Abstract
Microscale combustion has potential application in a micro power generator. This paper studied the ignition and combustion behavior of individual graphite microparticles in a micro-combustor to explore the utilization of carbon-based fuels at the microscale system. The individual graphite microparticles inside the micro-combustor were ignited by a highly focused laser in an air flow with natural convection at atmospheric temperature and pressure. The results show that the ignition of graphite microparticles was heterogeneous. The particle diameter had a small weak effect on ignition delay time and threshold ignition energy. The micro-combustor wall heat losses had significant effects on the ignition and combustion. During combustion, flame instability, photophoresis, repetitive extinction and reignition were identified. The flame structure was asymmetric, and the fluctuation of flame front and radiation intensity showed combustion instability. Photophoretic force pushed the graphite away from the focal point and resulted in extinction. Owing to large wall heat loss, the flame quickly extinguished. However, the graphite was inductively reignited by laser.
Highlights
Combustion of solid carbon-based fuels is an important research subject, and is indispensable for practical utilization of coal [1], biomass [2], solid waste [3], etc
Qu et al [8] reported that the graphite particles were heated gradually, and accumulated heat released the oxidation reaction that triggered the ignition of graphite
The other emphasis was to discover possible new combustion phenomena and burning behavior owing to large heat loss of the combustor wall, including photophoresis, repetitive extinction and reignition
Summary
Combustion of solid carbon-based fuels is an important research subject, and is indispensable for practical utilization of coal [1], biomass [2], solid waste [3], etc. Owing to complexities involved and appearances of new technology concepts for combustion, further studies of pure carbon (like char and graphite) combustion play a significant role in revealing the burning mechanism of carbon-based fuels [4]. Oxidation [6,7], ignition [8], and burning [9,10] characteristics of graphite have been extensively studied, experimentally, and theoretically and/or numerically. Makino et al [9,11,12,13] studied the burning characteristics of graphite in detail, including flame structure and combustion rate of graphite in a stagnation air or water vapor flow under high temperature
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