Ignition and Combustion of Single Micro-Sized Graphite Particle at the Micro-Scale

At the micro-scale, ignition and burning characteristics of single micron-sized graphite particle were investigated experimentally. Graphite particles in the form of fine powders were pumped into a micro combustion chamber and distributed sparsely. Single graphite particle is ignited heterogeneously by intense radiation from a near infrared laser source, in a stagnation air flow at the atmospheric pressure. Minimum ignition power and ignition delay of graphite particles are independent on the particle size. After ignition, some events, such as flame propagation, photophoresis, extinction, re-ignition and micro explosion, were identified during the burning. In general, the envelop flame front propagates quickly, and the flame becomes brighter gradually at the start up stage. The envelop flame then becomes weaker as the particle is consumed, and eventually extinguishes. The flame structure is always asymmetric. Photophoresis phenomenon was found during the burning, which results in the motion of graphite particle inversely towards the laser focal. Extinction of flame occurs because of large heat loss on the wall of combustion chamber at the micro-scale. Re-ignition possibly takes place after extinction under the inductive action of the laser. The repeatability of extinction and re-ignition was identified as well. Lastly, the event of micro explosion possibly takes place for graphite particle composed of fine powders. The smaller particles are expelled from the mother graphite, resulting from the diffusion limitation of heat lease of oxidation reaction.