纳米铝单颗粒与颗粒团燃烧的比较分析

Comparison of Combustion Characteristics Between Single Al Nanoparticles and Large Nano-Agglomerates

基于甲烷/氧气/氮气平面扩散火焰高温燃烧实验平台,从实验和理论分析两方面比较了纳米铝单颗粒和大颗粒团在燃烧特性和反应机理上的差异.实验中高分散、近似单颗粒的铝火焰呈现微弱的黄红色,而颗粒团在相同环境下呈现亮白色火焰,说明燃烧时前者颗粒温度要低于后者.并且相同环境下颗粒团的着火延时比单颗粒要长.从理论上对比了单颗粒和颗粒团的反应控速步,发现单颗粒主要受表面非均相反应控制,但颗粒团由于巨大的内表面积使得气相扩散成为可能的控速因素.颗粒团内近似绝热的环境使得颗粒升温加快,从而能产生更大的内应力来加速反应或促使颗粒团破碎,使得颗粒团能在低于铝熔点温度的环境下实现着火.最后,根据已有研究及分析,提出了纳米铝单颗粒和颗粒团在燃烧过程中的结构演变历程.

The combustion of single aluminum（Al）nanoparticles and large nano-agglomerate was compared experimentallyand theoretically based on a CH4/O2/N2 flat diffusion flame burner.In the experiment,the flame of singleparticles is very weak,with colors between red and yellow,while the flame streak of nano-agglomerates is brightand white.It implies that the temperature of single particles is much lower than that of large nanoagglomerate.Moreover,the ignition delay of nano-agglomerate is longer than that of free particles in the same environment.Based on the theoretical analysis,the reaction of single particle is found to be governed by heterogeneousionic diffusion,while the agglomerate is possibly controlled by gaseous diffusion due to its huge interior reactionsurface.In the large agglomerate,particles have an adiabatic environment to support the faster heating rate of particles.Huge heating rate will lead to large internal stress to break the agglomerate or promote the reaction.Hence thelarge agglomerate could ignite at low temperatures below the melting point of Al.Finally,the structural evolutionsduring combustion are proposed for single particles and nano-agglomerates.