Flame is prone to lose its stability in micro-combustors due to the large amount of heat loss from the external walls. On the other hand, heat recirculation through the upstream combustor walls can enhance flame stabi...Flame is prone to lose its stability in micro-combustors due to the large amount of heat loss from the external walls. On the other hand, heat recirculation through the upstream combustor walls can enhance flame stability. These two aspects depend on the structural heat transfer, which is associated with the thickness and thermal conductivity of the combustor walls. In the present study, the effects of wall thickness and material on flame stability were numerically investigated by selecting two thicknesses (δ=0.2 and 0.4 mm) and two materials (quartz and SiC). The results show that when δ=0.2 mm, flame inclination occurs at a certain inlet velocity in both combustors, but it happens later in SiC combustor. For δ=0.4 mm, flame inclination still occurs in quartz combustor from a larger inlet velocity compared to the case of δ=0.2 mm. However, flame inclination in SiC combustor with δ=0.4 mm does not happen and it has a much larger blowout limit. Analysis reveals that a thicker wall can enhance heat recirculation and reduce heat loss simultaneously. Moreover, SiC combustor has larger heat recirculation ratio and smaller heat loss ratio. In summary, the micro-combustor with thicker and more conductive walls can harvest large flame stability limit.展开更多
Present technology has been shifting towards miniaturization of devices for energy production for portable electronics. Micro-combustors, when incorporated into a micro-power generation system, create the energy desir...Present technology has been shifting towards miniaturization of devices for energy production for portable electronics. Micro-combustors, when incorporated into a micro-power generation system, create the energy desired in the form of hot gases to power such technology. This creates the need for a design optimization of the micro-combustor in terms of geometry, fuel choice, and material selection. A total of five micro-combustor geometries, three fuels, and three materials were computationally simulated in different configurations in order to determine the optimal micro-combustor design for highest efficiency. Inlet velocity, equivalence ratio, and wall heat transfer coefficient were varied in order to test a comprehensive range of micro-combustor parameters. All simulations completed for the optimization study used ANSYS Fluent v16.1 and post-processing of the data was done in CFD Post v16.1. It was found that for lean, premixed fuel-air mixtures (φ= 0.6 - 0.9) ethane (C<sub>2</sub>H<sub>6</sub>) provided the highest flame temperatures when ignited within the micro-combustor geometries. An aluminum oxide converging micro-combustor burning ethane and air at an equivalence ratio of 0.9, an inlet velocity of 0.5 m/s, and heat transfer coefficient of 5 W/m<sup>2</sup>-K was found to produce the highest combustor efficiency, making it the optimal choice for a micro-combustor design. It is proposed that this geometry be experimentally and computationally investigated further in order to determine if additional optimization can be achieved.展开更多
本文针对微型涡喷发动机的氢气分级微混燃烧室出口温度场进行优化,通过构建Work-bench和UG联合仿真优化方法,且基于近似模型和遗传算法,建立了多参数驱动的优化设计流程,获得了氢气微混燃烧室最优参数组合的掺混孔孔径和轴向位置,以及...本文针对微型涡喷发动机的氢气分级微混燃烧室出口温度场进行优化,通过构建Work-bench和UG联合仿真优化方法,且基于近似模型和遗传算法,建立了多参数驱动的优化设计流程,获得了氢气微混燃烧室最优参数组合的掺混孔孔径和轴向位置,以及关键参数对出口热点温度的影响规律,并针对最优方案详细分析了燃烧室内流场、组分场和温度场的演化规律。研究结果表明:高温区集中在微混单元出口的0~20 mm内,燃烧室出口热点受外壁孔径影响最为敏感,减小外火焰筒掺混孔径和增加内火焰筒掺混孔径有利于提升出口温度分布均匀性。最优方案中内、外火焰筒掺混射流涡长度分别达到了29 mm和34 mm,出口温度分布系数(Outlet Temperature Distribution Factor,OTDF)仅为0.13,NO_(x)排放为3×10^(-6)。展开更多
基金Project(51576084) supported by the National Natural Science Foundation of China
文摘Flame is prone to lose its stability in micro-combustors due to the large amount of heat loss from the external walls. On the other hand, heat recirculation through the upstream combustor walls can enhance flame stability. These two aspects depend on the structural heat transfer, which is associated with the thickness and thermal conductivity of the combustor walls. In the present study, the effects of wall thickness and material on flame stability were numerically investigated by selecting two thicknesses (δ=0.2 and 0.4 mm) and two materials (quartz and SiC). The results show that when δ=0.2 mm, flame inclination occurs at a certain inlet velocity in both combustors, but it happens later in SiC combustor. For δ=0.4 mm, flame inclination still occurs in quartz combustor from a larger inlet velocity compared to the case of δ=0.2 mm. However, flame inclination in SiC combustor with δ=0.4 mm does not happen and it has a much larger blowout limit. Analysis reveals that a thicker wall can enhance heat recirculation and reduce heat loss simultaneously. Moreover, SiC combustor has larger heat recirculation ratio and smaller heat loss ratio. In summary, the micro-combustor with thicker and more conductive walls can harvest large flame stability limit.
文摘Present technology has been shifting towards miniaturization of devices for energy production for portable electronics. Micro-combustors, when incorporated into a micro-power generation system, create the energy desired in the form of hot gases to power such technology. This creates the need for a design optimization of the micro-combustor in terms of geometry, fuel choice, and material selection. A total of five micro-combustor geometries, three fuels, and three materials were computationally simulated in different configurations in order to determine the optimal micro-combustor design for highest efficiency. Inlet velocity, equivalence ratio, and wall heat transfer coefficient were varied in order to test a comprehensive range of micro-combustor parameters. All simulations completed for the optimization study used ANSYS Fluent v16.1 and post-processing of the data was done in CFD Post v16.1. It was found that for lean, premixed fuel-air mixtures (φ= 0.6 - 0.9) ethane (C<sub>2</sub>H<sub>6</sub>) provided the highest flame temperatures when ignited within the micro-combustor geometries. An aluminum oxide converging micro-combustor burning ethane and air at an equivalence ratio of 0.9, an inlet velocity of 0.5 m/s, and heat transfer coefficient of 5 W/m<sup>2</sup>-K was found to produce the highest combustor efficiency, making it the optimal choice for a micro-combustor design. It is proposed that this geometry be experimentally and computationally investigated further in order to determine if additional optimization can be achieved.
文摘本文针对微型涡喷发动机的氢气分级微混燃烧室出口温度场进行优化,通过构建Work-bench和UG联合仿真优化方法,且基于近似模型和遗传算法,建立了多参数驱动的优化设计流程,获得了氢气微混燃烧室最优参数组合的掺混孔孔径和轴向位置,以及关键参数对出口热点温度的影响规律,并针对最优方案详细分析了燃烧室内流场、组分场和温度场的演化规律。研究结果表明:高温区集中在微混单元出口的0~20 mm内,燃烧室出口热点受外壁孔径影响最为敏感,减小外火焰筒掺混孔径和增加内火焰筒掺混孔径有利于提升出口温度分布均匀性。最优方案中内、外火焰筒掺混射流涡长度分别达到了29 mm和34 mm,出口温度分布系数(Outlet Temperature Distribution Factor,OTDF)仅为0.13,NO_(x)排放为3×10^(-6)。
