Experimental Study on the Ignition Process of Single Coal Particles at Microgravity

Abstract

In this paper, the first Chinese microgravity (μ-g) experimental study on coal combustion was introduced. An experimental system used to study the ignition process of single coal particles was built up, complying with the requirements of the 3.5 s drop tower in the National Microgravity Laboratory of China (NMLC). High volatile bituminous and lignite coal particles with diameter of 1.5 and 2.0 mm were tested. The ignition and combustion process was recorded by a color CCD and the particle surface temperature before and at the ignition was determined by the RGB colorimetric method. Comparative experiments were conducted at normal gravity (1-g). The experiments revealed that at different gravity levels, the ignition of all tested coal particles commenced in homogeneous phase, while the shape, structure, brightness and development of the flames, as well as the volatile matter release during the ignition process are different. At μ-g, the part of volatile was released as a jet, while such a phenomenon was barely observed at 1-g. Also, after ignition, flames were more spherical, thicker, laminated and dimmer at μ-g. It was confirmed that ignition temperature decreased as the particle size or volatile content increased. However, contradicted to existing experimental results, provided other experimental conditions except gravity level were the same, ignition temperature of coal particles was about 50-80 K lower at μ-g than that at 1-g.

Blowout of non-premixed turbulent jet flames with coflow under microgravity condition

“…The experiments were conducted utilizing the drop tower [18] in National Microgravity Laboratory of China (NMLC), which has an effective height of 83 m providing a microgravity environment with the level of 10 −3 -10 −4 g for 3.6 s duration. A schematic of the experimental apparatus is shown in Fig.…”

Volatile Release and Ignition Behaviors of Single Coal Particles at Different Oxygen Concentrations Under Microgravity

“…Under such a temperature, the coal particles with size of ∼ φ2.0 mm were subjected to a heating rate of 150-200 K/s, which was calculated in our previous studies [20,25]. To ensure ignition occurred in the drop time, the particle was sent into the furnace for preheating for 1.0-1.5 s before the drop (Tang et al 2010;Zhu et al 2009). During this period, validated by 1-g experiments, no volatile was released.…”

“…Thus, ignition of single coal particles occurs in an environment with quasi-onedimensional mass and heat transfer, thereby the associated experiments become ideal to discover fundamental phenomena, to explore the instinct mechanisms and to provide more accurate data for coal ignition/combustion (Katalambula et al 2000;Liu et al 2014;Gieras et al 1985;Gieras et al 1986;Wendt et al 1999;Tang et al 2010;Zhu et al 2009;Zhu et al 2011). For this reason, several μ-g experiments on coal ignition were conducted, mostly by utilising the drop towers Katalambula et al 2000;Gieras et al 1985;Gieras et al 1986;Wendt et al 1999;Tang et al 2010;Zhu et al 2009;Zhu et al 2011) and the effects of the flame transition (Gieras et al 1985;Gieras et al 1986), particle shape (Wendt et al 1999), coal type Davini et al 1996) and particle size Tang et al 2010) have been investigated. However, the existing experiments were mainly limited to air condition.…”