研究目的
To experimentally investigate the ignition and combustion characteristics of individual aluminum particles below 10 μm.
研究成果
The designed experimental apparatus can provide direct observation for investigating the ignition and combustion behaviors of individual aluminum particles below 10 μm with high spatial and temporal resolutions, by combining laser ignition and microscopic high-speed cinematography. Direct observation shows that, on heating, the diameter and circularity evolution of an individual aluminum particle includes three stages—thermal expansion, melting and evaporation. As the laser power density increases, the duration of each stage shortens. Moreover, the thermal expansion and ignition of individual aluminum particles are heterogeneous.
研究不足
The heat loss of the combustor wall could not be ignored due to the heat conduction from the aluminum to the wall during heating.
1：Experimental Design and Method Selection:
A specific in situ diagnostic experimental apparatus was designed for directly observing the ignition and combustion behaviors of individual aluminum particles, with a submicrometer spatial resolution and a temporal resolution of tens of microseconds.
2：Sample Selection and Data Sources:
Aluminum powder was purchased from Changsha Tianjiu Corporation, Changsha, China. Its purity reaches
3：8%, but it contains impurities of Fe, Si, Cu, O, etc. List of Experimental Equipment and Materials:
A continuous near infrared laser set at 1064 nm and TEM00 was used. The laser power was varied from 0 to 600 mW by tuning the modulated current magnitude. The high-speed camera (Phantom Micro M310, Vision Research Inc., Wayne, NJ, USA) was used to record the images during the ignition and combustion of aluminum.
4：Experimental Procedures and Operational Workflow:
The laser beam was split into two beams by a splitter (7:3). The dominant beam was again shaped by a beam expander (3×), dichroic mirror and objective lens to focus on an individual aluminum particle and ignite it. The other beam directly reached the power meter (S350C, Thorlabs Inc., Newton, NJ, USA) to measure the ignition power.
5：3). The dominant beam was again shaped by a beam expander (3×), dichroic mirror and objective lens to focus on an individual aluminum particle and ignite it. The other beam directly reached the power meter (S350C, Thorlabs Inc., Newton, NJ, USA) to measure the ignition power. Data Analysis Methods:
5. Data Analysis Methods: Digital microscopic images by calibration were utilized to identify the key ignition and combustion processes and to obtain parameters such as ignition delay and flame propagation speed.
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