköhler number(Da)concept.Results have shown that aluminum combustion is mainly controlled by diffusion as Da>10,by chemical kinetics when Da≤0.1,and codetermined by both diffusion and chemical kinetics when 0.1<Da≤10.Finally,an empirical formula was proposed to predict the combustion time of multiscale aluminum particles under high pressure,which showed good agreement with available experimental data.展开更多
Homogeneous mixtures of CH4/air under moderate or intense low-oxygen dilution（MILD） combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation（EGR）,espe-cially C...Homogeneous mixtures of CH4/air under moderate or intense low-oxygen dilution（MILD） combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation（EGR）,espe-cially CO2 in EGR gases,on ignition characteristics.Specifically,effects of CO2 addition on autoignition delay time were emphasized at temperature between 1200 K and 1600 K for a wide range of the lean-to-rich equivalence ratio（0.2~2）.The results showed that the ignition delay time increased with equivalence ratio or CO2 dilution ratio.Fur-thermore,ignition delay time was seen to be exponentially related with the reciprocal of initial temperature.Special concern was given to the chemical effects of CO2 on the ignition delay time.The enhancement of ignition delay time with CO2 addition can be mainly ascribed to the decrease of H,O and OH radicals.The predictions of tem-perature profiles and mole fractions of CO and CO2 were strongly related to the chemical effects of CO2.A single ignition time correlation was obtained in form of Arrhenius-type for the entire range of conditions as a function of temperature,CH4 mole fraction and O2 mole fraction.This correlation could successfully capture the complex be-haviors of ignition of CH4/air/CO2 mixture.The results can be applied to MILD combustion as ＂reference time＂,for example,to predict ignition delay time in turbulent reacting flow.展开更多
为实现燃烧室组件的精确建模及其动力学特性的仿真研究,以零维时滞燃烧室模型为基础,考虑燃烧室内喷射、雾化、蒸发、混合、化学反应过程,采用针栓喷注器SMD(Sauter Mean Diameter,索特尔平均直径)经验关联式以及液滴高压蒸发理论对液氧...为实现燃烧室组件的精确建模及其动力学特性的仿真研究,以零维时滞燃烧室模型为基础,考虑燃烧室内喷射、雾化、蒸发、混合、化学反应过程,采用针栓喷注器SMD(Sauter Mean Diameter,索特尔平均直径)经验关联式以及液滴高压蒸发理论对液氧/甲烷推进剂组合的燃烧时滞进行求解,建立了基于液滴高压蒸发理论的变时滞燃烧室模型。基于1 kg/s级推力室开展热试车验证了变时滞燃烧室模型的准确性,结果表明:所建立的变时滞燃烧室模型可以较为准确地预测燃烧室的压力以及温度动态响应过程,与试验结果相比,稳态压力以及温度误差均在6%以内,压力参数动态响应时间的误差在14%以内,仿真结果具有较高的精度。基于变时滞燃烧室模型开展仿真研究,研究发现:液氧液滴初始粒径以及燃烧室温度作为影响液氧液滴寿命的主要因素,主导着液氧时滞的变化;变时滞模型可以根据工况参数动态计算推进剂燃烧时滞,启动初期喷注器雾化效果较差,液滴最大粒径达到800μm,且燃烧室温度低,进而导致燃烧时滞偏大,最大达到了1100 ms,约为稳定工作状态下燃烧时滞的40倍。本文所建立的变时滞燃烧室模型可根据工况参数对燃烧时滞进行动态计算,相较于传统时滞模型,其燃烧时滞的变化趋势更符合发动机实际工作过程,同时其室压的响应时间、稳态值也更接近实验值,该模型未来可为实际发动机时序设计等提供仿真支撑。展开更多
基金supported by the National Natural Science Foundation of China(Nos.U20B2018 and U23B6009)。
文摘The ignition and combustion of aluminum particles are crucial to achieve optimal energy release in propulsion and power systems within a limited residence time.This study seeks to develop theoretical ignition and combustion models for aluminum particles ranging from 10 nm to 1000μm under wide pressure ranges of normal to beyond 10 MPa.Firstly,a parametric analysis illustrates that the convective heat transfer and heterogeneous surface reaction are strongly influenced by pressure,which directly affects the ignition process.Accordingly,the ignition delay time can be correlated with pressure through the p^(b)relationship,with b increasing from-1 to-0.1 as the system transitions from the free molecular regime to the continuum regime.Then,the circuit comparison analysis method was used to interpret an empirical formula capable of predicting the ignition delay time of aluminum particles over a wide range of pressures in N_(2),O_(2),H_(2)O,and CO_(2)atmospheres.Secondly,an analysis of experimental data indicates that the exponents of pressure dependence in the combustion time of large micron-sized particles and nanoparticles are-0.15 and-0.65,respectively.Further,the dominant combustion mechanism of multiscale aluminum particles was quantitatively demonstrated through the Damköhler number(Da)concept.Results have shown that aluminum combustion is mainly controlled by diffusion as Da>10,by chemical kinetics when Da≤0.1,and codetermined by both diffusion and chemical kinetics when 0.1<Da≤10.Finally,an empirical formula was proposed to predict the combustion time of multiscale aluminum particles under high pressure,which showed good agreement with available experimental data.
基金Supported by the National Natural Science Foundation of China (50206014)the Shuguang Scholar Program of Shanghai Education Development Foundation (05SG23)
文摘Homogeneous mixtures of CH4/air under moderate or intense low-oxygen dilution（MILD） combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation（EGR）,espe-cially CO2 in EGR gases,on ignition characteristics.Specifically,effects of CO2 addition on autoignition delay time were emphasized at temperature between 1200 K and 1600 K for a wide range of the lean-to-rich equivalence ratio（0.2~2）.The results showed that the ignition delay time increased with equivalence ratio or CO2 dilution ratio.Fur-thermore,ignition delay time was seen to be exponentially related with the reciprocal of initial temperature.Special concern was given to the chemical effects of CO2 on the ignition delay time.The enhancement of ignition delay time with CO2 addition can be mainly ascribed to the decrease of H,O and OH radicals.The predictions of tem-perature profiles and mole fractions of CO and CO2 were strongly related to the chemical effects of CO2.A single ignition time correlation was obtained in form of Arrhenius-type for the entire range of conditions as a function of temperature,CH4 mole fraction and O2 mole fraction.This correlation could successfully capture the complex be-haviors of ignition of CH4/air/CO2 mixture.The results can be applied to MILD combustion as ＂reference time＂,for example,to predict ignition delay time in turbulent reacting flow.
文摘为实现燃烧室组件的精确建模及其动力学特性的仿真研究,以零维时滞燃烧室模型为基础,考虑燃烧室内喷射、雾化、蒸发、混合、化学反应过程,采用针栓喷注器SMD(Sauter Mean Diameter,索特尔平均直径)经验关联式以及液滴高压蒸发理论对液氧/甲烷推进剂组合的燃烧时滞进行求解,建立了基于液滴高压蒸发理论的变时滞燃烧室模型。基于1 kg/s级推力室开展热试车验证了变时滞燃烧室模型的准确性,结果表明:所建立的变时滞燃烧室模型可以较为准确地预测燃烧室的压力以及温度动态响应过程,与试验结果相比,稳态压力以及温度误差均在6%以内,压力参数动态响应时间的误差在14%以内,仿真结果具有较高的精度。基于变时滞燃烧室模型开展仿真研究,研究发现:液氧液滴初始粒径以及燃烧室温度作为影响液氧液滴寿命的主要因素,主导着液氧时滞的变化;变时滞模型可以根据工况参数动态计算推进剂燃烧时滞,启动初期喷注器雾化效果较差,液滴最大粒径达到800μm,且燃烧室温度低,进而导致燃烧时滞偏大,最大达到了1100 ms,约为稳定工作状态下燃烧时滞的40倍。本文所建立的变时滞燃烧室模型可根据工况参数对燃烧时滞进行动态计算,相较于传统时滞模型,其燃烧时滞的变化趋势更符合发动机实际工作过程,同时其室压的响应时间、稳态值也更接近实验值,该模型未来可为实际发动机时序设计等提供仿真支撑。
