基于彩色火焰图像的铝、硼纳米颗粒燃烧特性

用彩色数码相机拍照结合图像处理的诊断方法研究了铝、硼纳米颗粒的燃烧特性和机理,得到了铝、硼纳米颗粒火焰的形貌特征、温度分布及着火时间等。燃烧实验中使用多元扩散平焰燃烧器(Hencken燃烧器)提供可控的高温环境,利用固体颗粒乙醇溶解-超声分散-雾化-干燥的给粉方式产生高分散的纳米气溶胶,并在不同工况下对纳米颗粒火焰进行拍照。从所得彩色图片中提取红、绿、蓝三色通道信号,结合普朗克辐射定律获得颗粒的辐射强度信息及温度信息。结果表明:不同环境温度会导致不同的颗粒变温历程。高温环境下铝、硼颗粒经着火后颗粒温度逐渐下降,而低温下由于氧化层多晶相变的影响铝颗粒温度先缓慢升高而后缓慢下降,硼颗粒温度则几乎维持恒定。硼颗粒着火过程可分为着火延时和着火两个阶段,通过火焰图像定义了相应的时间,测得的硼颗粒着火延迟时间为1.17~2.98ms,着火时间为0.31~0.85ms。

Combustion characteristics of aluminum and boron nanoparticles based on flame color images

The combustion characteristics of aluminum and boron nanoparticles were studied based on the optical diagnostics using a color digital camera and subsequent image processing and their morphologic features, temperature characteristics and the ignition time were obtained. In the experiments, the multi-diffusion flat flame burner (i.e. Hencken burner) was used to support a tunable high temperature ambience. A series of processes including dissolving the nanoparticles into the ethanol, ultrasonically dispersing, atomization, and diffusion-drying were used to generate well-dispersed nanoparticle aerosol. The flame images of the nanoparticles were recorded by a color digital camera under different experimental conditions. The signals of red, green and blue channels were derived from the color images to obtain the radiation intensity and the information of particle temperatures based on the Planck's law. The results indicate different particle temperature profiles at different ambient temperature. At a high temperature, the particle temperatures of Al and B decrease directly after ignition. At a low temperature, the particle temperature of Al increases slowly to a peak and then decreases due to the polymorphic phase transition of the alumina shell, while the particle temperature of B is nearly constant. The ignition process of B is divided into ignition delay and ignition stage, and the time could be defined from the flame images. The time of ignition delay for B ranges from 1.17 ms to 2.98 ms and the ignition time ranges from 0.31 ms to 0.85 ms.