Numerical simulation on response characteristics of coal ignition under the disturbance of fluctuating heat

Owing to coal commonly existing in a fluctuating thermal environment, a two-step parallel reaction model for coal ignition was established to explore the development of coal ignition under fluctuating thermal convection, fluctuating thermal radiation, and convection-radiation coupling (CRC). To be specific, this included temperature evolution in a coal mass and fluctuating periodic characteristics. The nonlinear gain of coal spontaneous combustion caused by oscillatory heat flux conditions was researched. The results show that the thermal fluctuation at 0.1 Hz is conducive to coal ignition. The ignition delay time (IDT) exponentially decreases with the growth of both the thermal convection velocity and radiation heat flux. Under external thermal disturbance, the temperature, convection velocity, oxygen concentration, and depth of the sensitive area all vary periodically. Under different types of heat disturbance, the temperature and convection velocity fluctuate with an increasing trend, while the oxygen concentration fluctuates with a decreasing trend. There is a low phase difference between the temperature and the convection velocity while the phase difference between the temperature and oxygen concentration is about 90 degrees Besides, the peak fluctuation of the oxidation rate of coal changes inversely with the depth of fluctuations of the sensitive area. (c) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.