The influence of temperature distribution over a carbon particle on its ignition and combustion characteristics

The work conducted a study on the influence of heat flow by thermal conductivity into the depth of a carbon particle on the characteristics of its ignition, combustion, and extinction in air heated to a high temperature. Physical and mathematical modeling of the processes of high-temperature heat and mass transfer and the kinetics of parallel chemical reactions on the surface of carbon particles was carried out, which made it possible to determine the induction period, time and temperature of particle combustion, critical diameters at which their extinction occurs. An analysis of the influence of the temperature gradient along the particle radius, caused by non-simultaneous heating of the layers of the carbon mass, on these characteristics was carried out. The studies were carried out for carbon particles with initial diameters of 0.2 ÷ 1 mm for the gas temperature range of 1200÷1400K, which are usually implemented in combustion devices. As a result of studying the dynamics of particle heating, it was found that significant temperature gradients are observed along the particle radius, both at the moment of ignition and at the moment of its extinction. During extinction, the temperature gradients are much higher. For the studied intervals of gas temperatures and particle diameters during extinction, the difference in temperatures of the center and surface of the particles is on average 400÷500K. At the moment of ignition of particles, the temperature of their center is lower than the surface temperature by 100÷400K, and this difference is greater, the larger the initial diameter of the particle and the higher the gas temperature. It is proved that failure to take into account the uneven heating of particles into the depth of the carbon mass leads to inaccuracy in determining the main characteristics of ignition and combustion for the studied interval of particle diameters: for the induction period - by 50%, for the burning time from 7% to 17%, the burning temperature - by 100K, for the diameter characterizing extinction, by approximately 5 microns. It is proven that it is necessary to take into account the temperature gradient, especially at the stage of particle ignition.