Trap, ignition, and diffusion combustion characteristics of active carbon micro-particles at a meso-scale studied by optical tweezers

Abstract

To study combustion characteristics of solid fuels at the meso-scale, this paper presents a study on trap, ignition, and diffusion combustion characteristics of active carbon micro-particles at a meso-scale by optical tweezers. In the meso-scale combustor, minimum trap power for active carbon micro-particles with a diameter of 7.0 m is 3.2 mW, and the trap velocity is in the range of 103.770.0 m/s. The active carbon micro-particles in static air flow can be ignited when the laser power is 3.2 mW. The effective diameter, perimeter, area and roundness of the particles have little effect on the minimum power for ignition. The ignition delay time is ～ 48 ms for active carbon micro-particles with a diameter of 3.0 m, and it will decrease till below 6 ms with increasing laser power. After ignited, the active carbon micro-particle shows flameless combustion first. The diffusion combustion velocity agrees with the diameter square linear-relationship, and the velocity is of 15.08.0 m/s. Then the active carbon micro-particle continues to carry out combustion reactions with bright flames repetitiously, and the flash frequency is 29.1 Hz. For the active carbon micro-particle with a diameter of 3.0 m, it can burn out thoroughly in an overall time ～ 0.648 s (including the heating and combustion processes). Results demonstrate that ignition of the active carbon micro-particle heated by high power density laser belongs to the combined ignition mode. Before volatile matter precipitates, the active carbon micro-particle is ignited heterogeneously and carries out a flameless combustion. However, after the volatile components are precipitated, it is ignited homogeneously, and the ombustion flame always shows a spheried shape.